DIY Insulating with spray foam kit

Cool thanks for your info. Our steel studs are very square because I built them myself :-)

I used 1x1 for everything but the floor so there will be 2 inches of foam between the studs and 1 inch of foam over the studs...no cold steel touching the inside of the camper. Outside of camper is aluminum sheet 0.063 thick. Bonded to steel studs with 1/16" spacing and Sikaflex 252 adhesive sealant. No galvanic action there.

Everything is expensive though when you do things right. Makes me just want to buy a camper and not know what they did underneath. I am not one to cut corners, so I could never build these for a living.

Jfet wrote:
hi westend,

I got some of the 2 inch R-Max TSX-8500 exposure rated polyisocyanurate foam (expensive!) now. Do you think I need to aluminum tape the sides of the foam when I cut them to fit inbetween my wall studs? The foam would otherwise be exposed on the 2 inches of thickness, but would be pressed up against my steel studs.

No, I wouldn't seal the cut foam. I'm guessing the thoughts about sealing the foam are generated from consideration about moisture absorption? I wouldn't worry about it. You can do some experimentation with absorption by soaking a small piece of foam under water. Weight down the foam piece under water and let it soak for a few days (weeks, months?). Remove the weight and see if you have the same amount of flotation. A trip to the beach will also show that most extruded/expanded foam is difficult to saturate.

One advantage to metal studs is that it bespeaks the walls being set up on a jig in the factory, resulting in cavities that are plumb and square. I did not have one cavity that was plumb, some differing in dimension by as much as 1/2", latitudinally, in my wood-studded trailer. Every piece of foam needed to be measured and custom cut. If you have metal studs, I would strongly suggest you investigate the use of an additional thermal break between the studs and the interior paneling. It may be that the climate in your area doesn't warrant it but conductive heat transfer from the outer siding through the studs can be significant. At one point, I added up the surface area of the stud and ceiling joist faces and came up with a figure of around 40 sq. ft., IIRC. That is equivalent to having a 4'x8' sheet of paneling that is close to ambient temp inside the trailer. As mentioned, I installed a thermal break of 1/4" fanfold insulation across the walls. The fanfold insulation is cheap and is easy to install on wood studs, staples were used. With metal studs, it would need to be glued with foam adhesive.
Fanfold being installed:

hi westend,

I got some of the 2 inch R-Max TSX-8500 exposure rated polyisocyanurate foam (expensive!) now. Do you think I need to aluminum tape the sides of the foam when I cut them to fit inbetween my wall studs? The foam would otherwise be exposed on the 2 inches of thickness, but would be pressed up against my steel studs.

With a foil face and fiberglass reinforcement, your Iso foam permeability to water vapor will be under 1 Perm. That is about as good as it gets. A vapor barrier of 4 mil polyethylene sheet will decrease vapor transfer into the wall. A thermal break of 1/4" extruded polystyrene (fanfold insulation) stapled across the studs and Iso foam will offer relief from conductive heat/cold transfer through the studs. That thermal break shouldn't be underestimated, IMO.

I cut and installed extruded polystyrene and friction fit it into the cavities. This was followed by sealing any voids or cracks with foam adhesive. It's not necessary to attach the foam sheets to the inside of the siding.

Good luck with your TC!

I decided I am going with exposure rated polyisocyanurate block foam (doesn't require sheet rock thermal barrier) although I think the only difference between this and non-exposure rated is the aluminum facer and fiberglass reinforcement. I want to use the Dow Thermax but you can't find this stuff on the west coast. A similar product is Rmax TSX-8500 polyisocyanurate. Both of these are rated at about R13 for 2 inches thick.

I couldn't find anyone that could spray polyisocyanurate. I think the block foam will be ok...will use a bit of sikaflex to fix it to the aluminum siding and steel frame on our camper build.

Spray foam, even of high density, is not totally closed-cell. It does get clogged with water, given a chance - ask boaters. And then it takes forever to dry, in enclosed space in the wall. Luckily for us Rv-ers, it doesn't get a chance to get soaked very often. On the contrary, fiberglass wool gets soaked with water easier, but also dries completely in a few days. Under the floor, however, I would rather use block foam or spray foam than fiberglass wool.

Anyone use it or something similar to insulate the overhead in the front cap of a MH or know someone that does it?

Hi Jfet,

Apply the fire proof foam. Some of it can be heated to 2000 degrees without burning.

Thanks. One other quick question. Is there a major concern about the foam during a fire? I have heard the smoke is very very toxic....we were planning luan over the foam...is this enough or do we need to look for specific fire rated foam?

You are correct, it is the same foam used in homes. I don't know if they trim flush to the walls or leave that to the installer - you will have to ask them.

Home installs they usually use a hand saw to bring the foam flush with the wall surface. A good foam guy will have no problem spraying and filling the cavity but not overfilling it.