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Help: steel beam transfer heat to outside

jwstraz | Posted in Energy Efficiency and Durability on

How do I fix losing heat through a steal beam that penetrates my home’s heat envelope, without removing the beam?  A room on the ground floor of my house used to be a garage and has a concrete slab on top of it.  The slab is attached to an iron beam, the length of which is exposed to the exterior.  I lose a significant amount of heat through this beam.  Is there a way for me to insulate the beam on the outside?  What else can I do?

Because the beam supports the concrete slab, it would be costly to remove it entirely.  I look forward to your thoughts.  I am in Washington, DC (zone 4A).  The house is masonry construction.

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  1. Jon_R | | #1

    A picture would help. Yes, insulate it.

  2. Expert Member
    BILL WICHERS | | #2

    In DC I’d think that beam would be more of a concern stealing you air conditioning :) I’m out there frequently and roast in the summers.

    Anyway, the easiest way to insulate that beam is probably with one of the smaller 2-part spray foam kits. Even only a 1/2-1” coating of foam will make a huge difference compared to the uninsulated beam. I wouldn’t try to insulate it any other way since it would probably be a huge pain to try to cut and cobble rigid foam to fit, although I supposed you could maybe just box around it and not try to follow the contour of the beam.


  3. jwstraz | | #3

    Just uploaded a photo. I need my hand held. How exactly to insulate it? From the outside of the house? The inside?


  4. Expert Member
    BILL WICHERS | | #4

    From your pic, which I assume is inside, if that gap between the steel piece and the wood is pretty even, you might be able to just stuff a piece of rigid foam in the gap and call it done. Mineral wool might work too, but may be more difficult to insert fully.

    You could probably use canned foam but it would be messy — I think you’d have a hard time keeping it from falling out while you applied it. A small 2-part spray foam kit will cost more, but is probably the best way to insulate this.

    I can’t comment as to insulating from the other side of the wall since you didn’t post a pic of the other side.


  5. jwstraz | | #5

    Many thanks, Bill. The photo is from the outside. The framing you see is my back deck. I cant get to the beam from the inside right now because there is a drywalled frame in the way. I'm having work done soon which will involve removing that wall. It sounds like I could insulate at that time. Is it possible to insulate the beam on the outside? The insulation would be exposed to the elements.

    1. GBA Editor
      Martin Holladay | | #6

      First of all, can you tell us your name? (I'm Martin.)

      It looks like this area is mostly protected from UV light by the deck framing. You can use closed-cell spray foam to insulate the beam. The spray foam will fill the gap between the steel beam and the parallel deck ledger. If it's not exposed to sunlight, the cured spray foam will last for decades.

    2. Expert Member
      BILL WICHERS | | #8

      Yes, you can insulate from the outside. Spray foam would probably be best an easiest and should have enough protection from sunlight as mentioned by Martin. If you can get some rigid foam in there, that would work too. I’d use EPS or XPS for that (not polyiso) since in this case you want something that won’t care if it gets wet.

      When you have access from the inside, I would definitely apply spray foam to the inside of that beam.


  6. Expert Member
    Peter Engle | | #7

    It looks like the beam is the white surface below the deck ledger and flashing?

    If so, a sheet of rigid foam insulation glued to the beam would help. The flashing could be bent out and over the top of the foam to form a drip edge. If you want it to look nice, cover the foam with aluminum coil stock first, then form the flashing into a drip edge over the coil stock.

    There's not much point in using more than an inch or two - your masonry walls will also pass quite a bit of heat through them unless they are also insulated. If you are insulating, you should try for continuity of your insulation, so insulating the steel beam on the outside and masonry walls on the inside wouldn't be a great idea. If you are going to demo the inside soon anyhow, I would consider insulating the inside of the masonry walls with continuous rigid foam insulation and the exposed portions of the steel beam with spray foam insulation. If the geometry and/or access makes this difficult, an inch or two of rigid foam on the outside would still help.

  7. jwstraz | | #9


    Many, many thanks for your suggestions. My name is Josh. I really appreciate your thoughts.

    A few of you mentioned masonry insulation. I didn't realize that was an option. Others had told me that insulating bricks is problematic for condensation reasons. I'll look into it further but would welcome any suggested resources. I'll dig around this website as well.

    Thank you all again. This was a big help.


    1. GBA Editor
      Martin Holladay | | #10

      For more information on insulating an older brick building, see "Insulating Old Brick Buildings."

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