I have a house in Houston within an uninsulated floor/crawl space. The house is about 3-4 feet above the grade with lattice work concealing the crawl space so it is also vented, which I do not plan to change.
The house floor is constructed as:
2×12 at 16″ supported by built-up members at the perimeter and center with 3/4″ T&B OSB floor decking, with 15# felt and Oak floors.
I am planning on covering the soil with a “vapor retarder (barrier) to reduce moisture from the soil, however, I am not sure about how to insulate this area.
I have thought about using fiberglass batts with wire mesh (chicken wire), but think it becomes a perfect home for rodents. In this hot/humid climate, will the batts tend to trap moisture in the floor system? I was considering “unfaced” for this application.
I have also consider foam insulation (board or sprayed). I like the spray idea since it will completely seal the underside of the house from not only air, but insects and other “things” that live under my house. My concern with using the spray foam is that it creates a true “vapor barrier” and would not allow the floor to “breath”. Is this a problem? It is my understanding the moisture typically travels from the exterior to the interior in this climate, so the spray foam would stop the moisture for entering and does not “seem” to be a problem to me. Any moisture that does enter is removed via air-conditioning.
Finally, if using foam, it was my understanding foam typically needs to be separated from the interior by a thermal barrier (1/2″ gypsum board/sheathing) according to the building code (IRC 2000) and if so, it would be a headache to install that first then the insulation.
Suggestions? Comments?
Thanks in advance, Glen.
Replies
I think you need to get someone in your area to answer your questions; why not give a local insulation company a call and find out what is the local accepted practice and what they recommend. The reason is the hot humid climate you describe, which is unlike the climate were most of us Breaktimers live. For example, I live in NC where it is cool and dry... (this week) :^)
I will add some thoughts though. When insulating a crawl space "ceiling". the insulation is installed up against the floor so that there is no airspace between the insulation and the floor. If it is fiberglass insulation, it is held in place by insulation support wires that are roughly the diameter of a coat hanger.
Definitely put the plastic on the crawl floor, although it would also seem that you need to figure how to keep wind driven rain, etc from getting in the sides of your open crawl space. Or, maybe you cold hold the plastic 3' or so back from the house edges so it won't end up with water standing on top of the plastic.
I have never personally used spray foam but will say if you want to use it, the combination of the 3/4" T&G subfloor and the hardwood floor will provide you the 15 minute fire shield rating that I believe is required by the IRC. Also, if you decide to use foam, check with your local inspections dept to see what they require. Some areas require it to be covered even in a crawl space. Even if you don't do what they require, at least you will know what they think is good... Another caveat of foam is the possible infestisation by insects, according to some reliable sources here, as although insects don't eat foam, it makes a nice cosy nesting area. Investigate foam that is treated with some kind of insecticide or insect repellant like a borate (sp?). You may find spray foam to be cost prohibitive too.
Re the rigid board foam, it is not clear to me you would install it such that it would really be an air barrier - unless it happens that there are no wires, pipes, support posts, etc under your house. The whole idea of insulation, besides the R-value, is to create an air barrier.
Let us know what you find out and what you decide...
Matt,
Thanks for the suggestions. I agree FHB/Break Forum is geared toward the Northeast, but before talking with local contractors I wanted to get some other options.
The problem I have is finding a contractor that is knowledgeable and does not say, "That is what we always do" or "I have been doing it that way for 30 years".
Each situation is unique and finding the "best" products to suit that application is always an uphill battle. I will let you know my progress.
Try http://www.buildingscience.com Lots of good scientific info when it comes to insulating.
MES