We often say "on the floor".

We say "they laid tiles/carpet on the floor". What about pipe or cable?

is it correct to say "they laid pipe in the floor" or "they laid pipe under the floor"?

  • 1
    There's no absolute right and wrong here. There's no doubt pipes are usually laid under a floor, but personally, I might well use in if the pipes were actually what we call "underfloor heating" (i.e. - pipes that are supposed to give up heat underneath the floor, as opposed to simply being used to carry the hot water to radiators). That's to say, if the pipes are considered to be "part of the [heated] floor", you'd probably lay them in the floor. Much may depend on exactly what the speaker considers to be "the floor" (maybe he thinks it's just "the carpet"). Jan 5 at 16:06
  • Generally, pipes are laid before floors are built. Just saying. And tiles are laid on a concrete or cement floor. And you run pipes under a floor.
    – Lambie
    Jan 5 at 18:20
  • The choice might even be affected by which floor and what processes are involved. If the work is happening in the space below wooden floorboards, then "under" could make sense. But sometimes on a ground floor, it means chiseling into a concrete slab; this seems more "in" than "under." Jan 5 at 21:50
  • I would say it might even depend on when in the process you are talking about. As the pipes are actually being installed in a building under construction? The workers for that might well say "in", as the surface isn't even there yet to be "under". Later, when the building is complete, someone just talking about what was done might well use "under", as there is now a surface to reference. Jan 6 at 2:46

1 Answer 1


Cast is also commonly used for such work in the construction industry, my line for over 3 decades already. The pipe is cast together with the concrete floor, forming part of the latter.

In is used in such descriptions:

They laid (or cast) pipes in the floor (slab).

For cables, we say

They laid (or ran) cables in conduit cast in the floor (slab).

Under is less common and is usually limited to cases with a raised floor or similar:

They laid pipes (or air-conditioning duct) under the raised floor.

They laid (or ran) cables in cable trunking under the raised floor.

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