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Brian, Architect
Category: Home Improvement
Satisfied Customers: 3123
Experience:  Licensed Architect- 17 years, L.E.E.D. AP
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I want create a deck from a 200 square feet flat roof. The

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I want create a deck from a 200 square feet flat roof. The roof is rubber. and I want to layer sleepers on top of it, and then decking on top of the sleepers. I have a spare roll of roofing rubber. and would put strips of that below the sleepers, to reduce the wear on the roof.

There is a parapet wall, and I could pay a contractor to install beams (joists?) that I could build a deck on top of, and which would take all the weight off the existing roof. But I am trying to avoid that cost. Obviously there are issues with drainage and leveling to sort out, but is it a reasonably approach?


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Customer: replied 3 years ago.

I realized after I posted the question that I had not given enough information. I suspect that I should provide another paragraph of details. Is that the information that your expert is waiting for?


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Yes, it is a reasonable approach. I do this all the time in deck designs. The deck essentially floats on the flat roof; do not secure it or you will get leaks. You will want to taper the sleepers to give you a level top, producing a flat deck. Sleepers should be pressure treated and definitely install a 4" strip under each, to act as a wear layer.

The only concern I have is the size of the existing joists under the flat roof. You need to verify that they are adequately sized to support the extra weight of the deck. 2x10's at 16"o.c. would be nice to see.

You will also need to install a scupper through the parapet. You essentially cut a hole or slot through it and flash it well so that the flat roof can drain. You probably already have one or some other drain that is currently draining the roof; if you do then no need to add anymore drains/ scuppers.

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Brian, Architect
Category: Home Improvement
Satisfied Customers: 3123
Experience: Licensed Architect- 17 years, L.E.E.D. AP
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