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We recently raised a dipped section of our flat roof in order to reduce ponding. We're not sure we've raised the roof enough. Here's what it looked like as the rains died down.

Do you all think we need the roof raised here? Or did we raise it enough?

enter image description here

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2" deep puddles on a flat roof are a definite problem, and imply at least 16 feet of problem if the minimum 1/8" slope to drain is to be restored/preserved/maintained. And if that makes new puddles, even more area needs to be fixed.

I'm not clear on your (non-described) process, but this mess seems ripe for building up a proper surface with rigid foam and a new membrane, rather than jacking the roof boards from underneath, if that's what you have been doing.

Regardless of process, the entire roof surface needs to slope at least 1/8" per foot towards the drains. No part of the roof should actually be "flat".

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Yes, we all do...it was just funny how you asked. But, from me, yeah totally. If you can raise it then by all means do so. And/Or, call your roofer who did such a horrible & woefully incomplete job.

You'll have to greatly expand your puddle zone in order to keep everything not only sloped toward the scupper but also toward the center or the line of the scupper. Think of the roof as a sink, shower or tub, but the drain's not in the floor. You MUST have 2 pitches to direct any & all water to that single point.

Now, the raising issue. Of course, shim & re-shim as you raise & until your happy with everything. But, once you feel the job is complete you MUST re-secure the roof with short screws (1/2" if you don't know the thickness) into the roof decking & nails or screws into BOTH sides of the joists.

You should use galvanized bent Mending Plates or L-brackets. You want, at least, as many bracket points as there are nails that you backed out. FYI, the best support would be to cut the nail shanks off with a Dremel & cut full length wood wedges to replace your shims. Finally, glue everything that you can for best re-connection & to also ensure that shims don't fall out over time.

  • This is extremely helpful. – Stephen Callender Feb 25 '16 at 12:04
  • Yeah, losing the water is great, but losing the roof is bad. – Iggy Feb 25 '16 at 12:44

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