If I spray-foam my basement walls, do I need to add mechanical ventilation?
user-5546173
| Posted in Energy Efficiency and Durability on
I have a 2 story house plus full basement in Maine (climate zone 6). Foundation walls are uninsulated concrete; floor is concrete. House was originally built around 1955; 2nd story addition was put on around 2005.
In the summer we have A LOT of humidity in the basement. To help alleviate this – and also to better insulate the house – I’m considering spray-foaming (w/ two-part spray-foam) the basement walls.
My question is – if the basement walls all become air-sealed – will it become necessary for me to also install mechanical ventilation to maintain/improve air quality in basement?
Thanks!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Jeffrey,
A home that is very tight (that is, a home with a low level of air leakage) usually needs mechanical ventilation in the rooms where the occupants spend most of their time. For more information on this issue, see Designing a Good Ventilation System.
I doubt whether your plan to install spray foam on your basement walls will change the air leakage rate in your older home very much -- but it might, especially (a) if you now have a lot of leaks at your basement rim joists, and (b) if your plan to use spray foam to seal the leaks in your rim joist area.
Even if your house is very tight -- tight enough to need a mechanical ventilation system -- you don't necessarily need ventilation in your basement. It all depends on how much time you spend down there. If you live upstairs, you probably don't want to invest a lot of money in improving the air quality in your basement.
There are many possible reasons for a damp basement. Before you install spray foam on your basement walls, you may want to investigate why your basement is damp, and to take measures to address those problems. Here is a link to an article that might help you: Fixing a Wet Basement.
If the humidity is exclusively a summertime phenomenon it's usually air leakage, in which case increasing ventilation rates with an active system would INCREASE rather than decrease summertime humidity problems.
Air sealing, and using a heat pump water heater in the basement would likely take the edge off it, putting the latent-heat of that moisture pulled out of the air to good use.
Thank you to both of you!!
"Air sealing, and using a heat pump water heater in the basement would likely take the edge off it, putting the latent-heat of that moisture pulled out of the air to good use."
Thats an interesting idea, instead of a dehumidifier in the summer for people who have high humidity basements this could kill two birds with one stone