I am having a "double" french drain installed around my single car garage. One french drain will go around the outside perimeter of the garage and another drain will go around the inside perimeter of the garage. Both drains will empty into the same 30 inch by 18 inch sump pit located inside the structure. The sump pump will be 1 hp with a battery back up. I am having a new 6 inch garage slab poured with rebar/ crushed stone/vapor barriers as well. The structure is on grade and my lot is very level. There is a natural swale that is 170 feet away from the structure that ultimately feeds into a storm water culvert. I live in New Jersey and we have a 30 inch frost layer. Given the length of the run, I can't dig a trench with enough pitch to have it flow naturally. I was planning to use solid 2 inch schedule 40 pvc as the discharge connected to the pump and then I was going to put the 2inch pipe inside a 4 inch schedule 20 pipe and then bury the whole thing in a 6 inch deep trench. My hope is that the 4 inch pipe would add an additional layer of "air insulation" as well as act as an additional layer or protection against tree roots over time. The trench would be fairly level and my hope is that 1 hp pump is enough power to move the water the 170 feet (a few sump pump experts assured my 1/2 hp was enough since I don't have a big vertical run ). The pump doesn't run continuously, but my garage is at a "low" point on the property, so when it rains/ snow melt, all of the water collects around the base and seeps through the cracked garage floor. The building was built in 1940 and it doesn't currently have a french drain system. Could I use a 2 inch schedule 40 pipe for discharge and "insert" that in another larger diameter pipe to act as insulation or should I use a 4 inch schedule 40 pipe for the discharge? My concern with using a 4 inch pipe for the discharge is that the diameter is too large to move water through it with enough force and I won't really have the ideal pitch.
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Sump pump discharge pipe diameter.
- Thread starter Jr5k
- Start date
greenskeeper
Well-known member
without seeing the property, why can't you just discharge the sump pump at the surface a short distance from the building? How much water is going to collect in the sump?
Thank you for your reply. The building collects a tremendous amount of water. The building is 16 feet wide by 30 feet deep. The building has been collecting water for years to the point that I can not put anything on the floor (in case of a heavy rain). We recently had a heavy storm and the water level reached 10 inches in the garage. It is currently used as my workshop but I have to elevate things that would normally go on the floor. Discharging the water 30 or 40 feet away from the building would just transfer the water further away from the building but it would just become a small pond elsewhere on my property. The swale is the ideal spot to get the water off my property and it would not affect my neighbors’ properties either. I don’t mind doing the work, I just want to get it right.
If you are putting in a new slab maybe consider lifting the building a foot to improve the water situation.
As for the pipe, just run the 2" PVC and if you are concerned about the pipe freezing up run a couple lengths of heat tape in the pipe. You could lay insulation on top of the pipe, it will help.
As for the pipe, just run the 2" PVC and if you are concerned about the pipe freezing up run a couple lengths of heat tape in the pipe. You could lay insulation on top of the pipe, it will help.
Thank you for your reply. I will raise the building 12 inches and pour a higher foundation. I didn’t think about heat tape. That might be the way to go. I think I have enough defenses against water planned for the structure, I wanted to make sure I had a way to get it as far away as possible without causing problems elsewhere in the yard and I don’t want the pipe to freeze and back up on me. I was going to add a freeze protection fitting as the discharge exits the building. Thank you.
go with the 4 inch
my sump pump goes into a 4 inch at the back corner of my house
the 4 inch goes 200 feet and is buried only 12 inches since it had to go over a septic line
it drains to open air at the end of the 200 feet
it only drops 4 inches in that 200 feet since that is ground level at the end
it has been running fine for over 15 years in northern Illinois weather
the 4 inch never get full
there is always air above the flowing water but the 4 inch drop is enough for it to drain dry before any freeze occurs
my sump pump goes into a 4 inch at the back corner of my house
the 4 inch goes 200 feet and is buried only 12 inches since it had to go over a septic line
it drains to open air at the end of the 200 feet
it only drops 4 inches in that 200 feet since that is ground level at the end
it has been running fine for over 15 years in northern Illinois weather
the 4 inch never get full
there is always air above the flowing water but the 4 inch drop is enough for it to drain dry before any freeze occurs
D45
Well-known member
I buried 90 feet of 1-1/2" SCHED 40 PVC for my sump line
No issues nearly 7 years later
No issues nearly 7 years later
Innovate1
Well-known member
No way you should have to run that line 170'. In that distance a heavy rain will cause a LOT more water than is coming from the pump. You need to raise the floor enough to keep it above the water and/or slope and grade the ground to carry water away from the building. If you have that much flat ground there is no way a pump will be able to handle all the water.