Insulating Under Floor Joists
I’m in southern Louisiana in CZ2A (humid). I’ve got a small raised house and want better insulation under the floor. About 12 years ago, I put fiberglass batts held up with chicken wire to keep animals from it, but occasionally raccoons have robbed a little here and there anyway. The insulation did help, but I’m sure it’s not fully doing it’s job since it’s exposed to wind.
By raised, I mean it’s floor joists sitting on blocks. There is no crawl space wall or skirting to insulate the sides. Pretty much all the insulation advise I see is to insulate the sides that I don’t have. The joist bottoms are about 24″ above the ground. Joists and plywood are both treated.
I was wondering if I could add about R10 or so of EPS or XPS foam board below the joists and tape the edges and seams to seal out air. This would keep all sun exposure off the foam boards. Can I use foam boards if left exposed like this? I’m pretty sure I have a vapor barrier under the laminate flooring by the way. I remember putting a plastic underlayment when installing it.
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在温暖，潮湿的气候下，内部的蒸气屏障是无名的，因为A/C将内部表面保持在外部空气露点以下，并且您可以在完成后面凝结。因此，我们可以希望您使用的底层不是完整的蒸气屏障型材料。
If not, then using foil-faced polyiso insulation might be your best bet. The foil facing is a vapor barrier (not retarder), and depending on the brand and type, can be relatively rugged. Also, taping the foil facing with foil tape is easy and permanent. The insulation will keep all of the lumber inside at least some of your thermal envelope and that tends to keep it dryer. The taped surfaces will stop the wind washing that you are correctly concerned about. The end result should be more durable and comfortable than what you have now.
I agree with everything Peter said regarding vapor issues.
If you're having racoon problems though, they can scratch and chew through polyiso or any other type of rigid foam. You'll want to put some plywood sheathing over the foam for physical protection. You don't need it for structure, so you can get by with 3/8", maybe even 1/4" plywood here. The only downside to the thinner material is that it will sag more between supports and will look worse.
Bill
I am having a sun porch insulated, and it's a similar situation. Raised about 24" on piers. My insulation guy came up with a solution, where we'll attach plywood to the bottom of the joists and he will blow cellulose into the joist bays.
我在CZ6中，因此在洛杉矶可能无法使用。