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Community and Q&A

Troubleshooting a Basement Prone to Flooding

jenniferz5 | Posted in General Questions on

My basement has several floor drains that are not clogged and work beautifully to collect any water that may accumulate due to (in the past) well pump leaks, hot water heater draining, etc.  This morning, however, the basement has 6″ of standing water due to the soaked ground after the torrential rain last night.  I purchased a sump pump and am hoping for the best. My question:  I had planned to finish the floor as per recommendations here (dimple mat with floating floor).  This seems like a bad idea now!  Is there any way to finish the floor knowing that every five years or so (we have lived here that long) we may get a rain event that causes water to enter the basement to this magnitude?

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  1. kbentley57 | | #1


    Was the water standing, as you say, around the drains, or were they simply unable to keep up with the water infiltration? Do the drains you have now lead to daylight somewhere else on the property?

    There are a few solutions to problems like this - one is installing an interior perimeter drain that connects to your existing drains, if there's not one already. Another is adding a catch basin to these as an 'overflow' with a plunger activated sump pump for when the rainfall overburdens the current system, and pumping it out to daylight.

    Can you identify an area where the water is coming in, or is it generally 'all around'? Up from underneath? Through any penetrations?

  2. woobagoobaa | | #2

    Waterproof vinyl plank flooring should be an option for your finished floor.

    Might be useful ...

    That and the dimple mat would tolerate an occasional flood (pump failure, etc.)?

    1. jenniferz5 | | #4

      Except that vinyl is not at all a healthy flooring for a "green" home. It is a tough call - maybe click/floating Marmoleum instead?

      1. woobagoobaa | | #7

        AFAIK Marmoleum is not waterproof.

        Whatever you are considering I recommend get samples and dunk test them to gauge waterpoof claims.

      2. user-7513218 | | #8

        Old vinyl had health issues due to ingredients no longer being used. You may be opposed to vinyl in general, but it will not cause any health issues.

  3. jenniferz5 | | #3

    Hi Kyle,

    The water is standing all around the basement to about 6" up the walls. When I purchased my sump pump at the local hardware store (mom & pop store where the owners work there and have lived here in town their whole lives), the owner told me that the rain was so fast and furious that many people have water in their basements due not to the drains being clogged (they go to daylight, top of a hill, nothing blocking them), but due to the ground being so saturated that the water gets in via these drains. He advised me to cover the drains with plastic and a rock to stop the intrusion (done) and use the sump pump (done).

    I think your advice for a catch basin with sump pump is a great idea. If I do this, will I then be able to add the dimple mat and floating floor? There is a portion of the basement (in a corner, under the stairs) where I won't be adding flooring, so I could place the catch basin there. Will this work?

    1. kbentley57 | | #6


      Covering the drain with plastic and a rock might keep out the bugs, but not the water :).

      The general idea is to remove a section of the concrete floor around the perimeter, excavate to the bottom of the footing, or close enough to the bottom so that the pipe can be covered, and fill with fabric / crushed stone / drain pipe, and ran to the sump basin where it will be removed. This puts the bottom of the basin as the lowest point in the whole drainage system, and with a stout enough pump, you shouldn't see water intrusion ever again. Many people install two such basins / pumps, in case one fails. It's not a bad idea since you're already in there, and adding a second pump / basin is only a marginal cost.

      I think that I would install a system like this, and wait a year or so to let things dry back out and watch to make sure you don't have other problem areas. Another fix that sometime can go along with this (that I've seen, not used) is to have dimple mat along the walls, feeding into the perimeter drain, as sort of a 'catch the water from wherever' type system. Here's a few GBA articles on doing just that.

  4. jenniferz5 | | #5

    Another question - is there a way to add a valve of some sort to the floor drain that can close if water is flowing the wrong way, i.e. into the house instead of out?

      1. kbentley57 | | #11

        I'm afraid that wouldn't stop an event like this one. it may postpone the infiltration momentarily, but with 6" above the concrete surface, it would likely have found its way upwards through the interface between the slab and basement walls anyways.

    1. user-5946022 | | #22

      Yes, a backflow valve will 100% prevent water backing up in the line downstream of the floor drain from coming up the floor drain and filling your basement.
      HOWEVER - based on your description, it does not sound like that is the source of your problem. To devise an effective solution, source must be pinpointed.
      I'd start with the drain. Are you 1000% sure the area drains in your basement gravity drain to daylight and are not connected to a storm system? Can you check were the drain daylights? Can you confirm it is not somehow clogged or restricted?
      If the basement floor/area drains are flowing freely and daylight (ie not connected to a municipal storm system that got overcharged and backed up), then the water is likely entering from elsewhere - ie it is not coming up through the drain and filling your basement.
      So then you need to figure out where it is coming from.
      One possibility is the ground around your house is so drenched that small amounts of water are coming in through many locations. The only solution to keeping water out if this is the case is to address your foundation drainage. Either clean out what you have, or install if you don't have any. Some people have had success installing a ground gutter from the edge of the house 6' out, but they require maintenance.
      Another possibility is that your gutters & downspouts are tied to a drainage system, and that system was overcharged. In this case your leaks may have come through at specific locations.
      One solution for this is to clean the gutter/downspout system so it has max capacity, and seal all the points at which water can breach the system, usually at the joints.

  5. walta100 | | #10

    When I look a real estate. I ask myself could water collect by this house? Could the tiny creek get 17 feet deep? How much higher can the lake get before the dam overflows? I understand that ship has sailed but next time, think about it.

    The first question is can you drain your basement to daylight on your property?

    If not are you willing to bet the cost of you improvements that when it rains your home will still have electric power to run the pumps you will need to keep the basement dry?


    1. kbentley57 | | #12


      Solutions, not rhetoric. No disrespect.

    2. jenniferz5 | | #13

      Hi Walta! I was hoping you would show up to this party, as you always have good advice. Thank you.

      I am on a hill, with waterproofing around the house, no streams (etc.), and floor drains in the basement that go to daylight where water falls 5-10' over a hill. Many mistakes were made when I bought this house, but the basement has been dry. The problem (as I understand it) is that when Ida roared through last night (I am in NW CT) the rain was too much, too fast and the ground couldn't contain it. My dear, very knowledgeable professionals at the hardware store told me to plug the drains so it would stop coming in [I do not have proof that this is where the water is entering, but they are usually right] and use the sump pump. I'm down to 3-4" (from 6"), so I'll know more soon, I hope.

      1. user-5946022 | | #23

        Has water been continuously flowing at full force out of where your basement drains daylight at the hill? If so, it is possible this is the issue.
        If not, there is another issue. In any case if your drains daylight onto a hill, the water intrusion is not backup. It is water breaching the waterproofing system. If it were my house I would want to fix that, but that is often easier said than done.

    3. Aaron_P2 | | #14

      It sounds like there may be a few causes being suggested.

      One is that water came up the floor drains: Do you know if the gutters/downspouts are possibly connected the floor drain piping somewhere? Are any of the perimeter footing/foundation drains connected to the floor drains? I would think either of these and/or potentially a back up of the larger storm/sewer system could cause a backflow of water through the drains into the basement. I would think a properly installed backflow preventer could help, but a plumber/plumbing engineer might be best to contact. Ideally I would think if you can divert some of the flow to prevent future backups that would be better (like new separate downspout piping).

      The second is that with the heavy rain you may have had a high level of ground water that made it's way up from under the slab. This would lend towards more of some sort of internal basement drain and sump pump system. As Walter said these aren't ideal as they typically don't run in power outages. (there are battery backups and I have seen somewhere a water pressure venturi system if you have municipal water pressure)

  6. Andrew_C | | #15

    I hope you get the help you need to uncover the root cause of the water intrusion.

    Regarding the future of your basement – I predict it will get wet again. And even if you don’t have leaks, if you don’t have insulation under the slab, you’ll have other moisture problems. That’s just the way it is for basements, in my experience in the Midwest.

    My recommendation is leaving the concrete bare. After you get the water intrusion problem fixed, you may want to do some testing* to see how much water vapor comes up through the slab on a normal basis. Based on those results, you may wish to try paint or epoxy. Personally, I’d avoid anything more than that. Teenagers don’t care about basement floors, and neither do storage items (stored in clear plastic boxes, and not directly on the floor, right?) If you must, lay down very low nap rugs or indoor/outdoor carpet and figure that you might have to pitch it if water or mildew become a problem.

    Good luck, I know a lot of people have suffered from water intrusions this year. Not fun.

  7. jonny_h | | #16

    So the one thing that is concerning me here is that you say you have floor drains that go to daylight downhill, but yet your basement is still full of water. My first step would be to go get your eyes on the outlet side of the floor drain pipe. If the basement is full of 6" of water, that pipe should be full-bore shooting water downhill! If it's not, that means somewhere along the way the pipe is clogged. I wonder if maybe the floor drains were tied to the same pipe as the downspouts and/or foundation drains, and over time debris has partially or fully clogged the pipe, such that in the major rainstorm water backed up into the basement. The ideal situation would be to have the foundation drains, floor drains, and downspouts each independently draining to daylight downhill. (Actually around here, I think floor drains are generally treated as sanitary sewer, and cannot just go outside, but that may vary by location)

    I still think the first step to understanding is questioning why the basement filled up despite having floor drains going to daylight -- as those two facts seem in opposition.

  8. walta100 | | #17

    I think Jonny-H is on the right path. Was the water outside deep enough to submerge your daylight drains exit point?

    Being an old house we can’t be sure what pipes are connected together under the concrete. If the house is older it was common to drain storm water to the sanitary sewer drains making it possible the water in your basement is sewer water and a health risk. The combined storm/sanitary systems will often backup when large rain events happen.

    I would be tempted to put a garden hose in the floor drain and see if water exits to daylight as you think it should.


  9. jenniferz5 | | #18

    The first thing I did was check to see if the drains outside were gushing water - not a drop! Last week (ironically) I poured water down the drains just to make sure they were draining (they were); however, at that time I didn't think to ask someone to stand outside and make sure water was exiting where it should. I think you have hit on the solution! Is there a way to clean out these drains myself - baking soda, vinegar? A giant plumbing snake? I would hesitate to use boiling water in the PVC. Is there a non-toxic product that serves this purpose?

    We are on septic and do not have gutters (roof overhangs and a metal roof).

    The sump pump did the job and we've cleared out everything wet. It was very little - Rubbermaid is brilliant for basements.

    1. Expert Member
      NICK KEENAN | | #19

      If the drains are clogged they need to be mechanically cleaned -- probably a snake and then flushing with water to move the material along. Chemical drain cleaners wouldn't work on the stuff that would clog a basement drain -- not that they ever work that well anyway.

      I'm a little confused about what's going on. Do your drains exit to the surface? When you checked if they were draining, did you see water coming out somewhere? Or did you just pour water down and it disappeared? You really want drains that exit to the surface, anything else has a finite capacity. If it's not draining now it's probably not clogged, it's saturated.

      1. jenniferz5 | | #20

        Last week I poured water down into the drain in the basement and said, "Yay! It works." I did not check the drain at the exit point - rookie mistake.

        After all of this great advice, I think it is obvious that the drains are clogged. The pipes go off the side of an approx. 8' hill, about 2' out, so they don't get blocked at the exit; the clog must be in the middle somewhere.

        I'm going to use my wet/dry vac to get up the last of the water on the floor; I'll open up the drain cover and vacuum out the pipes, too, in case the blockage is close to the surface. Then, I'll use my trusty baking soda and vinegar combination, finishing with the plumber's snake, if needed. I'll flush water down the pipe after each step to determine whether the next step is necessary - someone will be watching at the exit points this time!

        Just for kicks and giggles, I'll add a backflow valve, as I think it couldn't hurt and may help.

        1. Aaron_P2 | | #21

          I wouldn't be so sure the floor drain is connected to that outlet you see off the hill. It could just be the outlet for foundation drains, since you don't have gutters or downspouts. I think assuming it is clogged may be a mistake - it might be worth having the drain scoped to see where it goes and what it is connected to. Not sure how much a plumber would charge in your area, but there are sewer inspection cameras for $300-$400 on Amazon as well.

          Without gutters/downspouts, I'm wondering if the foundation drains may be able to keep up with moderate amounts of rain and just got overwhelmed with a heavier rain? Likely the roof area of the house is dumping all it's water right next to the foundation and so the heavier the rain you have a compounding of the roof area and any yard water that is making it's way to those foundation drains. Just a guess based on the limited information.

          1. jenniferz5 | | #25

            I may have to get it scoped - that's a great idea.

            We have had very heavy rain in the past, so I have no idea how this happened.

  10. jenniferz5 | | #24

    The basement is now dry, I have been trying to clean and toss whatever got wet, and I have sprayed down about half of the basement floor with 10% hydrogen peroxide. Better, but not great.

    Yesterday I used the ShopVac to try and clear out one of the drains (as per Dr. Google) and I am pretty sure I sucked up some sewage (and could have kept on doing so if I had not stopped). Odd because my sewage drain is at the ceiling of the basement. There is still "water" sitting at the bottom of that drain (maybe 6" down from the floor). None of the other drains seem to have this issue. We are on septic; is it possible that the floor drains drain into the septic tank via a separate pipe? It seems that there are a mix of PVC and cast iron drains (the sewage-y drain is cast iron). Could some of the drains go to daylight and be on a separate line? The house was built in 1953, but I have only lived here 6 years, so I don't have much info.

    Finally, I am behind on so many projects, but one of them was to put a dimple mat on the "dry" (for 6 years) basement floor and 12" up all walls (taped with Siga), cover that with 1" Rockwool ComfortBoard (taped), then plywood, then some type of waterproof flooring; what would have happened if I had done this and then had this flood? Where would the water have gone? [This is no longer the plan, obviously, but I am genuinely curious.]

    1. Expert Member
      BILL WICHERS | | #26

      I wouldn’t recommend using a shop vac to clear drains. You could suck up nasty stuff, or empty traps. A snake is a better option. There are some garden hose accessories that work too, but sometimes they come rocketing out of the drain and make a mess so a snake is the preferred option.

      Floor drains will sometimes be hooked into the sanitary sewer, which would be your septic system. If that’s the case, your septic tank would have to be set below the level of your floor drains. I suppose that’s possible, but it seems unlikely. I’d expect the floor drains to be more likely to drain into a sump pump or drywall, or to daylight as you mentioned.

      I don’t see a problem with the drain backflow preventers, but I’d try to find a proper solution to the problem too — backflow preventers like this are a backup plan, but shouldn’t be considered a “solution”. You should add some rain gutters too, and set things up so that they direct runoff away from your foundation and also away from your septic leach field.


  11. walta100 | | #27

    I think it is unlikely anyone would knowingly connect the floor drains to a septic tank but it is an old house and over time desperate people sometime make poor choices and do things necessary to solve today problem quickly.

    If you decide to spend the money to scope the pipes make sure the person doing it has the equipment to mark the pipes location and depth on the surface above each pipe so you have some chance of understanding what pipe connects to each other and where.


    1. Expert Member
      BILL WICHERS | | #28

      >"I think it is unlikely anyone would knowingly connect the floor drains to a septic tank but it is an old house and over time desperate people sometime make poor choices and do things necessary to solve today problem quickly."

      It may be code. An example: in my area, drains in truck wells on commercial buildings used to be connected to the storm sewer. The code was changed some years back and those drains are now required to be connected to the sanitary sewer. The reason? Truck wells don't just get runoff in them, they can also get oil, grease, fuel dribbles, who knows what else from whatever is loaded or unloaded from the trailer. The sanitary sewer is better able to handle nasty stuff, the storm sewer usually just drains to a waterway somewhere.

      I usually see basement drains connected to sumps (with sump pumps) in areas where septic tanks are installed. There may be some areas with codes that require that the drains be connected to the "sanitary" drain, so the septic system, which is why I mentioned it as a possibility.


  12. jenniferz5 | | #29

    UPDATE and a question: I got another inch of rain in the basement due to a rainfall just following the one above. I used baking soda and ACV on all three drains to clear them out. One still has standing water, but drains well (I'll have it scoped by a professional asap). No more water in the basement since, but the real test will be a heavy rain.

    My new plan is to create a "curb" from the N wall in my basement to just past the floor drains (they run about 3' from the N wall) with cinder blocks. I'll seal the bottom and sides of the cinder blocks, thus attaching them to the floor and each other, with caulk (so that if this doesn't work, I can pull them up easily), and prime them with a "water blocker." Within this area, I'll place a sump pump that drains to daylight (I'm going to snake the hose through one of the holes left in the sill plate by my old oil tanks that are no longer in residence, continuing the hose through the garden and over the side of the hill).

    On the other side, I'll place a dimple mat, then a layer of Rockwool, then Tatami tiles (EVA foam tiles like gyms use). The dimple mat may be overkill, but if a smidge of moisture gets in from the floor it will add a layer of protection. The Rockwool is Comfortboard 80, 1.5" thick, just enough to add a bit of insulation. The Tatami mats are easily removable if we ever have another water event.

    This is a cheap fix, but I don't need fancy and I don't want to spend even more money on the house if I don't have to. The most important question for me is, will this work?

  13. walta100 | | #30

    From my post #27
    “I think it is unlikely anyone would knowingly connect the floor drains to a septic tank but it is an old house and over time desperate people sometime make poor choices and do things necessary to solve today problem quickly.”

    In retrospect I have decided I was wrong and in fact my basement floor drains are connected to my septic system.

    I now think the unusually large rain event you had submerged the drain field of your septic system and the septic system backed up into your basement yuck.

    When was the last time you had your septic tank pumped out? If it has been more than 5 years I think you are overdue.


    1. jenniferz5 | | #31

      Hi Walta,

      I get the septic tank pumped every 2-3 years, whatever is recommended by the man doing the job. It was just pumped early this summer, so I would be shocked if this was the case. However, the water does smell "sewagey."

      The septic tank is on the other side of the home from the floor drains, and is (to the top of the tank) about 5' higher. The drain field is adjacent to the basement, not on the side of the drains (the N side), but is on the W side of the home about 15' or more away from the house.

      I'd love to hear your thoughts.

  14. walta100 | | #32

    Was the flooding in the basement a onetime event or has it happened several times?

    Good to know you have been doing your maintenance.

    Without knowing for certain where the floor drains go to we do not understand what failed and are reduced to guessing.

    If you wanted to open the lid on the septic tank and look inside. You could put tracing dye down the drain followed by 30 gallons of water If the tank turns green you will know the floor drains go to the septic and if something else turns green you will see where the drains go to.


  15. jenniferz5 | | #33

    UPDATE 10/27/2021:
    A local "rooter" company just came out to scope the drains and solved the mystery. The interior PVC drains on the North side of the basement apparently drain into a dry well on the SW corner of the basement. This dry well is surrounded by brick and consists of an iron pipe opening into a square divot in the concrete.

    Due to the recent heavy rain and high water table, the old (1953) dry well can't take all of the water.

    May I:
    a. surround this dry well with concrete blocks, sealing the blocks and their contact points, and insert an automatic sump pump? My manual sump pump is in this area now (see photo).
    b. dig a larger hole around the dry well and install a sump pump?

    Either way, I plan to insert drain backflow preventers in the PVC floor drains that lead to the dry well to atleast slow the outward flow (we used tennis balls and concrete blocks this time and it did help a great deal).

    1. Aaron_P2 | | #34

      That sounds like generally good news to me - at least the septic and those floor drains don't seem to be connected.

      My first preference is to avoid pumps if possible for storm systems as there is more maintenance and potential for failures in those systems. My first thought would be to have the dry well enlarged/rebuilt and designed with an overflow set lower than the floor drain elevation. That way the dry well can typically catch the water and release slowly over time in typical rain, but in heavy enough storms the overflow will ensure it can't backup into the house. I don't know if that dry well location would allow for an overflow to a nearby hill or outfall location to ensure that water doesn't drain back towards the house.

      It would reasonable to have a sump pump (automatic for sure though), but depending on the ground temperature and depth of the dry well and pump piping, there may be winterization steps required. I would also check and verify the operation of the pump, check valve, and other components of the system regularly to avoid issues in the middle of a storm. There should also be backup plans for at least short term power outages (typically battery or generator).

      1. jenniferz5 | | #35

        Thank you for this detailed response, Aaron!

        We do have a whole-house generator that automatically turns on during power failures.

        Since my home was built in 1953, and there was a stacked-stone stairway to a concrete landing built just ouside of the dry well location, I think a well-maintained sump pump system might be my best bet. Since this is obviously ouside of my wheelhouse, I will call in an expert to install.

        Thanks, again.

        1. Aaron_P2 | | #36

          That makes a lot of sense with the whole house generator. It may be pretty simple for you then.

          FWIW, it might be worth looking into a duplex system (two pumps) that comes with a controller and alarm.

          Something like this from Liberty Pumps is what I am thinking, but you don't need the basin if you put it inside the existing drywell:

  16. Expert Member
    NICK KEENAN | | #37

    Is the dry well inside or outside the basement? If it's outside in your climate you might have trouble with a pump freezing in winter.

    I doubt very much that a "rising water table" is actually your problem. Most likely what you're seeing is the surface soil is saturated. The reason this distinction is important is that if the surface soil is saturated a deeper dry well can solve the problem. So can improving runoff management around the house.

    1. jenniferz5 | | #38

      The hole to the dry well is in my basement, but I have no idea where it leads. As I mentioned to Aaron, "Since my home was built in 1953, and there was a stacked-stone stairway to a concrete landing built just ouside of the dry well location, I think a well-maintained sump pump system might be my best bet. "

      The dry well will need to be excavated in order to place the sump pump, but I am not sure what we'll find when we get there. Now that the basement drains have stopped flowing into the basement, I am seeing some puddles in a few areas, so the hydrostatic pressure is still at work. What a mess.

  17. jenniferz5 | | #39

    Another update, thanks to my local plumber. When he came out to give me a quote on a sump pump last week, he said to just plug all of the drains and fill the dry well with hydraulic cement! So, I plugged all of the drains on Friday (before the big rain event yesterday) and kept my little sump pump at the mouth of the (plugged) dry well pipe. [The dry well opening in the floor has missing cement around it, clearly allowing water in.] The basement was DRY except for the little bit of water that came through the area around the dry well!! May I proceed with the hydraulic cement to close up that dry well, or will I be inviting more problems?

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