What is the best way to insulate a Metal structure from the Inside?
Hello. I am very worried about the proper insulation of my all metal home kit I recently purchased, steel super structure and studs, roof and siding. The metal siding acts as the sheer wall and so I can't insulate between the siding and the exterior studs, besides a very thin foam vapor barrier that was included. I read all the articles here that say cavity insulation won't work well because of thermal bridging. What about close cell spray foam? Would that work over the studs & could the dry wall be screwed through the spray foam or would that mess up the thermal break? Or EPS foam sheets on the inside of studs before dry wall? I need R38 in roof (4:12 pitch) and R21 in the 6" x 10' H exterior walls. Was planning on cathedral ceiling in most of the house (2,052 SF) and 9' ceilings over 685 SF. I'm so confused as to how this design passed title 24 here in CA, and stressing I'll have a bad design that won't pass 3rd party verification. Thanks so much for any help.
Switching to closed cell foam would not make a difference, the type of insulation changes nothing. It’s a simple matter of having metal pass through the thermal envelope every 16 to 24 inches around the entire building, which can reduce the ‘effective’ R value of whatever insulation is there, by as much as 25%. So you can think of insulating between metal studs as if you were paying a 25% premium on the cost of insulation, since you will only be getting about ¾ of the performance you paid for.
Having thermal bridges can also cause condensation as well, when humid air meets these cold spots in a wall. Here is our page about thermal bridging, check this out first –
Thermal bridges and thermal breaks – how to build energy efficient walls
The fact that you are in California means the stakes are probably a bit lower for you, as you are likely in an area where it is quite dry I assume? Condensation therefore isn’t a problem. Also it is not as extreme a climate as if you were in the northern states or Canada with really hash winters.
And a question back to you, what does the manufacturer say? Ideally you would have a seamless blanket of insulation surrounding the home either inside or outside of the metal stud wall, that would be the best design. And the idea that you cannot insulate outside the metal or risk wind shear, is that the recommendation from the manufacturer? Adding insulation to the exterior of walls is very common, so I’m not sure how that would negate the structural integrity of the frame.
And honestly these aren’t issues a homeowner or even a builder should have to concern themselves with, since a manufacturer should have the solutions to provide you. And as for 3rd party verification, that should be resolved ahead of time in the permitting process so that by the time you start building you know for sure you will pass inpection if you follow the plans. If you give us a few more details we can probably help more, but I think your first step is to find out what the manufacturer suggests.