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  #1  
Old 2022-07-12, 10:12 AM
Mudstrap Mudstrap is offline
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Default Water and condensation on the basement insulation

I just bought a new house and I saw humidity condensation on the plastic that covers the isolation at the top of the walls in the basement. The problem is on the front and the back of the house but not on the sides. I'm wondering if someone has ever seen this kind of problem in a house and what kind of specialist I should consult to find the cause. My neighbor who also bought a new house in the same project before us has the same problem and mold developped on the R-12 Fibreglass thermal insulation wool. Any advice is very appreciated.

Last edited by Mudstrap; 2022-07-12 at 10:14 AM.
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Old 2022-07-13, 10:32 AM
Halton Home Inspector Halton Home Inspector is offline
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This is a common issue. Mostly in the summer when the foundation walls get warm because of the heat and being exposed to the sun. In the basement the air is cool and because the foundation is warm, the air in the home between the foundation and the barrier is also warm. This air condenses on the cool plastic vapour barrier.

There is often no way to improve this but if or when you finish the basement you could remove all of the current insulation and have 2 pound foam installed. This insulation forms an intimate contact to the foundation and blocks all air flow.
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Old 2022-07-14, 08:44 AM
Mudstrap Mudstrap is offline
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Originally Posted by Halton Home Inspector View Post
This is a common issue. Mostly in the summer when the foundation walls get warm because of the heat and being exposed to the sun. In the basement the air is cool and because the foundation is warm, the air in the home between the foundation and the barrier is also warm. This air condenses on the cool plastic vapour barrier.

There is often no way to improve this but if or when you finish the basement you could remove all of the current insulation and have 2 pound foam installed. This insulation forms an intimate contact to the foundation and blocks all air flow.
Thanks a lot for your reply. Can you post a link to the 2 pound foam product you refer to?

Can the pink insulation dry if I temporarily remove the plastic? I'm affaid that mold will develop over time...

Last edited by Mudstrap; 2022-07-14 at 08:47 AM.
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Old 2022-07-14, 06:03 PM
Halton Home Inspector Halton Home Inspector is offline
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Originally Posted by Mudstrap View Post
Thanks a lot for your reply. Can you post a link to the 2 pound foam product you refer to?

Can the pink insulation dry if I temporarily remove the plastic? I'm affaid that mold will develop over time...
If you finish your basement then spray foam insulation is an option for you. It is considered the best insulation but it also costs more than Ruxol and fiberglass. My advice would to just do that research when you are ready.

Mould will not grow on new clean fiberglass insulation. You could cut open the plastic vapour barrier. Cut large unpside down V shapes and run a dehumidifier.
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Old 2022-07-19, 10:12 PM
Mark & Lynda Mark & Lynda is offline
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Can the pink insulation dry if I temporarily remove the plastic? I'm affaid that mold will develop over time...
If the basement is unfinished, I would not worry about it. It will happen every summer as warm air enters through the rim joists and condensates. It will eventually dry. If you cut open the vapour barrier there is the likelihood the problem will get worse.

I had the same problem every year until this past year when I ripped it all down and threw it out and had the walls spray foamed.
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Old 2022-08-06, 10:55 PM
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Inspector Phil Acker Inspector Phil Acker is offline
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Hold the boat!!
When I inspect new homes in Ottawa, I will see moisture on the vapour barrier during the first summer after the home is occupied. Before you start cutting the vapour barrier, ripping out wall insulation, and/or retaining a contractor to have spray foam applied, your very first step should be to take a chill pill.

Do none of these as your first step.
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Old 2022-08-06, 10:59 PM
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Your first step for any homeowner in Ottawa that has a basement in their home is to buy a dehumidifier. Set up the dehumidifier so that it has a hose connected to a floor drain or condensate drain, set the dehumidifier to 50%, and turn the unit on. Leave the dehumidifier running year-round.
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Old 2022-08-06, 11:12 PM
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Let me start with physics. A new foundation in a new home has multi tens of gallons of water to give up as the concrete cures. In hot, humid weather, the moisture will not be drawn to the outside, as the outside air is already hot, humid, and vapour saturated. Rather, the moisture from the foundation will go to the interior, where the temperature is cooler, and the interior air is not fully saturated with moisture. The moisture escaping the foundation condenses on a cool surface, which is the vapour barrier. The condition is most prominent where the home is being air conditioned, as the basement temperature and the dew point for condensation allows the moisture to condense.

To prevent condensation of moisture on the vapour barrier, you need to reduce the indoor humidity, Get the basement ambient humidity below 50%. To do so, you must buy a dehumidifier.
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Old 2022-08-06, 11:35 PM
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So why do I make this as the way to go if you see moisture on the vapour barrier? It comes down to my observations during new home inspections. When I see a home with moisture on the vapour barrier, the basement humidity is above 50%. I do not see this issue when the following is observed:
a] the homeowner has a dehumidifier in use, connected to a drain, and set for 50%
b] the homeowner has a hygrometer, which measures indoor humidity, and understands that if the humidity is above 50%, it is likely that they need to take an action to reduce the humidity level to between 30% and 50%.
c] the homeowner turns off the whole-house operation of the HRV during the hot, humid summer months. At the HRV control near the thermostat, set the HRV to the "off" position. Be aware that the HRV is designed to improve air quality by exchanging indoor air with fresh outdoor air, but it does not control indoor humidity, When the HRV is running, it will equalize the indoor humidity with the outside humidity.
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  #10  
Old 2022-08-09, 01:08 PM
Mitsuko Mitsuko is offline
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Quote:
Originally Posted by Inspector Phil Acker View Post
.....The moisture escaping the foundation condenses on a cool surface, which is the vapour barrier. The condition is most prominent where the home is being air conditioned, as the basement temperature and the dew point for condensation allows the moisture to condense.
To prevent condensation of moisture on the vapour barrier, you need to reduce the indoor humidity, Get the basement ambient humidity below 50%. To do so, you must buy a dehumidifier.
Phil, what I don't understand in your explanation is this:
The water from the foundation wall condenses on the EXTERIOR SIDE of the vapor barrier. The vapor barrier (the polyethylene plastic sheet) is attached pretty tight to the studs, without any gaps or openings. In our basement there is a red tape on top and bottom and over the ends of the plastic foil. This might be not hermetic but is tight enough. The moisture escaping the foundations will be trapped between the wall and the moisture barrier.
If you have high humidity in the basement it's on the INTERIOR SIDE of the vapour barrier and will condense there. I haven't seen the latter but have seen condense on a naked, not insulated, sealed (painted) concrete wall (in older houses).
It was my understanding that the indoor humidity will cause condense on the inside and the construction humidity, on the outside of the vapour barrier and both don't mix, unless the vapour barrier is damaged, open etc.
There is a product called MemBrain, a vapour retarder, which lets the construction moisture to get out/through, but doesn't let the indoor moisture to get in.

Last edited by Mitsuko; 2022-08-09 at 01:53 PM.
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