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?
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.
(m Ransley) wrote:
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.
(m Ransley) wrote:
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.
Chris Lewis, Una confibula non set est
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