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Grebus 09-30-2007 05:56 PM

Adding downspout to torchdown roof
I have a torchdown roof with built-in gutters. One side of the roof only has one downspout in the middle, and water is pooling up at the ends of the gutter instead of draining into the middle. I'd like to add downspouts at both ends, but I'm not sure how to do that. Can I just cut through the membrane, drill a hole in the sheathing and add some sort of scupper to attach the downspout to? Thanks in advance...

Ed the Roofer 09-30-2007 06:29 PM

Before I comment on your situation, it would be helpful to attach some photos to your next post.

Also do the same at the other forum I saw that you posted the same question.


Grebus 10-01-2007 11:56 PM

5 Attachment(s)
Here are some photos:

Ron6519 10-02-2007 07:11 AM

I would think that was specialized work to get it right and alot of effort for a little pooling of water. The roofing industry might have a filler compatible with the menbrane you could use to level the area. If the roofing guys don't pop in, you could go down to the local roofing supply house with the pictures and inquire there.

Ed the Roofer 10-02-2007 12:13 PM

The best way to add a drain in the low spots, would be to create a sump, where the entire roof section for 3" X 3" is recessed slightly lower than the rest of the roofing materials.

The sump pan would have to be stripped in with successive courses or plys of roof membrane. Since this wil be getting done after the fact, you will wind up with seams facing the flowage of water towards the new drain, which is not good nor adviseable. Also, due to the stripping in of new plies onto the sump pan and the drain bowl and clamping ring, the elevation will be risen slightly around both the sump pan and drain bowl with locking clamp down ring.

If their is a recovery board or insulation board undwr the existing roofing material, then you can take a sawzall or keyhole knofe, (drywall knife blade), and cut the roof materials around the exterior perimeter of the drain sump pan on a bevel to create a slope to minimize the lifted elevation which will occurr when the new materials get stripped in.

If there is no board under the roof material, you will definitely still wind up with high spots preventing proper and efficient drainage.

It is not an easy task and requires actual built up and modified bitumen roofing skills to do this properly.

Also, it looks like their is at least one exposed nail on the cantilevered portion near the exterior wall, just under the white cap metal. All exposed nails should be patched to seal for future leak possibilities.


Grebus 10-02-2007 12:45 PM

Thanks for the replies. I wanted to get some feedback on the amount of ponding in the pictures. The pics were taken in the afternoon after it had rained most of the night and day before. Does this seem like it's excessive or is it not that bad, particularly since it is over a cantilevered area?

My other thought was to add an external gutter, but I'm not sure what modifications that would require with this type of roof. Any thoughts?

Big Bob 10-02-2007 01:17 PM

does not look like you have a ponding problem that can't wait til your roof is ready to be replaced. At that time be sure the roofer installs the drain the right way as Ed has advised.

Ed the Roofer 10-02-2007 01:44 PM

There are 2 commonly accepted interpretations on the definition of excessve ponding water.

Either 48 hours or 72 hours after the last accumulation of moisture, there should be no substantial ponding water remaining.

Remember, morning dew which settles on the entire surface and accumulates together enough to create a flowage downward the slope can make a limited amount of ponding water too.

It would be best to check it out at the end of the afternoon if it has been slightly sunny and it has been72 hours since the last rain or moisture accumulating condition has occurred.


the roofing god 10-07-2007 09:50 PM

The Existing Downspout Looks Like It Should Be 3-coursed W/tar And Membrane To Seal It Properly,if You Select The Right Spot For The Drain,cut The Holes Per The Drain Pipe Size,install A Drain Sleeve Secured W/ring Shanked Cap Nails,and 3-course It In(tar,membrane,tar)w/ A Trowel

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