To Sump Pump or Not

[Roger Ramjet]

I have a 4 year old house built on a high water table. For this reason the builder did not dig out a full basement. It has a 4'.8" all concrete crawl space. The foundation is poured. Except for 2 recent episode over the past

2 years (one yesterday when we got about 4 inches of rain), it has remained dry. There are no footer drains since there was no place low enough on the property to run them out to (lower than the footer). The two episode were unusally high amounts of rain. The first episode resulted in an 1.5" to 2 inches of water. The second episode resulted in about four 16 gallon wet vac cleanup. No big deal. I want some piece of mind since the oil burner is down there (not on blocks due to the low clearance) and was thinking about putting in a sump pump. I read the building plans for my property and the spec of the crawl floor is 4 inch concreate, wire mesh and 8 inches of compacted gravel. The water is seeping thru the function of the floor and walls around the entire perimeter. My guess is ground water intrustion although I was under the impression the 8 inches of gravel should of prevented this . There appears to be no surface drainage issues, although approx 60 - 75 from the foundation is a retension area (drywell) for driveway and rear roof runoff. The backyard slopes down to this retension area

I have some question about installing a sump.

1) Does it make sense for this application? I ask that because if i have to go down 3 feet for the pit, my guess is the sump will cointinuously run because i would intrude into the water table.

2) Does it make sense to put in a sump without exterior or interior footer drains feeding the pump?

thxs.

[m Ransley]

You only need a pit deep enough to activate the float switch ,Im guessing but 8" - 12" should do it if the float is adjusted. It makes sense to put one in.

[Nick Hull]

You might consider a very shallow sump with a marine bilge pump. They can pump down to within 1/8".

[Dave]

One thing you should worry about is if the crawl space is damp, it is a good breeding place for termites and other critters. If you have vents I would open them up in the summer. At any rate, I would do anything possible to get it dried out. I would also spray it occasionally.

[Roger Ramjet]

Dave, Its not damp at all. Matter of fact 2 days after the heavy rains and seepage, i just went down there to fetch the shop vac and its pretty bone dry. What was your sugesstion about spraying about? Spray with what?

I did some research and the fact I have a nice thic gravel base, just putting in a sump without any accompyaing drains will work. This abbreviated system (no drainage tile) is most appropriate where water infiltrates only one area of the basement, or where the basement floor was poured over a gravel bed. Many homes built over the past 30 years have several inches of gravel beneath the concrete floor. The gravel was used to bring a slightly over-excavated floor back to grade. Because water seeks the path of least resistance and will migrate sideways before it moves up, moisture beneath the floor will move through the layer of gravel to a sump pit before flooding the floor.

[Chris Lewis]

According to Nick Hull :

He needs it deep enough to penetrate significantly into the gravel bed, and allow for operation of the float switch (without too much short-cycling). I wouldn't consider less than 6-8" penetration into the gravel layer, or 12" total (to allow for decent float travel). I'd prefer 16-20" in total. Check out sump pit shells dimensions for an idea of "routine practise".

Once he cuts a hole thru the concrete, going another 8-10" is easy. Insert perforated bucket (or pre-made sump pit shell) to prevent gravel collapsing into pit.

[Dave]

I would get a pump sprayer and mix up some insecticide and spray the ground and joists for insects.