I’m building a house on fairly good soils in an otherwise pretty wet area in Western Oregon. I’m trying to determine the best configuration for my drains. The soil engineer said a footing drain is unnecessary, although I will put in a sump in the crawlspace. The site is very flat (6″ of slope over 150′) The nearest ditch is 150 feet away.
–Do I need to pump my gutter drains out to the ditch or will the natural water pressure of the water coming down the downspouts carry the water away?
–If I do need to pump the gutter drains, can I have them pumped by the sump, or will they backflow into the crawlspace too quickly?
–What type of pipe should I use? (I was planning to use 3″ Schedule 40 to connect the gutter drains and use 4″ADS to run out to the ditch.)
Replies
The basement sump has two purposes
one is to catch and dispose of any water that accidentally gets in IF or WHEN the other primary drainage systems fail
The other - sometimes perforated drain lines under the slab lead to the sump pit in places with a high water table where rising hydralic pressure can lift the slab or leak into the house
The exterior drians - there are two - completely independent of one another. You need a perimeter drain at or just below footing level, perforated, with a sock to keep it from silting up, surronded with washed 3/4" stone and a landscape fabric or other geotextile to keep the fines out of the gravel. This must lead downhill to daylight, possible the ditch you are speaking of.
The other exterior drain for the gutter drops is not perforated and should not lead ito the same perimeter drain at footing level. The whole idea of eavestroughs and drains is to lead the water AWAY from the foundation, not to inject it in. I usually run it about two feet below surface, keeping it pitched to drain the way I want it to go too.
If you cannot lead these to daylight downhill, you need to dig a drywell or a sump pit. Sump will pu,mp up and away. Drywell is a hole about septic tank size. Drystack concrete block in a circle and fill the center with 3/4" stone. Cover with the geotextile to keep fines out, and lead the drains into this, preferably at least 40-50 feet away from the foundation in a dowhill direction. A lot of airspace is left in the drywell that is filed with the water and then gradually disperses it - percolates into surronding soils. But if the water table is too high, a drywell won't work, it'd have to be a sump pit
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what ever you do, do not drain gutters to a sump in your crawl space!!one of the most costly renovations I have done was to repair massive damage to a 1/2 finished 1/2 crawl space down stairs.sump pumps can easily fail from power outages during a large storm or just plain old mechanical failures piffin's suggestions are spot on.a little extra effort now will reward you later.
good luck, Z
The rule of thumb for drainage pipe is to keep a 1/2% slope for smooth wall pipe like schd 40 PVC and 1% for corrugated pipe like the ADS. 1/2% is equal to 6 inches over a 100 ft run. Since your lot is flatter than that, your going to have to make the drainage pipe continually deeper as you move away from the house.
Draining to daylight is best, but it sounds like that's not an option for you due to a flat lot, so your going to have to install some type of drywell. My first choice in your part of the world, where there is a lot of rain, is a real drywell like Piffin was explaining. If your soil is sand and gravel, you might get away with a long run of perforated pipe (at least 20 ft, the longer the better) buried in crushed stone instead of the dry well, but forget about it if the soil has even a little silty or clay.
You can do a quick test for silt and clay - grab a handful or soil, add a little water to make it just a little wet. Pack it tight in you hand and try to squeeze out a little ribbon between your thumb and first finger. If it just breaks into granules, it's sand and gravel. If you can get even a little ribbon of soil, you've got some silt or clay.
Edited 6/10/2006 8:01 pm ET by FlashGordon
Lets try to answer what I think you are asking.
On a lot that graded is properly, the house would be on dirt that is 3 ft. higher than the street if its 150' away. I assume your lot is totally flat, so the top of your stemwall should be 18" above adjacent grade not just 6". If your stemwall is 3' high, then the dirt can be higher than adjacent grade to keep water from seeping under your house. I am guessing your have no basement.
Here is a bit of "Magic" to "Pump" your raingutter water uphill to the street without an electric pump. Just run 3" ABS or PVC plumbing drain pipe with glue fittings and joints to the street/stormdrain/stream. At the house run with an elbow to extend the pipe a couple of feet higher than the other end. With the roof gutter going into this pipe, the water will go uphill. Disadvantage is that the pipe is always full of water, unless you have a "T" outlet that you can open and drain.
You are obviously in a land where it never freezes
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Your right Piffin, I keep forgetting local conditions. I'm in Southern California where I don't worry about frostline, icedams, humidity, tornados, sunstroke and maneating mosquitos. We worry more about outrageous home prices, skin cancer and earthquakes.
Back to the original question, maybe combining your idea of a "T" fitting at its lowest point to drain into a dry well. Forget dry wells if your on solid rock in Colorado, volcanic rock in Hawaii or clayey soil of Texas.
I also thought raising the house 3' would be good so you don't have to worry about drainage. But 3' is not high enough for residents along the Mississippi. Also, some guys are on a tight budget and cannot afford a concrete / foundation bill that is twice as much.
I do not mind you keeping me in check, cause I do a lot of things out of the norm. I learn a lot from others mistakes and mines :-)