I would like to add osb for flooring in my attic for some light storage. With 2×4 trusses and R30 insulation this becomes a problem. I realize the bottom cord of the truss probably is not designed for this, but the area I want to cover with osb is almost totally supported by hall walls below that run perpendicular to the trusses. Any ideas on how to build up the bottom cord of the truss without compacting the insulation?
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I have a garage attic where the previous owners laid OSB over the 2x4 bottom cords for storage. I wasn't crazy about the loads on the bottom cords and needed more insulation. I removed the OSB and blew in 14" of insulation over the existing R11 bats. I ran 2x4's horizontally just above the insulation and parallel to the bottom chords . I attached them to the vertical truss webbing right above the junction where the horizontal, diagonal and vertical members of the truss meet. Then I laid the OSB back down. The floor space is a little smaller and headroom a little less, but I think it's a good trade for not putting all that load in the center of the span of the bottom chord. We don't put anything too heavy up there, mostly empty boxes and Christmas decorations etc.
Edited 2/28/2009 11:37 am ET by Tyson
Unless those trusses are unique and specifically designed to bear on those hall walls, they are not supporting anything. They are only Partition walls and have nothing to do with supporting trusses.
But IF I imagine this situation right based on what is common, and IF those walls are capable of holding a small load, I would keep framing for this platform entirely separate from the trusses and build pony walls or stick up from the hall walls going past the trusses without connecting to them, and platform at the desired elevation. I keep in mind that almost every such platform ever built with the intention of getting only a light load, ends up with a heavy load, like Everrst, because it is there.
You MIGHT be able to just screw 2x4s side to the truss webs and that is easier,and it MIGHT not hurt anything, but what's the cost if you do, and it does?
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In my attic I ran 2x6s at right angles to the bottom chords, to support a catwalk. Blew in cellulose. It's only 9" of space, compared to the 18" or so depth of the insulation elsewhere, but it's still plenty, given that it's only a narrow strip.