How should this TPO roof downspout have been handled?

This is a commercial roof.

As far as I can tell the water will all enter the wall, until the volume is high enough that some can find the downspout. How should this have been done?

While I can refer this to a roofer and will, I suspect they’ll just use caulk and rosary beads, and call it done.

Doesn’t appear to be flashed in properly, so recommend a qualified roofer to repair it.
Seems like that should have been an open scupper in lieu of an unprotected open drain without a debris bonnet.


I agree with @mcyr

Here is a pre-fab version. Whether pre-fab or fabricated in the field, the TPO should have been flashed over the edge of the scupper.


A “qualified roofer” simply caulked the gap on the other two similar downspouts.
Caulk seems insanely risky for this application, which is why I’m posting.

The roof has zero scuppers, two roof edge overflows, and three mid-roof downspouts. Each mid roof downspout is similarly constructed. Two have caulk in the gap, one is just open to the air as pictured.

Ah, but that one can’t be used, because that’s for a wall scupper, not for a toilet style downward drain.

Why did they use a downspout? Likely because that’s where the original tar and gravel roof downspout was, in this 1940’s building.

A round TPO downspout is:
Anyone seen a square version of this used in the field?
Have a picture of a better way to do this?

The other issue with the prefabricated units is they end up leaving water puddles.
This is an old school wood decked roof, not a more modern foam insulation base. With the foam you can carve the foam to create the drainage pattern needed.

The should have added a new substrate in my opinion. You can’t just slap TPO onto anything. How did they fasten it? I can see loose pieces over that transition. I would be surprised if the roof would stand up to any type of manufacturers warranty.

And this is just amateurish.
I would write hard.

As far as a prefab drain, they probably make it, but it does not matter. You can make this in the field. You can also buy prefab corners.

I’m sharpening my keyboard now for the report.

The roof is springy, feeling like there is a foam layer below, but there is not. It feels like it is not really attached much at all except maybe at the edges.

It’s close to 8000 square feet.
According to PF Data Server-PFDS/HDSC/OWP
The NOAA " Precipitation Frequency Data Server (PFDS)" and

The 10 year frequency is 2.7 inches per hour.
There are three 3x4 inch downspouts, and two 3x4 inch overflows.


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You can use wood decking. But it is hard to get proper slope or contour for drainage. The covering must be ballasted, mechanically fastened (12" on center at seam) or fully adhered.

And you are evaluating drainage, which is good. Go get 'em, looks like the customer got screwed.

The old decking is likely rough cut 1x10 boards, installed in skip fashion (or installed butted to each other, but shrunk in the last 70 years). Gluing to that is unlikely :-).

To add to the cake, the leaking downspout leads to an enclosed porch like structure subject to California’s EEE inspection (remember the Irish students in Berkeley CA that fell to their deaths after a balcony failed — this is literally three City blocks away from that site).

To add to the cake, the owner JUST finished refurbishing ALL the stucco due to dry rot, without identifying this as a likely source of the rot in the first place.