Floor Insulation
I bought and am remodeling a house built in the 1920’s with dirt floor vented crawlspace and an addition that was built in the 60’s had to tear out and replace the entire floor in the addition had bulk water flooding into crawl space under heavy rain and it had rotted the entire floor out i have since remedy that issue with exterior drains and fixed/ replaced and sealed blocks in the foundation. I am going to be putting down 10 mil poly on the dirt floor and looking to insulate the floor i seen an article on GBA or FHB that had foil faced polyiso on bottom of joist and batt insulation in between is this best way to go about it?. The crawl space floor is about 6-8 inches from the bottom of joist for large portion of the house and foundation walls are 1-2 block high. What are my options here? One corner of the house has good amount of room to get under there i was thinkin of insulating that corner and building little room to house my pressure tank and manifold for water along with pump for the septic these will be the only thing running in the crawlspace and will be confined to one side of the house. Any help and advice is appreciated. Thanks
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This might be the article you're thinking of: https://www.finehomebuilding.com/2012/03/08/how-to-insulate-a-cold-floor
For some reason it never comes up in searches but I refer to and share it often.
TurtleHoller,
The chances of you being able to access and do a good job of insulating the underside of such a short crawlspace are pretty low. Have you considered encapsulating it instead?
https://www.greenbuildingadvisor.com/article/building-an-unvented-crawl-space
Yeah, I did think about encapsulation but there is 30' or so of crawl space I can not access. That's why I was leaning toward the insulating joist. The only way I could access that portion would be to tear up the floor in the original house but it's in good shape I would like to avoid that.
I have insulated from above with a very short crawlspace like that, by tearing up the flooring and floor sheathing, essentially pocket-screwing flat, pressure-treated 1x4s to the bottom of the joists, dropping pressure-treated plywood on the lips the 1x4s create, applying a thinnish layer of closed cell foam to the top of the plywood, filling the rest of the floor cavity with climate-friendly cellulose insulation, then installing new floor sheathing and finished flooring.
If that sounds like a lot of work, it was. If you can run a high-quality vapor retarder over the soil and wrap the outside perimeter with rigid foam or mineral wool, that would likely be significantly easier and still perform well.
If you do choose to insulate the floor, the crawl space needs copious ventilation and a vapor retarder on the soil or else you will get excessive moisture build-up. On my project we ran ropes through the crawlspace, cut holes in the vapor retarder and pulled the membrane through the space. Perfect coverage isn't necessary, but the more soil you can cover, the better.