Edumacate me about basement drainage and sump pumps
March 11, 2017 2:40 PM Subscribe
So, we bought our house a few years ago. It's a small one-story job, built around 1940 or so. The previous owners told us that the basement flooded years ago due to backup from the sewer system and after that episode, they installed a backflow prevention valve and a sump pump. I'd love to know more about how this basement is protected from moisture since I can't seem to figure it out myself.
We're planning refinishing a large basement room and have discovered some moisture on the foundation walls, which has prompted looking into basement waterproofing from the interior.
There appears to be a large PVC pipe leading into the sump pump. I have no idea what it's draining or where it's coming from. The sump never fills and the pump never operates, though I test it to make sure it's still operational. There is also a floor drain in the basement floor.
Question -- what the heck is supposed to drain into the sump? I don't think there's an interior weeping tile system since the concrete in the basement looks old and undisturbed. There's no sign of a waterproofing membrane on the interior. Is it possible there's a perimeter drain that I'm not aware of? (The perimeter of the properly looks undisturbed.) How could I tell? And if there is, could it be that making the basement less damp could be accomplished by making sure the drain system is working and sealing the foundation walls, rather than going through a whole waterproofing process?
(Yes, I can just ask the previous owners but they aren't particularly responsive...)
We're planning refinishing a large basement room and have discovered some moisture on the foundation walls, which has prompted looking into basement waterproofing from the interior.
There appears to be a large PVC pipe leading into the sump pump. I have no idea what it's draining or where it's coming from. The sump never fills and the pump never operates, though I test it to make sure it's still operational. There is also a floor drain in the basement floor.
Question -- what the heck is supposed to drain into the sump? I don't think there's an interior weeping tile system since the concrete in the basement looks old and undisturbed. There's no sign of a waterproofing membrane on the interior. Is it possible there's a perimeter drain that I'm not aware of? (The perimeter of the properly looks undisturbed.) How could I tell? And if there is, could it be that making the basement less damp could be accomplished by making sure the drain system is working and sealing the foundation walls, rather than going through a whole waterproofing process?
(Yes, I can just ask the previous owners but they aren't particularly responsive...)
Best answer: Is there a pipe or hole or tube in the sump pump's "well"? My perimeter drain system goes directly into the well. I also have a PVC pipe OUT of the sump pump -- are you sure the PVC doesn't go OUT? Mine dumps into my back yard near a gutter outlet. (Pro-tip ... we made a little fake stream lined with waterproof fabric and disguised with river rocks that carries the gutter and sump pump a further 25 feet from the house, so the sump isn't constantly pumping out the water, having it soak back down next to the house, and repumping it out again. WORKS GOOD.)
In my area in 1940, definitely french drains would have been built around the foundation and probably they'd be connected to the sump. It would help to know what was common in your area around the time. If you have a homeowner's insurance AGENT, they often know what's common in the area. (And they can also often recommend contractors.)
If you call a few basement contractors for quotes, they'll come examine the current system and tell you what they think it's doing, and what it'll cost to upgrade it/waterproof you. (I found estimates varied WILDLY -- some quoted three times as much as others for the same work.) But from their proposed work orders you'll get an idea of what needs to be done (i.e., things they all agree on). And then some of what they propose you can probably do yourself anyway; we hired the new drainage system put in (our system was old and failing) what with the jackhammering and specialized drains, but we sealed the walls ourselves, it was tedious but not hard.
posted by Eyebrows McGee at 3:45 PM on March 11, 2017 [2 favorites]
In my area in 1940, definitely french drains would have been built around the foundation and probably they'd be connected to the sump. It would help to know what was common in your area around the time. If you have a homeowner's insurance AGENT, they often know what's common in the area. (And they can also often recommend contractors.)
If you call a few basement contractors for quotes, they'll come examine the current system and tell you what they think it's doing, and what it'll cost to upgrade it/waterproof you. (I found estimates varied WILDLY -- some quoted three times as much as others for the same work.) But from their proposed work orders you'll get an idea of what needs to be done (i.e., things they all agree on). And then some of what they propose you can probably do yourself anyway; we hired the new drainage system put in (our system was old and failing) what with the jackhammering and specialized drains, but we sealed the walls ourselves, it was tedious but not hard.
posted by Eyebrows McGee at 3:45 PM on March 11, 2017 [2 favorites]
That was brief my apologies.
Basement walls are often moist. You don't describe what degree of moisture you have. It sounds like not enough to drip to the floor and accumulate. Without more info, probably nothing unusual. Installing a french drain outside is often recommended to reduce such moisture. But that system drains out away from the house, not to the sump pump.
If the past issue was a backed up sewer, that means that higher pressure developed in the line leading to the street. If the floor drain is connected to the sewer line, the basement floods up through the drain, or through the lowest drain, a utility sink, or a toilet. Moisture on the walls has nothing to do with this.
Where does the sump output lead to?
I'm going to guess the PVC pipe is connected to the floor drain? Maybe. It's hard to guess, as you've described it. Could you take some photos.
For your refinishing, I recommend looking into the current spray foam technology. Perfect use case here, and there are more and more contractors doing it.
posted by humboldt32 at 3:53 PM on March 11, 2017
Basement walls are often moist. You don't describe what degree of moisture you have. It sounds like not enough to drip to the floor and accumulate. Without more info, probably nothing unusual. Installing a french drain outside is often recommended to reduce such moisture. But that system drains out away from the house, not to the sump pump.
If the past issue was a backed up sewer, that means that higher pressure developed in the line leading to the street. If the floor drain is connected to the sewer line, the basement floods up through the drain, or through the lowest drain, a utility sink, or a toilet. Moisture on the walls has nothing to do with this.
Where does the sump output lead to?
I'm going to guess the PVC pipe is connected to the floor drain? Maybe. It's hard to guess, as you've described it. Could you take some photos.
For your refinishing, I recommend looking into the current spray foam technology. Perfect use case here, and there are more and more contractors doing it.
posted by humboldt32 at 3:53 PM on March 11, 2017
greatgefilte: "Question -- what the heck is supposed to drain into the sump?"
It's protection against flooding. If say you leave the sprinkler on when you go away for a long weekend and the neighbours dog tips it over so it is pointing right at a basement window that lets the water through the sump will prevent your basement from filling with water. Replace sprinkler/dog with say broken water pipe or your water heater springing a leak.
greatgefilte: "There appears to be a large PVC pipe leading into the sump pump."
Usually that pipe is actually leading away from the sump. You want to find out where it goes so you can ensure the exit is unobstructed.
posted by Mitheral at 7:04 PM on March 11, 2017
It's protection against flooding. If say you leave the sprinkler on when you go away for a long weekend and the neighbours dog tips it over so it is pointing right at a basement window that lets the water through the sump will prevent your basement from filling with water. Replace sprinkler/dog with say broken water pipe or your water heater springing a leak.
greatgefilte: "There appears to be a large PVC pipe leading into the sump pump."
Usually that pipe is actually leading away from the sump. You want to find out where it goes so you can ensure the exit is unobstructed.
posted by Mitheral at 7:04 PM on March 11, 2017
Response by poster: Thanks for the advice so far. My newbie status as a homeowner is showing through.
Just to clarify:
-Yes, of course there is a PVC pipe connected to the sump pump, and it empties in our front yard, away from the foundation.
-There is an additional PVC pipe emptying into the sump well. I don't believe it's connected to the floor drain because we've used the floor drain to drain our boiler's expansion tank and there's never been any water collecting in the sump. (Plus, as far as I know floor drains aren't allowed to connect to sump outlet drains?)
-The backflow prevention valve is then, I assume, in line with the sewer line?
-The exposed foundation walls in the unfinished parts of the basement show some efflorescence but aren't damp, and there's been no obvious water leakage elsewhere. The walls behind the finished part of the basement have some dampness to them but this is the same room that had a lot of water damage when there was a flood years ago (as evidenced by the water-stained hardwood in that room). Could some of this dampness have been from the interior of the room rather than coming from outside?
humboldt, how does the spray foam help with waterproofing?
posted by greatgefilte at 7:53 PM on March 11, 2017
Just to clarify:
-Yes, of course there is a PVC pipe connected to the sump pump, and it empties in our front yard, away from the foundation.
-There is an additional PVC pipe emptying into the sump well. I don't believe it's connected to the floor drain because we've used the floor drain to drain our boiler's expansion tank and there's never been any water collecting in the sump. (Plus, as far as I know floor drains aren't allowed to connect to sump outlet drains?)
-The backflow prevention valve is then, I assume, in line with the sewer line?
-The exposed foundation walls in the unfinished parts of the basement show some efflorescence but aren't damp, and there's been no obvious water leakage elsewhere. The walls behind the finished part of the basement have some dampness to them but this is the same room that had a lot of water damage when there was a flood years ago (as evidenced by the water-stained hardwood in that room). Could some of this dampness have been from the interior of the room rather than coming from outside?
humboldt, how does the spray foam help with waterproofing?
posted by greatgefilte at 7:53 PM on March 11, 2017
Have you installed a dehumidifier? If not, you should (and I can recommend a model).
posted by languagehat at 7:52 AM on March 12, 2017
posted by languagehat at 7:52 AM on March 12, 2017
Response by poster: Yes, we've got one that runs through the summer months.
posted by greatgefilte at 6:26 PM on March 12, 2017
posted by greatgefilte at 6:26 PM on March 12, 2017
Current spray foam technology, using closed cell recipie is essentially vapor barrier and insulation in one. The contractor can adjust the application from something that resembles rhino lining like you see in pickup truck beds, to puffy. Applying it eliminates the air space where condensation normally forms.
posted by humboldt32 at 6:54 AM on March 13, 2017
posted by humboldt32 at 6:54 AM on March 13, 2017
Best answer: There are several unrelated issues.
1. Sewage Backflow - This happens during times of heavy rain in an area of combined storm and sanitary sewers. The rain overfills the sewers so much that it starts to back up into people's homes, especially when they are on the low end of the street sewer lines. The backflow preventer installation will stop that from happening.
2. Groundwater and ground moisture - Even during dry weather, if you have clayey soil you will always have ground moisture. The only way to permanently fix basement wall moisture is to have a contractor dig around the perimeter of the foundation wall and backfill with stone to the footing. They can also put a rubberized membrane on the exterior of the foundation which doubly protects the basement. Note that this can cost some big money.
3. Drainage issues - You may want to have an expert look at your yard to see if there is adequate drainage away from the house, especially with downspouts. Faulty downspouts can bring lots of water into your basement.
posted by JJ86 at 3:02 PM on March 14, 2017 [2 favorites]
1. Sewage Backflow - This happens during times of heavy rain in an area of combined storm and sanitary sewers. The rain overfills the sewers so much that it starts to back up into people's homes, especially when they are on the low end of the street sewer lines. The backflow preventer installation will stop that from happening.
2. Groundwater and ground moisture - Even during dry weather, if you have clayey soil you will always have ground moisture. The only way to permanently fix basement wall moisture is to have a contractor dig around the perimeter of the foundation wall and backfill with stone to the footing. They can also put a rubberized membrane on the exterior of the foundation which doubly protects the basement. Note that this can cost some big money.
3. Drainage issues - You may want to have an expert look at your yard to see if there is adequate drainage away from the house, especially with downspouts. Faulty downspouts can bring lots of water into your basement.
posted by JJ86 at 3:02 PM on March 14, 2017 [2 favorites]
Response by poster: Thanks, all, I think we might just end up going the spray foam route as it seems to be the most efficient.
posted by greatgefilte at 7:58 PM on March 14, 2017
posted by greatgefilte at 7:58 PM on March 14, 2017
um, wait are we saying spray foam to prevent water intrusion? because that's definitely NOT what it's for. It's also not a vapor barrier, and a vapor barrier and a waterproof membrane are not the same thing either. I would recommend doing a lot more research on your options before doing anything.
This is a good primer on waterproofing below grade concrete, discussing mostly exterior waterproofing options, which are expensive as retrofits.
This is an interesting newer product that uses a chemical crystalline structure to physically seal the voids in the concrete, making it waterproof.
posted by annie o at 10:00 PM on March 20, 2017 [1 favorite]
This is a good primer on waterproofing below grade concrete, discussing mostly exterior waterproofing options, which are expensive as retrofits.
This is an interesting newer product that uses a chemical crystalline structure to physically seal the voids in the concrete, making it waterproof.
posted by annie o at 10:00 PM on March 20, 2017 [1 favorite]
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posted by humboldt32 at 3:17 PM on March 11, 2017