blockingjoistsstructural
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 2×10 on 16-inch centers.
For Future Viewers:
Right idea, but WAY too complicated for minimal support & no screwing for the flange. With NO FLANGE in place, build a frame first, not piece by piece in the floor. With a Flange in place you'd build it without the right side's {bottom} joist attachment so you can dry-fit everything & finish inner attachments to then LASTLY screw to the joists.
Stand up 2x4's to be attached to joists LAST. Then, bridge the Stand-Ups with 2x4's On-Flat. You screw through the Stand-Ups & into the ends of the On-Flats (do just the left Stand-Up {top} configuration if a Flange is in place).
Then, you bridge the On-Flats with a shorter On-Flat. First, screw that in from the left Stand-Up to hold it in place & toe-nail screws on either end at the Flange side. Also, toe nail what can fit On-Flat on the right side {bottom} of the Flange Finish by just screwing outward (& angled upward for this Askers I-beam pictures) through the Stand-Ups & into the joists.
This should be snug to the Flange's underside collar or the drain pipe, depending on your subfloor elevation. The On-Flats even allow you to cut or drill the platform frame for an actual tight fit complete circle. Of course, adjust this proven design to your actual application.
Ended up creating a bridge under the subfloor gap using a 2x8 that sits on a 2x4 sistered to the nearest joist. I used construction adhesive and screws to attach both subfloors to the bridge. There is no longer any bounce in the floor.
Best Answer
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.