How should we insuate a steel header?
We are putting a 2″ wide rolled steel curved header in a 2×6 wall. Our thinking is that we need to position this header as close to the inside as possible with as much ISO foam to the outside as possible to prevent condensation on the steel. We’ve decided to use 2-1/2″ of ISO which only gets us R16.25 if my math is correct. This allows us to put 3/4″ of wood on the inside of the steel so we have something to fasten interior trim to. There is 1/2″ Zipwall exterior sheathing. There is no exterior foam sheathing.
The question is, since this is a hollow steel beam should we fill it with spray foam which would increase total R value? Or would that spray insulation isolate enough of the steel that it might cause condensation and therefore be a bad idea?
Thanks for any insight you can give us.
I need to add that we are in the Champlain Valley in Vermont. So that is 6A on the climate map.
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Replies
Roger - what is your location?
Roger,
Steel is so conductive that I don't think it makes much difference if you fill it with foam or not. With R-16 outside of the steel, I think you will be OK either way.
Nevertheless, if you are framing a house with 2x6 studs in Vermont, you should strongly consider installing exterior foam sheathing on all of your walls. It will never be cheaper to do than now.
Roger, can you use C-channel instead of hollow tube? It might take a bit more steel, but you would have a better chance at good insulation.
Thanks for the answers.
Martin, I agree with the exterior foam, but it's not happening on this one. Am I to gather from your response that filling the steel with foam would be a good thing then, giving more insulation?
Michael, that is a good thought and worth looking into. Of course, that means getting the engineers involved....
Thanks again.
You should get the engineers involved anyway--even if Martin is right about the minimal gain you would see from insulating inside the hollow header, it should be insulated to prevent condensation WITHIN the beam. Or install outsulation, as Martin advised. It may require web stiffeners but the engineers should be able to design a solution that allows for insulation.
Sorry Roger - missed the last line of your post!
Roger,
As long as you get air sealed foam on the outside of your beam, you will be fine. I would prefer a closed cell, spray applied foam but understand that this is not a viable option if you are not using spray foam elsewhere. If you use board stock, just be careful top get the detailing right. Filling the beam with foam will make no difference since the steel will conduct to defeat the cavity insulation.
Thanks again for all of the responses. And James, no you didn't miss it..... thanks for alerting me...I edited to get the important location info in after your post.
Torsten- we will be using spray foam to seal around our ISO as we put this header assembly together. We are having foam sprayed as our main insulation later.
Thanks again.