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I am doing some remodeling and want to run a 6-inch HVAC (kitchen exhaust hood) duct through the floor joists. There is one section where the path is impeded by a standard floor joist cross-brace. Can I replace that one cross-brace with two horizontal pieces of blocking between the floor joists? Should I use one at the top by the subfloor and another one at the bottom? How thick should they be? Would 2 by 10 work?

Floor joists are 2x10 on 16-inch centers.

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up vote 3 down vote accepted

Usually the HVAC subs knock them out and leave them out, but if you place something like a 1X4 or heavier between the 2 joists at the bottom, it would stabilize the movement of joist deflection. Make sure it is a tight fit.

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