We are in the process of rebuilding (from the foundation up) a cottage in Northern Ontario. The original building was lacking in ventilation in the crawl space which caused the whole floor/joist system to rot. The building will be approx 25 x 35 and I'm wondering how much ventilation we should have in the crawl space? Also, we will want to winterize the building and I could use some guidance on how to insulate as well as proper use of vapour barrier. The floor of the crawl space will be dirt.
Answer:
Crawl space is a major source of mildew but that can be corrected. First, all insulation has to be removed from the crawl space ceiling - house floor. The whole dirt floor, with all its irregularities, has then to be covered with an impermeable material (6mm polyethylene, an old swimming pool liner, etc.). This has to be firmly and permanently sealed to the existing, well-applied perimeter wall vapour barrier – which should be covering insulation rated at least R-20. It also has to be taped to all perforating structural components (plumbing, support posts, etc.). That looks after the crawl space for most of the year. The vents (minimum two on adjoining walls allowing for 1 sq. ft. of vent for every 500 sq. ft. of floor space) on the walls have then to be adjusted so they can be opened and closed from the outside. This will negate the need for anyone to crawl around down there for seasonal adjustment of ventilation.
