Fixing a wet basement
August 6, 2015 1:46 PM   Subscribe

I'm seeking some advice on the best way to stop our basement from flooding.

This spring, we moved into a century-old house in western MA in a river valley. (So wet basements are an issue around here.) We saw no flooding in the basement from snow melt during the slow warm-up, but when we had rainstorms the basement flooded twice to a maximum depth of maybe 2". We dropped a small sump pump from Lowe's ($130 or so) into a hole in the slab where the sewer clean-out is located, and that has worked so far to prevent water coming into the basement. That said, there is standing water in the hole, and the air is moist if we don't run the dehumidifier after it rains.

We believe the foundation walls to be fieldstone, skim-coated with concrete. Initially we thought the walls were not leaking water, but now we realize they must be because previous owners put some sort of waterproof coating on them and that coating is now coming off. The slab is perhaps 3" thick and not very level, and it was likely put in some time after the house was built. Based on what we can see in the clean-out hole, there is probably not a footing underneath the foundation wall. The basement is about 24'x25'.

We do not intend to finish the basement, but we want to prevent mold and moisture damage - and would like to use it as a workshop space and limited storage space for things like tools. The hot water heater and boiler are attached to the basement wall about 2-3' above the slab, so it would take a lot of flooding to reach them.

We have made sure the downspouts are directing water a few feet away from the house. We may want to regrade the uphill side of the house, but the water is coming in all four sides of the basement (and through the slab/foundation joint) so it's clearly being caused by hydrostatic pressure, which regrading won't address.

Two basement waterproofing contractors have given us estimates on the work they would do. Contractor A quoted about $7,000 to put in an interior perimeter drain, sump pump, and outlet to the front yard (which is downhill of the house). Contractor B quoted about $9,300 to put in an interior perimeter drain, sump pump, and a rubbery membrane on the walls to direct the water seeping through the walls into the perimeter drain.

Our questions are:

-Is a perimeter drain plus sump pump the best way to go?
-Would a gravity drain be better than a sump pump, if the geometry works to put one in? It would be simpler but could freeze in the winter. Then again, when the ground is frozen the basement doesn't seem to leak.
-Is the wall membrane worthwhile?
-Are these prices reasonable?
-Are there other options we should consider?
-Does it make sense to wait until we've been there through a full year with the sump pump and dehumidifer before spending more money on a more complicated solution? The current pump has worked so far, but it's small and depends on the electricity working - if the power goes out in a storm we don't have battery backup.

Thank you!
posted by john_snow to Home & Garden (21 answers total) 4 users marked this as a favorite
I have only DIY experience with basement waterproofing, but I think I have a decent handle on the basics. A functioning perimeter drain should depress the water table under/ immediately around the house enough to eliminate the issues of hydrostatic pressure against the walls and floor. In combination with decent overhangs and functioning gutters, there shouldn't ever be appreciable liquid water against the outside of the walls, so the rubber membrane seems like overkill to me, especially since you don't intend to finish the basement. I'd wait a few months after the perimeter drain was installed, chip off any loose coating, give it a coat or two of paint and call it done.

I have no strong opinion about gravity vs. pumped evacuation of the sump. If you went the gravity route, I wonder whether it would be worth running a soil heating cable along/around the part of the pipe above the frost line. That would give you the ability to thaw the pipe out if by some chance it ever froze solid. Probably unnecessary, though.
posted by jon1270 at 2:25 PM on August 6, 2015

Oh, and this:

We dropped a small sump pump from Lowe's ($130 or so) into a hole in the slab where the sewer clean-out is located, and that has worked so far to prevent water coming into the basement.

This hole in the slab, is it a lined sump? If the walls of the hole are dirt then using it as a sump is a bad idea because you'll be pumping dirt out from under the slab, and potentially from under the walls if it's close to the edge of the basement. That would be Very Bad TM. If it is lined (e.g. with plastic or crockery) then how is the water getting into it?
posted by jon1270 at 2:31 PM on August 6, 2015 [1 favorite]

@jon1270 - i'm no expert, just curious, but in your first comment are you describing an interior perimeter drain, or an exterior one? the question is about an interior drain (and it's not clear to me if an interior one is capable of lowering the pressure to the point that no water enters, or whether it's mainly cleaning out water that does enter).
posted by andrewcooke at 2:37 PM on August 6, 2015

I really think you should start with the exterior work before you do anything inside.
If you can use the natural elements to keep water out before it gets in, you won't need to do any interior work. Besides, if you do all of this interior work but never stop the flow into the house, now you are just part of a stream, basically. In one way, out another. Stop it before it comes in. Of course contractors want to sell you expensive interior work. That's their job.

Get a smart landscape contractor to give you some plans to direct water away from your house. This starts with managing the water coming off your roof, and then managing the water on the ground. It should all have a clear path away from your house.
You need correctly functioning gutters, grading to direct water to a safe place away from the house, and maybe some new fill/plastic liners and maybe even a french drain system to really move water away.

This should take care of the vast majority of water. If there are still water problems after this, then do the sump work. But I think you won't need it, and your foundation will appreciate being kept dry.
posted by littlewater at 2:47 PM on August 6, 2015 [1 favorite]

it's not clear to me if an interior one is capable of lowering the pressure to the point that no water enters, or whether it's mainly cleaning out water that does enter).

Enters what, exactly? Interior isn't as good as exterior but it's probably cheaper and less disruptive of landscaping.

If there are still water problems after this, then do the sump work. But I think you won't need it

Having had problems that fit the OP's description, I can say with certainty that there are some problems that grading and gutters just can't fix. If your house is in a low spot with a high water table, a sump is all there is to do. That said, it occurs to me that there's no way a gravity drain can work in such a situation; if gravity were enough to take the water away from the house then the perimeter drain would be unnecessary.
posted by jon1270 at 2:52 PM on August 6, 2015

OP says there is an uphill side so I'm assuming there is a downhill side. Yet OP says water comes in on all four sides - so there are 3 sides of the house that are downhill sides that are still letting water in. Managing the uphill side might be a harder project that might not be landscape-able but maybe you could get that hill water pointed past the house, too.
posted by littlewater at 2:59 PM on August 6, 2015

Yes, it would help to know how steep of a "hill" we're talking about.
posted by jon1270 at 3:10 PM on August 6, 2015

Take a look at some of the Holmes on Homes episodes where they flood proof. They always seal and put up an exterior waterproof membrane. Probably because in places with winter frost you can't be confident that the water won't flow against your house because of melt-refreeze-melt ice blockages/dams. Water getting into your walls and going through freeze-thaw cycles in not a good thing.

Make it right!
posted by srboisvert at 3:11 PM on August 6, 2015 [1 favorite]

Water getting into your walls and going through freeze-thaw cycles...

Unlikely if the basement is heated, besides which the house has apparently survived 100+ years as it is. Which isn't to say an exterior membrane wouldn't be nice, but if the budget is limited then there could be a perfect-is-enemy-of-good thing in play here.
posted by jon1270 at 3:18 PM on August 6, 2015 [1 favorite]

Response by poster: Thank you all! To answer a few explicit and implicit questions:

1) The slope is relatively gentle - maybe 1 foot in 8 or 10, roughly 5 to 8 degrees I think? I haven't had a chance to measure it. It also varies some across the property.

2) The water table is very high here - we are in a river valley with a lot of rain and snow every year (about 44" of each). All of the houses in the neighborhood, and most of the houses in the region, have damp basements. Landscaping the uphill side may help, and we do want to do it, but I doubt it will fix the problem entirely. We have also had the gutters cleaned and the downspouts equipped with extensions to direct water 6' or more away from the foundation, but that hasn't solved the problem. I should emphasize that we have standing water in the cleanout pit even when it hasn't rained for a week, which makes me think it's just the high water table that we're fighting.

3) Based on preliminary research, excavating the outside and trying to waterproof it is probably not a good idea, for the following reasons:
3.1) The foundation is fieldstone, and the mortar (which we can't see because of the concrete skim coating) has had 100 years to degrade. If we remove the dirt on the outside, we risk destabilizing the foundation. I have no idea what the chance of this is, but any chance larger than zero is unacceptable to us.
3.2) Even if we waterproofed the outside of the foundation, hydrostatic pressure could still drive water through the join between the foundation wall and the slab. It seems like we'd have to seal the slab as well.
3.3) It sounds like the cost could be much more than putting in an interior system.

4) The clean-out hole is not lined. It's dirt/ sand. I see your point about pumping dirt out - that hadn't occurred to me. Have you seen anything online or elsewhere that indicates it's a real problem? The only advice I've seen about unlined sump pits is that they tend to reduce the life of the pump because debris gets in the pump.

5) The basement is not heated per se, but it's always at a liveable temperature (well, maybe 40 in the winter) because 1) heat from the first floor warms it and 2) most of it is below grade, and I don't think the frost line is all that deep here.

6) Re: the gravity drain - our immediate neighbors have an interior perimeter drain that goes to a gravity drain connected to the storm sewer (which conveniently for them is in front of their property). It apparently works OK for them. I think the idea is that the lowest point in their basement is higher than the storm sewer grate, so the water that comes in the walls drips down, goes in the perimeter drain, and then goes out to the sewer. I haven't seen their setup firsthand so I'm speculating here.

7) An exterior french drain might help, or it might have no effect. I like the idea of keeping the water out entirely, rather than dealing with it once it's gone through the walls, but on the other hand a lot of sources say that exterior french drains clog/silt up pretty quickly.

Thanks again!
posted by john_snow at 5:36 PM on August 6, 2015

I see your point about pumping dirt out - that hadn't occurred to me. Have you seen anything online or elsewhere that indicates it's a real problem?

Not with an unlined sump specifically, but I knew a guy several years ago whose basement slab was undermined by a water leak that gradually sent several inches of dirt from under his house. There were no symptoms for years, until one day when half the house dropped several inches. If I remember right the damage was into six figures. A sump might not behave the same way, or might only be a problem in certain soil types.

It apparently works OK for them. I think the idea is that the lowest point in their basement is higher than the storm sewer grate, so the water that comes in the walls drips down, goes in the perimeter drain, and then goes out to the sewer.

Ah, if the municipality will allow you to tap into the storm sewer, I can see that working. Such setups were emphatically not permitted in the city where I last lived, so I was assuming you meant that you'd have the drain empty out the side of the hill you live on and if that were possible, then the water table wouldn't be so high in the first place.
posted by jon1270 at 6:35 PM on August 6, 2015

Just to clarify what we're talking about, when you say "perimeter drain," do you mean a drain channel sitting on the floor at the bottom of the wall, or perforated tile sunk in a trench after cutting out a strip of the slab around the perimeter of the basement? In all my previous comments I was assuming the latter. If you're only contemplating installing a drain channel at the bottom edges of the walls to catch drips and route them out then that won't do anything to depress the water table or reduce hydrostatic pressure under the slab. To get the water table down, you need drain tile BELOW the floor level, not on top of it.
posted by jon1270 at 6:42 PM on August 6, 2015

In re. jon1270's comment about the pump being in a dirt-lined hole -- more to protect the pump than the hole, I have my pump sitting in a large plastic pail that I drilled a large number of small holes into. This has been the space for the pump for the eight years I've been here and was definitely the place for it before, and I haven't seen the hole getting bigger...

I am in emphatic agreement with "the house has apparently survived 100+ years as it is. Which isn't to say an exterior membrane wouldn't be nice, but if the budget is limited then there could be a perfect-is-enemy-of-good thing in play here." I live in a house that is coming up on 100, in a village full of old houses. In wet springs many of them have hoses coming out of basement windows to the street, pumping away.

The contractors I have had in to assess the problem have all had very different takes, and a for-real permanent fix that would make it a usable, moisture-free basement only comes at a ridiculous price.

People here very occasionally have the expensive fix done, but mostly we are a village reliant on sump pumps and dehumidifiers. It seems to be the normal way for the unfancier sort of old house. Every professional who I have had assess the wet basement situation (thanks, lying seller who I did not have time to go after legally) has been confident that leaving it as is will do nothing worse than leaving me with an intermittently moist basement. Anyway, for what that's worth if you start getting estimates and start leaning towards "leave it." You might get estimates for larger-than-shed-size small outbuildings if you just want a simple workshop space; it could easily be cheaper than fixing the basement dampness.
posted by kmennie at 6:51 PM on August 6, 2015

When I was talking French drain I was talking about the kind that you install in tubes 6 feet or so away from your house in a trench 3 feet deep or so, no need to remove dirt by the foundation.

Most sumps in my area are fed by tile near the perimeter of the basement walls, as Jon is mentioning.

There's a few ways to approach this and without really seeing it, it's hard to give good advice.

Call a few more contractors to get more opinions. Call one that does inside and outside work before you decide.
posted by littlewater at 6:54 PM on August 6, 2015

One other idea, that I considered in my last house and almost went with. Go to Home Depot and get a standard heavy plastic sump crock. Drill dozens of smallish (maybe 3/8") holes in the bottom and lower parts of the sides of the crock. Cut a hole in the slab that's maybe a foot or so larger in diameter than the crock, and dig the hole out several inches deeper than the crock. Dump in enough gravel (stones too large to fit through the drilled holes) so that the top of the crock, sitting on the gravel, is at floor level. Then fill in more gravel around the crock, up to about 4" below floor level, and top with concrete. Drop your sump in that instead of the hole you're using currently.

This sort of thing would work better in highly permeable (i.e. sandy) soils than in clay, but the idea is basically just a deeper, more stable version of what you're doing now. Not as good as a footer drain, but cheap and probably helpful.
posted by jon1270 at 7:02 PM on August 6, 2015 [1 favorite]

RE jon1270: covering the outside of the crock with landscaping fabric should filter out the sand.

Water powered backup sump pumps are available. Mine has saved my basement a few times when the power has failed (my water bill was huge, but it was better than cleaning up the mess).

My basement has an interior perimeter drain that runs into the sump pump crock. The sump pump runs a lot when it rains, but the basement stays dry as long as yhe pumps are working.
posted by H21 at 8:39 PM on August 6, 2015

FWIW a lot of these perimeter drains that sit on top of the floor work by keeping water from accumulating inside of hollow concrete block walls. Small holes are drilled through the inner wall of the block, into the cavity, at the base of the wall, and then covered with the drain channels that route the water to a sump. This isn't possible with a fieldstone foundation because the wall isn't hollow. Catching droplets after they've already come into the basement and run down the wall won't achieve the OP's goals.
posted by jon1270 at 2:17 AM on August 7, 2015

I think you're right about not waterproofing the outside of fieldstone. That said, exterior waterproofing with a dimpled menbrane should include weeping tile at the footing, which in modern construction would be below the inside floor. We had it done on our century home and it's worked well (KOW) but our's is concrete, so it doesn't sound like an option fir you.

I think you're on track to the best real world solution, which is an interior french drain to a proper sump; break up the perimeter concrete about 3' from the wall, see if the foundation goes any lower that the floor. You want to have some 6" corrugated tubing (the type coverd by a nylon sock) run it to a proper sump as described by jon1270, pour gravel over it and skim with concrete. If you can keep the bulk of the water in the sump, rather than distributed under the floor, it's going to make a huge difference in humidity levels. The walls I wouldn't worry about. Exterior dimpled membrane is the only way to keep them from flaking.

If the corrugated pipe is below the foundation wall, it sould be set in far enough away to have to allow a 30 degree slope. Also, make sure the pipe gently and evenly slopes towards the sump. I'd put the sump towards the uphill side of the basement.
posted by bonobothegreat at 5:50 AM on August 7, 2015

Hey - you're probably my neighbor!
Our old house was built in 1840 and the foundation is a mix of field stone, brick, concrete block and concrete.

If you have fieldstone, you are likely to always get water - everything you do is going to be mitigation. Our house, when we bought it, would be weeping water between the stones during/after every good storm and in the spring thaw. We made some simple changes that fixed that for 95% of the storms and the rest could be managed with a dehumidifer.

Sounds like the contractors are prescribing a French drain, which I've seen in houses in the area to varying effect.

If it really is a water table issue, then a sump pump is a good idea, but make sure that the drain is well away from the house and doesn't go into the street or every fall and winter you will be turning the street into a skating rink.

You should also check two things that are cheaper to fix and often solve the problem (and these are the things we did that worked for us):
1. Are there gutters on the house? If no, consider installing them. If yes, make sure that the down spouts are redirected well away from the foundation. (also, be prepared for ice dams on the north side of the house in the winter and clean the fall leaves out of the gutters)
2. How is the grading? You describe that it slopes down to the front. Is it properly graded away from the house? FYI, if you re-grade at this time of year, it should be perfect for fall growth of grass when it gets reseeded.
posted by plinth at 6:38 AM on August 7, 2015

Response by poster: Thank you all, again - you have given us some very good food for thought here. We're definitely going to put the sump pump into a bucket or crock asap. We're also going to look to get at least one more opinion, maybe more. Sounds like there are some more options other than what has been recommended so far.

(hi Plinth!)
posted by john_snow at 6:12 AM on August 10, 2015

If you have a high water table, the issue is that water is seeping through your basement walls and floor. The correct, modern way to fix this is to excavate the foundation, apply a layer of waterproofing, put rigid insualtion boards (to protect the membrance) and then parge the whole thing (basically underground stucco). While you have excavated you should also place about 4"-6" of gravel down to the bottom of your footings, along with a perfoated drain pipe with the bottom of the pipe level with the bottom of the footing.

The other measures that have been suggested might mitigate the issue, but if you have a high water table, you really just have to actually waterproof the basement, there's not a quick and easy way to do this, because at the end of the day concrete/flagstones are just not waterproof (not even water resistant) - water will come in through capillary action under pressure. The numbers you got from the contractors actually seem cheap to me, given the amount of work that's needed to fix this.
posted by annie o at 6:41 AM on August 10, 2015

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