Air Gap 4 Insulation

[Niall]

I'm finally upto floor and wall building stage, the insulation manufacturer said for the best possible inslation value i should allow for an air gap between my insulation and the outter surface of the tear. Yet i have read in the forum that this is not normally the case ? I'm using Foilboard, a product made here in Australia.

http://www.foilboard.com.au/emasta/index.htm

Can anyone steer me in the right direction here ?

Thanks,

Niall.

[Arne]

Dead air is the best insulation... but, it needs something to keep it from moving around, which is why the air gap is filled with foam or fiberglass batting, both of which do not conduct heat very well.

If all we need was a dead air space, houses would have empty walls, not fiberglass insulation...

So, fill the gap with something that won't conduct heat energy. I use foam mainly because it is the right thickness and it becomes a half-assed structural member of what I build. That way, with full foam fill, I can use thinner ply on the walls and floor and build lighter.

[Ira]

Niall, the thing is, you're building a teardrop--not a house. So as far as the U.S. goes, we'll use 3/4" framing (1 by 2s) on the side walls so the 3/4" rigid foam insulation fits right in there. And the same sticks turned sideways for the roof give you 1 1/2" so you can stick two layers of insualrtion in there.

I guess there's just not really a point in trying to improve on this for the minimal gain you'll get in insulation factor weighed against how it screws up the other aspects of your build trying to do it differently.

[Niall]

Thanks Arne & Ira,

I did want to use 3/4 framing, but can only find 0.59 inch insulation board here, which was another issue. You have now fixed both issues for me..........i'll use the 3/4 inch framing and the insulation board with some 0.15inch foam which will fill it !

Thanks again.

Niall.

[Arne]

filling the cavity fully adds to the rigidity of the walls.... we can get 3/4 framing with 3/4 insulation, which works well.

[ninerhb]

The reason the manufacturer recommended an air gap is because you're using foil-faced insulation. Having an air gap in front of the foil allows it to reflect radiant heat back into a space, where it can then leak back out through the trailer wall. Having a foil barrier trapped against the wall will reduce it's ability to add insulation value. For something like a roof, this is pretty important. For the tear, it's probably not worth it, since you get structural benefit from sandwiching the insulation tightly.

Henry

[jp03]

Differance too is usage. Air gap mostly for housing, to allow slight air flow through the walls, up to the attic. This keeps the slim chance of fungus and wood rot starting, if a slight moisture gets in. Do not believe it will effect a camper any!

[caseydog]

The reason the manufacturer recommended an air gap is because you're using foil-faced insulation. Having an air gap in front of the foil allows it to reflect radiant heat back into a space, where it can then leak back out through the trailer wall. Having a foil barrier trapped against the wall will reduce it's ability to add insulation value. For something like a roof, this is pretty important. For the tear, it's probably not worth it, since you get structural benefit from sandwiching the insulation tightly.

Henry

You beat me to it. It is the foil that leads to the recomendation for the air-gap, just as you said.

Putting this stuff in the TD, you'll loose most of the benefits of the foil, but the foam inside will still do it's job.

I don't know how much of a gain in R-rating one gets by thin sheets of insulation vs. one layer of 3/4 plywood, anyway. It probably does more for weight savings than actual insulating value.

If you camp a lot in the winter, the most important insulation is in the floor. If you camp a lot in the summer, your roof insulation will be more important.

CD