I'm planning on adding a family room to my existing home. The floor will be about 8" off the ground in order to be at the same level as the rest of the house. I don't know how to insulate the floor. I'll be doing a standard wood frame floor but as it's so close to the ground, I'm not sure how I will secure insulation between the joists and below the actual flooring.
Answer:
This is not going to work very well because you're trapping moisture and that is not what you want. I'd rather see you go up a step or even two and then insulate the proper way. Here is a paragraph that I always include with house inspection reports when applicable. 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.
