I'm renovating a 2nd floor bathroom and I made the mistake of cutting out the subfloor flush with the wall shared by the doorway. The problem is that this wall sits between 2 joists so my new and existing subfloor butts up against one another in unsupported space.

Subfloor 1

Subfloor 2

My original solution was to install blocking but the issue is that there is round duct work that runs directly under the wall between the joists. I've considered adding another joist but there is only 5 inches of space between the joist and the duct work. What is the best solution given this situation?

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  • 1
    You need to get support somehow for that floor board. If you need to get an HVAC guy to temporarily remove that duct to add a joist or cribbing.
    – d.george
    Commented May 20, 2017 at 10:13

1 Answer 1


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.

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