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Community and Q&A

Water Intrusion During Construction

midnightgreen | Posted in Green Building Techniques on

I’m building a 12′ x 16′ backyard office and am considering using the method of construction of the foundation/subfloor I read about in this article:

However, I am wondering about how much of an issue rain would be in the time between finishing the floor, and building a roof etc that can protect against water. For example, it would seem that any amount of water that falls on the flooring could be bad as it would fall down between the subfloor panels and into the joist cavities, with no means of further escape. It seems reasonable enough to cover from water before any walls go up, but I worry about the stage where there is some framing on top, but uncompleted, which may be difficult to seal from water intrusion.

(As a second non-related question about this foundation, I don’t understand why they have a fully boxed out beam system, rather than just 3 beams on the piers… It seems they do almost nothing structurally…)

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  1. Expert Member


    I think you have hit on the Achilles heel of a number of the building assemblies we discuss here - that they are very vulnerable during installation.

    I'm in a similar position, having agreed to build a 400 sf recording studio, which has a pier foundation, with the underside of the floor 8" from grade. For various reasons the framing didn't get done during our long dry summer, and I have now told the client I am not willing to start until the spring, as I am not confident that any measures to keep the floor dry will be successful. My feeling is these close to grade floors, which rely on being pre-insulated, are pretty delicate to start with, and the risk of damage if they get wet is too high.

    That said, a few years ago I did manage to build a much smaller 100 sf bunkhouse with a similar floor assembly during inclement weather. In that case a pond liner was cheap enough to provide protection - and ended up as the underlayment for the engineered wood floor.

    To avoid the the complications of either jacking everything up and working from below, or building the floor upside down and flipping it, this project has what seems like a practical solution:

    1. midnightgreen | | #2


      Thanks a lot for the link. Their method is quite interesting.

      When you used the pond liner, did you frame the walls on top of the liner? And then trimmed the excess exterior liner material eventually?

      My loose plan was to temporarily cover the finished floor with 6 mil poly, prepare as much as I can of the framing next to the site, and then look for a good stretch of dry forecast to try and hotfoot it to get a roof on.

      Good luck with your recording studio project.

      1. Expert Member
        MALCOLM TAYLOR | | #3


        I laid the pond liner over the sub-floor, framed the walls, but when the project was at lock-up, rather than cut out the liner, I realized it was a nice soft underlayment for the floor, and left it in place.

        Watch that 6 mil, it's really slippery. Like being on skates!

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