INTRODUCTION
DRAIN FOR HOME FOOTING AND SLAB
Drain For Footing
Comment: Holes down? A contractor of more years than this custom home designer teed off a while back about how holes-down was wrong, wrong, wrong. The physics compel: water runs to least resistance and holes down offers least resistance to open pipe; holes down offers less opportunity for intrusion of silt and fines than, say, holes to the side or holes up; holes down offers less opportunity for water intrusion to interior with depth of dig, that is, you don’t need to bury it as deep to get the same result…or better.
-
At outside of footing base
-
With pipe bottom of face not less than 1 linear inch below footing top of face
-
With pipe bottom of face not lower than 2 linear inches above footing bottom of face
-
Covered by 3/4 linear inch river rock
-
To not less than 12 linear inches above, outside, below pipe and
-
Which rock shall be wrapped in needle-punched (a/k/a needled) lightweight to mediumweight, nonwoven, or polypropylene, geotextile fabric (a/k/a generically and too broadly, silt cloth) and
-
Wrapped rock shall extend not less than 2/3 up the foundation wall or not less than 6 linear inches from the finish grade top of face whichever is closer to finish grade top of face on the vertical from footing top of face and
Comment: This custom house designer notes that this isn’t the only way to lay-in a footing drain. Here’s a time-tested approach to materials and methodology that replaces stone with coarsest concrete sand layered in silt cloth and tamped.
The cautionary note therewith is that the drainpipe itself must be altered in its drainage apertures to smaller lets so as not to intake the sand. Very interesting. Russell H. Lanoie knows his very respectable, no-nonsense trade at ruralhometech and 4 web pages to follow.
Comment: In fact, most all PVC pipe for foundation drainage performs past this compressive strength level. Just trying in one more way to make sure you don’t buy that black, plastic, flop-around, corrugated landscaping pipe. This custom house designer prefers PVC Schedule 40 DWV pipe for this application.
-
May slope or lay level along the footing and shall slope away from footing in exhaust
-
May slope down at not less than 1/16-1/8 linear inch:1 linear foot and
-
May slope greater than 1/8 linear inch:1 linear foot but
Comment: For example, consider a foundation layout where perimeter drains are laid at two elevations – one just below frost level proximate to a SOG and one at the footing perimeter to a crawlspace. Fitting the high exhaust with a Y to the lower drain in the lower drain’s direction of flow, may be o.k.
-
Shall run
-
To light not less than 20 linear feet from foundation wall
-
To storm drain if permitted or
-
To drywell not less than 20 linear feet from foundation wall
-
Shall be connected only to itself and not to sanitary drainage systems and not to runoff drainage systems
-
Shall run separately and independently in lieu of connecting between lines of different elevations
-
Shall traverse across and below the building footprint in order to comply with good construction practices
-
Shall be solid Schedule 40
-
Shall be in diameter not less than the footing drainpipe diameter
-
Shall be in pitch not less than the footing drainpipe pitch
-
Shall drain to light or other code-compliant outfall
-
Not less than 20 linear feet from foundation and
-
Offset to other limits and conditions as codified or
-
Imposed by building authority having jurisdiction, engineering latitude, and good building practices
Comment: Firsthand, the last way you want to drain off basement water is with a sump pump.
There’s a pile of ways to screw it up.
And just when you need one, it stops working or the electric power’s gone dead.
Comment: George Southmayd in Connecticut taught us a long time ago and kind of far away from here that if you’re interested in getting water out of your house, crawlspace, basement, or whatever….no one knows more than the person who’s spent a heap o’ years repairing swimming pool leaks. Not just patching here and there. We’re talking backhoe, take-it-apart-and-put-it-together, think-about-it-very-hard, and don’t-be-in-a-big-hurry kind of specialist contractor.
- Additional footing drainage, including footing drainage interior to the foundation, may be required by local code or local conditions
Comment: In the case of unvented, or sealed, crawlspaces, it’s mandatory.
Comment: More critical keys to successful footing drainage:
-
Use smooth not corrugated pipe (cuts drag on flow and, thereby, sediment settling);
-
Wrap the pipe in needle-punched (a/k/a needled), lightweight to mediumweight polypropylene, or nonwoven, geotextile fabric (a/k/a generically and too broadly, silt cloth); and
-
Wrap the stone or other suitable, possibly recyclable drainage material around it in silt cloth (more particularly, needled, or needle-punched, lightweight to mediumweight polypropylene, or nonwoven, geotextile fabric);
-
Run stone not less than a foot out from the footing and wall and not less than 6 linear inches from finished grade top of face;
-
Use washed, screened bank-run (a/k/a run-of-bank, run bank, and pit-run) but
-
Don’t be setting the footing drain either above the footing top of face (to drain above interior floor levels, i.e., letting interior floor space act as a reservoir for the drainage system…no, no, no) or below the footing bottom of face (to guard against potentially undermining the footing with leached substrate); and
-
Never, never, never, never decrease the footing drain slope. Never. …..unless you’re pouring high drains into low drains with wye fittings in the direction of the lower drain’s flow. Otherwise, never.
Drain For Slab
Comment: The custom home building author has known some very professional drainage guys who commonly run footing drains at 1 linear inch in 10 linear feet and some even shallower. Not that he’s suggesting you do, just telling you what he’s come across over the years.
-
For exterior slabs-on-grade slope (including covered porches, screened porches, exterior steps, etc.)
-
1/4 linear inch per linear foot
-
Evenly and overall down and away from exterior walls
-
For garage floor slope
-
1/8 linear inch per 1 linear foot
-
Evenly and overall downward toward a floor drain or
-
Evenly and overall downward from garage head to foot, toward the exterior
-
For laundry room floor slope (if it suits you)
-
¼ linear each per 1 linear foot
-
Evenly and overall downward toward a floor drain
-
For tiled baths
-
¼ linear inch to ½ linear inch per 1 linear foot
-
Evenly and overall downward toward a floor drain
-
For driveway slope
-
Not less than ¼ linear inch per 1 linear foot
-
Evenly and overall downward from driveway head, i.e., throughout a driveway’s run
-
Possibly requiring a drain sump – passive or mechanical – along the way
-
Possibly requiring a crown
-
Possibly requiring slope on width rather than on length along the way.
-
For brick paver deck and walkway slope (and walkways in general)
-
For mud shower floor slope
-
A foundation top of face, including piers, stem walls, and similar, shall not be less than 6 linear inches over finish grade |
