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Dan S 05-20-2010 11:26 PM

converting wood to steel for window header
We would like to make a window in our kitchen a little taller and want to know if we could do this by replacing the wood header with a smaller steel header. The window is 4.5 feet wide and the header is currently a pair of 2 by 8s. If a steel i-beam of say 4 inches was the same strength, that would let us make the window 4 inches taller. But how does the conversion work? What kind of steel beam would be the same strength as a pair of 2 by 8s?

Daniel Holzman 05-21-2010 10:54 AM

In bending only in the vertical plane, an S3x5.7 is approximately the same strength as a pair of dressed 2x8 wooden beams, assuming you get A36 steel. If you get A60 steel, the S3x5.7 is stronger in bending. An S3x5.7 is three inches tall, and 5.7 lbs/foot.

This is simply a statement of equivalent strength, I am not designing this beam for you, and without an engineering analysis of your house, I cannot say whether this size beam is adequate, because I do not know the loads your header is subject to. Also bear in mind that if you use a steel beam as a header, you need to get it drilled so you can attach it to the vertical wooden supports on either end.

RoyalAcresRod 05-21-2010 03:39 PM

Why don't you move up the existing header? The steel header is going to quite successfully transfer the heat or cold from the outside into the conditioned space.

Too, the modern energy-efficient way to construct exterior headers is to use 1/2 inch foam between the 2Xs, instead of plywood or OSB, to lessen the energy loss at this area.

Unless there are special circumstances, I believe this header can be constructed from 2X6s. Most builders use 2X8 or 2X10 in all openings to have consistent window height throughout the home.

Gary in WA 05-21-2010 09:02 PM

In most of the 4 out of 5 charts here, your header may be border-line or even over-spanned:

Ouch, I wouldn’t say it’s ok without knowing the loads above or the year the house was built to say replace with another one of lesser strength. (A Structural Engineer would know)

I’d rather nail the header members tight together for strength and fastener penetration with the foam board (non-structural) inside, above the flat nailer for window treatment.

Be safe, Gary

Dan S 05-21-2010 11:51 PM

Thanks for ideas
I got several useful messages from the replies.

(1) I probably should talk to a structural engineer. Anybody want to guess at the likely cost of that? Even if I end up doing that, the info from the replies will help me ask good questions.

(2) Daniel Holtzman tells me that with A36 or better steal, a 3 inch beam could do the work of 2 paired 2X8s. So we do have hope for our idea. (He also points out that we need to get the steal beam drilled to attach it to the vertical wooden supports.)

(3) RoyalAcresRod suggests moving the whole thing up, which sounds good if I understand the idea. The 2X8s have a horizontal 2X4 running underneath. I guess that could go -- drywall could be nailed to the underside of the 2X8s? There are also two horizontal 2X4s running above the header that the ceiling joists sit on. Am I right that these don't contribute significantly to the strength of the header? If that is right, I guess one or both of those 2X4s could come out, so that the joists could sit directly on the beam? If we took all three out 2X4s, that would be more than a five inch addition to the size of the opening. Anybody see a problem with that?

RoyalAcresRod 05-22-2010 05:00 AM

Gary, thank you for the correction....I misread the given window length.

Dan...those 2 horizontal 2X4s above the headers are your top plates, if I read your post correctly. They must stay! As you observed, your ceiling joists are supported by these plates, which should run continuously throughout your home. They also act as firestops and should not be removed.

Daniel Holzman 05-22-2010 08:33 AM

The idea of using a steel S shape as a header should work fine, provided you select the appropriate shape. There are two available S3 (3 inch deep) shapes, one weighs 5.7 lbs/ft, one weighs 7.5 lbs/ft. Even if the S3x5.7 is too light, the S3x7.5 may be OK, as it has a greater moment of inertia. If the three inch deep shape is inadequate, you could move up to a 4 inch deep shape.

The key is to have a competent designer determine what the load is on your header. The header over a window typically carries a lot of weight, so it is essential to determine the load first, then size the header second.

Dan S 05-22-2010 01:44 PM

Thanks for the insights. A window installer says he can put me in touch with an engineer.

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