Originally Posted by cjm94
What do you think of just burying tile at the footing level to collect water and drain out on its own time. Does anyone see any issues with this idea.
Clint, hey exterior foundation drains are always a good insurance policy against damage to basement walls and here's why: (1) They help remove rising ground water which can undercut the footer (just like the interior drain will, but more importantly) (2) They help prevent hydrostatic pressure against the block wall at the frost line. Backfilled soil against your basement wall almost always has more air entrained in it than untouched soil even five feet away because all soils expand as they are removed and shed moisture. So when this backfill is reused from the original excavation it offers less resistance to water migration than the compacted virgin soils farther from the house. Point is, it's easier for any ground water or rain water to make it's way through the backfilled soil around the foundation. This becomes problematic during freeze/thaw cycles in fall winter when you get lots of rain and it has no quick means of escape. The water/moisture in the soil above your freeze line expands (as ice takes up more volume than the same amount of liquid water) relative to the water below the freeze line putting a shear stress point on your basement block wall. Assuming of course your walls will be properly water proofed on the exterior, these are the best arguments for installing an exterior foundation drain.
I'd definitely wrap your exterior foundation trench in filter fabric , install a 1” course of gravel then lay the drainage tile on this, holes down (this best drains rising ground water), then cover with more gavel up at least ½ the footing height, then wrap the filter fabric back around the gravel on top and pin it together. Add more gravel on top, a few inches, just don't crush the pipe if you're using the corrogated type. The filter fabric helps keep fine sediments from clogging the drain, but is pervious to water. I'm not sure why your plans call for connecting the exterior drain to the inner drain UNLESS you can't discharge the exterior drain by gravity feed to daylight somewhere on your property. If your lot layout doesn't allow a practical gravity discharge to daylight then yes, you will need to pump the water out just like the interior drain. I'd ask your architect, building inspector and foundation guy for a second opinion as they'll be most familiar with water tables, freeze/thaw cycles in your area. I personally don't mind the idea of pumping out water from the exterior drain line via the interior sump as long as you've taken precautions to keep sediments/silts out of the exterior drain line. It may run your interior sump pump more often during heavy rains but that's a better alternative than letting all that water remain trapped in the soil around your basment wall and footer.
One last piece of advice is to require your foundation contractor to install the foundation backfill in layers after you've installed the french drain system and make them mechanically tamp the ground to compact it. He might groan, but properly compacted backfill so that it's at least similar in density to the surrounding virgin soil will help keep water from migrating towards your basment wall horizontally in the soil, as water ALWAYS seeks the path of least resistance. Good luck with your project, CL.