BEFORE THE ARCHITECT – CUSTOM HOME DESIGNING BACKGROUND – HOUSE DESIGN ARTICLES
ALL ABOUT HOUSE FOUNDATION PROBLEMS and YOUR HOME DESIGN FOUNDATION PLAN FOR FOOTING DRAINAGE
By Before The Architect Copyright 2009
YOU MAY FREELY QUOTE THE AG WITH PROPER ATTRIBUTION
Remember being taught “Walk before you run”? You’re
crawling. Learning is discovering. Discovering unfolds, takes aging.
Before The
Architect
What's it like when the foundation footing drains too high . . . the opposite of
this . . .
QUESTION: WHASSUP WITH HOUSE FOUNDATION
PROBLEMS?
ANSWER: PRETTY NEAR NOTHING WITH A GOOD
HOME FOUNDATION PLAN TO DRAIN FOOTING.
 |
Drainage around house foundation
- essentially basement drain to drain footing - from runoff storm water and below-grade water pose primary concern for lots of folks. Loss of
property and health get involved |
|
House foundation drainage around foundation,
i.e., perimeter drain, is
fundamental to the safety of a home’s occupants |
|
These guidelines present aspects for your consideration to drain footing. Key among them – footing drain materials and methods, slab drain |
Footing Drain
|
Footing drains – |
o Shall be not less than 4 linear inches smooth, perforated drain pipe
o
Holes down
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. Got his shorts in a big wad, he did, and for naught.
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.
|
Footing drains – |
o Shall be not less than 4 linear inches smooth, perforated drain pipe
§ Holes down
§ At outside of footing base, as perimeter drain
§ 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
ü Covered by 3/4 linear inch river rock
Ø To not less than 12 linear inches above, outside, below pipe and
Ø 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
Ø
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
Comment: The AG 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.
o
Which perforated drain pipe shall be rated not
less than 2000 pounds per square inch compressive strength
Comment: In fact,
most all schedule 40 pvc pipe foundation drainage performs past this compressive
strength level. The AG’s just trying in one more way to make sure you don’t buy
that black, plastic, flop-around, corrugated landscaping pipe. The AG prefers
PVC Schedule 40 pipe DWV pipe for this application.
o May slope or lay level along the footing and shall slope away from footing in exhaust
§ 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
§ May not decrease slope anywhere throughout the run
§
Except that high drains may
exhaust to lower drains in wye or, preferably, slow-bend fittings in the
direction of flow of the lower drains
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.
o Shall run to
§ Light not less than 20 linear feet from foundation wall
§ Storm drain if permitted or
§ To drywell not less than 20 linear feet from foundation wall
o Shall be connected only to itself and not to sanitary drainage systems and not to runoff drainage systems
o Shall run separately and independently in lieu of connecting between lines of different elevations
o Shall traverse across and below the building footprint in order to comply with good construction practices
§ In which instance, that pipe in such traverse and otherwise no longer functioning as a groundwater receptor
ü Shall be solid Schedule 40 pvc pipe
ü Joints sealed
Ø In diameter not less than the footing drainpipe diameter
Ø In pitch not less than the footing drainpipe pitch
o 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: The AG and the Missus can tell you firsthand that 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: The Autocad Granddad 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.
|
More critical keys to successful footing drainage in the AG’s book of things to do are: |
o Use smooth not corrugated pipe (cuts drag on flow and, thereby, sediment settling);
o 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
o 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);
o 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 gravel, run bank gravel, and pit-run gravel) (cuts opportunity to gunk-up the pipes); but
§ Not crushed gravel around the stone
o 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
o 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.
. . . . . . .
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