Styrofoam vs fiberglass matt insulation

[ajcal225]

While I have my camper apart to do some structural repairs, I've been looking at its insulation. its basically 1" stryofoam sheets.

My understanding is that the foam sheet isnt as susceptible to water issues, won't wick moisture in and won't grow mold the way matt will.. but that it doesn't work as well, either.

I'll pretty much exclusively be using my camper in cold weather (california deserts during winter). This camper has a history of water leaks, which I'm working on now, but I feel like I should keep in mind when deciding on insulation.

Am I better off to leave the foam sheets in place, or to pull them out and replace them with fiberglass matt?

[Jfet]

I used 1 and 2 inch thick polyisocyanurate foam sheet. I used the exposure rated type but you can also get it with regular foil backing on both sides at Home Depot (not Lowes). I think it is about $30 a 4' x 8' sheet. It will not burn very well...doesn't hold a flame or go up like a matchstick. I think the 2 inch is rated at R13. I cut it with a jigsaw using a wood cutting blade...much easier than a knife and generates little dust unlike a table saw. I did wear a dust mask. I did our entire camper so know a bit about the stuff now.

[Led_67]

sabconsulting has a post on his reroof he did awhile back sabconsulting new roof and on the second page it shows how he insulated his roof in much the same way as previously discussed.

You could apply this to the walls as well.

Good Luck

[bob_nestor]

kohldad wrote:
Foam sheet are much better in campers. If the fiberglass gets wet, it loses it's insulation factor. Tends to sag over time from vibration and gravity. plus, when installed with pressure, foam also can provide rigidity to the structure, another plus.

Foam insulation has many variables which determine it's R value. The cheap white bead foam board is lowest, but high density foam actually surpasses fiberglass. 4" of high density with foil siding can exceed R-30 while the best batt fiberglass is R-15 for 3.5". If you want better insulation, do some research on different foam types and select a better one, though it will cost more.

If you want water resistance you'll want to use closed cell, not open cell. Another advantage of closed cell is it has a higher R value, but it also costs more.

[silversand]

I agree with silversand. I wouldn't use spray foam, but I don't think anyone recommended using it.

....Gaetan suggested touching up the perimeter of the block foam panels (after inserting, you may not have an absolutely perfect fit, and spray foam is a good lock-in material)...

Just use a hand saw or a sharp knife.

...I use an 8-foot long aluminum level as a cutting edge (I score the 2 inch or 1 inch thick foam sheets about 3/4 ~ 1/2 of an inch deep, then I snap the board in 2 by bending it: bang !).

[covered_wagon]

I would not cut any rigid foam on a table saw unless you wear a respirator. Two of us got sick for a long time from that stuff.

Just use a hand saw or a sharp knife.

BTW, We don't cut anything loose with rigid foam we cut it to pressure fit. Better built all around this way

[gbopp]

I agree with silversand. I wouldn't use spray foam, but I don't think anyone recommended using it.
Stick with the rigid foam boards. They will do a good job.

[The_Texan]

Call a local contractor and ask him who he uses for the spray foam that builders use on homes. It is closed cell, limited expansion and high R rating. Also, water proof so moisture is a non issue. Price is comparable to the closed cell sheets, but provides complete coverage, where the sheet will leave gaps as you cut and fit.

[ajcal225]

Good tip on the closed cell foam, I've installed that on walk in refrigerators before but forgot all about it.

I'll pick up a couple of sheets and get to work. Thanks!

[silversand]

Gaetan make a VERY good point:

I will only add: spray expending foam comes in latex (open-cell) and non-latex based closed cell spray expanding. Get the closed-cell limited expanding material (when it dries, the over-expansion foam can be cut with a blade)...also remember: most of the expanding foams are extremely flammable when being applied, and while off-gassing. This s why you need very good ventilation when applying (it is also recommended NOT to spray expanding foam into closed cavities: the explosive gasses cannot escape during curing).

Some closed cell foams now come with less explosive carrier, check your product carefully.

[gbopp]

Poor Man's Spray Foam

[Gaetan]

The bleu and pink foams will also had rigidity to the structure, you can also fill the gap with spray foam, the less expandable one.
Gaetan

[silversand]

.....like Buzzcut suggests, don't fool about with anything other than closed cell foam. There are MANY block foam compositions out there. Check the PERM rating and compressive strength (ASTM D1621) for the foam FIRST before settling on ANY for product (Water Absorption, ASTM C272, % by volume, max: 0.3 or better) ! Also, if the better PERM comes from a thin plastic veneer over the foam board, ask yourself: what if this thin veneer is scratched, perforated or abraded? If this happens, then you have just usurped your PERM/vapor barrier spec!

Remember this: try and build a toy boat out of glass wool (if you can) and a 2nd toy boat out of XPS closed-cell block foam, drop them in the bath, and see which one survives after a few hours. Now, remove from tub, and dry both off with a hair drier (you've only got 1 minute to dry both: which one will not dry, even after days?).

When glass wool takes on even a small quantity of humidity (forget about water!), it will virtually lose ALL its insulating value.

[Buzzcut1]

a third choice that is waterproof, lightweight, insulates well and easily cutable to fit the spaces is closed cell foam. You can pick up 4'x 8'x 1" sheets at most stores that sell foam for $75 per sheet.

[kohldad]

Foam sheet are much better in campers. If the fiberglass gets wet, it loses it's insulation factor. Tends to sag over time from vibration and gravity. plus, when installed with pressure, foam also can provide rigidity to the structure, another plus.

Foam insulation has many variables which determine it's R value. The cheap white bead foam board is lowest, but high density foam actually surpasses fiberglass. 4" of high density with foil siding can exceed R-30 while the best batt fiberglass is R-15 for 3.5". If you want better insulation, do some research on different foam types and select a better one, though it will cost more.