Is it proper to run 6mil vapor barrier up the entire concrete-block wall of a crawlspace (over the wall insulation) and staple it to the sill-plate? Should you also run the vapor barrier up the wood support posts for the flooring? I also understand it is important not to have any underfloor (crawlspace ceiling) insulation, is that correct?
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 (including the rim joists) rated at least R-20. It also has to be taped to all perforating structural components (plumbing, support posts, etc.). The sill plate doesn't even come into the picture because insulation covers both wall and rim joists and that covers the sill plate. 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.
