TL/DR ?- How does R-19 fiberglass batt insulation compare with 3" closed cell spray foam (my understanding is that each 1" of foam has a 6 to 6.5 R factor)?

I am looking to build a man barn for entertainment, games, poker nights, etc. Barn will be a 1200 sq ft, simple 30x40 design metal building. I am not looking to invest huge sums into this structure and that is why I am building a separate structure where I can control costs more easily then including game room in new house where builders want north of $100 per sq ft to build.

I am thinking of doing a rough finish out with exposed duct and spray foam on the ceiling and painting black. For the walls, I was initially thinking closed cell spray foam as well but due to the costs I was reconsidering. Would another option be to build 2x6 walls and put R-19 batt insulation in the walls with 1/2" drywall. I think the R factor on closed cell is like 6 to 6.5 so if I sprayed 3" in the wall then wouldn't that be the same as the R-19 insulation?

I know spray foam is the superior product with the added strength, efficiencies, etc. but in this application would the R-19 be an adequate option. I am trying to build this on a tight budget and adding another $5-6K for the walls with spray foam is hard to swallow. This building will be used a lot on weekends for games, sports watching, movie nights, but during the week it would not be used as much. I would like to keep it energy efficient but I need to balance upfront build costs with long-term energy efficiency. Any other insulation ideas that might be a better option that any of you have come across? Thanks in advance.

A neighbor had their metal garage sprayed & the off gassing odor was terrible. Maybe it was the product, maybe the installation process or that there is no hvac system - I don't know - but it was awful. Not sure how long it look to quit smelling or if it ever did totally.

Go with the batts

schwack schwack said:

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A neighbor had their metal garage sprayed & the off gassing odor was terrible. Maybe it was the product, maybe the installation process or that there is no hvac system - I don't know - but it was awful. Not sure how long it look to quit smelling or if it ever did totally.

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That usually means it wasn't applied correctly. If they lay too thick of a layer in one pass it won't cure properly and it will off-gas for longer. Also, the temperature when it is applied can make a difference.

The key to insulating a structure like this (or any structure) is to control air infiltration, which spray foam does well. Air barriers and careful sealing of penetrations also work well. There are diminishing returns past a certain r-Value when using any kind of insulation anyway. The downside to spray foam is that is can hide leaks and trap moisture depending on how it's applied. The roof will leak unless you use concealed fasteners. I believe some metal building manufacturers will not honor roof warranties if foam is applied underneath. Plus it looks terrible unless you cover it up with something.

For a structure that will only be used a couple of times a week, I would just make sure you have a air infiltration barrier on the outside, butyl tape seam all of the joints in the panels, and use batts. Personally, I wouldn't spray foam on the underside of a metal building roof. Also, repairs or changes in the future are a gigantic PIA with foam.

If I were building a structure like that for myself, I would wood frame it and use trusses for the span. I think they look nicer and have a warm bar-like feeling to them. For the roof, from the inside out, I would do plywood, 3-4" rigid foam insulation, and another layer of plywood, and then the roofing material. The underside would remain clean and you would create a complete thermal break between the roof and the interior. The walls can be insulated easily. You can use a Zip-Wall system for an air barrier or use a house wrap.

If you use it sparingly, then why is efficiency so critical?

During off times the ac will still be running to keep the temperature down and remove humidity. I could envision during the week keeping the barn at 78 in the summer and then in the winter around 63-65 or so and then on the weekends the program moves temp to 72 or so. I dont want to run huge heating and cooling bills during these off times so efficiency is still important to me even if not using on a daily basis like my home.

Have used spray foam in a similar barn/storage building and would highly recommend! No smell, sound control and thermal insulation is unmatched.