Q’s about crawspace encapsulation. Management of moisture post encap. While avoid air transfer(makeup air) between crawl and living area, as well as attic(vermiculite) – GreenBuildingAdvisor

Hello,

I am located in BC canada. I just bought a 1952 home, bit of a fixer upper.

One big area of concern is the vermiculite in the attic and how it may be disturbed by various other jobs needing to be done in the home.

One of the more pressing jobs is the crawspace. It has a very bad odor and the humidity is hovering around 80%. Currently it is a dirt floor. Luckily no visible mold.

I have approached a basement system company. They have recommended full encapsulation which includes the membrane and spray foam up to the subfloor. I do not believe they air seal the subfloor. They also recommend a single exhaust fan that would either pull air through various cracks in the subfloor or install a dedicated air transfer grill. The grill would meet BC code. The exhaust fan would be on a timer for 8 hours a day.

I have a couple  concerns with the plan. I am not sure whether they are valid or not.

1) With a exhaust fan (100cfm) would this not create a slight neg pressure and potentially pull air from the attic?

How can I be certain makeup air is not coming from the attic?

2) The fan only runs for 8 hours a day. With the fan off could lingering smell/radon/soil gases enter the home. Especially if an air transfer grill is installed ?

What I am really asking is, how can I properly manage the moisture in my crawlspace, while maintaining a balanced air system throughout the house. To be clear, I absolutely do not want the possibility of contaminating my home with soil gases from the crawl or asbestos fibers from the attic

Please advise. Thank you