I moved a bookcase today was surprised when I looked at the wall. There was a 1/2" gap between the wall and the floor (see photos). The bookcase was not heavy, only used to hold kids games. It was against an inside wall. In one direction, the gap extends a few feet into the room and then the wall and the floor meet as they should. In the other direction, the gap meets an outside wall and makes a 90 degree turn, then disappears in a few feet (see photo).

A window sill in that part of the room seems to have a new crack. I noticed a little cold air at the bottom of the window and then noticed a small crack in the windowsill. The crack seems new (see photos).

What should I think about doing next?

P.S. The paint chips in the photos are unrelated. I removed some old cable TV cables before I took the photos.

Update: Plan now is to take up some floorboards and see what we can see.

Extent of gap Gap_and_rule gap_under_window crack_in_window_sill

  • One of two things is likely happening. Either your foundation is sinking or your floor framing is rotting. Investigate those and update your post.
    – isherwood
    Jan 11 '18 at 16:49
  • 2
    I usually think of termites or carpenter ants when it is localized especially on a exterior wall.
    – Ed Beal
    Jan 11 '18 at 20:33
  • 1
    @isherwood If the foundation were sinking, I would think the walls would have lots of cracks.
    – Yehuda_NYC
    Jan 13 '18 at 22:54
  • Get a long level or a long straight piece of metal and put a level on top of it to see what slopes where. Preferably 6-8'+
    – Damon
    Jan 16 '18 at 5:26

I called in a competent contractor and here are his findings. He took up some floorboards next to the gap. There was a gap between the bottom of the sheet rock wall and the floor. He cut through the subflooring in order to be able to look at the joists. The joists were solid. There was no indication of infestation. There was an uninsulated heat duct running between the joists. He went to the basement and checked for termite damage and found none. His conclusion is that the gap between the second floor wall and floor is due to shrinkage of the wood, exacerbated by the heat duct running nearby. He said there was no need to do any work as nothing was really wrong.

BTW, there is also a gap between an interior wall and a poured concrete floor in my foyer, but that is not below the gap on the second floor. The two gaps are independent. The gap between the wall and the poured concrete floor is due to the dirt below the concrete settling. The contractor suggested to leave it be since it is not likely to get worse and the fix would be costly for little benefit.

It is nice to deal with an honest, competent contractor.

  • How old is your house? And did this not exist before you moved in? I know wood shrinks, but hard to imagine it would sink a floor that much. What does he mean by uninsulated duct? No taped? I would also imagine if this one is not insulated, others in the house would not be too. Do you have a whole house humidifier by chance?
    – eaglei22
    Jan 17 '18 at 16:13
  • @eaglei22 House was built in 1960. The gap was behind a bookcase and I only noticed it when I moved the bookcase. I do not know if it was there 8 yrs ago when I moved in. Uninsulated 8" hvac duct. I have seen similar but smaller gaps elsewhere in the house. I do have a whole house humidifier and use it in the winter. Why do you ask?
    – Yehuda_NYC
    Jan 17 '18 at 23:55
  • I was originally wondering if the moisture would negate the drying out of the wood due to heat, but seeing how old the house is, it wouldn't matter. But, I still feel there is more going on then what waa proposed. I'm not convinced.
    – eaglei22
    Jan 18 '18 at 0:10
  • @eaglei22 What do you suggest I look out for going forward? Larger gap? Cracks in plaster? Doors that do not close easily?
    – Yehuda_NYC
    Jan 18 '18 at 1:51
  • Did you put a level on the floor as suggested by Damon?
    – eaglei22
    Jan 18 '18 at 14:40

Here is a good article:


Reading your answer, I am not convinced shrinkage is the issue. Although repairs may not be necessary, you still want to make sure the integrity of the structure is still there. But given the diagnosis of shrinkage from a heating duct, I am not convinced everything was looked at properly.

Can you post close up pictures of the crack, shining a flashlight on it? So we can see more of the sill if it's lifting or sinking.

If it were me I would get a second opinion; from someone or a company with experience like the one in the article posted.

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