Wet Basements Sump pump

Published on April 19th, 2016 | by Henri

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Bottom of sump should not be sealed

Q.  Should my sump for a basement sump pump have an open or closed bottom? Pump suppliers do not agree.

I have a 12-inch deep sump with an open gravel bottom. I have never had a need for a sump pump because my 50-year-old house has never had a drop of rainwater in the basement. Several weeks ago we had a very heavy rainfall and my basement flooded for the first time to about four inches above the basement floor.

I believe water entered the basement from the bottom of my open sump. This indicated to me that the ground water table outside was above my basement floor level. If my sump were closed at the bottom this would not have happened. Of course too, if I had a pump installed in the sump it could have pumped out the rainwater faster than it entered through the sump bottom.

Could I just fill the sump bottom with cement and not have to install a pump? I have been told an open bottom with a pump relieves the water pressure around the outside of the house foundation and prevents leakage into the basement. Please explain when the sump should be open or closed and when a pump is needed in each case.

A.  If the bottom of the sump had been sealed, it is very likely that the water would have come in at the joints of the floor and the walls — it may even have done so in this last flood. Hydrostatic pressure is very difficult to resist in residential housing as the cost is prohibitive. I agree with the person who told you that an open-bottom sump relieves the pressure.

The simplest solution to prevent future flooding is to install a good-quality submersible sump pump. Set the pump on the gravel at the base of the sump, but make sure to install a check valve at the pump outlet. Discharge the water outside onto a splash block on a sloping grade so the water will not recirculate back into the basement.

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