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Old 01-17-2012, 11:17 AM   #1
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22' loft

I have a loft that comes out from the wall 61/2 ft. The loft goes from wall to wall 22ft. It has a 4x6 cedar beam on the front with a support beam in the middle. I would like to take out the beam and replace the cedar beam with a steel I-beam. The loft only has decorations on it and the only access to the loft is through the attic. What size I-beam do I need. Will a 3/8" I-beam work?


Last edited by jonniebrook; 01-17-2012 at 11:20 AM.
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Old 01-17-2012, 12:42 PM   #2
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I'd suggest you ask an engineer who can look at exactly what you have. I don't know what you mean by "3/8 inch I-beam", as I-beams come with various flange and web thicknesses, as well as widths and heights. If you google for load carrying tables, you can get a fair idea of comparable members. Now....As a guess from having looked at tables a fair amount (I am no engineer), an I-beam that is as wide and high as your cedar "beam", and has 3/8" thick flanges and web will carry far more load than the cedar, and I suspect a 1/4" is plenty. If you don't pay an engineer a few bucks to look, go heavy on the beam; it's cheap.


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Old 01-17-2012, 03:02 PM   #3
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Steel I beams are not sized as 3/8", rather they are sized (at least in the United States) either as S or W shapes, with the nominal depth first, then the weight in lbs per foot. So for example, a W6x15 means the beam is nominally 6 inches deep (actually it is 5.99 inches) and is nominally 15 lbs per foot. All the other properties of such a beam are found on standard tables of steel beam properties.

As to what size beam you need, well we have no idea if the existing cedar beam is properly sized, so it would be dangerous and foolish to size an equivalent steel beam over the internet. This is really a job for a structural engineer or an architect, but if you don't care to pay for one, you may be able to go to a steel fabrication shop, show them plans for your house, and they may have an engineer available to size the beam for you. In most jurisdictions, you need a stamped plan to replace a header with another beam, course you may not need a permit, or you may be planning to do this job without one.

I realize you didn't ask, but just a word of advice, if you do this work yourself, make sure you use proper temporary support while replacing the beam. Also, make sure you carefully think through how you plan to attach the steel beam on either end, you may want to get the beam predrilled so you can use lag bolts or similar when connecting the beam to the posts, assuming you use wooden posts as supports.
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Old 01-17-2012, 03:08 PM   #4
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I don't know what your intent in replacing the beam is, but if a laminated beam would work, they can size them at the lumber yard with software from the manufacturer.
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