Why do I have moisture in my walls?

The inside of a wall filled with entrapped moisture

I just received a question that was too complex to answer quickly, and so interesting that it deserves an entire post. Unfortunately, it represents a situation that occurs far too often.

To summarize, the question came from a reader who opened a small hole in their wall and found condensation on the vapor barrier at the inner surface of the wall. The question is, what could cause this?

Here are some more clues:

  • The moisture was observed during the winter
  • The hole was cut in a south wall
  • The home has 3″ foam board sealed to the exterior wall
  • A 2×4 framed wall was built inside this wall and insulated with Roxul
  • A 6-mil poly vapor barrier was then applied just behind the inner sheet rock
  • They did not measure high moisture towards the outer wall
  • The wall was built during a humid summer

Before delving into this more deeply, we have to discuss a little physics, but just a little, I promise. (If you’re a chemist or physicist – cut me a break. I’m going to take liberties with the definitions so that I can describe this in a way that people can actually understand.)

You’ve probably heard of the “dew point” – it’s the temperature at which dew forms. Dew is just condensation and it occurs any time the temperature drops low enough that the water vapor in the air coalesces into liquid water. It’s also relavant to the “relative humidity.” The RH is 100% at the dew point and any temperature below it. This is why the windows in your bathroom fog up – they are at a temperature below the dew point of the air.

That’s about all the science you need to understand many moisture problems. End of physics lesson.

Any time somebody tells me they have condensation, the first thing I find out is the temperature of the surface where the condensation occurs. By knowing the temperature, it tells me something about how much moisture is in the air. If the surface is cold, like a bathroom window in winter, then I expect condensation because even relatively dry air will condense on a window at 35F!

But, when somebody tells me that the condensation is occurring on the “warm side” of the wall (like in this case), all sorts of alarm bells go off. Why? Because the air has to have a LOT of moisture in it to condense at 70F. And by a lot, I mean the inside of the wall has to be like a steam bath. After all, have you ever seen condensation on you walls when it’s 70F? The ONLY time I ever see condensation under these conditions is when I boil water on my stove and the steam condenses on my cabinets. We’re talking serious humidity.

If you’ve been paying attention, you’ll wonder “why is the condensation forming on the inner surface of the wall, shouldn’t it be forming on the “cold” side?

Ah grasshopper, you have learned well…

Look at the clues. This is a south wall. What’s the south wall? It’s the sunny side of the house. So it’s possible that the heat from the sun is heating the wall so that it’s actually warmer than the inside of the house. This has the effect of “pushing” the moisture towards the colder surface, which happens to be the side of the vapor barrier facing the inside of the wall.

Note however that I’m not convinced that there aren’t moisture problems elsewhere in these walls. I would want to take moisture readings using moisture meter that can probe all the way into the wall. Then I would measure the wall on the north side of the house. Since this never sees direct sunlight, the outer surface should always be colder than the inner surface. In this case, if there was moisture, I’d expect to see it on that surface and not the inner surface.

Where’s the moisture coming from?

This is the $10,000 question. The writer said that the walls were constructed during a humid summer. It’s certainly possible that building the walls under such conditions could lead to entrapped moisture, but it would have had to be really, really, hot and humid for the moisture to be high enough to cause problems during this winter.

My guess? There is a leak that allows “bulk water” into the walls. Bulk water is the building science term for rain or other liquid water. Bad flashing allowing rain in is one possibility. Ice dams  are another. This water could be dripping in, puddling at the bottoms of the wall, then evaporating and condensing on the vapor barrier.

The giveaway for this type of problem is to stick moisture probes into the wall at various points along its height, starting at the bottom, a few inches up. If there’s a leak, this substantial, there is likely to be a puddle at the bottom so the wood wood be saturated down low. Up higher on the wall, the moisture readings would likely decrease. They could also increase closer to the source of the leak.

The other test, as I mentioned, is checking moisture readings on the cold north wall. If water was entrapped in the walls during construction, there should be high readings on that wall.

The other thing I would do is measure the south wall far away from the area where moisture was discovered. If it is a leak, most likely the water is running down through one cavity. However, it is possible that a really bad flashing job is leading to lots of leaks, so this isn’t definitive.

So testing this type of problem involves poking a bunch of holes in the wall and reading the moisture with long probes, throughout the thickness of the wall cavity.

Now comes the ugly stuff!

In situations like this, I always recommend that people locate an area of very high moisture readings in the wall then cut the wall open from the inside to examine the condition of the wall framing. Persistent moisture problems lead to rotten wood, bug infestations and mold. You really have to examine the interior of the wall with your eyes. Just remember – sheet rock is cheap, wall framing and mold remediation is really expensive. So cutting out a foot or two of sheet rock is a no brainer.

Back to basics – why is this happening?

This wall was built in a way that makes something like this almost inevitable. In building science, we call this the dreaded double vapor barrier.

Building code in many places includes a misguided provision that requires a vapor barrier on the inside of the wall. In many places, that means 6-mil poly plastic sheeting. The idea is that you don’t want moisture from the house getting into the walls and causing problems. Unfortunately, this assumes that everything is textbook perfect – that the walls are built air tight and that moisture never gets into the wall. But they get away with this often because the outer wall is usually not air-tight. Most walls are pretty leaky and just contain plywood or OSB as the outer wall sheathing. When water gets into the walls, if you’re lucky, it will evaporate and go out the outer wall before it can do substantial damage.

In this case, the home has 3″ of board foam and that was air sealed with foam to the outer wall. That 3″ of board foam, while slightly vapor permeable, is very unforgiving. You’ve used a styrofoam cup for coffee. Do you see coffe pouring out? No, of course not. On a molecular level, water vapor is much smaller and it can pass through to some extent, but you can imagine, it’s a pretty slow process. If you pour a few gallons of water in your wall, sandwiched between 3″ of foam on one side and plastic sheeting on the other, where do you think that moisture is going? Nowhere fast, that’s for sure.


While it’s impossible to fully diagnose this problem from afar, let’s assume that there’s a water leak. Water is getting into the wall and can’t get out. Let’s also assume that no other areas of the home are showing moisture problems.

The first thing would be to find and fix the leak. This can be a tricky process and is far too involved to go into details here. But I’ll give you a hint – water mostly flows downhill. Check flashing. Check for ice dams.

After that, you have to assess the extent of any moisture damage to the wood in the walls.  Hopefully, there’s no damage yet. If not, you got to fix the walls.

On a longer term, this wall construction scares me. Eventually, there will be a leak into the wall that won’t be able to get out and it won’t be discovered until some serious damage has been done. Anything done at this point short of ripping out all the poly and rebuilding the wall is a band aid. You simply should not build walls with dual vapor barriers. To do so is to doom a building to failure.

There might be some less destructive ways of dealing with the problem enough to prevent the house from self destructing. *One possibility could be to cut out horizontal strips of the bottom and tops of the wall and remove the vapor barrier. This would at least give the moisture a way to slowly leave the wall cavities AND give a way to see if there was a water leak into the wall because you’d see staining on the sheet rock. There’s no guarantee that this would work however, but if it were my house, I might try something like this so I wouldn’t have to rip open every wall!

In fact, given the problems, I would probably do this at the bottom of the wall regardless, just to inspect all my walls for water damage. Cutting out a strip, say the bottom foot of the wall, is pretty easy to repair, and would give me peace of mind that other areas aren’t rotting out.


In very cold climates, interior vapor barriers ARE called for because even a small amount of moisture moving through the walls can condense inside the wall causing problems. Don’t take anything I write here as set in stone for all climates – it definitely is not. You are responsible for consulting a local engineer, familiar with building science and best practices in your area.



26 thoughts on “Why do I have moisture in my walls?

  1. I bought a 15 yo doublewide and was doing some remodeling, when i started pulling up carpet i noticed several areas with moisture, i got a meter and they read 20-30%, the high moisture goes up about a foot on the wall and about an inch out on the osb subfloor, no visibe damage but i do get a musty smell, had groundwater gettin in my crawl so i put in french drain about 6 weeks ago, no more standing water under house but my sheetrock isnt drying, these moist spots seem to be mostly on exterior and marriage line walls, do not wNt to put down hardwood until my moisture problem is solved

    • Good you found that and remedied the water problem. It’s really hard to dry things like that. It needs as much air movement and exposure as possible. Fans? If it’s been exposed to high moisture for years, it could be tough to get it down to normal levels. If you have access underneath, you could put a moisture barrier directly under the floor (not touching) to reduce the additional moisture that can absorb into the wood.

  2. Hi Ted,

    we live in York, PA. We bought the new house in oct 2018. Recently we found inside of OSB sheathing in couple of exterior walls has lot of moisture. Our home has Vinyl exterior walls and the home as wrapped with white vapor barrier. This is happening only in couple of exterior walls. Inside humidy during winter was between 24% to 35 %. Any suggestion how to repair it. There is no leak from outside as it is getting dry during summer.


  3. Hi – we live in Miami Florida. We purchased our home about 2 years ago and these last 4-5 months have been having major issues with humidity and moisture inside our home. Baseboards swelling, door frames expanding, laminate floor warping, and moisture in the walls. We painted and caulked around the windows about 6 months ago (they also pressure cleaned the roof, throwing that in just incase its important info). We recently changed out our AC unit and replaced our air ducts. We had a musty smell coming from a half bathroom and the moisture readings on a meter were super high. So we ripped open the walls and replaced a lot of dry wall that had growth on it. We didn’t see any leaks but did find that the previous owners ran a pipe through the concrete floor into the open crawl space and didn’t seal around it. So we sealed it before closing it up, and then sealed everything and closed up the space. I just used a moisture meter on the walls and it is saying that the majority of our interior walls are “wet” including the walls that were just replaced! I’m not sure what other info you need to help point us in the right direction but any insight would be HUGE… We are kind of stumped because we don’t know where the humidity and moisture are coming from. A little back ground, we bought from people who did a “renovation” before selling. We found that they did leave some openings behind things (in kitchen, bath, etc) and working on sealing those. Our house is on a crawl space, we can access about 70% of it. We don’t see visible leaks in the pipes under the house, and don’t see visible leaks from the roof. We have been told our attic could use extractor fans and insulation. We do feel a draft from the electrical outlets and at times our electric panel sweats. HELP!! Honestly, not sure where to turn…

    • It sounds like a ton of moisture is getting in – much more than from a few air leaks.
      When they replaced your ducts recently, did they test them to ensure that they were air tight? The system needs to be pressure tested to verify it was sealed properly. From your description, it sounds like a lot of moisture is getting sucked in from outside and brought into your house.
      This is assuming that your AC is running properly. The AC should be removing that excess moisture.

  4. I would like to get your opinion if i can. We had a scan done of our house and 1 of the images showed higher moisture.
    Would i be able to email you and show you the picture and get your opinion. ?

    Thank you

  5. Hi Ted,
    My bathrooms interior and exterior walls are forming moisture at the top where it meets the ceiling, when I shower. Water spots on the ceiling which reactivate and become sticky. The exhaust fan is a Broan 130 cfm, new 6″ flexible duct which vents to the roof, which I have on during shower and 1 hour afterwards.
    I’ve started also running a large and small vornado fans in the room during and after shower.
    Humidity jumps to 75 when showering. It will return to normal after 3 fans running for an hour.

    One interior wall corner is 10 degrees colder than the thermostat. The home is 3 years old on a stab, single story. The attic has a baffle with insulation, 2 insulation companies say I have plenty of fiberglass blown in. The interior walls have no insulation and exterior walls have bat insulation.

    Humility levels with out a shower going around 50.
    My builder says I need to get the RH to 30.
    What are your thoughts?

    • Moisture in bathrooms near and on the ceiling is really common, even with ventilation. My wife’s shower bathroom ceiling needs repainting for exactly this reason. The trick is, at those locations, there’s usually wood framing, so the insulation doesn’t protect the area from getting cold. Having a spot that is considerably colder than the rest of the ceiling or wall is common though often avoidable (see this on wind washing). Since you’ve checked the insulation and it seems good, it might just be an area that has less insulation and more ventilation from soffit vents. This diagram from BuildingScience.com shows how the air should flow:
      Protecting insulation from wind washing
      Whereas this diagram shows how it can go wrong:
      Example of wind washing through insulation
      That corner might also not get much heat – air circulation can be funny/unpredictable. Has anybody looked at that exact spot in the attic? I’ve seen cases where there’s plenty of insulation everywhere except one area, which has none.

      It does seem odd that it takes so long for the fans to clear the humidity in there. Usually our humidity controlled fans turn off within 10 minutes of showering. It might be how you’re using the fans because it would be difficult to circulate air in and out of a bathroom with free-standing fans. You’d have to have one blowing air into the bathroom and another blowing air out of the bathroom in order to get proper circulation. But again, the bath fan itself should handle the issue in a matter of minutes. Have you tried the “paper test”? Hold a sheet of paper up to the bath fan cover. It should suck onto the cover forcefully if it’s working well. If you get a feeble suction to the paper, then there may be an issue with the ducting from the fan to roof (though it sounds like you’ve already thought of this). Worth a try just to make sure.

      Are you located in a very dry environment? I ask because 30% RH is quite low. Typically 25% is considered uncomfortably dry. There’s some debate (see this article) about recommended levels, especially because it depends on locaiton. If you live in New Mexico, it might be 20-30% in Summer. But in most locations, 50% RH is normal and comfortable.

      • Thank you.
        I cannot get an insulation company check to verify wind washing.
        What expert would check for this?
        What would be done to correct the wind washing?

        Builder says, the house is wrapped in Tyvek.
        The exhaust fan seems to suck the paper towel.
        I am located 40 miles southeast of Chicago.
        The bath room moisture has been so bad it’s rusted the light fixture.
        And the floors are wet when shower is used.
        The 50% humidity is with 2 dehumidifier running, 30 pint and 70 pint.

      • What do you think of Accuvent?
        Could my high humidity and moisture when showering be due to wind wash?

      • I really don’t see how the humidity could be due to wind wash. The humidity problems are increased by poor ventilation. But it also seems that there has to be a big leak in your home or ducts that the blower door tests didn’t show. Did they do thermal camera scans during the blower door tests? Did they test the ducts?
        At this point, you need someone local to analyze the problem in detail.
        I’ve looked through some of the websites of companies offering these services around Chicago. Here are some promising looking firms:

  6. Hello,

    I am currently building a brand new home from the ground up and have a condensation issue with one wall which I’m not sure how to address. The city I live in requires R28 insulation for all new homes and built with 2×8 stud exterior walls with 24″ OC.

    The house has been framed, sheathing is done, Tyvec home wrap paper on the entire house, and this wall just had hardy siding installed on it a couple of days after the R28 insulation was put in. The current weather is rainy and on average about 48′ F right now. This is an exterior south facing wall on the 3rd floor (Master bedroom and master bath wall) of the home. I have AC and HRV thick aluminum/metal pipes running in this wall and behind these AC/HRV (HRV is mandatory by the city) pipes is foam sheet insulation between the sheathing and the pipes.

    The interior of the home is currently cold as well since their is no radiant heat right now as the boiler will be installed in a few weeks. This is the only wall in the entire home that is showing considerable condensation, but the main level (2nd level) exterior south facing kitchen wall has a tiny bit of condensation under the window.

    Another item of note, it had rained a lot over the past 2 months and the plywood sheating was quite wet, but we put the Tyvec paper on and the sheathing appeared dry before (roughly 3 – 4 weeks later) insulation was put in.

    Finally above this wall is an open air patio and we have put torch-on on it, will be putting tiles on top of the torch-on.


    Thank you in advance for your guidance and help.

    Best regards,

    • From what I understand, it sounds like your house is still partially open to the elements. So the humidity inside the house will more or less match the outside conditions. But here’s the important thing – there’s a time delay so the house has to catch up with outside conditions.
      This lets the humidity rise inside, and when the temperature drops, the walls cool off quickly and the condensation forms. Some areas more than others is natural due to different conditions throughout the house.
      You should be fine once the house is sealed up but you’ll want to get aggressive with dehumdification to ensure that everything dries quickly. You also want to be careful to avoid trapping water inside walls.
      In the meantime, you can leave fans blowing on the affected walls which will help to reduce the condensation while the house is open.

  7. We live in Tx and just recently (1 month ago) closed in a 150 sq ft covered porch with adding an exterior wall on to connect to back of house. We have a small window and a glass storm door (no interior door yet. We have yet to insulate or sheet rock and noticed condensation all over the vapor barrier sheet when we got a good rain. We dont know if it is from no insulation or moisture coming in from no interior door. We were planning on just sheet rocking roon since it is just a smaller area and didnt affect the inside of the rest of the home. Whether we insulate it or not is this condensation showing up now going to effect the walls once we seal it or is it just because its not got a door yet and not sealing the moisture out? What do you recommend insulation and a door?

    • I will need more information about the exact construction to comment intelligently. Where is the vapor barrier sheet? Is it right behind the exterior sheathing or on the inside of the studs? I’m guessing behind the sheathing since you haven’t yet added insulation. What probably happened with the condensation is that the moisture level in the room got high when it rained. Then the temperature outside dropped, cooling the vapor barrier. This then led to the condensation.
      You definitely need to make sure that the vapor barrier is dry before installing the insulation and sheet rock or you’ll risk trapping the water in the wall.

  8. I have an infestation bug of a variety of bugs…IE…ants, filth bugs that look like nats but have red backs on them and bite leaving red marks, little flying bugs that resemble tiny mosquitoes and spiders…these bugs are in the frame of metal windows and are massive. There is evidence of moisture in the walls which are ice cold and presents water spots even after painting them with semi gloss paint.. Ants are so bad they fell out of light socket when cover was removed for painting. How do I get rid of bugs and stop moisture? Please help as I am overwhelmed and believe it is making me ill with severe allergy type symptoms.

    • Wow, that sounds terrible! When it’s that serious, you definitely need to get a professional involved.
      Personally, I’d take a couple approaches.
      First, I’d get an exterminator in. The problem is, your infestation sounds so bad that it might require “tenting” your house. This is where they put a shroud over the entire house and gas it for a day. Nasty stuff. But I’m not qualified to advise you on that. Talk to a professional.
      Second, I think you put your finger on the problem when you mentioned moisture. Bugs and other nasty things like moisture. Here’s a few sources of high home moisture:
      – dirt floors in crawlspaces under the house. If you have these or any signs of basement moisture, call in a moisture specialist to get a quote on remediation. It won’t be cheap but the alternative is worse because the problem will keep arising. Bugs, mold, rotten wood etc.
      -excessive moisture from humidifier use. If you use a humidifier, then stop and let the house dry out. Especially in the colder months, people tend to over humidify their homes. During these months, I would try to keep humidity between 40 and 50 percent.
      – high moisture due to inside plants or other water sources in the house like ponds waterfalls etc.
      – high moisture from non venting gas and propane heaters. Besides being a carbon monoxide hazard potentially, these units spew out gallons of water as a byproduct of combustion. They are outlawed in many jurisdictions already and should never be used in a modern home.

      I hope some of these tips help. Your problems sound fairly severe so you should definitely get someone in there to check out the issues. Just make sure you have both a bug specialist and a moisture specialist come in because you have to deal with both problems.

    • Wow, that sounds terrible! When it’s that serious, you definitely need to get a professional involved.
      Personally, I’d take a couple approaches.
      First, I’d get an exterminator in. The problem is, your infestation sounds so bad that it might require “tenting” your house. This is where they put a shroud over the entire house and gas it for a day. Nasty stuff. But I’m not qualified to advise you on that. Talk to a professional.
      Second, I think you put your finger on the problem when you mentioned moisture. Bugs and other nasty things like moisture. Here’s a few sources of high home moisture:
      – dirt floors in crawlspaces under the house. If you have these or any signs of basement moisture, call in a moisture specialist to get a quote on remediation. It won’t be cheap but the alternative is worse because the problem will keep arising. Bugs, mold, rotten wood etc.
      -excessive moisture from humidifier use. If you use a humidifier, then stop and let the house dry out. Especially in the colder months, people tend to over humidify their homes. During these months, I would try to keep humidity between 40 and 50 percent.
      – high moisture due to inside plants or other water sources in the house like ponds waterfalls etc.
      – high moisture from non venting gas and propane heaters. Besides being a carbon monoxide hazard potentially, these units spew out gallons of water as a byproduct of combustion. They are outlawed in many jurisdictions already and should never be used in a modern home.

      I hope some of these tips help. Your problems sound fairly severe so you should definitely get someone in there to check out the issues. Just make sure you have both a bug specialist and a moisture specialist come in because you have to deal with both problems.

      • Thank you so much for such a speedy response. I’m on it. I will keep you informed of the findings of the professionals, the treatments and the end results. Keep up the good work and have a blessed day!

  9. Ted, We have a similar problem with moisture inside our walls but our situation is a little different.
    We built an addition to our existing home 12 years ago by adding a 3 car garage with children’s bedrooms above. We live in Mississippi where it gets really hot in the south. For several years, our Termite inspector found high moisture levels in all of the outer walls upstairs in this addition. I looked around in the attic for a leak and saw nothing. I really just didn’t put much more thought into anymore until last summer when I moved a picture. I saw that there was mold on the wall (it could easily be cleaned away with a washcloth and had not grown into the sheetrock). The termite inspector was due back at that same time, and this time his readings were close to 100% in some of the walls.
    Last summer, we opened up the walls (every outside wall in 3 bedrooms) and saw that there was dripping condensation with some mildew (since this had been going on for a while) inside the walls. A local contractor conferred with several experts and found no leaks from the roof entering into the home. The final conclusion was that the air conditioning unit that had been put in the upstairs was too large for the space and was putting out too much cold air. They a/c guys said that this caused a high humidity level inside the home and along with the heat outside resulted in condensation inside the walls.
    We replaced the air conditioning unit, added attic fans in the attic, let the walls dry out and then put everything back together. It was truly a terrible and costly summer. We purchased our own moisture reader and checked the walls every now and then feeling satisfied that the problem had been corrected when we saw that the moisture level continued to be low. Feeling pretty good about our repair, we stopped checking the moisture level.
    It is now a year later and the termite inspector was here again. Yes, his moisture readings were almost the same as they were last year! 100% in one exterior wall and 50-60% in the others. Apparently this happens in the summer. This time I don’t even know where to start. I don’t want to “correct” this problem again only to find out that we did not get a correct diagnosis of the problem once again. Your blog was the closest to describing our issue and I am hoping you might have some insight into our situation. Any ideas?

    • First, I have to say, I feel really badly for you and others who experience these types of situations. They’re truly heartbreaking and unnecessary.

      While what your air conditioning guy said could be partly true in that oversized air conditioners do not properly dehumidify the air, that is not what causes a high humidity inside of your walls.
      You’ve clearly done your homework, but for the benefit of others who may be reading this answer I’m going to go back to basics.

      The fundamental issue of condensation is a cold surface of staying in contact with moist air. If the surface is below the dew point off the air then condensation will occur.

      In humid hot climates like yours, the outside air contains a huge amount of water and the dew point is relatively high, so condensation occurs very easily. This is why beer cans or a cold glass will almost immediately get soaking wet and start dripping.
      In your climate, at a relatively normal temperature of 85 degrees F and a high humidity of 70%, water will start condensing inside of your walls if the sheetrock temperature is around 70 degrees. This is a very common condition and therefore it is extremely important to minimize the chance that outside humid air will come in contact with your cool walls. This is typically accomplished by the use of insulation and a vapor retarder on the outside of the insulation that is the vapor barrier prevents outdoor air from getting into the insulation and making contact with your walls.

      However this type of solution requires an excellent job be done on installing the vapor retarder, because as you know, air will find a way in. This is why by far the best solution is spray foam insulation applied directly to the back of your sheetrock. Closed cell spray foam is virtually impermeable to water, and therefore the outside humidity can never come in contact with your cool walls.
      Let me say that undoubtedly anyone who says the moisture is coming from inside your house during the summer should not be listened to. It proves that they are ignorant of the physics involved. The only possible way that interior humidity would cause a problem inside your walls during the summer is if you constantly had steam pouring into your living space!

      Now, here comes the really bad news. You really need to resolve this issue by ripping off the exterior of your home again and properly insulating and sealing the walls. Otherwise this will continue to happen again and again.

      You will be best off working with somebody familiar with building science in your area who can monitor the reconstruction process as an independent rather than general contractor who is making money off of your woes. You may wish to check Angie’s List for a spray foam insulation contractor then ask them who the best troubleshooting expert is in your area. There are a good number of people these days who specialize in moisture problems. However, do not just hire a moisture remediation or mold remediation company. I have found that many of these people are not properly trained in the science of moisture and just make money on selling band aid solutions.
      I hope I haven’t made too many typos, I’m trying to do this on this on a small screen without a proper keyboard 🙂 but I wanted to get back to you as soon as possible. Good luck I hope you can find a great person to help you.

  10. Hey Ted, I discovered something this past weekend in my home…
    First off, some history: we’ve lived here for 5 years. We purchased/moved in to our home in the summer of 2008. We painted EVERY room in our home and my question revolves around our bedroom. We’ve had our bedroom furniture positioned the same way since we moved in up until now, when we recently purchased a new set to replace this old one. We decide to paint our bedroom again. Being that we are now finished painting in the beginning of winter, I noticed a small interior corner of our southwest wall, where condensation was building up, causing the paint to not completely dry compared to the rest of the room.
    I had a feeling I knew what it was since our windows aren’t sealed worth a damn in this bedroom (or the rest of the house to be 100%) and I figured it may be an insulation problem. I put our space heater on it for a few hours to see what would happen. It did dry, but still remains quite tacky after 48 hours. Some moisture still condenses on it as well.
    The walls & baseboard feel much colder than my daughter’s adjacent room and even compared to the rest of our bedroom (inner attached walls). This area of moisture is the outside corner of our home, located over a crawl space addition where our furnace really has to work to heat the room to begin with.
    The front half of our home has service holes on the outside of the siding when they previous owner had blown-in insulation installed, but not on this newer addition containing our bedroom.
    I’ve never noticed it before due to our bedroom dresser sitting in this corner. covering it.
    Does this appear to sound like a simple insulation issue? The rest of our home doesn’t seem to have any issues and remains quite warmer. This moisture “patch” seems to be about 4 square inches, directly in the corner, coming up a few inches above the molding towards the carpet.
    If you have any ideas, I’d greatly appreciate them. Great, informative site also. I learned something this morning!

    • You made an astute observation. Good catch on the condensation and your notes.

      These issues are, as you noted, typically due to insulation issues. Since you’ve determined that the corner is much cooler, and hence the reason condensation is forming there, it’s almost certainly that. It is very common for builders to miss a spot or two. Fortunately, you’re not finding lots of cold spots which could indicate a bigger problem. Probably just an oversight.
      It’s also possible that there’s no room for insulation in that area. Sometimes, there’s so many studs and other wood in the wall that it’s just a solid block of wood, which provides pretty poor insulation!

      Sometimes, the problem can be made worse if the outside of the house wasn’t air sealed well and cold air blows into the wall and under the molding. My house is terrible this way around the perimeter. But my guess based on your description is insulation.

      You could drill a small (maybe 1/4″) hole in the center of the cold spot, carefully stopping as soon as the drill penetrates the drywall. Then probe in the hole and see if you can feel insulation by poking something into the hole (like a chopstick or other non-conductive object). You should be able to feel resistance from the insulation in the wall.

      You might be tempted to get a can of spray foam and fill the wall with it but I’d advise against it. When this stuff expands, it can do so with enough force to blow out the wall.

      To fix the problem, the real solution is to carefully cut out the drywall and fill the cavity. But most people don’t want to bother with that, especially if you’ve already painted and are just finishing up.

  11. Hay i am in a ground floor apt and 2 year’s the apt over me had a very bad leak because the pipes burst. ive noticed we have a lot of mould growning in the cornor of the bedroom i got a man to come and have a look with a moisture reader and it came up flashing 70??? i asked him was that bad and the fool said he was not too sure! i think he’s trying to take me for a ride can you give me any help or what way do the water moisture readings be??

    • Sorry to hear about that. The meters have different settings so I couldn’t tell you, but typically a number like that would be on a relative scale, of 0-100, and 70 would be a sign of high moisture. Flashing usually is a warning sign also. And of course, if you’ve got mold growing in there, that’s the sure indicator that there’s elevated moisture levels.

      However, it’s possible but not likely that a leak two years ago would be causing mold today. So they really need to find the cause of the moisture today. If they just clean the mold off the wall then repaint, the mold will just come back. Is the corner where you see mold against an outer wall of the building? If so, there’s a good chance that water is getting into the wall from above due to some construction issue on the outside of the building.

      I don’t know how it is in the UK but here in the US, there have been lawsuits relating to mold since some people have very adverse reactions to it. Because of this, most people want to deal with it properly because they fear lawsuits.

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