Thread: Negative Slope on flat roof

Hi all,

I frequently inspect flat roofs. Very often there is a negative slope, thus creating stagnant water which reduces the lifespan of the membrane.

For a tar and gravel (bitumen) roof, is anyone aware of anyway that the slope can be repaired? What about a negative slope on a "roll roofing"?

Thanks

Zane

Similar Threads:

• 2 Q's on 3 flat
• flat to pitch transition
• Flat roof, stucco headwall, and flashing details
• No slope to floor drain, 2nd story.
• Commercial: Stucco interface with flat work

Originally Posted by Zane Remenda

Hi all,

I frequently inspect flat roofs. Very often there is a negative slope, thus creating stagnant water which reduces the lifespan of the membrane.

For a tar and gravel (bitumen) roof, is anyone aware of anyway that the slope can be repaired? What about a negative slope on a "roll roofing"?

Thanks

Zane

.
One Way When it Rains it Pours – Roof Drains Explained

Reverse slopes can be corrected, but it is a bit expensive as they would need to cut the roofing back, install tapered roof insulation, then re-roof.

That area looks like a perfect spot for a roof drain.

That's a very saggy roof! How old is the building? I'd be concerned about unseen leaks that have compromised the roof structure. When full of water there would be enormous weight on the center. Is that a roof drain I see in the foreground, the rusty pipe sticking up a little? That would definitely be the way to go. Otherwise if you raise the middle you're looking at reroofing the whole thing, since it's tar and gravel.

Roll roofing shouldn't ever have a negative slope, it's not designed for flat roofs. But to increase the slope the repair Jerry suggested is suitable.

Its not all that uncommon, difficult to always get a positive slope, and could be difficult to correct. Likely easier to put another drain in.

I am surprised we don't see more pond pumps on roofs like that. The pump drains the puddle thru a drain hose and then shuts off. They are apparently common in jolly old England, where flat roofs are a curse.