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Community and Q&A

Decomissioned Pool With Floor Covering

tuckerson | Posted in General Questions on

We have a house with a large addition that at one point had a gunite pool installed in it. Subsequent owners decommissioned the pool and had a floor built over it and appear to have been planning to use the space as a master bedroom. We would like to make the large room our kitchen/living/dining area but what to do with the pool is the first big issue to work through. There is always a small amount of water in the deep end around a drain that someone appears to have tried to seal. I suspect hydrostatic pressure, but I’m not positive. I wet-vac’d all the water out one day and checked some days later and the water was back. The amount seems fairly constant. Meanwhile, I’m planning to replace all interior insulation in the room and add exterior insulation and siding, hopefully for a pretty airtight enclosure. I’ve had a few suggestions including putting in a sump pump, adding more concrete to the deep end to seal it, and of course, filling the dang thing in. I would love to avoid filling it in if at all possible not to save the pool but to save money. The pool is sound and clean other than the puddle and it could have storage potential (or a panic room as many have suggested!). Any ideas for a practical way to keep the water out and remove the moisture problem that doesn’t require a total fill-in? Zone: 5A

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  1. tommay | | #1

    Take off the drain cover and put a test plug in the drain pipe.....

  2. tuckerson | | #2

    Thanks for the idea. One issue is that the drain was already “sealed” with some sort of cement-like compound. See photo, which I just took after removing the water again. Looks like it was meant to be a permanent fix. Guess I could try adding another layer.

    1. maine_tyler | | #3

      You may be better off cleaning out what there and setting some hydraulic cement or other sealant deeper in the hole, rather than a skim seal.

      It seems like investigating where the drain leads would provide some clues. Tough to tell what's going on from on-line. If it seems to be ground water, perhaps treat it as a basement with similar water entry remedies used for basements.

    2. tommay | | #5

      If you can, try to monitor the area to see if that is where the water is truly coming from. If it is, break out the old concrete to see what you are dealing with, then either a mechanical plug or hydraulic cement as Tyler mentioned.

      1. tuckerson | | #7

        I'm not in a huge rush with this project, so I like the idea of doing some more investigation as you and Tyler are suggesting. I'll report back.

  3. MattJF | | #4

    The safest option would be to fill it, pour a slab and move on from there as a normal assembly.

    Keeping the pool there in some form basically makes it a basement. The question is, “Is your pool a good basement?” I don’t think anyone here can answer that as there are a lot of variables. I would suggest you define how you might want to use it and then get an engineer to sign off on the plans. The main reason for this is that if anything weird happens with it, you don’t want insurance to deny the claim when your kitchen ends up in the deep end. I think you are well outside the bounds of much of the prescriptive code.

    Something basic I am curious about is how the floor was installed. Is it joists resting on the pool deck/slab and then flying over the pool. I would not expect the edge of the pool to be designed as a footing. I think the joists would likely need to rest on sleepers a set distance away from the edge depending on the slab thickness.

    The more I think about it, vapor and condensation management are a real challenge with this assembly. This is in addition to the current bulk moisture issues you are having. Unless the slab and pool happen to be insulated, there is a risk that they become a condensing surface beneath your floor. This becomes more of a problem if you add air permeable insulation In the floor. The ideal solution is foam board or spray foam against the concrete, just like any basement/slab assembly. Yours just has weird curved walls and maybe floor joists sitting on the slab.

    A vapor barrier is also good to have below or above the concrete, I don’t know much about how a pool is constructed.

    How has the current assembly done so far? I would start monitoring dew point and temp.

    Depending on the existing setup and your energy, comfort, and resiliency goals, filling it may make a lot of sense.

    The real answer is, tear the floor out, skate the pool and put the kitchen elsewhere.

    1. tuckerson | | #8

      Thanks, Matt—that's the first time making it a little skatepark has been suggested. I'll add it to the list.

      I took some pics of the floor assembly, attached. It is not a flying floor but 2x12s connected to joist hangers connected to 2x12 ledger board, with an additional run of PT wood between that and the concrete. An AdvanTech subfloor sits on the joists.

      Apart from the persistent puddle in the deep end, I haven't noticed any other issue with the pool structure itself such as cracks.

      Great thoughts on vapor/condensation management. I've had an inspector mention it will be all the more of an issue if I proceed with exterior insulation, air sealing, etc. the room above.

      1. MattJF | | #11

        Interesting, I hadn't anticipated that the floor was installed with the pool. Was this assembly originally inspected? If it was, check what the your building file to see how they justified it. I would think this needs engineering sign off.

        I don't know much about pool construction, but the original intent of pool structure was not to have a floor installed there. Gunnite is apparently stronger than standard concrete, but he shape of the wall isn't ideal for a footing.

        1. MidVids | | #13

          The previous owner of our house left me with 2 quotes for work to put a floor over the pool. The plan was to raise the floor as the pool room is 12" lower than the main house. 1 quote was to place joists over the pool (and whole room) without any other supporting structure so the joists would be sitting on the concrete slab of the room. The 2nd company was going to put sono tube supports through the slab and hang a steel beam across the length of the pool and then hang floor joists from it. So it appears that the 2nd company was thinking that the slab shouldn't carry the weight of the floor.

  4. MidVids | | #6

    Hi Michael - so interesting to see your question as we are up against somewhat of the same challenge. We have recently purchased a house with a 1200 sq ft wing that had an indoor pool that has been "decommissioned" in the broadest sense of the word. The previous owner started to fill it in with sand. Ours was a vinyl pool. We have to figure out what to do to complete the process and prepare the room for future use or as the real estate agent said "just tear it down as it's a liability not an asset in it's current state". I sure would like to private message you to discuss or commiserate going forward. I can't find out much on the web on what to do. Scott

    1. tuckerson | | #9

      Sounds good, Scott. I don't see how to do that here, but I'm also still in the trial mode, so maybe I haven't unlocked PMs?

      1. MattJF | | #10

        Their forum software doesn't support PMs. Might be best to direct each other to another forum with PM's or ask one of the editors to help you out.

        1. MidVids | | #12

          Thanks Matt - I'll reach out to the editors next week. It's Thanksgiving weekend here in Canada so busy cooking the turkey!
          Michael - I'm also on the 10 day trial so we'll have to figure it out soon. Just for fun here is the current state of our "pool"!

      2. MidVids | | #14

        Michael - I'm not seeing any easy way to privately post our email addresses. I do have a Linkedin profile that you can search me by if you are also on there. I don't have any other social media accounts but my daughter says if you have FB she can search you there perhaps.
        Sorry to the other members who are getting pinged on this while we sort it out.

        1. MidVids | | #15

          I didn't get the normal email that my reply was posted so bumping it again. If we don't connect good luck with your project Michael.

          1. tuckerson | | #16

            Hey, Scott, I think I found you. Check at LinkedIn.

  5. kornhusker | | #17

    Hi Mike and Scott. I see you continued the conversation off this site. I would love to connect and see how things went. I am having the same problem. I purchased a house that had covered up an indoor pool and made a beautiful great room over it. Problem is, moisture destroyed the joists and subfloor so I am having to remove everything 10 years after purchasing the home! I am unsure the best way to fix the moisture problem before rebuilding the subfloor. Any info would be greatly appreciated. Thanks

    1. EauBoy | | #18

      Hi Kornhusker - Scott here. Not much has happened on my end but I'm getting ready to move forward. I'm very interested to find out why your joists rotted.
      This forum does not provide for private messages so we didn't exchange emails here but found each other on LinkedIn and did there. If you have it you can search for me (Scott Vidler- EMS Support Engineer) there and we can exchange emails addresses.
      Look forward to hearing from you.

    2. EauBoy | | #19


  6. hunterguy | | #20

    Hi Michael, Thanks for sharing... I am facing a similar issue here like others have posted. Very interested to know what you ended up doing (if anything) to make a kitchen/great room work on top of the pool.

    I think the obvious solution is to fill it in, but I have had a hard time finding details on how to properly do that. The wooden floors is an interesting solution because you could rip those out if a future owner actually wanted the pool.

    Would love to connect with anyone here in a similar situation! Seems like LinkedIn is a good way to find people.. you can find me at Hunter Browning-Smith on LI

  7. user-6824483 | | #21

    An empty gunnite pool becomes like a boat if you completely seal the drain. Rising ground water can "float your boat" in the Fall/Winter after dry summer weather. This can cause the pool to rise up causing structural damage unless the gunnite is anchored very firmly.
    I have a similar indoor pool but with a vinyl liner and concrete side walls. The pool floor beneath the liner is a porous cement / lime mixture. I once left the pool empty and the winter ground water floated the liner upwards about three feet until i refilled the water. In the summer the pool floor was dry.
    I didn't expect to see the ground water table rise that high during Fall/Winter because my house is on a hillside and the soil is sandy.
    My pool has no ground tile drainage and there is sandy hard-pan about three feet below grade forming a pool
    My pool floor is six feet below grade so I had three feet of ground water below the liner.
    I am planning to decommision my pool and build a floor over it.
    I may use precast concrete beams or corrosion proof steel trusses above a vapor barrier, with galvanized fasteners.
    See the GBA article on "concrete free crawl spaces" for good ideas on reliable vapor barriers. Any dampness/vapor will soon rot wood in an unventilated space.

  8. user-6824483 | | #22

    Some concrete pools have a hydrostatic relief valve which does allow ground water to flow up into the empty pool.

  9. user-6824483 | | #23

    Some other stray ideas I am considering (for comments/discussion):
    Use Insulated Concrete Forms (ICFs) to build columns or a centre support wall to stiffen the floor beams at the centre of their span.
    The forms could sit on a PT plywood (or other) base on my vinyl liner (or gunnite), or on sonotube footings with lateral bracing to existing concrete walls, top and bottom.
    Or maybe run sonotube concrete up to a center span lintel?
    Seems that the pool floor/subgrade should be well compacted/preloaded after many years under six feet of water -and it was compacted originally?
    I expect the vinyl liner will need replacement if I ever revive the pool.

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