Under the door trim I have discovered a small gap between my patio door and my floor. It is about 1cm in width and 3cm deep. At the bottom it is concrete and my flooring above this is concrete.

Should this gap be there? I am trying to track down a damp issue and at the bottom of this gap it is damp.

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  • I'm not quite sure what I'm looking at, there. Presumably, this is related to diy.stackexchange.com/questions/261947/… Did you address the exterior flashing/sealant issues raised in that question?
    – Tetsujin
    Dec 7, 2022 at 19:29
  • Yes it is related to that question. I did reseal the outside and inside of the door. I’m not sure how to check the flashing tbh. In the photo above there is black carpet then a small gap. I will try get a better photo
    – User1
    Dec 7, 2022 at 19:31
  • 1
    Wait, maybe that's the joint between interior and exterior concrete slabs. Is that right?
    – isherwood
    Dec 7, 2022 at 20:06
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    The implied question is what is under the tack strip? If you have two concrete slabs coming together there, the material between is an expansion strip, as expected. If not, there are other questions. More information, please.
    – isherwood
    Dec 7, 2022 at 23:11
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    Doors are put into rough openings. The bottom of the opening is "rough" and when the door including the door jamb is put into the opening, shims are used to set the door level and plumb. The shims create a gap between the jamb and the rough opening. These gaps are typically sealed in different ways (inside and outside). Dec 8, 2022 at 7:27

1 Answer 1



The door frame is leaking needs to be isolated from outside and inside

There is a humidity barrier between the outside concrete and floor that sits in that gap

Therefore the gap is normal to have and need it for that function

  • You're saying that it's normal to have a gap under a door frame that's not sealed against water intrusion? Wouldn't that allow wind-blown rain or snow to just blow right under the door or hot air to pass (move inside in the summer, causing higher AC bills, or move outside in the winter causing higher heating bills)? This seems very unlikely to me. Have a source saying this is correct?
    – FreeMan
    Dec 8, 2022 at 16:01

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