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Sub-slab vapor barriers, grade beams, and drain pipes

PJ Clem | Posted in Green Building Techniques on

I’m working on details of design for below grade basement with poured foundation walls and slab on grade.  Will install taped vapor barrier directly below slab, and want to install drain tile loop inside of foundation wall footings as well as radon mitigation vent capable of depressurizing all spaces below slab.

Site and design will require slab to be thickened in several areas under load-bearing interior walls.  Builder is calling this thickening a grade beam.

Any advice or reference for how best to run pipe across grade beams, both for drain tile as well as sleeves to connect slab cavities to radon vent?  The only options I can come up with are:

1) Run pipe through the grade beams, but this would also require the pipe to run through the vapor barrier, with concerns about properly sealing at the penetrations.
2) Run pipe under the grade beams, but this would locally interfere with drainage, and increase potential for erosion under the beam.
3) Run pipe straight through, but make grade beam discontinuous at pipe.  That is, slab directly above pipe would be only standard thickness.  I imagine extra reinforcement bar might help, but I am concerned that a discontinuity in grade beam would defeat the purpose.


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  1. Expert Member
    Michael Maines | | #1

    PJ, unless I'm missing something in your description, it sounds like the "grade beam" is just acting as an integral footing. The soil should be able to support a discontinuous footing unless you have unusual conditions, in which case you should get a professional engineer involved.

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