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Is it possible to eliminate thermal bridging in a steel beam?

Terry Goodwin | Posted in General Questions on

Hello,
We’re needing at least 2 beams to span the load of our 2 storey slab on grade home in a new construction. We need a 4 ply beam at 22 inches. The problem is the amount of beam exposed in the living room to accommodate the HVAC ducting. We don’t want to use steel, although it would be only approximately 12 inches in depth. Here’s what the builder has said regarding thermal bridging in the beam:
“Being a 2×8 wall now, we only need about 4” of bearing, and we could have solid rigid insulation between the beam and wall sheathing (3.5”), and also having the 3” of roxul on the outside for a total of 6” or more fighting the thermal transfer.”

We are in Energy Star Canada Climate Zone 3(the coldest) and have approximately 6277 heating degree days. I appreciate any help with this issue, but please no comments on the 2×8 wall construction…and yes I read everything on the site on wall designs.

Thank you very much.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Terry,
    I'm not sure what your question is. Perhaps the title of your post is the important question?

    Q. "Is it possible to eliminate thermal bridging in a steel beam?"

    A. Insulation slows down the rate of heat transfer; it doesn't stop it. Heat will always flow from a hot object toward a nearby cold object. So no -- you can't eliminate thermal bridging.

    Your contractor sounds smart. The R-value of 3.5 inches of rigid foam might be between R-17 and R-21. The R-value of 3 inches of mineral wool is about R-12. So you end up with something like R-29 or R-33 between the end of your steel beam and the outdoors. That should work.

  2. Terry Goodwin | | #2

    Thank you very much Martin!

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