I am building a house in climate zone 6a. I have gotten a few spray foam quotes and have a question about one of them.
I need to get r25 in the walls (2×6). They suggested 1.5″ of closed cell, followed by 4″ of open.
Also, the ceiling (2×10) needs r49, for which they suggested 3″ closed and 7″ open.
Edit: house has an erv system, idk if that changes anything
I guess I’m worried about creating a dew point inside the cavity, will either of these lead to that?
Thanks
Replies
Closed cell spray foam insulation is a high-density insulation material that provides a superior air barrier and moisture control. Open cell spray foam insulation is a lower density material that is used mainly for thermal insulation.
When combining closed cell and open cell spray foam insulation, it is important to consider the location of each type of insulation in the wall assembly to avoid creating a dew point within the wall cavity. A dew point is the temperature at which water vapor in the air condenses into liquid water. If this happens within the wall cavity, it can lead to moisture problems such as mold and rot.
In your case, the suggested insulation approach of 1.5" of closed cell followed by 4" of open cell in the walls, and 3" of closed cell followed by 7" of open cell in the ceiling is generally a good approach that should not create a dew point within the cavity. The closed cell foam provides a moisture barrier that prevents moisture from entering the wall cavity, while the open cell foam provides thermal insulation.
However, it is important to ensure that the installation is done properly to prevent any gaps or voids in the insulation that could lead to moisture issues. Additionally, the use of an ERV system can help to maintain healthy indoor air quality by exchanging stale indoor air for fresh outdoor air while also minimizing heat loss.
note, it is always best to consult with a licensed and experienced insulation contractor for specific recommendations on your project.