I've been troubleshooting a second floor cold air return that doesn't actually go anywhere. 1928 house, where 2nd floor was finished many years ago by other owners.

I'm replacing the floor so decided to take the opportunity to cut out some of the subfloor to help figure this out. Pictures below show the hole in my floor, and then looking down into it.

I'm planning to (hopefully) have some duct work run through this cavity for the cold air return. What I'm wondering is why those two boards are in the stud cavity, specifically the two that are between the studs. I'd like to remove them.


  • I don't think there's any fireblocking in places where there should be, so I don't think that is why they're there (plus they don't completely block the space)
  • The walls on both sides appear to be original, so it wasn't added later.
  • It appears to be nailed in at the time of the house build (I don't know how else the nails would have been driven, given the location).
  • There was originally no insulation. This was added 15-20 years ago without any knowledge or care that it would end up here.
  • The left cavity is most likely the original air return path for the second floor. While it is super small, there is a hole at the basement end of it, with panning/duct to the furnace.

I don't expect a definitive answer, but am hoping for some thoughtful guesses to determine pros/cons to removing them. enter image description here


The image directly above shows a top-down view into the floor opening:

  • The very top of the image is a floor joist
  • The insulation at the bottom of the image is sitting on the ceiling of a built-in buffet.
  • There's three studs and they're oddly oriented; rotated 90-degrees from normal. As far as I've seen, this is not typical in the house.
  • The horizontal board that runs across the entire image is slightly lower on the left side than the right side. I believe this is because theres a soffit above the buffet below that has an angled ceiling (see new photo).

Decided to add this photo to show what the other photo is looking down onto, in case it helps with perspective.

enter image description here

Second Edit:

Also decided to edit the original photo for a few more notes:

  • The boards I want to remove are at the ends of the two "path" arrows. The two boards between the studs, not on the surface of the studs.
  • I'd leave the longer board alone, it's probably holding the lathe for the soffit.
  • Just added some clarifications and additional picture. May 16 at 19:05
  • And to answer your question about the crosswise boards, they are fit between the studs. When looking up close (via a cheap endoscope) you can see a small gap between the boards and the stud on each side. May 16 at 19:21

2 Answers 2


After puzzling for a while I think I'm looking down at diagonal bracing between studs (and a plaster and lath wall inside face, which is what clued me in to direction - this is rather unclear, really. And the stud orientation is peculiar.)

Removing that might not be wise.

  • That was my first hunch, too--shear bracing let into the studs. But several things have me doubting... The slope doesn't look adequate, and I wouldn't expect a flat-stud thin wall to be a shear wall. Awaiting more info....
    – isherwood
    May 16 at 18:58

My best guess is that they were added as backing or to tie something together, such as the ceiling-to-wall corner. They don't seem critical, but there's some risk that cutting them out will cause cracks in the plaster.

I think if it was my home I'd go ahead with your plans, but try to use the gentlest means available to get them out. You may be able to cross-cut them and fold them out of position, releasing any fasteners.

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