Cathedral Ceilings – Mold and Moisture – Problems and Solutions

Rotten roof deck

Disclaimer: while I think all the information presented here is accurate and scientifically valid, you are advised to consult a *professional before changing your home. This article covers just one component of your home. Your specific home may have conditions that override the comments contained herein.

*By professional, I mean an experienced building scientist, not your local carpenter or roofer or even a structural engineer or architect. While many of these people are artists in what they do, most have no training in building science or engineering and cannot be trusted to properly design a roof assembly. Likewise, you wouldn’t hire a building scientist to swing a hammer and build your roof!
Cathedral ceilings are very popular – they give rooms a feeling of openness and an added aesthetic dimension. At the same time, they are responsible for a variety of building problems and homeowner heartbreak. What causes these problems and how do you avoid them?

There are a variety of climate zones. The south-eastern United States is hot and humid, while the north east is cold. The mid-Atlantic states, where I live, is mixed – during the summer it is hot and humid, during the winter it is cold. The south west is mostly hot and dry and the northwest is moderate in temperature but very humid! Each of these climate zones has its own particular building details. However, all must follow the laws of physics.

Physics tells us that moisture moves from areas of high humidity to areas of low humidity. If it’s more humid outside, moisture wants to come in. And when it’s more humid inside, the moisture will move toward the outside. Simple!

The trick is, the amount of moisture that air can hold depends on the temperature of the air. Warm air holds more moisture than cold air. And, at some temperature, the air reaches a point where it can’t hold more moisture. This temperature is called the dew point.

The next thing to know is that moisture in air is water vapor. Water vapor is much smaller than liquid water, so vapor moves through building materials much more easily than liquid. Water vapor is also lighter than air, so it rises up to the ceiling and through any cracks or holes. Warm air also rises, so there is a tendency for warm, humid air to exert lots of pressure on the ceiling. These concepts are also pretty simple. Just remember – humid air and warm air rise.

So what happens during the winter when you heat your house? The warm air in the house contains lots of water vapor. That warm air and water vapor rises up to the ceiling. If there are holes, like electrical boxes, recessed lights or ceiling fans, the vapor easily moves up into the space above the ceiling. What looks like a little hole to you looks like an open window to the tiny water vapor molecules.

Let’s look at a diagram of a typical cathedral ceiling during the winter….

Typical fiberglass insulated ceiling

The blue lines represent moisture trying to move from the inside of the house, where the air is warm, to the outside, where the air is cold and dry.

For most of the ceiling, the moisture encounters painted sheet rock, which stops air flow and most of the water vapor. However, a small amount of the vapor travels through the sheet rock slowly (thin blue lines). Where there are any holes, such as at recessed lights, air moves through the holes, carrying water vapor right up into the insulation. In fact, a small hole can transmit tens or hundreds of times more water into the ceiling cavity than moves through the the painted sheet rock.

As the water vapor moves through the insulation towards the cold roof and outside air, it encounters colder and colder temperatures. If the temperature reaches the dew-point, the water vapor condenses  into liquid water and can drip back down through the insulation and back onto the ceiling, causing water damage. Some people have experienced it literally raining in their living room when this happens!

In order to combat this effect, builders created the vented ceiling. This is a space between the insulation and the roof deck. At the bottom, there would be a soffit vent and at the top, a ridge vent. Such a construction allows airflow through the cavity. This airflow is supposed to carry away moisture that builds up inside the cavity. It is also intended to keep the roof deck cold to avoid snow melt and ice dams

Problems with the conventional vented roof

Problem 1: Moisture Buildup Within the Insulation

Thermal image showing air leaks

In moderate and sunny climates the roof may heat up during the day, warming it enough to carry away the water vapor and dry out the insulation. However, what if the roof doesn’t get much sun or the moisture moves through holes in the ceiling faster than it can get carried away?

The moisture in the ceiling cavity can accumulate until it leads to ceiling damage. This is prevalent when the ceiling has many recessed lights or, uses tongue and groove boards instead of sheet rock.

The thermal image shown here demonstrates just how leaky a tongue and groove ceiling is. The dark areas show places in the ceiling that are colder than the surrounding areas. The lightest areas are where the insulation is intact and the ceiling is warm.

Problem 2: Moisture Buildup on the Back of the Roof Deck

If the moisture makes it through the insulation without condensing, it tries to move up and out of the cavity. However, this space is like a refrigerator. As the air moves through, it gets colder. Eventually, it may form ice on the back of the cold roof deck. I’ve seen many roofs rotten and covered with mold because of this.

The next photo shows an example of this problem. The home owner was replacing a recessed light when the electrician found mold. After deciding to tear off all the ceiling sheetrock, they found that almost all of the plywood roof sheathing was moldy. It should be noted that this roof was built strictly to code….using fiberglass insulation and ridge/soffit vents and a gap above the fiberglass to allow air flow.

Moldy roof deck

Problem 3: Improper Venting

Almost every roof put on these days includes a ridge vent, even if  it is not necessary. This is done because roofing manufacturers have stated that they will not honor the warranty if the roof isn’t properly vented. Unfortunately, putting a ridge vent on an old house often creates these types of problems!

Older homes used gable vents, not ridge vents. Most older home do not have soffit vents. What do you suppose happens if a ridge vent is installed on roof that has no place for air to come from?

The ridge vent still pulls air out of the attic or, in the case of a cathedral ceiling, out of ceiling cavity. That air has to come from somewhere, and that somewhere is the house. Many of the problems I have seen are caused by the ridge vent.

Building rule #1: if it ain’t broke, don’t fix it!

Building rule #2: understand what you’re trying to accomplish before doing it.
I have no problem with ridge vents IF they’re implemented along with a proper amount of soffit vents. I have huge problems with ridge vents when installed without soffit vents. I also have a problem with improper use of ridge vents where they are inappropriate.

For my own projects, I use Cor-A-Vent. They make excellent products backed up by proper engineering and supported by excellent technical documentation. If you plan on doing any roof work, I strongly recommend visiting their site and reviewing their technical literature. If you only read one document, make it this one. I’ve also copied this document so that it is available below.


Now that you understand how and why things go wrong with cathedral ceilings (and roofs in general), let’s look at how to do them right. First, we need to know exactly what problem we’re trying to solve (building rule #2).

Refer back to the first diagram to the left – what problems exist?

  1. Warm, moist air enters ceiling cavity through holes and cracks
  2. Small amounts of moisture moves through the sheet rock
  3. Air and moisture easily move through fiberglass insulation
  4. Moist air temperature drops below the dew point
  5. Intentional airflow from ridge vent draws moisture/humidity from the house

Solution 1 – don’t put holes in your ceiling

This is obvious, so why do people insist on poking so many holes in a perfectly good ceiling?

Typical recessed light fixture

The biggest offender is the recessed light fixture. Most of these fixtures, even those rated for insulation contact, are worthless in cathedral ceilings. You may as well just drill holes in your ceiling to let the heat and moisture out.

If you absolutely must install recessed lights, buy boxed fixtures rated ICAT – Insulation Contact Air Tight. Be warned that all ICAT fixture’s are not created equal. For example, The fixture to the right is rated ICAT, but I don’t recommend this style. Much better are the fully sealed box fixtures, like the next photo.

Boxed ICAT fixture

Next, be sure to seal the fixture to the sheet rock so that it is air tight. A continuous bead of high temperature caulk greatly reduces the air lost by mounting recessed lights.

Recessed light fixtures may be the most common hole in your ceiling, but there are others that cause similar problems.

Be careful of electrical boxes mounted in the ceiling. These are usually very leaky, and can lead to even greater problems than recessed lights. These can be found above ceiling fans, smoke detectors or ceiling mounted lights.

Most of these are sealed with caulk or foam. Note that you need to do this carefully so as not to interfere with the electrical wires and/or contacts in the box. Best, have a licensed weatherization contractor deal with it.

Solution 2 – Use Insulation that Stops Air Movement

Fiberglass is a cheap insulation product, but it is not a good one in all situations. It works by reducing conductive heat transfer, but it does almost nothing to slow air movement. It doesn’t matter whether you put three inches or three feet of fiberglass insulation in the cavity, it’s not going to stop air movement and the associated moisture movement.

Unfortunately, most contractors love fiberglass. Anyone can install it and it is cheap. Granted, almost everybody installs it incorrectly – they compress it (reducing the R-value) and they install it in areas with air movement, rendering it almost useless.

If you absolutely, positively must use fiberglass, then do it right. Install it flush to the sheet rock so no air can come between the fiberglass and the ceiling. Do not compress it – if wires must be routed, split the fiberglass so the wire runs through the middle. If it has to go around obstructions, don’t compress it – cut it to the exact size and shape needed. And finally, make sure everything is sealed air tight so no air is tempted to flow through the fiberglass.

A much, much better solution is to use dense packed cellulose insulation. This is cellulose insulation that is installed to approximately 3.5 lbs./cubic foot density. At this density, cellulose does not allow air movement under normal conditions. The way it is blown in also forces it into all the nooks and crannies – around wires and pipes and fixtures. It also can be used in a “hot roof” design. With this installation, soffit and ridge vents are not used. The entire cavity is filled with cellulose. For details, see this link. A PDF of the Applegate Insulation technical bulletin is also available below.

What about moisture? Cellulose insulation can hold a tremendous amount of water, dispersing it throughout the material. In this way, like a sponge, any small amount of moisture that gets into the cellulose spreads out rather than puddling up. In a properly made roof assembly, this moisture then moves towards the shingles and out. Note – there is some controversy about using dense packed cellulose in ceiling cavities. Read this building science article by Joe Lstiburek. The problem arises when you have very porous ceilings, like the tongue and groove ceilings. Because so much moisture passes into the ceiling cavity, it can overcome the moisture flushing capacity of the insulation and roof. This is especially problematic if you have a completely vapor impermeable roof, like a metal roof or a roof covered with a rubber membrane (like all flat roofs). To avoid problems, listen to Joe and don’t dense pack your cathedral ceiling if you have any doubts.

Even better than cellulose insulation is high density sprayed polyurethane foam. This foam creates an air-impervious barrier and is also very effective at slowing vapor movement when applied at adequate thicknesses (greater than about 2 inches). Because of these properties, foam is usually applied using the hot roof (no venting) method. Note that the amount of insulation needed depends upon your climate zone. Colder climates need more insulation.

Polyurethane foam also has an excellent R-value, about twice that of fiberglass or cellulose.

Solution 3: Understand the Physics

Usually, when I explain the unvented roof to people, they ask “where does all the moisture that gets in there go?” To this I reply – where does all the moisture in your house go? Are your walls rotting out? Has your floor collapsed recently? Is there mold growing anywhere? Mostly, they say “no – but that’s not the same.

In fact, it is exactly the same! The reason that your house doesn’t rot or have mold growing everywhere is because the humidity of the air isn’t high enough to cause condensation on normal surfaces. In the same way, when you apply foam, the air cannot come in contact with a surface cold enough for condensation to occur (unless you keep your house like a greenhouse!) The humidity within the ceiling cavity is the same as it is inside the house so you have no problems.

Except for one….

There is an unfortunate technique called “flash and batt” that has become popular among builders because it allows them to air seal using spray foam but keep the cost down by providing the majority of the R-value with cheap fiberglass. Unfortunately, many of these insulation contractors do not understand physics. In the cathedral ceiling example, they spray a thin layer of foam to the bottom of the roof deck, air sealing the cavity from the top. Then, they fill the cavity with fiberglass.

What’s wrong with this picture? The fiberglass allows the warm air from the house to move into the cavity, through the fiberglass. But, the air cools as it gets close to the thin layer of foam on the roof deck. If the foam is not thick enough (usually the case), then it will be very cold. Now, the moisture in the air condenses on the inner surface of the spray foam. Even worse, the air and moisture sealing properties of the foam then locks this liquid water into the ceiling cavity. Before you know it – rotten ceiling or rotten roof.

Now, you can do flash-and-batt in a way that it works, more or less. Remember the physics – we want to stop the air and moisture movement and prevent the water vapor from coming in contact with cold surfaces. To do this, you build your ceiling, install wires and fixtures and then spray the back side of the ceiling with foam. This seals everything and keeps the moisture in the house. The problem is, this means putting the roof on last! This is never done because you need the roof on as soon as possible to keep the weather out while you’re building the house.

So, if anybody says you can save a lot of money by doing flash-and-batt for your ceiling, send them packing – they don’t understand the physics of insulation and you’ll probably end up having to buy a new roof in a few years because your builder cheaped out on insulation.

Side note: Walls

Think about walls. They don’t require ventilation. They’re supposed to be sealed tight, and they don’t rot out (except when they leak, but that’s another story.) Why do we build ceilings differently than walls? Well, there is a slight difference – remember that warm, moist air rises. So ceilings are more likely to have warm, high humidity conditions than walls. However, the same physics applies.

As noted above, flash-and-batt is becoming more popular, but the same rules that apply to its installation in ceilings applies to it in walls – the foam must be sprayed against the backside of the sheet rock on the wall. It must not be applied to the outer wall sheathing with fiberglass on the inside. This is almost certain to lead to rotten, moldy walls. But, if you don’t do it the cheap way, then just spray the foam against the sheathing, but use enough of it so that the inner surface never gets cold.

Final Comments – Understanding R-Value

If you’re interested in more physics, see my notes on insulation and heat transfer.

Related articles and discussions

Caveat – if you read through discussion groups on this topic, you will find a lot of bad information. Information from builders, architects, engineers. I’ve sorted through the garbage and only included links to sources that appear correct. If you need to, go back and read “solution 3” above. The physics are simple. But the details can be complicated since the exact roof structures vary considerably and the devil’s in the details!

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135 thoughts on “Cathedral Ceilings – Mold and Moisture – Problems and Solutions

    • I think any vent chute would be fine. the main reason for this is to reduce wind from blowing in the soffit and through the insulation. once it’s up a few feet,the chute isn’t a big deal unless you put too much insulation in the cavity and it comes in contact with the bottom of the roof sheathing.

  1. Ted, thank you so much for this article. There is SO much information out there but this one really boils it down and is fact-based, so thank you. We are partway through construction of our rustic cabin in central Ohio. Has a full basement, open floor plan, true cathedral ceiling. The roof is on, and we are planning to do insulation soon. Here is our plan: tongue and groove pine, drywall, kraft faced R-30 fiberglass insulation batts, ventilation chutes, roof sheathing, synthetic felt paper, metal roof. Here is what I still am not clear on: do I need to provide any additional vapor barrier other than the drywall layer? Any aluminum backing on the batts? Do I need to seal the vent shoot? Anything I am missing? Someone suggested that instead of a traditional vent chute I use a foam board (with the edges bench to provide 1.5 inch airspace) and then apply caulk to make it airtight. Is any of this extra stuff necessary? Thank you for your insight!

    • The use of vapor retarder is dictated by your local building codes, so you should ask the building inspector. With sheetrock, especially if you paint it with a layer of latex paint, you probably don’t need another vapor retarder. While it may seem silly to paint it then cover it, it just helps minimize moisture soaking in.
      You’ve heard right about the chutes using foam board cut to size. However, this does run the risk of trapping moisture in between the ceiling and foam board. One purpose of the ventilation is to flush out any moisture that might get in there. So in your case, you don’t want anything above the batts that would prevent moisture from flowing up and out.

  2. I’m glad to have found you as we are having condensation on our cathedral ceilings. Are there supposed to be soffit vents for a cathedral ceiling? We have two attics, one on either side of the cathedral ceiling and there are soffit vents for these. We have a metal roof that was put on maybe five years ago or so with ridge vents above the attics and one on the cathedral part of the roof. My husband says we didn’t have this problem before the metal roof was put on but I’m not certain he knows for sure. The front wall of the room is all glass and the upper part of the rear wall is glass. Our a/c vents are in the floor, two of them at the front of the room, one at the rear and two in the center (it’s a large greatroom) so we don’t know if the cold air from the vents rising up to where the air is warmer might be causing the problem. There is more condensation closer to the windows at the peak but it is moving to the center of the peak some. I’m also wondering if our roof is put together like your diagram shows that it should be. The house was built in the early 80’s. One opinion was the washers used to install the roof might be cracking and causing leaks. I would think the whole roof would be leaking then but I haven’t been in the attics to see. Any thoughts you might have would be greatly appreciated.

    • Venting of cathedral ceilings is a complicated affair. Some insist that it is necessary, while others say absolutely not. In my experience, it is not the venting that makes a difference but rather it is the construction of the inside ceiling. It also depends upon your local weather patterns and even personal usage – the same construction might work fine in one area and totally fail in another.
      Metal roofs are unforgiving – they are essentially a perfect water barrier, so any moisture that accumulates under them cannot be absorbed and released, the way wood would allow. Metal roofs also conduct heat/cold extremely well. On a clear night, the roof can get very cold – much colder than a wooden roof. When the metal roof gets cold, moisture condenses on it. It will then form water droplets which will run down the roof and eventually drip off, causing leaks inside.
      Do you ever go outside and find dew on the car or other metal surfaces? With a vented metal roof, this can occur on the inside surface as well as the outside. Dew is just condensation that forms when the metal surface is cool enough to cause the water vapor in the air to condense. With a vented metal roof, the humid nighttime air will flow up the inside of the roof and can condense, leading to exactly the problems you’re seeing.
      As for conditions inside your home causing the problem, it’s possible but unlikely based on your description. Air conditioned air is very dry. The air conditioner acts as a dehumidifier, so it’s actually beneficial for reducing condensation problems. However, it’s still possible that excess indoor humidity could be getting into the ceiling cavity if you have lots of recessed lights or a tongue-and-groove ceiling or any other ceiling construction that allows any indoor air to rise up into the cavity above the ceiling. Vented roofs can actually make these conditions worse – as the air flows our the ridge, it can suck air through any cracks in the ceiling. In a totally sealed cathedral ceiling, you don’t have this sucking force. So look at the ceiling and see if there’s any way air from inside the house could be getting up inside the ceiling. With a solid, sheetrocked ceiling without recessed lights, it’s extremely unlikely that interior moisture is causing the problem.
      Your last mention of roof leaks is certainly possible, though that’s a leak and not a condensation problem. Given that you said the water is towards the peak rather than down low, I suspect condensation. Water vapor is lighter than air, so it floats up and typically causes more problems towards the peak.
      I know this is a lot to think about but these problems can be tough to diagnose. I hope I’ve given you some food for thought that might help you track down your water issues.

  3. Thank you so much for all of this information. We are presently building a garage with living quarters upstairs. The garage is 36 x 50 with four vaulted ceilings. We are finishing the inside ourselves. Before we put up the tongue and grove boards, I want to make sure everything was done correctly or if we need to do something else. The garage has ridge vents and soffit vents that are around the entire building. From outside in, this is what we have: shingles, waterproof plywood decking, aluminum heat shield, and R19 insulation. Is this sufficient?

    • I’m concerned with the construction that you’ve described. Aluminum heat shield is typically very moisture impermeable. If you put this above he insulation, it’s going to trap water in the insulation which can lead to serious issues. On the other hand, if the heat shield is mounted directly under the plywood decking and you’ve properly vented between that and the insulation, then you probably won’t have issues as long as your ceiling is solid – no recessed lights or other holes on the interior ceiling that would allow moisture from your living space to get sucked up into that cavity.

      You want to ensure that you’ve got at least a couple of inches between the top of the insulation and the underside of the roof decking so that air can flow freely from the soffits to the ridge vents.

      Also, if you’re using tongue and groove ceiling, you must make sure there is a moisture impenetrable barrier right behind the T&G boards. It is best to have a full sheetrock ceiling then put the T&G below that. By far, the worst moisture issues I’ve seen is when builders just nail a T&G ceiling to the rafters. Even using plastic behind it can fail because it become so full of holes and tears that moisture will go right past it. Another option, if you don’t want to use sheetrock is to use foil faced foam board, being sure to tape the seams with foil tape. You can then install the T&G ceiling under that – just remember to mark the rafter locations so you know where to screw through the T&G. The foil faced insulation, even 1/2″ thick, will provide great benefits. It will stop moisture from getting into the ceiling cavity and it will add some R-value. It’s also much lighter and easier to install than sheetrock. But whatever you do, make sure you have a ceiling of some sort behind the T&G boards or you almost guarantee that you will have moisture problems in the future and will have to rip apart the ceiling.

  4. Your article seems to exactly address the issue we are having with our ceiling: tongue and groove wood ceiling that condenses near the top and drips… we are on the water so humidity must be high. Question is, can we paint over the ceiling with something that would provide a barrier? If not, could we drywall the ceiling over the current wood ceiling? Since we just bought the house, it also looks like half the roof over the area that shows the most condensation is metal!whilenthe other is asphalt… we hope we don’t have to rip out the ceiling.


    • If you’re not averse to covering it up (we all love the look of T&G ceilings), then one of the most effective things is to attach a thick layer of foil-faced poly-iso board foam to the ceiling, then sheetrock over that. Best is two layers of foam, taping all seams with foil tape. Staggering the two layers by half the width of the foam board so that seams don’t align. This forms a virtually perfect moisture barrier and excellent insulation.
      If you go this route, you may wish to run some wires to junction boxes, being careful to maintain a thickness of foam to prevent moisture from getting above. This allows you to install lights or ceiling fans without affecting the integrity of your moisture barrier.
      Note – before you do this, I’d recommend that you cut out a small section of the ceiling boards so you can examine the interior of the roof assembly and the underside of the roof decking. You want to make sure the structure isn’t rotten or really wet before you seal it up.

      • Thank you for this advice! You are the only person I have found who knows about these ceilings. Would paint over the wood be another option?

      • I wouldn’t trust paint to seal all the moisture from getting through and into the ceiling cavity. It would be best to first cut a section to inspect the interior and identify where the moisture is coming from. It’s possible that there’s a moisture barrier behind the wood already and there’s no moisture inside the ceiling cavity. If that’s the case, then you might be lucky because that means the condensation you’re seeing is only because there’s excess moisture in your home that’s floating up to the ceiling and condensing on the cooler wood surface. This you could resolve through home dehumidification and moisture management.

      • Hello- should the foil portion of the insulated boards face out or in- toward the ceiling? Also- I had a contractor review your recommendation. If adding 2
        Layers of insulated board is too expensive and we only use one, could he first add a vapor barrier to the wood followed by the insulated boards? Thanks again.

      • Hi Kirk,
        Typically, the foil face would point towards an air gap in order for the radiant barrier capability to be effective. However, in this case, both sides of the foam board will be in contact with another surface, so it doesn’t really matter. However, for best application of the foil tape which you’ll use to seal the seams, you’ll want the foil facing accessible, i.e. out, towards the floor.
        You don’t really need the vapor barrier behind it since the foil itself is a near-perfect vapor retarder. As long as the seams are taped. Plus, you’ll be adding sheetrock which will be painted. The combination will be extremely effective at blocking moisture from inside the house.

      • Hello Ted- one other question. I tried to look above the ceiling boards and don’t think there is a barrier. However, I am not able to check for moisture in the space below the roof unless Instart tearing the ceiling out. We don’t have a lot of $ and the proceedire you recommend will be expensive enough. If we cover the ceiling up, what are the risks in the future? When it comes time to replace the roof, perhaps then we could look at the roof boards and insulation below. Right now, unjust want the inside to be nice and hopefully moisture free. Thoughts?

      • it really depends how bad the original moisture issues were and your confidence in the integrity of your roof. Also if there’s no signs of active mold or rot then you’re probably safe. I just always want to ensure that there’s nothing nasty hiding.

  5. I have a 1985 Justus Solid Cedar Home near the coast around San Francisco. We are experiencing condensation at the peak of our cathedral ceiling at mid-day on moderately warm days (77 degrees). Windows are open in the house, so there is not a substantial difference in the air between inside and out. Between the ceiling and roof are 2×6 rafters and 2 layers of 2″ Thermax and 1 layer of 1″ styrofoam. Asphalt shingles lay on 1/2″ plywood. There is no venting. According to the distributor, the house was designed for cedar shakes and skip sheathing. I’m wondering if adding soffit and roof ridge vents seems like a way to address the condensation?

    • You mention mid-day. Since the windows are open, there’s probably a lot of moisture flowing through the house from the morning when humidity levels can be near 100%.

      As the air warms up, the ability to carry moisture increases. So what can happen, is this humid air comes in contact with the wood which is cooler than the surrounding air because the temperature of the wood lags behind the outside temperature due to its thermal mass. This would lead to exactly the type of condensation you’re experiencing. It happens at the peak more often because water vapor is lighter than air so it accumulates at the peak.

      No amount of ventilation in the roof structure will help this. The condition, if my theory is correct, is exactly the same as why the mirrors in your bathroom fog up when you shower. The glass is cooler, leading to the condensation.

      When I experience condensation issues like this, I try a couple of things. First, avoid opening the windows in the morning when the air is super-saturated with water. Second, get a humidity monitor (very cheap on Amazon, ~$20-$40) and keep an eye on your interior moisture at the highest spot that you can read the monitor. If you can, keep the humidity below 60% using dehumidifiers or air conditioning.

      You can also “stir up” the air using a ceiling fan. This will help reduce condensation and flush the moisture from the peak (assuming the ceiling fan is moving enough air around).

      You can also get a remote reading laser thermometer (again, cheap on Amazon) (

      Use this to check the temperature at the peak in the morning and when you see moisture. You may notice cold spots. These will be prone to condensation. Circulating air, particularly in those places will help minimize condensation.

  6. My contractor and I are fishing for a good insulation solution for the loft in my new pole barn. The roof is metal sheeting on 2×4 purlins attached to the top of the trusses, the trusses are 2×8 and we are going to use corrugated metal for the cathedral ceiling on the inside. There is already a ridge vent, but since we used attic trusses, the ceiling will not extend to the soffit of the pole barn, we will have knee walls about 6′ from the sidewall; and the rest of the shed will not be heated. I don’t plan to put any holes in the ceiling and will caulk the areas where the steel is cut around each truss (every 9′). If we use fiberglass batts with plastic before putting up the steel ceiling and then add vents at the top of the knee wall in the cavity that we closed, would this do the trick?

    • It sounds like the space will be well ventilated, and since it’s not a living space, the interior moisture levels will pretty much match outside conditions so it should be more forgiving than a home.
      The main considerations will be how the insulation is installed. You always want clear air space of about 2″ or more on the cold side of the insulation. On the warm side, you want to ensure cold air can’t get between the insulation and the ceiling/wall in order for it to work well. They always say to think about how a good sweater fits you – if the cold air gets between the sweater and your skin, you get cold. Same for the insulation.
      If this is just a work space, and you won’t be adding moisture, then I don’t really see the purpose of the plastic. If anything, that will just trap moisture. I’d be concerned about trapped moisture resting against the steel ceiling and leading to long term rust/rot problems. Just plain insulation would allow any moisture to diffuse up through the insulation and be flushed out by the ventilation under the roof.

  7. Hi,
    Our house is located in western Massachusetts, was built in 1979 and is almost all cathedral ceilings. We bought it in 2003 and had the shingles replaced in 2005. Seems like they tore off only one layer of shingles on most of the roof and on the slope section removed down to the plywood and had to replace some as it was rotting. We continued to have a leak, sporadically, and had that roofer come back twice – once where he actually removed the ridge vent – and told us the roof job was not the issue. We had the chimney sealed 2-3 years ago (the leak appeared new the chimney), and rebuilt down to the roof line last fall – sealed twice – and we still have these sporadic leaks. I just went up on the roof with a different roofer, and there were many “soft” spots, and “ripples” in different places on the roof. He indicated that the previous roof job was not done properly. After reading your very informative article, I looked around and some of our ceiling has no sheet rock and a “stringy” looking material (can’t find a way to attach a pic but can e-mail it to you later). Also there are plenty of gaps between the sheet rock and the beams and chimney and some ceiling light (not recessed) fixtures. I’m guessing at this point that the roof/ceiling were not properly installed/ventilated when it was originally built as we have dealt with this leak, another in a different part of the house and severe ice dam damage over the last years, and noticed some water damage when we bought the house. While I am going to call several roofers to give us estimates, the first one said he thought it would be roughly $30K! Any suggestions?

    • Wow, that’s unfortunate. It sounds like a chronic problem that will keep rotting out the roof if left unchecked. Frankly, it’s a shame contractors aren’t held responsible for building homes like this. It’s criminal negligence.
      Glad you mentioned the ice dams. Those are often a giveaway indicator of warm air from the living space leaking up into the roof cavity. Either that or inadequate insulation down near the eaves.

      Given the severity of the issue, I would highly recommend that you get in touch with a local energy auditor who is qualified to diagnose these types of moisture problems. It comes down to a “building science” issue. A qualified individual with proper test equipment (blower door, thermal imaging camera, moisture gauges) should be able to help you pinpoint the construction issues and give you a plan of attack for rectifying them. This should cost $300-$500, which is inexpensive compared to the alternative repairs that it sounds like you’ll have to keep making if contractors try random repairs without knowing the true source of the problem.

      You might want to contact Building Sciences corp. and see if they can recommend a specialist in your area.
      I also Googled for some businesses in central/western MA that might be able to help:
      Cozy Home Performance
      Center for EcoTechnology – looks like they are deeply involved in training and may be able to give you a lead on a qualified consultant in your area.

      I hope you find someone local who can guide you through this process. If they’re good, they’ll be able to point you to qualified contractors as well.

  8. Thank you for your post any many responses.

    I live in Anchorage, Alaska. We recently bought a 30-yr old house with a 3-yr old roof (new roof). A ridge vent was installed; soffit vents were not. We have a hot roof, so no attic

    We are experiencing condensation. We’ve had drips from exposed beams inside, drips under window framing inside, and drips on the outside walls.

    In regards to lessening the condensation, I think a retrofit soffit vent system would be a good place to start. Is there a system that you recommend? Other thoughts?

    • Before you change anything with your roof, it’s important to learn exactly where it’s coming from and what is the cause of condensation. Can you tell if the condensation is coming from above the ceiling, and dripping down the beams or inside the walls and dripping down the window framing and walls?

      It sounds like you could have high moisture inside your house. At high moisture levels, condensation will form on any cold surface and no amount of roof venting will alleviate this. On the other hand, it could be that the ridge vent without soffit vents is causing moisture from inside the house to get sucked up into the roof construction, allowing the moisture to condense on the cold parts of the underside of the roof.

      If you really think that the condensation issue is inside the ceiling, then you want to start small. Cut an exploratory hole in the ceiling where the condensation is dripping so that you can see and feel in the ceiling cavity. If the water is coming from inside, then you can take further actions.

      Should you install a soffit vent system, I really like the Cor-a-vent system. It provides large amount of ventilation into the roof structure and can be done hidden. We did this for our house.

      Also, check for moisture generators in your house. Ventless gas fireplaces. Unvented bath fans. Plants. Humidifiers. It is quite important to maintain a low humidity level (40% is a reasonable level) in colder climates or it is very difficult to avoid condensation.

      • Yes, it’s classic signs of condensation. I’ve had two roofing companies out to confirm.

        In fact, we have low moisture inside the house. I’ve seen it as low as 17%. It’s probably all getting drawn through the roof!

        Cor-a-vent looks great. Unfortunately, no dealers in Alaska. I’ll look for something similar locally or check into shipping.

        (Incidentally, both roofing companies wanted to replace my <5-yr old roof to the tune of $20G! Let’s hope that getting some air moving through there solves my condensation issue . . . )

  9. Hello T D

    I have a small cabin 16′ x 20′ with cathedral 9/12 pitch roof. Someone built with no venting whatsoever. it has asphalt shingles and the rafters are packed with unfaced fiberglass insulation with no ceiling finish material installed. Its been this way for over 10 years and there is no sign of mold. I purchased t&g pine paneling to install on the ceiling but am reluctant to put it on. There are no lights or electrical boxes on the ceiling. It is in the pacific NW where there is much rain. Should I install a Plastic vapor barrier over the unfaced fiberglass before installing the pine paneling?

      Thank you
    • So to be clear, the fiberglass is exposed, just wedged in between the rafters under the roof?
      One thing that likely saved your roof are the relatively mild temperatures (I’m assuming) which reduces the condensation potential – the colder the more likely to have condensation.
      If the ceiling is that accessible, I would personally remove the fiberglass and either spray-foam directly to the underside of the roof or cut board foam and put that in there, maybe a couple layers, then use caulk or foam to seal the edges. After that, I’d add the T&G ceiling and you’d be pretty safe.
      An alternative would be to simply add a layer of board foam, sealing the seams (imagine how you would sheet-rock the ceiling, but instead of rock you use board foam). That would provide an excellent moisture barrier and insulation. You would then put the T&G right over that as your aesthetic ceiling.

  10. In Southern California, I see new beautiful homes in Los Alamitos (3-4 miles from the beach) being sold for 1.2+million that have beautiful vaulted ceilings with recessed lights. Selling realtor claim that it passed city engineer and inspection. I also bought a home in a neighboring city and have vaulted ceilings and would really like to put in recessed lights. Are ICAM lights out of the question? And are these Los Alamitos homes screwed in the future due to possible mold growing in that small space due to the recessed lights?

    • Recessed lights aren’t always a disaster. Moisture problems are much worse in chilly climates. SoCal is warm and dry so condensation is unlikely. If it does happen, then it would probably dry out before it does any damage.

      • Thank you TD! We really want recessed lights in our vaulted ceilings. I’m going to go with the box enclosed version that you have described in your articles. If there are additional places you can suggest where we can obtain some I’d appreciate that as well.
        Best, Charles

      • You might also consider flush mounted LED lights. They look like recessed lights but don’t have the disadvantages. The light is high quality these days and they’re much more energy efficient -you can save hundreds on your electric bills every year. Plus, you never have to replace blown bulbs.

  11. My home is in Northern CA. Summers can be 100′ and winters are mid-high 40’s. I have two different interconnected roofs, one is 8/12 pitch and the other is 4/12, and the rafters are 2×12’s that are 24″ on center, and 24 feet long. I have 1 (2 1/2″) sofit circular vent centered between each rafter, and I have ridge venting the entire ridge cap. I have overlapping styrofoam corovent sheets (4′ X 24″ ) with 2 linear 7″ vents from end to end, totally filling the ceiling between each rafter from the sofit end to the ridge end. I have coils of chicken wire sitting on the 8′ header plate over each sofit vent that the styrofoam sheets fit over to rush the circulated air from the sofit vent up the 2 ventpaths in the corovent sheets up to the ridge vent. I have R30 insulation over the styrofoam corovent sheets from sofit end to the ridge end. I’m getting condensation dripping on the glulam and into the insulation near the ridgebeam. The ridgevent and single sofit vent holes do not seem to adequately vent the roof. Do I need to add another sofit vent or two between each rafter? The styrofoam corofoam vent sheets and coiled chicken wire would cover more sofit vent holes. Should I add vent holes in the 2X10 sitting on side edge on top of the 6″X24″ glulam ridge beam (rafters criss-cross over it and are nailed together) to help cross ventilation from side to side? Do you have ideas / solutions for me Mr. Inoue?? Thank you in advance. Please reply to me via my email.

  12. We have a two story house with attic space limited to some drywall and recessed lighting. We have T&G slanted walls and live in Washington state near Seattle. We noticed during an unlikely winter with snow that the heat was rising up the stairway hallway and melting snow on the roof. When the temperature outside warmed up the water started dripping through the T&G. The roof was replaced with metal long-standing seam and they realized there was foam installation. Roofers added ice and water shield, but I am not certain this fixes the condensation issue over our stairway.

    Are we the unlucky ones? or does the moderate climate were in help with the water vapor?

    • Well, that certainly sounds like you had a condensation issue. Humidity can be an issue in Seattle, so if this was condensation, I’d expect a repeat if it gets cold again. The challenge will be ensuring that it dries out quickly so that you don’t have the inside of your ceiling staying wet enough to lead to mold and rot problems. I’d be concerned about that.
      Do you know how much foam insulation was under the roof? Did they leave that in place and put the metal roof over the existing insulation? With that in place, if you had enough insulation, you really shouldn’t have condensation problems. So I suspect that there’s something going on that’s allowing the humid air to come in contact with something that’s not insulated well.
      If you have repeated issues with this, I’d strongly suggest doing an exploration behind the T&G – pull a couple boards around where you see it leaking and examine the sub-roof above that point and also check to ensure that the wood is not staying wet. T&G is a pain to remove because you have to carefully slice off the “tongue” on one of the boards so you can remove it. But it’s doable with the right tools and a steady hand.

  13. Hello, I am currently experiencing a moisture problem with my 6-12 cathedral ceiling. It is tongue and groove pine on the interior, plywood and shingles exterior, and fiberglass insulation. The roof is constructed of rafters and the tongue and groove pine is attached directly to the rafters. Moisture is dripping from light fixtures and running down the inside of the exterior walls. I currently have a ridge vent, but no soffit vent or soffit for that matter. Would it be in my best interest to seal off the ridge vent completely?

    • If they put the tongue-and-groove boards directly to the rafters with no intermediate airtight barrier then basically you’re out of luck and you have to rebuild your entire ceiling or your roof will rot out.
      I hate to be the bearer of bad news, but that’s just physics. The T&G boards are completely open to air and moisture. Likewise, the lights are letting more moisture up into the ceiling cavity.
      Is any water dripping from between the T&G boards? It’s possible that there’s an air barrier between that and the rafters. In that case, you might be able to get away with just installing air tight recessed light retrofit to the existing fixtures. I’ve done this with all my recessed light fixtures and they’re great.

      • Thanks for the quick response. I do believe that there is a moisture barrier between the pine boards and the rafters. I currently have track lighting (no cans). The water is coming from the electrical connection box of the light. I only notice this issue in the very cold winters or high heat and humidity of the summer. Didn’t know is sealing the ridge vent would be of benifit or not.

      • You might be lucky. However it’s difficult to tell where the water is starting to condense. it’s probably just dripping out the hole.
        The problem is, without an inspection, you can’t really tell what’s happening in there.
        Can you think of any other way that moisture could get into the ceiling cavity? I’d be very hesitant to tell you to seal the ridge vent. I might try that for my own home, knowing that removing it would reduce the sucking of the moisture from inside the house into the ceiling. But I’d only do that because I have various test equipment that would let me keep an eye on the cavity moisture levels. Since vents are required by code in some areas, I’d be negligent to recommend that to you.
        I think there’s a pretty significant chance that there are moisture problems greater than what you see so it would behoove you to have a local moisture specialist come in to analyze your ceiling issues. The problem is it can be difficult to find somebody who will give you an accurate analysis because this is something of a specialty area. Where do you live? I might be able to do a quick search in your area to see if anybody around there looks competent for the job.

      • No, unfortunately I don’t know any other way moisture is getting into the ceiling cavity. I am currently running a dehumidifier that shows a humidity level well below 50%. The home does have a crawl space, but it stays pretty dry. I live in Saint Louis, Missouri and we have been experiencing temps in the teens and lower, however the moisture was much worse today when the temp was in the 40s. Your help is greatly appreciated.

      • I have an idea of why the water was worse when it warmed up. When it was really cold, the condensation froze on the roof deck. It only started dripping when it became warm enough to melt.Then there was a lot because all the ice buildup melted at once.

      • One more option is to contact Building Science Corporation in Massachusetts and ask if they have a listing for moisture specialists in your area that have gone through any of their training.

      • This company looks promising. Give them a call and see if they are set up to diagnose moisture problems like you have.
        Here’s another company that specializes in these types of issues:

        In the event that you do have to pull down the tongue and groove ceiling paneling (or for others thinking of this type of construction) the safest and most cost effective way of installing this type of ceiling is to do the following: batts in the cavity with a 2″ gap between the batt and the roof. Soffit and ridge vents to ventilate above the batts. Either sheetrock or insulated foam board screwed to the rafters to form an air-tight separation between the living space and roof cavity. Nailers (1″x3″ boards) affixed under that to the rafters. Run wiring through in this space so you don’t have to penetrate the air barrier. Then the tongue and groove ceiling material, which is purely aesthetic, is attached to the nailers.

        From outside to inside:
        roof sheathing
        2″ air gap
        insulation batts
        foam board (2″ polyiso gives ~R13 and reduces thermal bridging for a much better overall R-value)
        Tongue and groove ceiling.

        Hope this helps you and others. This is unfortunately a very common problem.

  14. We didn’t do enough research and followed well meaning, but false information. We now have a new construction vented cathedral ceiling that leaks from a condensation issue. It mostly happens after a cold day 9 fahrenh to 34 or so the next day. Shingled roof, foam baffles, fiberglass insulation, sheetrock. We feel like our best option right now is just to seal up gaps where possible ( one ceiling fan at peak around exposed beams, and especially two attic spaces ( on sides of loft style room upstairs. The attic spaces need sheetrock. One has a vent space going outsidd from bathroom fan. The worst dripping is in cold side of house attic spa ce with no sheetrock. Any other suggestions? One drastic idea is to foam cathedral ceiling with spray foam on inside… crazy? Any idea if just minimizing air flow through to space will keep condensation to a minimum? Appreciate any suggestions… thank you!

    • Yes, fiberglass provides no barrier for moisture from the house going up and condensing on the underside of the cold roof, regardless of ventilation above it. If it were all sheet-rocked and air-sealed, you’d be much better off.
      Compared to a water molecule, fiberglass strands are the equivalent of a person walking between ropes that are spaced one rope across the United States. Really. So any moisture from the house, carried by air, just passes right through the fiberglass and lands on the roof.
      You need to be especially careful about any gaps in the bathroom ceiling – huge amounts of moisture will escape around any gaps between the fan and the ceiling. You also need to run the bath fan for 15-30 minutes after the shower is used in order to flush out moisture.
      Spray foaming can be very effective as it provides a near-perfect air seal and is almost moisture impermeable.
      Also be aware of any moisture sources in the house. Showers, as I said are one of the biggest sources. Humidifiers are another one and one of the most notorious causes of moldy roofs, so if you have any humidifiers, don’t use them and see if the condensation stops.

    • Thanks for the reply! We will try these things. Since the rest of the cathedral ceiling space is already buttoned up, we can really only close up the attic spaces. Do you see any potential problem with spray foaming these areas even though the rest of the ceiling will have fiberglass?

  15. We have a hunting cabin that was built 10 years ago and only gets used 9 days per year in central Wisconsin. The vaulted roof is constructed from I-joist over a glulam ridge beam and is a 6/12 pitch. We installed chutes, fiberglass insulation, soffit vents, and a ridge vent. Now 10 years later we have a major issue with black mold on the glulam ridge beam. Poly was installed on the under side of the joist and the ceiling is random pieces of doug fir (not tongue and groove) that were nailed to the joist. I’m trying to figure out where the moisture problem is coming from. I am not sure if it’s from the ridge vent (that’s my initial guess) or moisture from inside the building. We only heat it 9 days a year with a wood stove so I don’t think there would be much moisture from inside. Seeing the amount of black mold I’m assuming it would take a significant amount of moisture for this to happen.
    Any thoughts would be appreciated.

    • Usually moisture problems arise from inside or underneath the house. The moisture enters the house when it’s warmer and higher humidity in the ground/outside. Then, when the temperature drops, the moisture will condense on the first cold surface it meets.
      Since moist air rises, it will “pool” at the ceiling so the ridge beam is a likely spot for the mold to form. Additionally, since the beam is a better heat/cold conductor than the insulated ceiling, it will be colder in the cool weather, another thing that makes it a moisture/mold magnet.
      The trick is finding sources of moisture that may be leading to excess moisture in the house. For example, dirt floor under the house/basement (assuming no basement, but dirt under the cabin?) That dirt holds tons of water which will want to come right up through the floor if the floor isn’t super-tight.
      That would be my guess without more info – ground moisture entering through the floor/foundation. Moisture builds up in the house, then condenses on the cold ridge beam.
      You could try leaving a dehumidifier running in the house, which drains into a sink/toilet so you don’t have to empty the reservoir. The problem is, most dehumidifiers don’t operate when cold. OTOH, the moisture is probably building up in the fall months when it’s much more humid and more temperate. Then, in the evening, as the temperature drops, the beam cools and the moisture condenses.
      Ideally, you could purchase a relatively inexpensive recording humidity monitor that allows you to download months of data to your computer via USB. This will log relative humidity in the house and tell you when the humidity is getting too high. I did a quick check on Amazon and it appears that there are a variety of poorly rated devices that are <$50 and highly rates ones closer to $100.

      • Thank you for the quick response. It is slab on grade construction so the moisture could very well be coming through the slab. If a dehumidifier isn’t
        possible are there other options to control the moisture?

      • Offhand, I can’t think of anything. Unfortunately, this type of thing is fairly common in homes that are completely shut down when not in use. Typically, I (and many building science people) recommend to keep homes above the mid 50’s for exactly this reason.

  16. I am having a home built in Oklahoma with a cathedral ceiling living room and concerned about moisture problems. If I use open cell spray foam, should it be applied to the roof rafters/sheathing cavity or behind the cathedral ceiling cavity?

  17. I am building a home with a cathedral ceiling in Oklahoma and I am concerned about moisture issues. Regarding your the last paragraph or two under “Solution 2 – Use Insulation that Stops Air Movement” you mention spray foam being a good solution. Are you talking about open or closed cell? Should it be installed on the back of the cathedral ceiling cavity? Or up on the roof rafters/sheathing? Thank you.

    • Closed-cell spray foam is best because it has a lower moisture permeability. You can spray it to the back of the ceilings drywall if the roof is open or the underside of the roof decking if you need to do it that way. Ideally you would spray it to the back of the ceiling drywall and then you would ventilate the rest of the cavity from the soffits up to the ridge vent. Since you’re building the home and have control over the process you may also want to consider using board foam on the inside of the rafters before you put up the sheetrock. This would greatly reduce thermal bridging from the rafters and then you could fill the cavities with either open or closed cell foam and ventilate under the roof decking to flush out any residual moisture. You could even use fiberglass because the moisture levels getting through the board foam will be so little.

  18. We have cathedral ceiling in several rooms. The house is in NC. This has been an exceptionally humid summer but it is the the first time since the house was built (1984) that a severe humidity issue has developed in one of the three rooms with a cathedral ceiling. It is so bad that the ceiling gets a layer of moisture on it if the ceiling fan is not run during the day. There are also four large windows starting at 7 feet up between the kitchen and sun room (interior windows) that steam up as well. The crawl space under this room is dry. The windows, are mostly the older style Pella windows (two single pane pieces of glass with a 2 inch space between them). Humidity in the house is high although the HVAC is working properly according to to two HVAC companies. I have put a vapor barrier between the attic and upper portion of the room to no avail. I’ve read that moisture migrates from hot to cold as well as rising since it is lighter than air and this is made worse since hot air rises. If the moisture was coming in through the windows we would expect the problem to show up in all rooms with cathedral ceilings. Not the case. It must have something to do with the ceiling since the crawlspace has been ruled out. A new roof was put on by the previous owned 2 years ago and shingles were laid over the opening for the ridge vent. I corrected this deficiency several weeks ago but the problem continues. I wonder if air flow from the soffits to the ridge vent is blocked and casing the problem, But again, it is not a problem in other sections of the house. I will add that we added three skylights to the roof but the condensation problem is on both side of the cathedral ceiling wnad the skylights are only on one side. All comments and suggestions are welcome.

    • Can you think of any other factors that might have changed? Since you have such a long, trouble-free history with the house, it would seem that something had to have changed to cause the current humidity issues.

      A few things that I can imagine:

    • Vent fan(s) clogged – this could be bath fans or range hoods. It’s fairly common for birds and squirrels or other animals to get into the duct and clog them with debris.
    • Dryer duct – when was the last time you cleaned the ductwork from your dryer to the outside? These fill with lint after a few years, leading to very inefficient dryer operation and excess household humidity levels
    • It’s possible that the ridge vent has something to do with it but I kind of doubt that it would cause these type of issues.

      If you can, check all your vents, listed above, and get back to me. We should be able to troubleshoot this together before your roof rots out.

      • Thank you for the response. I will get back to you after checking the dryer vent but that is on the other side of the house.

  19. I am at a loss as to what to do with my roof. I live in the Pacific Northwest in a Justus solid cedar home with a Monier shake style concrete roof that has been on about 20 years and is in good condition. However, about 3 years ago bats and possibly mice have managed to get in the tiny openings between tiles and perhaps under the sheathing. I had the side and ridges foam sealed by an exclusion company and this has helped reduce the animal problem, but some are still are entering at night. Since that sealing I have noticed an increase in loud cracking sounds during the day and night which are apparently from built up heat in the sealed unvented roof on hot days. All ceilings are cathedral style tongue and groove cedar covered by a membrane, 3″ rigid foam insulation, 1×4 battens to hold the foam in place, solid plywood sheathing and a waterproof membrane, followed by tile hanging on wood strips. All interior lights are surface mounted and none penetrate the ceilings. I can replace the roof with composition, thereby sealing the roof even more, but am concerned that this would allow even greater heat build up and rapid temperature fluctuations than the tile. Some roofers have suggested that we could put ridge vents in, but I have read on some building sites and on ASHRE that venting a sealed roof design in the Pacific Northwest can result in increased moisture in the roof and lead to mold. I had a conversation with a principal at a very large roofing consultant company and he felt that just adding ridge vents would allow the lighter hot air to escape above the foam and resolve the heat build up and noise problem. I would appreciate your opinion on whether this would be a reasonable approach.
    Thank you-

    • From a physics standpoint, the cracking is probably due to structural members expanding during the day and contracting at night, as it appears you understand from what you wrote. I am concerned that the sealing process changed the dynamics of the roof, since you had good luck with it in the past and only recently experienced the cracking sounds.

      I’m unclear as to where the pests have gotten into. Given the construction you lay out, there wouldn’t appear to be any place for them to go except under the tiles. Sorry if I’m not visualizing this right.

      I’m also unclear in your construction as to how the ridge vents would improve ventilation? Where would the air move from/between? Sorry again, I’m just having a hard time seeing the logic behind the suggestions you’ve been given. The only thing that I can imagine is that he’s thinking that air will move between the foam and the plywood sheathing above. That could make sense if there’s enough airspace and venting at the bottom to allow air to flow into the cavity. But just adding roof vents without allowing for air intake at the bottom will result in minimal/no air flow and would be a waste of time.

      I also agree that venting a sealed roof in a humid climate is opening it up for problems. I would advise against doing anything that changes the basic configuration that’s been working all these years. However, if it’s venting in the way I described above, the moisture would probably be flushed out as air flowed through and the roof goes through heating cycles during the day. But again, if you haven’t had moisture problems in the past, I’d be very cautious about changing it.

  20. Great information! How do I figure out the problem with why paint is peeling off the top of my cathedral ceiling. Before reading this page, I thought it was too much humidity/moisture in the house, especially as a result of a broken oven hood that does not suck out any moisture while cooking in the kitchen. Another issue I thought might affect it is the attic next to the cathedral ceiling is not ventilating probably because the vent fan is not working. Now, after reading this page, I think the problem might be improper airflow through the roof of the cathedral ceiling because there is no ridge vents. The house was built in 1978, location southeast Georgia.

    • Could be any of those things. Since moisture rises and tends to accumulate at the peak, I’m thinking maybe your theory about moisture in the house could be accurate. It could also be possible that when the ceiling was painted, it was moist towards the peak and that moisture caused poorer adhesion of the paint.

      If the moisture is coming from the space behind the sheetrock, then there’d be a pretty large amount of moisture up there which would probably be causing issues with your roof.

      It would be worth inspecting the areas where the paint peeling is worst. I’ve found that cutting a small hole in the sheetrock (that can be easily patched) can be very revealing. That would tell you if there’s moisture/mold in the cavity or if it’s just accumulating inside the living space so you can address the real issue. Often people spin their wheels for years, trying this and that without success.
      Good luck. Please let us know how you make out.

      • I am thinking of putting some wooden trim at the top of my cathedral in order to cover up where the paint is peeling. Carpenters who have come by to look at the issue say that they would have to nail the trim into the ceiling into the sheetrock (i.e. drywall) in order to hold the trim in place. Do you think this would allow moisture air to seep in from the house and into the space between the roof and sheet rock thus contributing to the problem? Or do you think that the nailing trim to the top of the cathedral ceiling will not cause any additional problems? Thanks!

      • If you add trim as an aesthetic addition, it will minimally affect moisture one way or the other. Nail through the material isn’t going to change anything either in any sort of substantive manner. Where it starts making a difference is if there are actual holes, like for an outlet or light fixture, where air can freely move between the interior and the wall/ceiling cavity.

  21. Hi T.D. . . I have a bit of an issue and this article seems to touch on exactly what I’m seeing. I have a cape style home that was built in 52′ w/ gable end vents and a walk up attic. At one point the walk up became living space with knee high walls and the ceiling sheetrocked right to the peak and around the collar ties.

    The problem is that it’s a hot roof, no ridge vent and no soffits, because of the warmer air on the inside of the house in the winter (North East) I am getting some condensation near the peak on the inside of the sheet rock. This also happens in the summer when there is an air conditioner on and the hot air rises and gets forced up. There is a brand new roof on the house as the old one needed to be replaced, There are no rafter mates in the space between the sheetrock and the roof sheathing and the space between the roof and the sheet rock is completely filled with fiberglass insulation. I have NO idea how to resolve this now !!!!

    I could cut in a ridge vent but there are no soffits, I could add a hicks vent at the bottom of the roof but the area inside is full with fiberglass. What can I do to fix this issue once and for all ?!?!? I’m really at a loss, any direction you could provide would be greatly appreciated.


    • It sounds like you have a high moisture level in the house. Even with an insulated cathedral ceiling, the sheet rock will be colder than you might expect. If you have more ventilation then the sheet rock will get even colder and the condensation problem will get even worse.
      Humid air rises, which is why you’re getting condensation at the peak.
      I suggest getting a humidity meter (you can get one that measures air relative humidity for maybe $30.) Measure the humidity low in the room then measure it up near the peak. During the winter/cooler weather, you should be reading 40% or so. I suspect you’re up closer to 55-60%+ when you see condensation. The question is why?
      It could be as simple as bathrooms not venting the moisture when you shower. Check the bath fans to ensure good flow and run them while showering and 20+ minutes after you shower.
      Think about your home – are there any other moisture sources? Lots of house plants? Dirt crawlspace or basement? Anything like that can cause moisture issues like you’re seeing.

      • Hi T.D. thanks so much for the quick reply. I’m at a loss . . . the house is in the north east (Massachusetts) and currently the house is completely unoccupied as I renovate it so there is no source of moisture right now. I’m really at my wits end about this problem. To make the problem even more curious is the temp difference from inside to outside is not even that significant. It’s been a little cooler here lately maybe 30’s-40’s outside and the inside temp is set to 52.
        I am thinking that my only alternative, because I just got the new roof installed, is that I may have to rip out all the sheet rock and insulation on the inside in order to install proper vents then cut in a ridge vent and add hicks vents at the bottom of the roof. I’m freaking out, I hope I don’t have to do this but I’m not sure what other alternatives I’ve got.
        I’m thinking about cutting a good sized hole in the ceiling upstairs to see what is going on inside the rafter cavity to see if there is any damage in there or signs of water inside the rafter area.

      • Condensation on the inside doesn’t come from the outside so you can rip it apart and ventilate all you want but the problem won’t go away.
        I still encourage measuring the relative humidity indoors. There has to be a source of moisture. Wet basement? Something is causing the problem.
        Is the house closed up? It could be like the dew forming on the car at night. If the house absorbs moisture during the day, it will hold that in the building material. With the house so cold, it won’t take much to get condensation problems. That’s why houses should be heated even if vacant. Otherwise, they get moldy. Try turning the heat up to at least 60. Also, you might want to air out the house when the humidity is low.
        I’d turn up the heat and run a commercial dehumidifier until the humidity drops to an acceptable level.

  22. Hi Ted. Depressed. I have a 1980 3000sq.ft. 4 level split home in the country in Manitoba Canada which has a cathedral/vaulted ceiling. As you know our Winter’s can be brutal. Building Plans came from California and it was constructed by a home builder as his own home around 1979. They only lived in the house abt 3 yrs. We have lived in it 25 yrs. to date.
    The roof deck from the outside does not have sheathing but wooden slats. We just had the roof re-shingled again abt 3 yrs. ago. Asphalt Shingles are tacked to the slats. About 70% of the roof is not accessible because of the vaulted ceiling. I cannot access built in electrical boxes or vent hoses from the bathrooms and kitchen stove because its just too narrow a space. The South view from the Great Room and kitchen is almost all glass the entire length of the home (abt 40ft). 4 large sections of glass, a couple which are sliding units.
    The only thing on the inside ceiling (tongue & grove cedar) of the Great Room is two lighted ceiling fans and one set of lights over the dining room table. I have a skylight at the top of the stairs abt 5ft above a defective ceiling fan. Water started coming through the highest ceiling electrical (fan) abt 6 yrs. ago. That ceiling fan has now seized up and stopped running. The electrical lights work but that fan doesn’t. I also have two hanging ceiling light fixtures in the kitchen. The higher one (same elevation as the defective fan) has had water dripping down the electric wire into the glass globe a few yrs. back. Luckily no water from there in the last couple of years.
    Soffit vents are on both sides of the home (South & North). I also have 3 roof vents. I had tried a whirly a few yrs. back at the recommendation of a local roofer but it didn’t help so we had it removed 3 yrs. ago. We have circular gable vents at the East and West ends of the house. The attic insulation is cellulose and a bit of fiberglass in cavities here and there. The last 4 yrs. we have now been getting water leaking from the top of the glass window unit frames on the inside at about the same track downwards as the defective fan. There has been enough water to fill half an ice cream pail some years. Towels get sopping wet.
    We also have a real wood burning fireplace in the Great Room which we crank up during winter months. We burn all the time except when sleeping. We manage to get the temp up in the Great Room to about +24 Celsius or 75 Farenheit or highier. We also heat with a new high efficiency natural gas furnace and radiant cable ceiling heat in our upstairs bedrooms. I have looked inside the attic in the small area that I can get into and have noticed some water stains here and there.
    Shoveling the snow from the roof stops the water entry a bit because the roof gets colder on the outside when the snow is off. Last Winter I went up the roof to shovel the snow off and there was ice in spots 6 inches thick under the snow in places at the edge of the roof. I have rubber membrane over the soffit area. I really would appreciate advice which would stop the entry of water dripping into our home. We are getting older and are thinking of downsizing but I worry on passing on this white elephant to someone else. Its a beautiful home and property other than this issue. I can send you pics if you so desire.

  23. Hi I have read your article, I have a peeling ceiling in the bathroom and it is going black, I have no money to attain your solutions I was wondering if I stuck on styrofoam packing or sheets ,just to clean it up would it work and stay white or will the fungus spread.through them. I ws going to stick them on using a glue gun.

    • Peeling paint and mold growth are signs of excess humidity. In a shower, it’s really tough to control without a good bath fan that vents up through the roof. So your most important thing is flushing out moisture or the problem is going to get worse and worse. Over time, this can lead to rotten timbers that are supporting your ceiling or the roof above, so it’s not something to mess with. You HAVE to deal with the moisture properly or you’re going to end up having to pay a lot more later.

      So, number 1, make sure you’ve got a good bath fan. This should run the entire time you’re in the shower/bath and for about 30 minutes after you’re done.

      In the meantime, you should clean the ceiling where it’s moldy. Wear a good respirator because you don’t want to breathe those mold spores as you’re cleaning. Warm soap water should do the trick since the soapy water dissolves the “glue” that binds mold together. Lots of people use bleach, but I’d start with soap water.

      Once you’ve cleaned it, and it’s dried out well, you can repaint it with some good paint intended for bathrooms. Hopefully, you have another shower you can use because you can’t shower until the paint has dried and set. And if the ceiling hasn’t dried out well, the paint won’t adhere and will just fall off.

      That’s your starting point. If you just foam up on the ceiling without dealing with the moisture, the moisture is going to go up there still and rot things out.

      Good luck!

      • It’s really difficult to retrofit an improperly done job. Often, the best thing to do is ensure that humid air cannot enter the ceiling cavity where the insulation lies. I’ve seen many homes that have survived decades with the cathedral ceilings packed with insulation because there was a thick interior ceiling layer of plaster without any holes in it. Unfortunately, more “modern” homes often have these ceilings filled with recessed lights that allow copious quantities of humidity to move into the ceiling cavity. During the winter, the water condenses in the insulation and rots out the roof sheathing. The retrofit for these is to remove the recessed lights and patch up the ceiling.

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