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Supplementing Roof trusses to accommodate attic loads

Supplementing Roof trusses to accommodate attic loads

Old 08-08-17, 09:06 AM
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Supplementing Roof trusses to accommodate attic loads

I have a new build on-frame modular home. It has non-attic hinged roof trusses. If I run 2x8s from perimeter wall to perimeter wall with resting on the mating walls to lift the proposed floor above the truss bottom chords. Total span 26 feet with mate wall at 13 feet at 24" OC. Will I be able to walk around, store boxes and totes, and it be safe?
Old 08-08-17, 10:49 AM
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Technically it's probably a "no". Your interior walls are likely not load bearing so they can't be used to bear the load of the new floor joists you want to add. Also, 13' is the upper limit for the highest grade lumber. What you likely will get from your local retailer is probably only good for 10-12' span at 24" centers when carrying a 30 pound per square foot live load which is the lowest weight category in my span charts. If you tried it things might get a bit "bouncy" in the middle of the span but going to 16" or 12" spacing improves things dramatically.

A big unknown is the construction of your home and especially it's interior walls. No matter what you do for joists in the attic that center wall needs to carry the bulk of the load. Since you won't have ceiling height in the attic near the outer walls the majority of what you do will be in the center. Your center wall framing could be far from standard. Sometimes the center wall is wider than a standard wall because it was constructed as two thinner walls. That thinner wall is one of the exterior walls during manufacturing and transport. Then when those two thin walls are stuck together you have a wider than normal center wall. A big problem is that since it was never designed to be load bearing there might not be a doubled top plate and no headers over door openings.

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