Alternatives to SPF to insulate floor
I have a late 50’s ranch house with a vented crawlspace in the San Francisco bay area. There are remnants of old cellulose insulation in the vented attic, though very little remains. The rest of the house is pretty much uninsulated. Even though we are in N. California, the weather gets chilly, and predictably my hardwood floors (and stone/tile floors in the kitchen and baths) have been very cold this winter. I am in the process of finding a good contractor to do a whole home energy audit, and come up with solutions (as green as possible) to make the house more comfortable (i.e. warm) and maybe improve indoor air quality as well.
However, I am currently focused on finding a solution to the cold floors and vented crawlspace. All the articles I’ve read here and at BSC talk about true crawlspace encapsulation – meaning not just laying down the vapor barrier, but also sealing the crawlspace, insulating the crawlspace walls, and conditioning the space. There are numerous companies in the bay area that offer “crawlspace encapsulation,” but none of them are doing the insulating part, or even too much of the sealing part. They seem pretty much focused on the moisture/humidity control aspect. The crawlspace has a rat slab, and it seems to stay fairly dry in its current configuration.
A well regarded local insulation company, as well as a home performance contractor both recommend using SPF on the crawlspace ceiling, and not really doing much else in the crawlspace. The underfloor is a post and beam situation, making it challenging to install any type of batt or blown-in insulation. For a couple of reasons, I do not want to use SPF. So naturally that leads me to crawlspace encapsulation, which I think, in theory could solve the cold floor situation by making the crawlspace a conditioned space. However, as stated before, nobody in this area seems to do this type of thing.
So back to the basic question, how can I insulate the floors (without using SPF), or any other ideas to solve the cold floor problem? Radiant floor heating? I hope to find a good solution, then I can move on to make improvements to the rest of the house. Thanks….
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Zach,
You have two choices:
1. You can create a sealed, conditioned crawl space. If you keep looking, you should be able to find a contractor who can do the work. Here is a link to an article describing the work: Building an Unvented Crawl Space.
2. You can insulate the crawl space ceiling. Here is a link to an article describing the work: How to Insulate a Cold Floor.
I've done a couple of things not shown in Martin's article. One method is to attach a heavy fabric sheet (my insulators call it "canvex") to the underside of the floor joists, and then dense-pack it. The sheet billows a little bit so you get some coverage under at least some of the joists. Another method is to sheet the underside of the joists with plywood and then blow insulation in through holes that you plug. Neither of these methods are particularly good if there's ductwork running everywhere, but if you have a relatively unobstructed crawl they work well and are far more permanent than the typical batt installation.
Thanks for the responses. Martin's choice #1 seems appealing to me because it leaves the crawlspace ceiling open for access. There is no ductwork, but there are the typical plumbing and electrical penetrations - any future repairs or upgrades would be much easier without having to map it all out. I will continue to look for contractors, but I think in this part of the country they just are not doing it, I suppose climate is too mild.
David & Martin: if I do decide to attempt insulating the crawlspace ceiling, what about this idea from Joe L: http://buildingscience.com/documents/insights/bsi-064-bobby-darin-thermal-performance
- specifically leaving a cavity between the floor above and the insulation below - to specifically go for a warmer floor?
Zach,
Joe Lsiburek's detail works -- but only if you do an impeccable job of air sealing the rim joist (the perimeter of your crawl space). If you get any air leaks into that space above Joe's insulation, the performance of the insulation is drastically reduced.