spray foam vs ridgid foam board insulation?

[cody michael]

I am making a new shop in a metal building (like a polebarn but all metal) I was thinking of going spray foam but for about 1/3 the cost I can get 2in rigid foam with the tinfoil on outside. I have seen people use that and sprayfoam with little cans around outer edge/seams. This will only be heated when I am out there. Not sure if spray foam is worth while, any issues with putting rigid foam board up against outside wall? Is it better to keep it tight to the wall or have a little air gap?

[Jim Becker]

"In general" you might get similar R-Value for those areas that are covered. The major advantages that closed cell spray foam has in metal buildings including increased rigidity, superior infiltration containment compared to manually foaming cracks and the kicker...relief from condensation issues between the metal and the interior caused by temperature differential. If I were going to not use closed cell spray foam, I'd use fiberglas or rockwool with a poly vapor barrier after using rattle can spray foam to seal obvious openings due to ridges and poor fitting in the metal, etc.

[Scott T Smith]

An air gap is an insulator, so I'd space your foam panels 1" of so from the outer walls. This also solves the problem of condensation being held in place by the foam insulation against the metal panels and causing premature failure.

Spray foam sure works well though.

[cody michael]

"In general" you might get similar R-Value for those areas that are covered. The major advantages that closed cell spray foam has in metal buildings including increased rigidity, superior infiltration containment compared to manually foaming cracks and the kicker...relief from condensation issues between the metal and the interior caused by temperature differential. If I were going to not use closed cell spray foam, I'd use fiberglas or rockwool with a poly vapor barrier after using rattle can spray foam to seal obvious openings due to ridges and poor fitting in the metal, etc.

how big of an issue is condensation between the panels, my brothers polebarn is old (i would say 30-40 years) and has had no issues, his was build with foam tight to the metal.

I would like to spray foam but I don't think I can justify the cost for a building I won't be heating. I mainly need it relatively sealed up and want to reduce temp swings to reduce condensation on my tools.

[Alex Zeller]

Mice would be my biggest concern. I remember talking to a insulation contractor who said that spray foam works well to deter mice. His thought was that they usually take the path of least resistance. Why chew a hole through a board when they can just go through a crack. Rock wool should also be good but being loose they could use it to make nests. Foam panels should work well but you will want to spray foam to seal them up.

I worked at a company that never had a problem until a bakery moved in next door. With it came mice and raccoons. They destroyed the insulation. It took a couple years to figure it out though. Each year it cost more to heat until it got to the point the heating system couldn't keep up did the owner call a company to add insulation. With a fiberoptic camera they looked in the walls and ceiling and found the fiberglass was all but missing. They were going to do blown in cellulose but changed to spray foam (at a much higher cost).

[Jim Becker]

how big of an issue is condensation between the panels, my brothers polebarn is old (i would say 30-40 years) and has had no issues, his was build with foam tight to the metal.

I would like to spray foam but I don't think I can justify the cost for a building I won't be heating. I mainly need it relatively sealed up and want to reduce temp swings to reduce condensation on my tools.

Condensation isn't often considered for a farm building, but it's more relevant for "more finished spaces" that have things like insulation and HVAC because of temperature differences. In an open building, the stuff can just drip...which can be darn annoying if you are standing there, but things dry out if the moisture has a place to go. When you finish the interior, now you're causing barriers toward that moisture having 'someplace to go". With properly applied spray foam you not only get the structural benefits and sealing/insulation values, but you don't leave any space for moist air to condense onto the metal. Since you say you will not be conditioning the space, using other insulation methods would, as you note, be more cost effective. But they have to be applied correctly so that any condensation between the metal and the insulation from tempurature differences has a place to go.

[Steve Rozmiarek]

I agree with Jim's perspective on this. Installation of foam board is a lot more complicated than it seems too, you'll probably be recalculating the actual cost of sheets part way through.

[John Lifer]

Having had an unheated metal building in MS, yes a long way away, that had thin fiberglass with plastic backing, R value of about 5, maybe, I would recommend spraying it all. One time and you are done. If you ever wanted to heat this place, you KNOW it would be ready to go. And way less on filling gaps, getting behind poles and braces. Just spray and be done.

[Bill Dufour]

I have read that the thing to do is to use wainscoting for the siding. Do not spray direct on that portion use something like tyvex before spraying. that way if the bottom gets dented up by traffic it can be replaced fairly easy.
Bill D

[Erik Loza]

I agree with Jim's perspective on this. Installation of foam board is a lot more complicated than it seems too, you'll probably be recalculating the actual cost of sheets part way through.

My thought as well. Sheets "seem" cheaper up front but I suspect could more expensive in the end. I think the appeal of the spray-in stuff is that a crew can come in and do it all in one afternoon. Also, the spray-in stuff has a really nice sound absorbing character that I doubt sheets have.

Erik

[Leigh Betsch]

I had my shop 100% spray foamed. The best way to insulate around my attic was going to be spray foam. The foamer came over right away and convinced me to just spray foam the entire building rather than spray the attic and then fiberglass batt the walls. I never got a quote on fiberglass batts but to spray foam the underside of the roof and walls of a 33x40x10 shop cost me $8000. I'm quite sure this is at least 2x the fiberglass route, but it was quick and 100% air tight. The foamer said he does a lot of metal shops and really adds to the building integrity. All the parts are glued together. My shop is stick built, not metal pole, just think about it, its all glued together. It isn't going to come apart in a big wind!
The foamer said he doesn't quote R value because its really not apples to apples. His big selling point of foam is zero air infiltration.
Maybe I got up sold but I am very happy with the end result.

[Jim Becker]

My thought as well. Sheets "seem" cheaper up front but I suspect could more expensive in the end. I think the appeal of the spray-in stuff is that a crew can come in and do it all in one afternoon. Also, the spray-in stuff has a really nice sound absorbing character that I doubt sheets have.

Erik

And it adds significant rigidity to the structure.

[Ronald Blue]

I lined my shop building with plastic as a moisture barrier and then 6" of kraft faced fiberglass in the walls. It's pole building construction with column style posts. (Concrete base in the ground) Overlaid with white tin on top of that. Same type as the building was built with. Ceiling is lined with tin and 15" of blown in fiberglass. I used 3/4" OSB around the bottom as a more durable material from normal activities. The tin can be easily dented. Electrical is all in conduit. While I don't dispute spray foam has it's benefits I'd still have wanted/needed to line the inside. My building is extremely tight. Each person has to decide what works for them. Mine is extremely tight and quiet.

[Erik Loza]

And it adds significant rigidity to the structure.

That's a good point. Hadn't thought of it that way.

Erik

[Greg Hines, MD]

I had closed cell foam done all over my shop, and I love it. It does not have heating or cooling yet, but it is fairly pleasant in the winter or summer, at least for a while. Minisplit is on the list of things to add to it when I have the funds.

Doc.