Styrofoam Insulation

dusty · Post by **dusty** » Thu Jan 09, 2014 7:23 pm

I have almost finished installing insulation in the travel trailer that I am refurbishing. Today I over heard a comment at Lowe's that makes me wonder if maybe I have it installed wrong side out.

I am using 1" styrofoam that has an aluminum foiled sheeting on one side and on the other something that looks like a clear plastic sheeting. Both seem to be attached to the styrofoam with some sort of adhesive.

Question: Should the aluminum foil be on the inside or should it be on the outside where it would contact the outside aluminum sheeting on the trailer?

davebodner · Post by **davebodner** » Thu Jan 09, 2014 7:26 pm

I believe the foil should be facing an air gap, if possible. Otherwise it doesn't matter.

reible · Post by **reible** » Thu Jan 09, 2014 8:36 pm

I think the best answer is to call the insulation manufacture and tell them what you want to do and let them answer.

A couple of years back a major "manufacture home" builder ended up putting the insulation in wrong and have to payout damages and replacement work on their homes (some place in WI). If they could get it wrong so could any of us.

In the old days it was easy, the foil was on the inside as a thermal and vapor barrier. If you put it on wrong the vapors got the insulation wet, it became conductive and the water collected and rotted the walls.... This is another way to spell mold.

Now it is not uncommon to have have a plastic vapor barrier on the inside walls and an air barrier on the outside walls. Of course we are on the cold side of insulation picture so maybe it is different in the southwest.

Ed

wasatch · Post by **wasatch** » Thu Jan 09, 2014 8:43 pm

This is all I've got:
Rigid Faced Foam Insulation
Rigid foam insulation is made up of tiny gas bubbles. Over time, the gas can leak out, which reduces the effectiveness of the insulation. The U.S. Department of Energy recommends using rigid foam that is faced with foil or plastic, because this facing material helps slow down thermal drift and keep gas from escaping. When you use faced insulation indoors, position the faced side of the material so that it faces into the home; when you use it outdoors, the faced side goes on the outside.

Since yours is faced on both sides, I would think that both would act to slow down thermal drift but the foil side, installed facing the inside, would reflect infrared heat back into the heated space.

That's my 2 cents.

joshh · Post by **joshh** » Thu Jan 09, 2014 9:29 pm

davebodner wrote:I believe the foil should be facing an air gap, if possible. Otherwise it doesn't matter.

I second the air gap recommendation if there is room.

billmayo · Post by **billmayo** » Thu Jan 09, 2014 11:12 pm

Only use an adhesive made for the foam board like LocTite Power Grab Foamboard that I used to insulate my metal garage. Regular construction adhesive will destroy the foam board and not hold.

dgale · Post by **dgale** » Thu Jan 09, 2014 11:16 pm

wasatch wrote:
Since yours is faced on both sides, I would think that both would act to slow down thermal drift but the foil side, installed facing the inside, would reflect infrared heat back into the heated space. That's my 2 cents.

I can double-check with some contractor friends but am 99% sure this is correct - foil side should face toward living area and plastic side should face toward exterior. Foil reflects heat back toward you and plastic is likely a vapor barrier, which you would want on the exterior-facing surface.

JPG · Post by **JPG** » Fri Jan 10, 2014 12:49 am

dgale wrote:I can double-check with some contractor friends but am 99% sure this is correct - foil side should face toward living area and plastic side should face toward exterior. Foil reflects heat back toward you and plastic is likely a vapor barrier, which you would want on the exterior-facing surface.

In AZ I would think reflecting heat back towards 'outside' would be an objective.

reftech · Post by **reftech** » Fri Jan 10, 2014 1:11 am

The outer aluminum skin of the rv will act as the radiant barrier for external radiant heat. The reflective side of the insulation can be turned toward the inside to be a barrier for the radiant heat escaping to the outside. Both metal sides, the rv skin and the reflective skin on insulation are vapor barriers. Fill voids in wall spaces snugly.

dusty · Post by **dusty** » Fri Jan 10, 2014 6:42 am

JPG40504 wrote:In AZ I would think reflecting heat back towards 'outside' would be an objective.

The heat in Arizona, especially in July, August and September, is certainly a major consideration BUT I have a very effective roof mounted AC. The trailer is 8' wide and 19' long; not a large space to heat or cool.

With this in mind, I installed the rigid foam insulation with the aluminum foil to the inside thinking I needed to reflect the heat back into the trailer during the cold times (which are few). The cooler months, however, are the times that we will use the RV the most.

Hope I am right.

Thanks for the replies. At least I know that there was not a clear and obvious answer to my question.

BTW: I asked at two different Lowe's and two different Home Depots and got an equally balanced set of opposing answers.