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waterproof deck

TLJ | Posted in Construction Techniques on January 11, 2004 06:09am

Has anyone had any experience with a walkable deck surface over a finished, climate-controlled living space?

I have a customer who wants to add on 12′ x the length of the house for a screened-in porch on the upper level and finished living space below. There are numerous products available online, but I need more info. All input would be appreciated.

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  1. alwaysoverbudget | Jan 11, 2004 06:45am | #1

    i'm pretty sold on edpm rubber, then place some runners down that have rubber glued to the bottom of them and start building from there.i've got this on my home and it works great. i do wonder 20 years from now how to replace,but we'll cross that bridge when we get there.larry

  2. nwilhelm1 | Jan 11, 2004 03:28pm | #2

    EPDM is an option. First consideration will be type of finish spec'd for floor of exposed upper level. Once this finish is decided, appropriate waterproofing materials can be selected. Please note that if joist are framed at say 12" O.C., you might consider shortening to 10" O.C. to minimize any lateral movement. Any movement will, over time, have an adverse effevt on the waterproofing system.

    Best Regards

  3. slykarma | Jan 11, 2004 05:50pm | #3

    There is a heavy duty vinyl system out there that is an attractive deck surface as well as code-approved roof membrane. The one brand I've have experience with is Duradek <http://www.duradek.com/>. This is a Canadian product but I'm sure there are other manufacturers in the north wet (its not all cedar here, y'know). They have dozens of colours and textures.

    Prep is pretty straightforward. Min. 5/8" plywood sheathing over joist system with 1-1/2" cant strip at the base of all walls and 1x2 nailed along rim joist for drip edge. Then the Duradek is applied with glue and rolled down. Duradek must be applied by a licenced applicator to get warranty, can't speak for the other brands.

    This product has become a standard material option here in BC and is quite commonplace for decks, even where ther is no living space below. I have even seen it used as a membrane over a condo parkade suspended slab to keep out water from landscaping above. Very tough and not that expensive.

    Your other option would be to use torch-down or other rolled roofing product as a membrane over framing and sheathing, then put down sleepers of cedar or that new plastic wood stuff parallel to joists, then conventional decking of your choice over that perpendicular to sleepers.

    Lignum est bonum.
    1. TLJ | Jan 12, 2004 07:02am | #4

      Thanks guys for all your suggestions. The Duradek looks like a reasonable option. There are a number of installers in the ST. Louis area. I'll check them out.

      I appreciate all the input.

  4. davidmeiland | Jan 12, 2004 07:07am | #5

    I've done a couple of decks over modified bitumen roofs. The framing is basically just sitting there on the roof, not connected at all, and we built both in small enough sections to pick up and move (long narrow sections) so that cleaning and repair could be done. I remember that one inspector wanted very tight gaps between the decking so that hot cigarette butts couldn't fall down and melt the roofing.

    1. TLJ | Jan 13, 2004 03:23pm | #6

      David, thanks for your reply. The main difficulty I'm facing with building a walkable surface over a waterproofed deck is accomodating the total thickness involved. Because I'm looking at adding on a two story addition to an existing two story structure, I'm limited in how thick the between-story floor structure can be. Add to the thickness the slope required to drain the upper deck, and I've got a total floor thickness of maybe 16" or more. That would represent a considerable loss of headroom below. There exists now a ceiling height of approx. 7'6" in the lower story (it's a finished basement). If we go this route, we'd have to drop the floor of the lower story 7". It's a possibility.

      1. davidmeiland | Jan 13, 2004 06:43pm | #7

        You could use something like Gaco, which is a walkable membrane and goes right over the subfloor with minimal buildup. It's not the most aesthetically pleasing stuff, and it would mean your walking surface would be sloped. You could also do a waterproof tile install that would add approximately 1-1.5" and probably also be sloped. The decks I described were 1" mahogany decking on 2x4 sleepers laid flat and so were 2.5"+ thick.

        1. TLJ | Jan 13, 2004 06:53pm | #8

          I'll check into that, thanks. It might serve the same function as the Duradek mentioned above.

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