Waterproof Your Flat Roof Deck
Waterproof Your Flat Roof Deck The biggest mistake homeowners make: building a beautiful roof deck-wood planks, planters, string lights-directly on
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- Service Area: Brooklyn, NY
Either way the boards are the cheap layer. We tell you up front which kind you've got and what comes up to reach the leak, so the cost of putting the surface back is in the number before we start, not added after.
It depends on how the floor was built. Pavers on pedestals and floating tile lift straight up and go back down after, so the membrane underneath can be repaired or replaced without scrapping the surface. Wood decking screwed to sleepers usually has to come up, because the fasteners and the framing sit right on top of the part that needs the work.
A roof deck has to seal like a roof and carry weight like a floor, and those two jobs pull against each other. Foot traffic, furniture, planters full of wet soil, a hot tub or a grill someone added without checking the load, all of it presses on a membrane built to shed water rather than take a beating. So the roofing gets specced for how the deck is used, not just for the weather. FlatTop works flat and low-slope roofs across Brooklyn every week, and a good share of that is the usable kind: brownstone terraces, rear balconies, and the common roof decks over apartment and office buildings that tenants are out on all summer. We read how a deck gets used before we pick the membrane and the surface, because a deck walked on daily fails in different places than a roof nobody touches. FlatTop is licensed and insured in New York and certified on the membrane systems these decks get built on.
A deck that gets light use can sit on the same single-ply we'd put anywhere, an EPDM or TPO sheet with pavers floated over it on pedestals so feet never touch the membrane. A deck where people walk directly on the waterproofing needs a surface built to be stepped on. A fluid-applied urethane like Tremco Vulkem or a Sika deck coating goes down in one piece with no seams to step on and wears like a floor. Over a structural slab on a busy terrace, hot rubberized asphalt such as American Hydrotech 6125 buries the waterproofing under the wearing course entirely. We spec which one fits your deck and your budget instead of defaulting to whatever installs fastest.
Every railing post, door threshold, drain, and hose bib on a deck is a hole in the waterproofing, and the deck lives or dies at those holes. We set railing posts in surface-mounted bases bolted to blocking and flashed over, or run the membrane up a curb the post sits on, so nothing penetrates the seal raw. Door sills get a metal pan flashed into the membrane and turned up behind the frame, high enough that water standing at the threshold can't reach the inside. These details are slow, and skipping them is what makes a deck leak at the first hard rain.
Water that gets under a paver deck still has to reach a drain, and a deck laid dead level just holds it against the membrane the same way a bare roof would. We build the fall in under the surface with tapered insulation or sloped sleepers so the waterproofing sheds toward the deck drains and scuppers. Pedestal systems help, since the open space under the pavers lets water run free to the outlet while you stand on a level floor above it. A clear path off the roof is what keeps the membrane from sitting wet through every Brooklyn summer.
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Tell us what you're dealing with: a deck that's leaking below, a balcony you can't trust, or a bare roof you want to turn into usable space. A few photos of the surface, the door, and the railing get us started from the ground.
We get up top and read it. The waterproofing under the surface, the door sills, the railing connections, and how water leaves the deck. On a leak we lift the surface and flood-test the details until the opening shows itself. On a new build we check what the structure can carry.
You get it written out: the membrane or traffic coating, the flashing at every penetration, any drainage or slope work, and what it takes to put the surface back, each line priced on its own. Anything structural that needs an engineer is flagged right here.
We seal the roofing layer, flash the posts and the threshold, set the pavers or decking back over it, and water-test the finished deck before you walk on it. The before-and-after photos are yours to keep.