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Old 10-14-2008, 10:51 PM   #1
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Joist question

My friend just bought a house with a really nice walk in attic. It has 2x6 with 16" centers that span about 11 feet to a bearing that is in the middle of the house. Then there is the same on the other side.

He wants to build a bedroom up there and I did the calcs and he will have to beef it up of course.

I have tried to find where there are span tables for sistered beams but can't find anything.

The 2x6's are marginal at 11 feet with a 40 psf live load but I have never been one to build on marginal floors.

Since he needs as much ceiling room at possible I really didn't want to go with sistering 2x8's and wanted to sister some 2x6's on the existing 2x6's.

Any ideas of comments.


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Old 10-14-2008, 11:04 PM   #2
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Doubling the joists will certainly stiffen the floor, but I don't think it will be adequate. A 5-1/2" deep joist spanning 11' is just too shallow, even with them doubled up. The deflection will be very perceivable when walking in the room. You can get away with a 30psf load in a bedroom though.

There isn't a table that shows spans of sistered members unfortunately...Or at least I've never seen one by a lumber trade organization or a model code.

You'd spend a small fortune in materials, but flitch plates might be a decent option.


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