I have an eighty year old home that's had both major additions and minor additions over the years(~750 to 1750sq ft) and an uninsulated front porch was one of them. Previous owners have added blown in insulation to the walls and ceiling, I'd like to finish with the floor. The porch rests on what looks like cinder blocks, creating ~16inches of crawl space (no vents) with an opening to the drafty/unfinished/unheated but warm basement (big old funace). I believe I'm clear on your process for insulating a porch crawl space, I'm wondering how to access the area without tearing up floor (3" oak). Would rigid foam on the sides of the walls and a loosely placed ground sheet only cause more problems?
Answer:
Yes becasue rigid foam in a situation like this is not continuous therefore, you have a vapour barrier problem and that is what controls condesnation. The ground sheet should not necessarily be loose. You may have to modify this but I'm sure you can related to how it works: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.
