Conditioning converted under house space/ averages 70% RH
I’ll give a little info before question. I’m working on a house in Cal. Bay Area. Crawl space was partially dug out creating a 12×30 room into hillside with another 300 sq’ of crawl space 5′ in height down to 2′. Crawl was originally vented via foundation vents. House has sub-drainage system of separate solid and perforated to manage roof and foundation bulk water. Unfortunately crawl rat slabs were poured on grade with no vapor barriers. Room slab was poured 5″ on 6″ of gravel with no vapor barrier. Concrete mix was batched with Xypex. Area averages 70% RH. No mechanicals.Room is planned to function as a gym space. My thought is to install an inline 300cfm fan w/humidistat and perhaps a passive return connected to living space. Insulating space with rigid on foundation walls and perhaps sprayfoam on exterior stud walls. Is the this plan sound? How about the lack of vapor barriers under concrete. I will add, cardboard storage boxes left on both slabs for years haven’t shown any real deterioration.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part