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Discussion Starter #1
I'm considering installing a sump in my basement (doing a finish job and would rather not have to tear stuff up again if I can help it). We've had water issues since buying the house, but redirecting the gutters and installing a french drain has solved that problem.

I'm in the middle of replacing an existing drain that is leaking and had to cut the slab in order to do it. We've had a significant amount of rain the past month. While no water is coming in the basement anymore, I have noticed (since cutting the slab as you can see in the picture), the water does nearly rise to the top of the slab.

My question:
Will cutting a hole and putting in a sump pit with perforations help keep the water down or would I need to run field lines into the pit in order to actually make any gains with the water removal?
 

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Master General ReEngineer
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My question:
Will cutting a hole and putting in a sump pit with perforations help keep the water down or would I need to run field lines into the pit in order to actually make any gains with the water removal?
Ayuh,..... The water table will drop, in a circle around the basin, without any laterals feeding it from under the floor,......

If you add laterals, it'll lower the water table in the bigger area covered, probably at a quicker rate,.....

Puttin' in laterals is a 'ell of a job,.....
If the outside work fixed the water problems,.....
I'd just do a bigger sump pit for insurance,....
 

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retired framer
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If you have gravel under the slab it might work, a pipe just creates a hole in the gravel to make the water travel faster.

When you dig the pit, you will be able to see how fast the water will go down in your open areas.

You only need to lower the level 6 to 8 inches so don't drill holes all the way to the bottom of the pit. Or you will be continuously pumping water you don't need to.
 

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Discussion Starter #4
Thank you... the ground beneath the slab is pretty rocky/gravel backfilled so I'm hopeful that will aid in the water flow to the basket. Just didn't know if I would be wasting my time pumping water from a small area or if I would need to have some field lines to help draw in more water. Since it hasn't cleared the slab I'm assuming i will be fine, but only want to cut the slab once. If that makes sense.
 

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Where and how does the French drain outside run and is it deeper than the basement floor level?

Where away from the house does the French drain dump/empty to?

The field lines or laterals need to go around the perimeter of the foundation. None are needed in the middle.

If, after you install the pit with no laterals, water starts to seep between the foundation and floor slab onto the floor on the other side of the basement, then you need laterals.

With or without laterals, the water may rise in the pit partway and stop. How high it stops may vary from week to week and depends on climate conditions outside. If the far side of the basement stays dry then the pit can stay partly full, with the pump stopped indefinitely.
 

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Discussion Starter #6
Where and how does the French drain outside run and is it deeper than the basement floor level?

Where away from the house does the French drain dump/empty to?

The field lines or laterals need to go around the perimeter of the foundation. None are needed in the middle.

If, after you install the pit with no laterals, water starts to seep between the foundation and floor slab onto the floor on the other side of the basement, then you need laterals.

With or without laterals, the water may rise in the pit partway and stop. How high it stops may vary from week to week and depends on climate conditions outside. If the far side of the basement stays dry then the pit can stay partly full, with the pump stopped indefinitely.
Thanks that makes sense. The french drain is below the slab on both sides of the house and it empties on to a sidewalk/driveway area that slopes to another drain taking the water over the hillside.

The only other complicating factor is that this slab is part of a split level renovation project done back in the 80's. The builders also installed a french drain inside the foundation (the part attached to the renovation) which ties into the drain on the sides. I really think that if I keep up the maintenance on the french drains I should be alright, but want the sump as extra insurance. We've gotten over 10" of rain so far this month and it hasn't crested the slab so I should be good.

Thanks to everyone for their input!
 

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If you have a French drain lower than the basement floor around the perimeter outside then, barring some very esoteric individual case situations, you do not need laterals (a kind of French drain) on the inside of the foundation.

I need to think about why the water in the cut you made is nearly at the slab surface before commenting more about that. If at any point along its length the French drain (inside or outside) is completely full (I would say more than 3/4 full) of water the French drain system as a whole is defective, deficient, or in need of maintenance.

Water must not lap up against the foundation at any time. Do not have a depression around the foundation filled with mulch or other material more porous than the soil in general or sand.
 
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