Insulation Required to Limit Thermal/Condensation Issues with Steel Beams
I am hoping for some advice that I can’t seem to find searching the articles I’ve read.
We are planning a small 1 bed 400sqft cabin that for various reasons is likely to require a steel ‘portal’ frame super structure. I won’t get too into the details of why we need steel, but essentially due to the design and a very high wind location timber frame won’t seem to cut it structurally according to the structural engineer. Location is south coast of the United Kingdom, call it marine 4c I’d guess.
It is looking like we will end up with about 6 vertical steel posts and a steel box frame in the roof. The steel frame will be infilled with standard 2×6 walls on 24″ centres to be filled with Rockwool.
My question relates to how best deal with the thermal issues of the steel posts and beams.
We can wrap the entire structure in 1-2″ of high spec R8/inch Kingspan Kooltherm. Or, as is commonly done here, we can also insulate the interior with 1″ of Kooltherm prior to drywall. I understand this latter approach doesn’t warm the sheathing but it is a common method here.
Is there a minimum external insulation value to limit/prevent thermal bridging at the steel sections? If we have a continuous air barrier (Intello for example is widely available) on the interior side of the steel would that also alleviate risk of condensation forming on the steel?
Could we also insulate to the interior and keep all the steel on the outside of the thermal envelope and outside our air barrier? If warm moist air isn’t reaching the steel shouldn’t that alleviate condensation risk?
Please let me know if clarification is needed, any advice appreciated as always.
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