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Community and Q&A

What goes wrong when perforated drain pipe is not fully covered in stone?

Ryan Lewis - Zone 4A | Posted in GBA Pro Help on

What happens when 4″ perforated pvc under a basement for say an interior french drain has a small amount of its surface exposed? Is there a good reason for wanting the pipes buried?

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  1. Expert Member
    Zephyr7 | | #1

    Do you mean the pipe has some surface exposed above the gravel bed where the pipe will be in direct contact the concrete slab? That shouldn’t be a problem. The gravel primarily serves two purposes: provide a drainage area that won’t get waterlogged while carrying water to the drain pipe, and to help keep the drain pipe from getting clogged.

    You do want to make sure the concrete can’t yet into the pipe while the slab is being poured though. If your pipe is deep enough in the gravel that the holes are fully covered then you’re probably ok. The only other concern I would have is that you want the pipe towards the bottom of the drainage area so that water doesn’t pool beneath the pipe, so be sure to check that.


  2. Walter Ahlgrim | | #2

    If this is a new basement slab it should be set on a bed of gravel, the pipes is basically irrelevant in that any water will flow around the rocks and find the lowest spot hopefully that it the pit for your pump.

    If the pipe is a retrofit around an old slab. The contractor needs to be careful not to disturb the soil supporting the foundation and ultimately building, especial if it is an old rubble stone foundation.

    Be sure you do not get concrete in the pipe.


  3. Expert Member
    Malcolm Taylor | | #3


    In and of itself having the pipe partly exposed doesn't affect much, but it may indicate that the pipe is placed so high that is can't perform any useful function.

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