Deck To Addition - Insulating The Floor

Tickridgescott

Hi,
I am adding a small (300 sq ft) addition to our small house. I built a deck out there a few years ago and had poured substantial pier footings to hold the deck as I thought that one day I might want to add a screened in porch. Well, now it is going to end up being an actual addition (ie 4 season).

My question is in regards to insulating the floor. We live in southern ohio and so we get moderately cold winters but not extreme. I am planning to remove decking boards, install 1" or 1.5" of pink or blueboard and then plywood on top. My thought is that although 1" will give only R-5 protection from heat loss or gain, it is a totally uninterupted surface of insulation and therefore wood be very decent. PLUS, an extra r-1 or so for the ply.

Any comments/suggestions on this would be appreciated. I am limited on the thickness of the insualtion due to wanting it to match floor inside. I know I have room for 1" of foam, possibly 1.5". The deck is only a couple inches off the ground and so there is not room to get under it and insulate the bays between the joists.

Thanks,
Scott

greg24k

What does the code calls for in your area? Your Architect or you (if it's your own house) should have all that information on the plan when you apply for a building permit. Building department will tell you what will fly and what will not.

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IHI

For as small as that is, and since it'll be open to the house, you will not want a cold floor radiating the winter bluster inside. Do yourself a huge favor, anty up the extra coin and have it sprayed, you absolutely will not regret it. The only thing you will regret is doing it the way your describing, hating the cold floor, and then years later finally biting the bullet and having it sprayed making 5x's the mess vs doing it right, now.

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woodchuck2

X2, i am not to keen on the spray foam insulation but this is a perfect example of where it can be very usefull and beneficial. I helped my BIL do this same thing last year, we pulled up the floor and put screening on the bottom of the floor joists first and then had it sprayed. The floor for this deck was 2X8 pt so there was plenty of insulation. We then put the 5/4 flooring back down with a sub-floor on top of that. Then it was carpeted. For the walls we used fiberglass insulation and covered the walls in pine v-joint as well as the ceiling.

Tickridgescott

Thanks for the replies. My other thought was to do just as is described, I was planning on attaching furring strips on the side of the PT 2x8s at the bottom and lay in concrete board in the bays, caulk around the edges (all as a way to keep out possible vermin since we live in the woods). I was just trying to save a step, plus the inch of insulation would have gotten me up higher where i needed to be.

I do have sort of question something though. I called the only spray foam insulating contractor in our area and he suggests only 1" of high density closed cell spray foam, says it is only R-7 but that you can't just look at r value(due to it totally blocking air) and because it is high density will insulate every bit I need, and better than 8" of fiberglass (not that I would put that in floor). Now my question is this.... If this is really true why cant I get a 1" high density insulation board and do the same thing and sve myself time and money. The thing about this is that since it is a small job for him (the insulation contractor) and he has certain costs just to come and set up, it is going to be fairly costly (did not find out how much yet).

I am thinking the alternative to his claimed 1" high density spray as 1"
Polyisocyanurate Foam Board

I just dont see what the difference would be if it is both high density board and same r value. In fact the foam board would provide complete thermal resistance to any thermal bridging.

Either I am missing something or....?

Tinstaafl

Why not? Yes, you need to stop air flow, but once that's done, insulation is insulation. Completely filling the cavities would be about as good as you can get, but economic reality says that a hunk of foam board with fiberglass on top would do just fine.

deck king

The advantage of closed cell foam is that it does not allow moisture/ thermal transferance. if you stop air flow and humidity the R- factor is not as important. That is why Tyvek with taped seams works so well!
Also if you Google "spray foam" there are companies that sell inexpensive DIY kits!