What can be done in the space under a raised home?
Sallies2
| Posted in General Questions on
I live in New Orleans. Nothing is insulated and my home is approx 3 ft off the ground with plain dirt under there. We are considering enclosing the sides (with open lattice) but what can I do about the ground? Is there a sheet insulation or a plastic vapor barrier kind of idea I can just roll out and cover the ground with? It is a very long, old (ie not air tight) home with little splits here and there where you can feel the air coming thru the floor. My electric bill is very high, of course, and NOLA is termite central. Is there an inexpensive easy DYI way I can upgrade?
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Replies
http://www.lsuagcenter.com/nr/rdonlyres/d33f711d-dc4b-4e4c-9ed6-a97dce9db026/79805/pub3187insulatingraisedfloorslowres.pdf
https://www.finehomebuilding.com/2012/03/08/how-to-insulate-a-cold-floor
https://buildingscience.com/documents/digests/bsd-111-flood-and-hurricane-resistant-buildings
See Figure 1.
https://buildingscience.com/documents/bareports/ba-0704-building-a-durable-and-energy-efficient-home-in-post-katrina-new-orleans/view
See figure 4 (similar to figure 1 in first link.)
You'll see a theme of using rigid foam with fluffy stuff. Conversely you could use closed-cell spray foam (see first link).
Thank you, I appreciate the quick reply.. I will be reading these, especially the first one. But its hard to use most foams - termites love foam. I was hoping some kind of ground cover over the dirk that is the underside of the house would deter them a little.
A ground vapor barrier isn't going to deter termites much, if at all. They can chew through 10 mil plastic without much trouble, and their path to your structural wood would be at the foundation piers, where the vapor barrier would have a gap anyway.
Foil faced rigid foam (seams taped for air tightness) on the underside of the floor joists could help. Cement board or fiber cement siding applied to the under side of the floor joists would help too but it's harder to air seal as tightly, and would require adding fiber insulation in the stud bays for insulation.
A copper-flashing wrap around each of the foundation piers would also help. Copper is toxic to the gut flora that allows termites to digest wood fiber, and it doesn't take much copper leaching down the foundation piers to make the path too toxic for them to establish a termite superhighway through it. (Copper clad sill gaskets are useful on poured concrete foundations for the same reason.)
Filling the joist bays with a cellulose insulation product that only uses borate fire retardents can help some, since borates are also toxic to the same gut flora. But once they've tunneled into the joists without going through the cellulose it doesn't help TOO much. IRC code min is R13 in your climate zone 2A, and a full cavity fill is arguably over-kill from an R-value point of view, but from an air-tightness and as part of a termite mitigation design it's still reasonable. (It doesn't need to be "dense packed", just filled.)
If your home is on piers, you may be able to use metal flashing to make it more difficult for termites to invade without detection.
You can discourage many types of insects by air sealing your home. Sealing up cracks and holes will also improve your home's efficiency and comfort. See this article (https://www.greenbuildingadvisor.com/blogs/dept/musings/getting-biggest-bang-your-air-sealing-buck) as well as the sidebar links.
Sallie,
It's definitely a good idea to cover the soil under your house with ordinary 6 mil polyethylene. For an adequate job, just cut out openings as needed for the piers, and hold the poly in place with bricks or stones. For a fancier job, you can tape the polyethylene seams and tape the poly to the piers or the footings with housewrap tape or a high-quality European tape.
For a do-it-yourself insulation job, I would agree with Dana that you should install a continuous horizontal layer of foil-faced polyisocyanurate on the underside of your floor joists, with or without fluffy insulation (mineral wool or fiberglass) between the joists. Before beginning this insulation job, it's a good idea to seal any large cracks in your floor with caulk. But even if you skip that step, a well-sealed layer of polyiso foam (with taped seams, of course, and a sealed perimeter) will go a long ways toward reducing air leakage.
For more information, see "How to Insulate a Cold Floor."