Need Advice on Insulating Platform

[sarafina]

Here is a picture of a platform we built this summer:

http://i13.photobucket.com/albums/a294/sarafina159/Fri-FinishedPlatform.jpg

It will have 2x6 pine tongue & groove flooring put down on top and we are putting a yurt on it (kinda like a round tee-pee) as a weekend cabin in Arkansas. There is no subfloor - just the 2x6 flooring boards.

The beams are 4x6 treated pine. I would like to insulate under the floor, but I am not sure what kind to use or how to secure it to keep it from falling or getting caught by the wind underneath and ripping it off. The platform is 30' in diameter and about 27" off the ground. The beams are on 4' centers.

Any suggestions?

Thanks.

[CThomp]

Spray foam...if you can get an installer out there. Other wise you'll need to put in the insulation and then attach some treated ply to the underside of the platform to keep the insulation from falling out.

[David]

You can get DIY kits of spray foam. My concern is the depth...you need a very thick amount of insulation. What location is this?

[CThomp]

I'm not trying to take over this thread but who has the best deal on a spray foam kit. I've seen that Tiger Foam stuff on the net but that looks crazy expensive.

[sarafina]

What location is this?

Northern Arkansas, center of the state.

[David]

Northern Arkansas, center of the state.

Ah, okay, not that much insulation needed then. You may still need a deeper cavity.

Also, instead of plywood, you may be better off sealing it with rigid foam.

[CThomp]

Rigid foam...good call. Won't rot, easier to install, and alot lighter. Some fiber glass batts covered by the rigid foam would be easy then.

[sarafina]

Thank-you for your replies. I was thinking of using a staple gun and stapling plastic straps from beam to beam to hold the rigid foam boards in place.

[CThomp]

You can fasten the rigid foam boards directly to the wood. But if you're paranoid about it plastic straps won't hurt.

[David]

You actually can't fasten the rigid foam well to those beams. They are 4' apart, not 16" oc. And, they run longer than 10'. That's not enough nailing to keep them up.

If it were me, I'd hang some 2x4 PT joists flush to the bottom of the beams (with joist hangers). I'd face nail 2x4 blocking.

Then I'd use 4'x10' sheets of 2" rigid foam fastened with plastic capped nails. Be sure they work with the new PT standards - if you can't find any, then use non-treated wood -- but try, try, try to use treated wood. You can't use more nails to make it fasten better, either. Stick to 6" spacing on the edges, 8" in the field (middle).

I can't decide if I'd tape the seams. On one hand, you want to let out any moisture. OTOH, you want to keep all moisture away from your framing members. Unless you want to use a TyVek wrap, which supposedly allows moisture out, you don't have a weather resistant barrier. Don't use tarpaper. I lean towards taping with the best tape you can find. Such good tape gets expensive, and so does spray foam.

Forget the plastic straps. Who knows how well they stand up to the weather?

I'd still use spray foam sprayed from above down onto the rigid foam. There are two types, closed-cell and open-cell. Go with closed-cell. Closed-cell doesn't wick moisture, so no moisutre should be getting in. Oepn-cell is good for an attick, because you'd want a leak in the shingles to wick thru the foam and dry to the inside of the attick. In your case, open-cell would allow moisture wick into your home -- not good. Keep in mind, water won't wick 'out' either. So if/when you spill something onto your wood flooring, you'd better get it cleaned up!

Sorry for rambling...

[CThomp]

Seems like you could get away with running the rigid foam on the 4' centers? Better safe than sorry.

I think after all that work would you better off putting in the 2x6 t&g and then spray foam from the bottom?

Less work, less thought, and no worries. Closed cell though definitely. Especially at R-7 per inch or so you could do 2 or 3 inches and have sealed insulated floor?

[David]

When/If you remove the t&g floor, you destroy the insulation if it's sprayed up to the floor. So my position is still in favor of spraying down onto the rigid foam.

And, if you favor spraying up, I still wouldn't skip the rigid foam. It'll protect the spray foam which is not meant to be exposed to the elements, while rigid insulation is.

While one could get away with supports spaced at 4', I wouldn't want my house at risk. Go the extra mile, in my opinion: do it once, do it right (if budget can allow for it).