I have a townhouse at Mt. Tremblant (Que)that is built on the side of a hill. The backside of the foundation is built directly onto bedrock. I have removed the rock back even with the rear wall and will reform the back wall to cover the vertical sufaces. Water will however, continue to run through the rock. My question is: I want to pour the floor, what sort of drainage tile should I lay under the crushed stone before I pour the floor? My idea is to put drainage lines to a sump pump cover this with crushed stone and then pour a normal concrete floor.
Answer:
You're into the normal rural form of basement floor construction: gravel, perforated drainage tile (complete with sock), more gravel and then a 3" concrete pad. The drainage tile starts at the sump hole, wanders around the basement and then returns to the sump hole. Although most I've seen have only 5 to 6 inches of gravel, in this case, I think I'd want at least 8 - two inches under the 4" tile and then 2 above it. To keep the basement from causing too much atmospheric humidity, I'd also want to treat the sump specially: Sump pumps should never be allowed to operate alone. There should always be as much back up for them as possible. One system is to have a second pump on hand for urgent, quick replacement. This means that the actual hook-up would probably be better done with hose clamps and radiator hoses than corrodable, threaded joints. Another is to install a "T" with a threaded cap somewhere along the interior line so that if the hose plugs for whatever reason (frost, collapse, vermin, etc.) another hose can be attached inside and there is no embarrassing gap in service. The preferred system incorporates two pumps in the same hole (both of them submersible) set at slightly different levels for being activated. Sump holes should also be fitted with covers which have weather stripped holes only large enough for the various protrusions (pipes, wires, etc.) through them. Three-quarter-inch plywood makes a good cover and if the necessary holes are drilled in a straight line, the plywood can be cut to fit around all the protrusions, the edges of it properly weather-stripped and put in place. This keeps an otherwise large surface of water from evaporating into the basement and substantially raising humidity levels there.
