Sub-slab drainage details
New construction, planning out the foundation and basement details … I’ve asked our builder to install drainage pipes under our basement slab (~1000 sq ft), and have them connect through the foundation to the footer drainage pipe. Builder says ok (even though he considers this overkill), but it’ll cost us dearly in extra gravel. Had originally planned for a 4 inch layer of gravel (topped by 2 inches of XPS, then poly.) Builder says to install the 4 inch drain pipe properly would require about 8 inches of gravel. Alternatively, he said, we could try just digging a few trenches where the gravel could reach 8 inches in depth, and set the pipes there, leaving the rest of the sub slab area with only 4 inches of gravel. Just wondering … how is this normally done? With a deep bed of gravel? I’ve heard that 4 inches of gravel beneath a slab is standard and should be sufficient, but then how do you install 4 inch drain pipes therein? What about this idea of a few trenches with 8 inches of gravel?
Also, is there any merit to the idea of sub slab drainage being somewhat “overkill”? (We’re on modestly sloping land, but don’t know much about soil profile or groundwater level at this stage.)
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