Roof drain sumps / tapered insulation

I would be having 2% slope everywhere, not just 4 feet from the drains.

It depends on the code (of course). What code is enforced in the project's locale? Do you have a copy of it?

Generally, flat roofs are either discouraged or disallowed due to ponding and roof maintenance problems. I believe the IBC has a 1/4" per foot minimum slope for smooth membrane roofs. (This is for the entire roof, not just in the vicinity of the drains.) If you have internal drains, that itself brings a whole additional set of design parameters involving secondary drainage and local ponding at the drains. It's not as simple as "How much slope do I need around a drain?"

IBC 2018 ,

Thanks for the reply thus far. I agree that flat roofs are discouraged and we will typically want to put a 1/4:12 slope in the roof. Where I'm unclear on is when there are internal drains, are sumps required at internal drains? Let's say there is a monoslope roof that is sloped 1/4:12, would it be acceptable to use crickets on either side of the roof drain to divert water into the drain since there is already a 1/4:12 slope allowing water to flow downward? Take this image for example, does this need an additional sump? It looks like it can meet Section 1611.2 (thanks HTURKAK) without one.

No idea on the sumps - I leave that to the architect. I do know that secondary drains are not to be installed in sumps, though.

Your image there is NOT a point of free drainage. Free drainage is typically an edge with a certain length relative to the tributary flow area with no obstructions (no parapets, etc.). Internal drains and scuppers that don't meet the length requirement are not considered free drainage as they are susceptible to blockage/clogging.

At least flat roofs are not discouraged in my zone and moreover ,it is common detail to use with warm roof over large areas..The detail that you have posted is also typical for cold climate so the rainwater downspouts and inlets will not get freeze. My past experience is , ( the slope is provided by structural frame and typical flat insulation ( rockwool ) is laid over the deck ..The sides are provided with tapered insulation to get a drain swale and necessary number of roof gullies provided ).

This one was done in a similar to nearly all buildings I've done where alternate lines of steel beams are raised or lowered to provide about 1-1/2% minimum slope. The spaces in the 'valleys' are built up using rigid insulation to provide slopes to the area drains.



You can just see a bit of an image of the drain areas. Added: I never leave the roof drains to the architect. The tapered insulation needs to go from 1' width and 0" thick at the drain to 8' or 12' wide and maybe 4" thick at the wide part.

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