How NOT to insulate your house

Sometimes insulation hides bigger problems.

The other day, I was talking with a friend of mine – an energy auditor who was a builder for decades. The topic came around to bad advice that “experts” give about insulating. It’s something that we both feel passionate about because homes get ruined and people get sick when innocent people follow this bad advice. We both adhere to a similar do no harm philosophy of  “if it’s worked for decades as-is, don’t mess it up!”

There’s a science to building and the tighter and more energy efficient you make a home, the more important it is that you do things “right.” It’s like the difference between making a log raft and a submarine. A log raft is leaky, but it’s forgiving because it floats by virtue of the logs. It doesn’t have to be water-tight. A submarine had better be water tight and structurally sound or you’re going to drown and get crushed by the intense pressures of the ocean.

Unfortunately, unlike boats and submarines, homes today are often built in the cheapest way possible, with little regard to physics. Renovations are even worse because people often hire unqualified “low-bid” contractors to do the work without realizing that the few thousand dollars that they save on construction may cost them tens of thousands to fix or even send them to the hospital due to mold or poor indoor air quality.

The problem is, people familiar with building science are extremely rare, as are the chances of finding a builder who knows how to make a healthy, energy efficient home. That’s why you’re here reading this now – you want to learn what not to do when insulating and how to do it right.

#1 – Insulate the attic after air sealing and reducing moisture

Adding insulation is one of those jobs that people think can be done blindly. Just throw some pink stuff up in the attic and you’re good to go, right? Wrong.

If you’re lucky, you’ll get away with this. If you’re not, you could end up with an unhealthy, moldy attic. Why?

Many homes are leaky and have insufficient insulation in the attic. This allows a lot of heat up to the attic. Warm spaces have less condensation risk than colder space so when you add insulation to the attic floor, you’re intentionally blocking some of that heat from keeping the attic warm. This makes the attic colder and a colder attic with moisture leaking from the house can result in condensation, mold and wood rot.

Bath fan ducted into attic

This is one of the main reasons that energy efficiency experts tell you to air-seal the attic where the insulation will be installed and ensure bath fans are properly vented before insulating. Air sealing reduces the amount of moisture that that can get into the attic, reducing the chance that you’ll end up with a mold problem. But, you want extra protection in the system because some moisture is inevitable. Maybe you got away without proper attic ventilation in the old house, but as you tighten things up and insulate, it becomes increasingly important to have good attic ventilation.

I personally don’t care whether you use gable vents or properly matched soffit and ridge vents, just do it right. If you use gable vents, it’s best to have two of them – one on each side of the attic to provide a good cross flow of air. If you use a ridge vent, you MUST have an equal or greater volume of air coming in to the soffits.

And that picture at the top of this post? That’s a wet mess of insulation caused by the builder neglecting to put an air and moisture barrier behind the bath tub. Instead, they were lazy and there’s a big hole with fiberglass draped over it – that’s worse than useless!

#1a – Turn off the humidifier

Humidifiers can destroy a home and make you sick. The more you tighten and insulate your home, the less you need to use humidifiers. And yet, I see very tight, new homes, being built with whole house humidifiers that dump gallons of water into the air. Moisture finds the tiniest cracks and holes and moves into spaces like the walls and ceilings. Much of it ends up in the attic where it can rot out your roof.

My advice to people as they add insulation is always “turn off the humidifier.” If the house is still too dry, find out where the air leaks are and plug those because that’s what causes dry air.”

I know this personally. Before I weatherized my own home, we’d have a humidifier going all winter. The air was so dry that my lips chapped and lightning would fly every time I touched the dog. But ever since we dealt with all the big air leaks, the humidifier hasn’t run once. It’s comfortable in the house all year round.

#2 – Choose your insulation carefully

Insulation is not a “one-size fits all” product. Insulation, like cellulose, that works great in the attic and the walls should not be used in many basements and crawlspaces where it can get wet. Likewise, fiberglass, which is ubiquitous, shouldn’t be used for the band joists in the basement or any other place where air sealing is required since fiberglass is does nothing to stop air movement.

You have to think about why you are using insulation in each location. For example, the band joist is often leaky, letting cold air in. It is also probably very cold because it may be exposed to the outside temperatures, making it a likely candidate for condensation. This tells us that you want an insulation that air seals and keeps interior moisture away. The perfect product for this is closed cell spray foam (as in the link above).

What about wall insulation? Walls are *usually* fairly air tight on the inside and leaky to the outside, with a few holes for electrical outlets and such. In general, walls are pretty forgiving about the type of insulation that’s used, but you can still screw them up. For example, a lot of building codes call for vapor barriers on walls, but using a vapor barrier on the inner wall AND using a tight outer wall can lead to horrendous moisture problems inside walls. This is an entire article itself, so I won’t go into more detail here. Just know that a conventionally built wall is usually forgiving, but if you start doing anything different, you need to be really careful.

Another insulation location is the attic. As noted in #1, you need to air seal before you insulate. But what if you could air seal and insulate in one shot? In fact, spray foam does exactly this. I love the stuff. Rather than having to spend days or weeks in a dirty attic, carefully caulking every crack and filling all the holes with cans of foam, and then carefully laying out insulation, you can instead just remove the old insulation and have a foam contractor come in and in a day or less, your attic will be completely air sealed and insulated. It’s really a superior way to insulate. I used it in all my own renovations and the results are awesome.

There are other places that are critical to consider. For example, cathedral ceilings. I’ve seen a lot of problems with insulated cathedral ceilings, especially those with tongue and groove planks instead of sheet rock. Because of potential moisture issues, I would personally never use a loose insulation like fiberglass in these ceilings. Moisture goes right through fiberglass and will condense on the cold underside of your roof. Even if you use vent chutes to provide an air space above the insulation, you can still have problems. So in choosing insulation for a cathedral ceiling, you really want a material that stops air and moisture from reaching that sensitive roof deck. Again, the ideal material is usually closed cell spray foam.

#3 – Insulate continuously: like a jacket for your home

One of the biggest mistakes people make is ignoring the big insulation picture and how it all connects together. You can do everything I’ve written about above perfectly and not have the insulation work at all. How?

Imagine an ice chest. This is just a box of insulation, sealed on all sides. Ideally, this is how a house is made. But what would happen if you took the top of the ice chest and moved it a couple of inches away from the cooler? It’s not air tight any more and whatever is in the chest would end up at room temperature. Same thing with a refrigerator – what happens if you leave the door open? The fridge has to run continuously to try to get cold while all the heat from the room rushes in. Any child would look at these examples and say “duh!” If this is so obvious, why do highly paid builders often construct houses that are no different than an ice cooler without a lid? Or to use the jacket analogy, would you wear a jacket with the zipper wide open?

Unfortunately, the more complex the home’s design, the harder it is to ensure continuous insulation. Modern homes, with a dozen different roof lines and a hundred walls can be difficult to deal with properly. I’ve seen contractors start by insulating under the roof in one place then switch to insulating the walls in another, rendering the roof insulation meaningless.

One trick to use is the “pencil trick.” Take the architectural drawing of the house and, without lifting the pencil, draw a single line representing the insulation around the house. Wherever you lift the pencil would be a discontinuity where outside air could short-circuit the insulation, rendering it useless.

#4 – Be smart – Don’t break the original home’s design

Going back to the “do no harm” principle, you have to be really careful not to “break” the working design of the house. I’ve seen insulation contractors do really stupid things that lead to moldy, rotten homes. If a house was built 50 or 100 years ago, and it’s never had a mold problem, there’s probably a good reason why. For example, there are a lot of older homes build with plaster and lath. These have an air gap between the exterior stone wall and the plaster interior wall. That air gap allows water to drain and dry out. But yet we see people putting cellulose and other non-water resistant insulation into that gap. That’s like sticking a sponge in there. It will soak up the water and likely end up in a moldy, rotten mess and useless insulation.

There are other stupid things you can do. For example, pretty much every roof that goes on gets a ridge vent. But why add a ridge vent to a 50 year old home that already has gable vents? Worse, that 50 year old house won’t have matching soffit vents. The result is a house that is less energy efficient and more prone to mold and rotten roofs because the ridge vent sucks the humid air out of the house and into the attic.

If something doesn’t make sense to you, don’t let the contractor do it. Sometimes they’ll be offended and say something like “I’ve been doing this 30 years, I know what I’m doing.” Well, maybe they’ve been doing it wrong for 30 years! If you have any doubts, get another opinion or two. Or post a question on my Q&A section. There’s a science to this and there’s a good chance that your contractor doesn’t know the science. I’m not saying that they’re not a good contractor, but they may simply not be knowledgeable about the current best practices. Regardless, if they’re not willing to listen or back up what they say with facts, you should find another contractor.

#5 – The home is a complex system

I touched on this in #4 with the discussion of the ridge vents. A building is a lot like a human body – what you do in one place affects things in another. Just like adding a ridge vent can lead to increased energy bills and a rotten roof, you can do other things that have unintended consequences.

For example, many utility rooms with furnaces or boilers have large vents that provide fresh air into the room. Often, people look at these as sources of cold drafts (which they are) and close them up. The problem is, they were put there for a reason – they supply fresh air for the combustion that the heater is doing. Closing the vents and sealing the utility room can lead to improper heater operation or even carbon monoxide problems which can lead to illness or death. Unintended consequences can be deadly.

Another example of unwanted side-effects of insulation – spray foaming a house without ensuring adequate air supply.

I’ve been known to say “a house can never be too tight.” Unfortunately, you can screw things up by making a house very tight without considering fresh air and humidity requirements. Using spray foam, you can make a house that has extremely low air leakage, so you have to consider introducing fresh air using an HRV (heat recovery ventilator). There are standards for this (See ASHRAE 62.2 and related). Basically, you want a certain amount of fresh air per occupant in the house. For typical families, this amounts to about the amount of air introduced by a bath fan. Not much! But often, people adding spray foam insulation either don’t consider or don’t know about the fresh air requirements, and the results can be horrible.

Concrete example: you make a house super tight at the same time as you remodel the kitchen and add a powerful new range hood. When you run the range hood, it creates a suction so powerful that it can sucks the exhaust fumes from the furnace and water heater back into the house. Again, this can kill you. No joke.

Less extreme example: you tighten up your house and then you find that every time you make a fire in the fireplace, you end up with a huge amount of smoke in the house because there’s just not enough air going up the chimney. To compensate for this, you have to open a window whenever you have a fire.

There are numerous situations like this that can occur if you “just insulate” without considering the complex system that is your home. Please, go into these renovations with open eyes. If you have any concerns, call in a trained energy auditor/building scientist. I’m also happy to answer questions posted here. But be aware that in order to do this right requires a series of precise measurements that take into account a variety of factors about your house and various appliances in the house. In some areas, these measurements are required if you are adding a certain amount of insulation or doing significant renovations.

15 thoughts on “How NOT to insulate your house

  1. Excellent post! My parents are looking at insulating their turn on the (last) century farm house. It has 3m walls, cement ceiling and corrugated tin roof with 1 working chimney, multiple vents and open door way entrance (and as a result lots of “wildlife” up there). The house gets quite chilly in the winter when the temperature drops to 0ºC. They are favouring the spray foam option and I was wondering what you think about that?

    1. Wow, that’s a tough one. Honestly, it sounds too complicated for a recommendation without being there to evaluate the nuances of the design. I’d also warn that if you ask a professional insulator, many will sell you on their solution whether it’s good for the house or not. Your parents could waste a lot of money on foam and have it make a minimal improvement or worse, cause a problem elsewhere in the house.

      Your best bet would be to get a comprehensive overview and recommendations from an independent home energy consultant. For about $500US, it’s a great investment. You want someone who doesn’t have a stake in selling you a specific solution and will be honest and direct with you.

      Good luck! Sorry I can’t give you more advice.

  2. I ran into something like this. Sealed & insulated the attic, and then had a new roof put on. The roof plan was to do a ridge vent and “retrofitted’ soffit vents, something called edge vent. Well… the attic insulators dense-packed the cellulose down into the crannies where the ridge vents were supposed to be venting. Needless to say they didn’t draw air very well. :( I went up with a stick and a shop vac and tried to get it out of there, but it’s nigh impossible.

    Is there any way to actually measure attic ventilation?

    1. I can’t think of a good way to measure ventilation that is reasonable given the large areas involved. If you had an attic that just had gable vents, you could measure pressures at each vent and combine that with the opening area to compute air flow but the measurement would vary tremendously with wind and temperature so I don’t think it would be terribly useful.
      In the situation you ran into, you might be able to tape plastic under the attic hatch (inside the conditioned space of the house), then use a manometer to measure the pressure there. With a properly sealed hatch, you should get zero but chances are, you’d have a negative pressure relative to the house, indicating air flow from the house to the attic. There are techniques you could use to quantify the actual air flow at that location, but again, it’s imperfect since there are usually so many places that air can move from the house to the attic.

  3. Have you ever worked with “Retrofoam”? We have a house built in 1979 with a master bedroom upstairs loft area and it only had an inch of styrofoam in the cathedral ceiling for insulation and batting in the walls. We’ve had all sorts of problems with the AC maintaining temperature and high humidity, so we had Retrofoam injected into our walls and ceiling, but the problem didn’t resolve. After we had the AC unit fixed, as it was also part of the problem, it’s maintaining temp, but we still have a humidity problem. Prior to the foam we had humidity around the same % and were running a dehumidifier which increased the temp of the space. I’m just baffled that we can’t figure out how to make the AC unit do it’s job and keep the humidity level down. And now, I’m not so sure we didn’t just make the situation worse. Any advice?

    1. Unfortunately, I haven’t. I investigated it and talked with an installer a number of years ago and it looked quite interesting but opted not to go with it because the installers in our area didn’t seem reliable/experienced with it.
      The one big problem I have with any injected product, whether it be foam or other product is that you’re at the mercy of the installer to do a good job unless you validate the job with an infrared camera. A friend of mine had a foam job done in his walls that was a total dud – when I looked at it using IR, you could see that the foam just dribbled down the wall and didn’t fill the cavities.

      I mention this because it’s very hard to know what’s going on inside of the walls without a test like combining a blower door and IR camera. It costs a few hundred dollars, but it’s well worth the expense because otherwise you’re just guessing and can spend thousands of dollars trying things that may or may not work.

      Humidity problems are a dead giveaway that you have a leaky house. A blower door test with IR scan should show you where the leaks are. It might be something systemic in the way the house is built or it could be something as simple as a bad duct in your attic which is the cause of the worst problems I have seen.

      So my advice, is find a good energy auditor locally who has experience in troubleshooting using IR and a blower door. You may have to interview a few people to find someone who isn’t a “production” energy auditor. These days, there are a lot of people just doing cut-rate energy audits but who really don’t understand building science and troubleshooting. You want a trouble-shooter. Explain your problem and listen carefully to their reply. If they seem to have a generic cook-book, they’re probably not a troubleshooter. If they can clearly explain what causes your type of problem, it probably means they’ve got some experience. Make sure they use a blower door and an IR camera. If they say they don’t need one or the other, send them packing!

      Good luck. Please let me know how it goes. I think your problem is very solvable.

  4. Thanks Ted!
    Your tips on attic insulation are very helpful. I’ve been researching a variety of things that can be done to increase energy efficiency while designing an addition. One topic is geothermal energy for the home. After speaking to several geothermal professionals/installers, one thing they all recommended was to first take a hard look at the energy efficiency of the existing home. And, consider a conditioned attic space.

    It appears to be an effective method of reducing the costs of geothermal installation; better insulated attic and home overall calls for a smaller and less expensive geothermal system. Further research suggests the attic is a great place to start with respect to energy efficiency. Your tips are extremely helpful in that regard. Again, thanks for the detailed info and photos.

    1. Yep, energy efficiency is definitely the first thing to look at if you’re looking into geothermal. One thing that is often overlooked is that a more efficient home is also more comfortable because the temperature is more even. Also, as you noted, it helps reduce the cost of geothermal. More comfortable and less expensive is a good thing!

      Good luck with your projects :-)

  5. Hi, I would be interested in your opinion regarding adding exterior foam to walls. I worked as a carpenter up to15 years ago and am a certified R-2000 builder. My own home (20yrs) is r-28 walls, strapped with 2×3 to protect the vb and provide a chase with a hrv the home has performed perfectly even at -55f temperatures. I am planing to build a smaller home for retirement and because there are more windows in smaller walls, the many headers, jacks and corners, I am considering adding exterior foam. Because of my background, I am having trouble with the idea of omitting thr VB. We use to omit the tape at the top of the walls to allow the typecast to breath into the vented soffit. Can the interior walls be build both foam and VB and the top exterior be vented with 1″ vent plugs to vent into the soffit. Thank you

    1. With your background, you should be writing these articles! :-)
      It sounds like you’re working in extreme environments up there. In such cases, the risk of condensation is much higher than down here where things are milder.
      The fundamental theory that guides recommendations is to ensure that warmer, moist air from inside the house can’t come in contact with any surface cold enough to lead to condensation. With enough exterior foam, you should be able to maintain inner surfaces at warm enough temperatures (roughly 50F), but you clearly have to be very careful in your construction. With your background, I’m sure there’s nothing new here.
      The “gotcha” that sometimes bites even experienced builders is adding too much insulation inside of the exterior insulation because that insulates the wall cavity from the warmth of the house. In doing so, it can allow the surface between the exterior foam and the interior insulation (usually the exterior sheathing and the 2x studs) to get too cold. That’s where the serious VB comes in to minimize the moisture that gets into the wall cavity. Problem is, with a tight exterior AND a tight interior, you’ve got the dreaded double VB situation that can lead to real problems. If any moisture gets in there, it can get trapped and build up over time.
      Given the severe temperatures you’re dealing with I’d be really careful. Read through for their info on cold climate considerations. And be very skeptical about any solution that needs to be ‘perfect’ in order to work.

      Sorry that this isn’t a more definitive answer to your question. I hope there are a few kernels of information that you can use.

  6. Fireplaces or stoves should have OUTSIDE AIR for COMBUSTION. Many stoves offer this as an “optional” kit and fireplaces can be retrofitted (good luck finding someone who understands it much less do it).

    1. Great point. In the “old days” with leaky homes, people didn’t worry about it. Now that we’re tightening up millions of those leaky old houses, outside combustion air becomes necessary. Fortunately, new home building codes require this but as you noted, there seem to be a lot of contractors inexperienced with this. Our best bet is educating the consumer so they can insist on proper combustion air.

  7. Great post, many people don’t quite know what goes in to insulating a home properly, and its a real shame that some companies out there are more than happy to charge people for a poor quality job – look out for these people!

    1. Thanks for the comment. If there are ever any warnings you have for people, please pass them along. I’m doing my best to help educate the public but it helps to hear from those of you doing the work because you guys are often fixing problems that others have caused. Send photos of the big disasters you see :-)

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s