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Exposed steel beam that’s causing a thermal bridge

Simon Y | Posted in Green Building Techniques on

I have a very contemporary style house that probably isn’t the best for chicago’s cold winters and hot summers.
There are exposed steel beams that penetrate through to the inside of the house and have cause a lot of moisture issues.
i have used closed cell spray foam on the inside of the house around the beams, but is there any way to cover the beams on the outside to further prevent thermal bridging?
the beams are both vertical and horizontal.
i’ve attached a picture of the house.
thanks for your help!
sy

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Replies

  1. Robert Van Wert | | #1

    Simon,

    We addressed an issue that sounds similar to that (can't see your attachment) by insulating the exterior of the steel.

    While not ideal, it certainly helps in reducing the temperature difference between the inside and the outside. Ideally, but not always feasible, the exterior portion of the steel is removed to eliminate the bridging.

    Another idea we had but did not employ yet was to also insulate the interior of the steel to try to keep it "cold". In our case, the steel was touching so much internal framing that it really wouldn't have helped.

    If your case is similar to ours, your biggest concern (if they are structural members) is the joint at the interior / exterior. This is where the steel will rust and eventually fail.

  2. User avatar GBA Editor
    Martin Holladay | | #2

    Simon,
    Evidently your attempt to attach a photo wasn't successful; I suggest that you try again.

    Modern architects who incorporate uninsulated steel beams that penetrate a building's thermal envelope managed to graduate from architecture school without learning even the bare elements of building science -- which is unfortunate, especially for people who have to live in buildings they design.

    Robert is right. If you want to prevent condensation, rust, and high energy bills, you'll have to insulate the steel beams on the exterior with spray foam insulation or rigid foam. Then you will need to protect the insulation from the weather with some type of flashing, roofing, or cladding. With some designs, this is easier said than done. Good luck.

  3. Peter L | | #3

    Martin,

    Would a steel roof SIP pose a similar problem if the roof SIP overhangs the wall to form a 24" soffit? The underside of the steel SIP would be exposed to the exterior and then when it transitions to the interior the steel would thermally bridge to the interior ceiling area. I assume a wood roof SIP would also pose a thermal bridging problem in such a condition since the OSB is continuous. Of course steel is considerably worse at bridging than OSB.

  4. User avatar GBA Editor
    Martin Holladay | | #4

    Peter L,
    You're right: If you want to use steel-faced SIPs, you don't want any roof overhangs. I suppose that any needed roof overhangs could be created with 2x framing material installed on top of the SIP roof panels -- but that is an extra, expensive step.

    Any thermal bridging through OSB-faced SIPs is minimal -- after all, the OSB is only about 1/2-inch thick, and OSB is much less conductive than steel.

    PERSIST buildings (which usually have walls and roofs built with framing lumber, not SIPs) are often built without any roof overhangs; the overhangs are framed after the rigid foam has been installed on the exterior of the walls and roof. For more information on the PERSIST technique, see Getting Insulation Out of Your Walls and Ceilings.

    If any GBA readers are curious about steel-faced SIPs, here are some links to manufacturers:

    http://www.precisionfoamfabricators.com/why.php

    http://www.permatherm.net/index.php

    http://www.steelsip.com/What-Are-SIPs-.php

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