Hello I have wood balcony that I made by making my first floor longer then my second floor, so basically my balcony is unfinished uncovered part of my second floor and fenced all around. In any case, I need help finding flooring material for my plywood based balcony terrace. I used a blow torch to lay down a bitumen roll, which is works and makes my first floor waterproof, however, when I put outdoor furniture it makes holes in the bitumen floor/roof and looks ugly as balcony flooring. I tried putting down luxury vinyl plastic floor planks on top of the bitumen, but then water and moisture accumulates underneath the vinyl floor planks.

Please help. A neighbor contractor suggested that I pour cement on the balcony and tile it. But I don't think cement and tile is 100% waterproof and could leak down on my first floor. Second, I have concerns with the weight of all the cement and tile bearing down to my first floor.

At Lowes and HD I've seen Trex composite deck flooring planks, which sit on four rails. Perhaps this will work? since the water and moisture can run down between the rails on these composite trex decking planks?

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    A picture would be super helpful.
    – MonkeyZeus
    Commented Mar 28, 2022 at 17:32
  • I think a deck is the way to go, but just comments since I've never done this myself (I've built a deck but not on top of a building). My gut feeling is you want to have maximum drainage from your floor onto the bitumen - i.e., not something solid/nearly solid (like planks) right on the bitumen because then water would get stuck and not drain properly. A deck, even if this cases just a few inches high, uses just a few supports so if they are arranged properly nothing blocks drainage and relatively few places to worry about puncturing the bitumen. Commented Mar 28, 2022 at 17:47
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    Without more detail, a random suggestion would be wood sleepers aligned with the fall of the floor (to allow water to drain), supporting some sort of wood (or wood-like) decking material. Also, be sure to carefully & thoroughly repair any damage already done to the roofing, as you don't want to hide the damage below the decking and let water slowly seep into the 1st floor ceiling.
    – FreeMan
    Commented Mar 28, 2022 at 17:48

1 Answer 1


I've rebuilt such rooftop platforms. This type of situation is known to be troublesome. It's very difficult to waterproof nearly flat areas and keep the lumber underneath dry enough that it doesn't rot. If you have managed to do that, a floating wooden deck is a common strategy.

Cut tapered, pressure-treated sleeper joists to match your slope. If the surface isn't flat, you'll need to pull string lines and take periodic measurements so the deck ends up flat. The sleepers need to be fully supported as they probably won't be tall enough to span between shims, for example, and you want the weight distributed as evenly as possible.

Look for any pressure points on curved flashing, etc., and round the lumber to match. Those are the points that will wear through first. Consider laying strips of scrap membrane under each sleeper as extra protection.

Then install common decking. Be sure that your screws don't punch through the roofing. If your sleepers will be very short in the vertical you may need to assemble your deck panels upside-down, screwing through the sleepers into the decking.

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