Drain tile on exterior basement

cjm94

I am building a new block basement I put drain tile on the inside to a sump basket. I drilled into each block core and have 1/4 O.D. tube from each core to the tile as suggested by the inspector. tubing will be under poly and concrete floor.
My question is on the outside tile I have seen plans to connect the outside tile to the inside and then pump it out with the sump. I do not like the idea of bringing in water on purpose to pump it out. 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. It is very sandy soil and I dont forsee any drainage issues but tile is cheap and the hole is dug easier now then later
Thanks Clint

AGWhitehouse

The magic words. I'd put in as much exterior drainage and do the best waterproofing now and you'll thank yourself down the road. The interior footing drain shouldn't need to do any work if you've done the exterior right.

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jomama45

This is a common fear to some degree, but trust me, it's far better to get the water inside to a sump crock than to let the water lay on the exterior for an extended amount of time. Do you already have cross-bleeders through the footings?

$49 Handyman

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.

AllanJ

You do not need both an interior perimeter drain and an exterior perimeter drain. Since you are just builidng the foundation, it is better to put the perimeter drain on the outside.

An interior perimeter drain is installed when it is easier to do that compared with installing or repairing an exterior perimeter drain.

It is proper to install a connecting pipe between an exterior perimeter drain and an interior sump pump pit, either to let the sump pump handle the water collected by the exterior drain or to let water collected by the interior drain follow a downhill pipe to daylight (the latter limited to certain ideal topographies).

It is possible to have a sump pump on the outside provided that the pit has an insulated cover (perhaps more than a foot thick) for cold climates. It is recommended that the pit (inside or outside) have at least 3 cubic feet (about 20 gallons) of capacity below the bottom edges of the perimeter drain pipes entering into the pit and not occupied by gravel or crushed rock.

It is not proper to direct gutter water or rain water or surface ground water into any perimeter drain system unless there is a sump pump that can handle all that water and send that water some distance from the house. It is not desirable to use the sump pump and perimeter drain for this purpose since the workload will be greatly increased and overtax the batteries or generator fuel supply in case of power failure.

A perimeter drain must either have a sump pump pit or a downhill pipe to somewhere away from the house with no capacity limit. It won't accomplish any useful purpose with the water just sitting there to drain off on its own.

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jomama45

You do here per code. And I can't think of one good reason you wouldn't put both in at the time of construction.

With sandy soils as the OP suggests he has, I wouldn't expect the pump to run much if at all. As a matter of fact, he could just install the sump crock for now & monitor the water level before installing a pump. But, when you his area gets socked with a "100 year flood" or days of heavy rains, he'll be glad he has the crock to pump out of. I can't tell you the number of times I've entered a customers home to look at there foundation water problems and the first thing out of there mouth is "the strange thing is we've never had water in our basement ever before"......... Never say never, and always have a good system in place with at least one back-up plan.............

cjm94

Lots of great info. Thanks guys