Is it necessary to keep an air-space between insulation and the sub-floor in a crawl-space type foundation? The house has a full basement that is heated, and there will be limited access to the crawl-space from the basement. I had originally planned on installing fiberglass batts between the joists with the vapor barrier in contact with the bottom of the sub-floor. Some books show insulating with R-19 batts, with an airspace between the tops of the batts and the bottom of the sub-floor. I would think that R-38 insulation would provide for a warmer floor. The floor system will also be cantilevered over one end of the foundation by 18″. Thanks for any tips.
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
You don't have to sacrifice historical elements of a house in the name of energy efficiency.
Featured Video
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
no air space put insulation in direct contact with the subfloor, if you leave a airspace and a piece of insulation falls the underside of the floor in that cavity is exsposed to cold air if you have 3/4 plywood or better you can skip the kraft facing the ply has a better than a 1 perm vapor barrier. we normal have customers have installed material that is the same thickness as the joists or beams used this allows for a better installation(within reason) We use a lot of 11.25 tjis and use r-30 with lath supports friction fit to the top of the bottom cord
In discussion with the homeowner we both agreed on closing the access off to the main basement, installing vents in two sides of the foundation (for cross-flow ventilation) and insulating between the joists with R-38 insulation. Thanks for the air-space tip!
I'm not trying to make life difficult for you but have you considered spray on foam for that application? Its not typical and not sold at HD but it is far superior to fiberglass. In a few years the fiberglass will sag and eventually fall out. Spray foam will seal everything, is a very good vapor barrior and a good insulator that will never sag. It will also make the floors as it actually bonds to the wood. Material cost is much greater but the installation cost is much less. I (one guy) did 350sf of floor from underneath in 3 hours. That included dressing up with a balaclava to keep the foam from falling into my hair and face, setting up the equipment, spraying and cleaning up. How much will the labor cost you to do that job? Two guys for a 8 hour day? You can order the foam and have one of your guys do it in no time. Just a suggestion.
http://www.fomo.com
I think in the future if I bid on a similar project, I would definately consider it, and would do my best to sell that option. I am already way beyond this part of the job, but one thing that I discovered is how inclemant and unpredictable the weather can be in Wisconsin... You can cover the floor but some water will somehow find a way in... It's all dry and weather-proof now, and I've fastened lath strips to make sure the insulation cannot fall. I'd will bookmark the website for future reference. Thanks!