Building out garage attic


Old 01-07-14, 09:57 AM
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Join Date: Jan 2014
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Building out garage attic

We have a 22'W x 60'D garage built in 2009. We want to build out the attic for a gameroom. Heaviest item would be a bar sized pool table.

Garage was built with a gabled roof design, 2" x 12" ceiling joists and floored with T&G OSB.

Problem is that according to the on line calculators my joists will not support the live loads for a living area. Joists are 2" x 12" #2 YP on 16" centers. Joist span is 20' 9" from plate to plate.

How best to beef up the joists to adequately support the loads. Have access to the joists from bottom with the exception of the front 20' which is a port cochere (sp) for parking cars. This area has plywood ceiling which could be removed if necessary.

Not experienced at this. Please help.

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Old 01-07-14, 10:02 AM
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Any reason you could not add a beam down the center? That would split the span.
You would need to cutout the floor and add footings.
If it was sized right and the right material was used it would not need a center support.
Old 01-07-14, 10:17 AM
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Join Date: Jan 2014
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Beam is no problem. Problem is the columns to go with it. Can't really go this route.

Was hoping to add or sister joists from the bottom as I have access from below.

Sorry, but I do not know what a footing is.

I do not plan to do the structural part of the project myself. I just need understand how it should be done before hiring a framing contractor. Down here in Texas many framing crews can cut & nail boards but that's about all. I do not want to rely on them for advice...

Thanks for the reply.
Old 01-07-14, 11:30 AM
Join Date: Oct 2008
Location: New England
Posts: 9,995
A 21' 2x12 is a rare piece of wood. Is it possible it is part of a truss where there are metal plates attached to vertical 2x4's that extend up to the rafters?

If not, then a sister made out of I-joists (2x on top and bottom with osb between) would easily span that distance.


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