I had a builder friend that automatically put in both interior and exterior drain tile as a standard on the 1000's of houses built. He would not allow a deduct for only one set. Since it was standardized and installed with all new construction, the cost was not that much and he never paid a lawyer to defend him on a problem. Since it was standardized, he did it right with plastic weep hoses to drain the block cores into the rock around the interior drain, since he discovered that no barrier on the exterior of a wall is 100% perfect.
He even had the flexible plastic pipe pre-cut to length and carried in all foundation vehicles.
He built in several different elements (soils, terrain, etc.) with the same crews, so a standard was the inly way to go. - The interior tile prevents the excessiv upward pressure on the basement slab that contributes to cracking and slab leakage.
I'm not sure what people are doing now with the radon mitigation systems. I put in one as a prophylactically which consisted of a length of 4" slotted pvc snaked across the basement floor and coming out through the floor at a tee. This tee could be connected to later and run up to the attic, or through the attic to the atmosphere. It would also be possble to put a fan on it.
Where I'm going here is that for drainage and radon, maybe we'll end up just running 3 or 4" slotted drain tile every 4' oc below the slab and have everything end at the sump pit or at the sump pit and some evacuation point.
Once company here is putting in prophylactic radon mitigation systems standard, but I don't know if they are relying on just the perimeter tile or what. There was talk of a state law to call for radon mitigation systems to be standard which would be a bit strange because I'm not sure if there is any code for the interior/exterior drainage tile.
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