Basement Drainage System Idea--NEED SERIOUS INPUT!!!

Discussion in 'Remodel Forum & Blog' started by DIYFreak, May 7, 2008.

  1. DIYFreak

    DIYFreak New Member

    May 7, 2008
    We have a basement water seepage problem which seems to occur predominately during the spring thaw timeframe. Prior to finishing the basement 3 years ago, I did work with gutters, grading, etc, which I thought had solved the problem, but as we have seen recently, shows no avail.:mad: We recently had record amounts of rain, on top of a heavy snow filled winter, which caused water to seep into cracks in the floor and at the base of the walls (note: the foundation is made of concrete block). This is the most water I have seen come in since I bought the house in 2001.

    I feel, that at this point, the only really effective remedy will be to install a drain system along the footing, with a sump and sump pump to discharge the water. Due to several limiting factors, I have found it difficult to decide on a good approach. :confused:

    What I am considering now is installing a combination (partial inside/partial outside) perimeter drain system with an outside sump crock located in a large window well (sump below the frost line and sealed/insulated from outside air). The drain tile would be routed along the side of the footing on the inside, following most of the perimeter, except for the area of the bathroom. An exterior drain tile would be routed along the bathroom area to avoid costly demolition/excavation of the bathroom and plumbing under the slab. Only one outlet from the interior will exit under the footing and out into the sump crock. The outside drain tile will stay outside and drain directly into the sump crock at a different inlet hole. The sump pump discharge pipe will have a check valve, as well as measures incorporated to prevent a clog, caused by freezing during the winter.

    The drain pipe used will be pvc with holes at 4 and 6 o'clock, laid on a 2" bed of 3/4" clean gravel, and then backfilled with the same type of gravel. The gravel will be encapsulated in a filter fabric. Cleanouts would be located at points along the pipe path to facilitate flushing out of silt on a periodic basis, in order to prevent clogging.

    By taking this approach, I am:

    A. Minimizing the excavation of permanent exterior structures such as a very large concrete porch, part of a parking lot, half of my driveway, etc.

    B. Preventing property line issues with respect to the excavation.

    C. Preventing costly demolition of an existing bathroom.

    D. Keeping the basement interior envelope closed off to outside moisture (hence, the sump crock outside), thereby, preventing mold growth caused by the sump, radon infiltration, and a flood in the basement caused by a pump failure, or power outage.

    E. Preventing a clog formation after 10-15 years of silt buildup.

    F. Saving cost by doing the work myself (unfortunately I don't have 5-10 grand to throw around for a commericially installed system)

    By taking this approach I am hoping to have the most effective perimeter drain system, with the least potential for problems.
    I am not sure I have any other effective options for dealing with this problem, at this point. I have researched, studied, and racked my brain for more than a month now.

    Can anyone, with experience, give me opinions/advice concerning this approach? Am I overlooking anything? Am I heading in the right direction? OR, am I barking up the wrong tree?
  2. DIYFreak

    DIYFreak New Member

    May 7, 2008
    No input????

    Hmmm. . . I might be getting close to some kind of a record--The thread with the most views and no replies.:D:(
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  4. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    That is one of the most well written questions on foundation drains that I have ever see.

    I've found that water in basements for several reasons.

    1) the yard has been graded to drain toward the house.
    Code calls for a 2% grade away from any foundation. Sometimes this is only for a short distance, and you wind up with a valley between the foundation and the rest of the lot.

    2) Underground springs: water following a seam and popping up where it doesn't belong. This means even if the land is sloped from the house, and the foundation is sealed on the outside before backfilling, it may be even lower than that. I remember one foundation I cut on a hill side that had a spring in the crawlspace. I drained it with a 4" drain on the downhill side, and continued farther down the hill with it.

    If water is not coming up from the floor, but coming through the foundation wall, there is a chance that sealing the wall, and having perf pipe to drain away water will do the job.
    It's nice if you can gravity drain it, but if you can't, then using a pump and check valve should move it.
    Last edited: Jun 13, 2008
  5. Fistor

    Fistor Geotechnical Engineer

    Mar 18, 2008
    Geotechnical Engineer
    Vancouver, BC
    Hi -

    You have some good ideas there, but I want to add some thoughts for your consideration, as I have a lot of experience with foundation and underslab drainage. By the way, good on you for identifying the only real solution - foundation & subgrade drainage.

    1. Perimeter drains: it is important that you have proper perimeter drains at footing level. While I can understand your rationale for making a combination inside/outside system, I would avoid that if possible, and would keep the drains OUTSIDE the building perimeter, for two reasons:
    1 - more complicated = more that can go wrong. A simple, gravity dominated drainage system, draining to a sump & pump if needed, is best. The drainage material should be located level with the underside of your footings, and is the simplest in terms of construction and operation.
    2 - odors. There will come a time when water accumulates within the drainage material itself (a half drained pipe, water pooled at the base of the gravel, etc.), and unless you have a 100% assurance that you will be able to remove all of this water, you may experience odors in your basement from stagnant water.

    Not sure what the soils are beneath your basement floor slab, but typically the slab, which would be 12 - 18 inches higher than the base of the footings, would be underlain by 4 to 6 inches of free-draining material (gravel or clean sand). Weep holes through the foundation wall would connect to the drainage around the exterior of the wall. The pipes (your suggestions seem reasonable), located at footing level, would be below the slab, and therefore, drain out the slab area. By having the drains themselves within the building lines, I could foresee that sometimes water would remain in at least some areas beneath your slab.

    2. Filter material: Your gravel selection is correct, but often filter fabric may silt up and clog, depending on the surrounding material. If that applies to your area, a way around that is to use "natural" materials as the filter - place a 6-in wide zone of 3/4-in gravel around the pipe, then backfill above/around that zone with finer gravel (say 1/4-1/2-in rounded gravel, which up here we call "pea gravel"). The finer gravel will have smaller voids between particles, and also fill in the gaps at the edge of the zone of drain rock around your pipe. "Clean" sand (i.e. no silt, clay, or other fines) should be the only other backfill you use around this area and against the basement walls. Never use clays, silts, organics, etc.

    3. Control of runoff: Terry is right - it is very important to have external grade sloping away from the structure. I will defer to Terry's expertise on the actual grade requirement, but the slope is important - in particular if you have adjacent areas that transmit runoff relatively quickly - such as asphalt, concrete walks and driveways, etc. Anything you can do to improve surface drainage will help reduce the rate of water inflow around your basement, though it won't eliminate it.

    (Note: based on your problem description, the source is runoff and surface melt, not u/g springs, which in actuality would be either trapped pockets of water, or artesian pressure. If it were artesian, the water inflow would not be seasonal. Therefore, it's that much more important to control surface runoff where possible.)

    I realize you don't want to rip out external features, but because you have a case where whatever subgrade drainage system you have (if any) is already failing, the best thing to do is to bite the bullet, and do it right, the first time. Exterior perimeter drains, FTW!

    If you happen to know any reputable contractors, see if you can get some free advice, even if you do the actual labour yourself. :)
    Last edited: Jun 13, 2008
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