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Community and Q&A

Vapor Barrier Construction in an Indoor Pool Room

rooby | Posted in General Questions on

Hi all. I am building a two-story addition onto my house with an indoor pool room on the ground floor and living space above. The location is in Park City, Utah, climate zone 6a. We have been searching for experts on vapor barriers in wall/ceiling construction around the pool room and specifics about what type of vapor barrier to use, how to vent (or not) the walls and ceiling of the natatorium and how to mount the support beams, interior wall surfaces and ducts without penetrating the vapor barrier. I would love any tips on the above and/or leads to expert consultants.

A few details about the space: The room is about 20’x40′. We will have a pool cover, desiccant system, negative pressure and climate controls to keep the air temp slightly higher than the water temp. We have a water wall feature that will not run continuously, but creates additional humidity while running, which has been accounted for in our dehumidification calculations. The ceiling will have air ducts recessed into the joints, creating a crenellated ceiling surface that must be vapor sealed. We will then cover the ducts with a drop ceiling of treated cedar planks that will be vapor permeable. We will also have exposed steal I-beams to support the structure above. We had planned to have Venetian plaster walls, but are flexible about exact material. One wall will be an interior wall connected to the rest of our house, while the other three walls are exterior walls exposed to the hot air in summer and cold, snowy weather in winter.

We have contemplated a 20mm plastic liner vs a liquid applied vapor barrier (like Rad Guard or epoxy paint). I am unclear if the plastic liner will work in a crenellated ceiling, if a liquid applied vapor barrier can be applied to a ceiling at all and most of all if there is a preferable material for this purpose. So question #1 is what is the best material for us to use as a vapor barrier?

Whatever vapor barrier we use, we will have to install and somehow seal some kind of brackets over or within the barrier for attaching our ducts, ceiling and wall materials. We plan to use stainless screws for the I-beam and will likewise need to seal the screws and mounting surfaces of the I-beams. Question #2 is how to attach these wall and ceiling surfaces and support beams in a way that does not penetrate the vapor barrier.

I have been reading a lot about the need to vent the walls, ceiling to remove any vapor that slips past the vapor barrier to protect the walls and the rest of the building, but it is unclear to me how to do this. So question #3 is how to create the proper air flow or air tight environment within the walls and ceiling of the pool room.

Our contractor has built several indoor pools, but never had success with the vapor barrier construction. The same goes for several other builders and architects we have contacted in our region. It appears that no one here knows how to construct a successful vapor barrier. Any ideas would be very, very much appreciated!

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  1. MartinHolladay | | #1

    You're barking up the wrong tree. You don't need an interior vapor barrier.

    This type of room absolutely, positively, needs a bulletproof air barrier, as well as an adequate continuous layer of insulation, on the exterior side of the structure (in other words, continuous insulation on the exterior side of the wall sheathing). Just so we're clear: all of the insulation needs to be on the outside of the structure. If you have living space above, you'll need some type of double floor -- or you'll have to install horizontal SIPs above the floor underlayment (above the pool ceiling).

    Good luck.

    1. rooby | | #2

      Thank you for your fast reply! It has been our understanding that we need both the vapor barrier on the inside to prevent moisture from getting out of the room and into the walls AND an air barrier on the outside. How can we keep moisture out of the walls from the highly humid pool room without a vapor barrier? Regardless, what materials would you suggest for the air barrier and insulation? Thanks so much!

      1. MartinHolladay | | #5

        Q. "How can we keep moisture out of the walls?"

        A. Your interior air always contains moisture, whether the room has a pool or not. This is normal. It doesn't cause problems unless the water vapor in the air (which always exists) condenses and turns to liquid. If you install continuous exterior insulation, there will be no cold surfaces where condensation can occur.

        Q. "What materials would you suggest for the air barrier and insulation?"

        A. Lots of options exist. Taped Zip sheathing makes a good air barrier. Insulation options include polyisocyanurate and semi-rigid mineral wool panels.

        1. rooby | | #8

          Thank you, MartinHolladay! I really appreciate your recommendations!!

  2. paulmagnuscalabro | | #3

    If you haven't already, you might check out this article from Building Science Corporation:

  3. rooby | | #4

    Thanks, paulmagnuscalabro! I have seen this, and it is one of the most helpful posts I've read about this topic. I'd still love some more specifics on the construction and materials, but that may be wishful thinking, as not many people do this kind of building. :)

  4. walta100 | | #6

    Seems to me you need an expert in this tiny niche.

    The few experts there are unlikely to hang out on this forum and dispense free advice. Even if you get some free advice, it may not be worth what pay for it. I think if you can afford to operate an indoor pool the expert is likely to cost less than a few months of the electric bills for heating and dehumidifying.

    My guess is there will be lots of large windows and when it is zero outside the surface temp of the glass will have will keep the indoor humidity below 60% and lots of water will be dripping off the windows so plan ahead and install drains.


  5. rooby | | #7

    Thanks, Walta -- we do indeed have lots of large windows, and condensation there is a big consideration. You're also right about me needing an expert. I'm very happy to pay for expertise, and have reached out to several consultants, builders and architects, but haven't yet found anyone who can help me. That's why I turned to this forum, (which has been so informative to me over the past few months!). If anyone out there knows of an expert in this arena, I'd very happily take your recommendations!

    1. paulmagnuscalabro | | #10


      Re: consultants
      I'd recommend reaching out to Kohta at Building Science Corporation. BSC is definitely one of the best building science consulting firms out there, and if they've got the bandwidth to take on your work (everyone is so busy right now) they'd be a huge value-add to the team.

      Re: Lots of windows
      It'd be worth considering triple-pane windows (highest quality you can afford). You may not ever make your money back in ROI, but at least they'd be less likely to fog up.

      1. rooby | | #11

        Good suggestion, paulmagnuscalabro. Thank you!

  6. Expert Member
    Akos | | #9

    I'm wondering if an HRV would make more sense for humidity control than a dehumidifier in cold climate. I guess the one benefit of a dehumidifier is the heat generated plus the latent heat of condensation goes to heat the pool area.

    Quick google says there are commercial pool HRVs (ie Lifebreath 700 Pool), they are actually reasonably affordable.

    1. rooby | | #12

      Thanks, Akos, I will look into that!

      1. Expert Member
        Akos | | #14

        Did find this:

        I like the hvac supply detail above and bellow the windows to keep them clear.

  7. frankcrawford | | #13

    As far as products using the directionally smart (variable) SIGA majrex vapour barrier material and tapes, installed as a combined air and vapour control layer would be a good option.

    Small planet supply sells it out of Washington state. They also have a lot of experience installing and detailing it.

    Perform a blower door test when the air control layer materials are accessibly so errors and gaps can be repaired.

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