Drain Tile Location - Residential Basement 1

[DPanos]

I am building new construction and was wondering what side of the foundation wall/footing should I put the drain tile. On the exterior side, interior or both? Is putting it on both overkill?

Thanks!
Dpanos

 

[GeoPaveTraffic]

When I built my house I placed a perforated pipe on the outside and a second set under the floor slab on the inside. It is cheap and easy to do when building, very costly and disruptive to do it after the fact if you later determine you need it.

Mike Lambert

 

[concretemasonry]

GeoPaveTraffic is correct about the real cost in the end.

I had a friend that was builder and never wanted a complaint about a wet basement.

Every home he build had both interior and exterior linked perforated drains below the level of the footings. He also put in 3/4" plastic tubing into the cores of the block walls leading into the gravel around the perforated pipe. He did this on every home because the cost was so low if it was a routine process that did not slow construction (all 3/4" pipe precut, etc.). If was cheaper than later repairs and got him a good reputation for doing things right and not just to the minimum in the end. - Over 2000 homes at different sites without a problem.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[BigInch]

If it's drained around the outside, how's water going to get to the inside.

Independent events are seldomly independent.

 

[concretemasonry]

Biginch -

Water travels laterally AND upward (capillary action).

A single french/perforated drain system below the footing bottom, can be very effective if you can cut off other sources of water laterally and from lower areas than accumulate when the upper levels have high moisture contents. - It is never and idealistic situation that you see on a 2 dimensional drawing.

That is why it is cheaper in the end to do it right in the beginning if you understand the mechanics and real cost.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[GeoPaveTraffic]

Also, two sets of pipes give you a backup if one becomes plugged or has some other problem.

Mike Lambert

 

[DPanos]

Thanks all. What is the typical additional cost to expect if you add the drain tile in the interior side of the footing also. Assuming about 250 linear feet. Thanks!

 

[BigInch]

I've done plenty of slabs in compressor buildings, maintenance garages, even restaurants, with an outer grade beam wall of 3.5 feet, pvc sheeting under the slab and around the exterior grade beams. Never had any complaints.

PS. You'd have better luck if you used 6" diameter pipe. 3/4 will plug sooner or later, if not immediately.

Independent events are seldomly independent.

 

[DPanos]

I am using 4" preforated drain tile fabrique covered and looped. with 12" pea gravel with 2" min. under drain tile.

 

[cvg]

foundation slab is a lot different than a basement - pvc sheeting alone is not adequate and will not reduce water pressure on basement walls, only reduce seepage.

 

[BigInch]

True. Water goes straight through PVC sheeting.

Independent events are seldomly independent.

 

[oldestguy]

First of all don't use gravel as backfill, since it is not a filter and can plug. ASTM C-33 Concrete fine aggregate is best (Concrete sand).

In some areas it is a good idea to do some interior drainage also, since water under pressure from a distance can rise up due to that pressure inside the basement (I've seen that). There we solved it by underlaying the slab with clean sand and placing the pipes at no more than 15 foot spacing, since the hydraulic gradient in sand was 7:1 flowing laterally. Yes, then the interior pipes at the footing also are needed (in addition to those outside).

In addition, remember that surface water on the ground outside can seep in much more easily in that loose backfill than beyond, so divert all surface water away with positive slope. Many more basement problems are due to surface water getting down there, rather than ordinary high ground water at basement level. Extend downspouts out beyond the backfill. That may mean at least 10 feet out. I speak from experience in the house I recently moved into. Former owner had a sump pump running frequently with every rainfall. After I fixed the outside, sump pump never runs. My fix consisted of waterproofing the ground surface also with a mix of bentonite at 5 percent in 4 inches. 10 ft. extensions on the downspouts also.