Question Unusual Roof

Just saw this today and found it unusual. This is an existing home connected to an add-on made by finishing the garage and patio. It appears to be 2 roofs that were connected. The connection is pretty much flat with solid plywood sheathing under it and I saw no signs of leaking (even though we had hard rain the night before). Besides the potential for that drain to clog, I see no problems but I was hoping for some insight from those with more experience

Butterfly roof, the ones I see have a higher than average leakage propensity.

Where’s that unprotected roof drain routed?


It drops into a flower bed in the back yard

Welcome to out forum, Chris!..Enjoy and participate. :grinning_face_with_smiling_eyes:

I agree with Dominic on the leakage factor.


I appreciate the help gentlemen. It appears to be in good shape now but I’ll let my client know about the propensity to leak

Thanks, I’ve been lurking for awhile but first post today


Nothing wrong with a butterfly roof when done properly.
That drain should have a bonnet on it to prevent blockage.


Thank you Marcel

Chris, it looks like there has been a lot of standing water in the valley, too. That is problematic.


Yep, I think the drain is too high. Also, that last 1 foot between the drain and the end of the house may not be sloped/contoured to the drain.


I saw that too while I was on the roof. It had literally stopped raining about 2 hours before I was up there and there was no standing water but it certainly looks like standing water is a problem. Thanks again for the help

Well, Lets take a guess, it looks like the roof is about 38’ long, and it looks like it rises up about 25’’ on the high side, so that is not to bad of a slope for a flat roof. :thinking:

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It’s not if, but when, for the drain to clog. So your next question is what’s the consequence of a clog? How high up will the water go, and what will it effect.

The solution to that is… a scupper. The idea of a scupper is like the emergency spillway on a dam. You hope never to use it. But, if you need it, you need it. The water should then drip out somewhere super obvious and annoying, so somebody notices and clears up the regular drain (dripping directly onto a walkway for example is perfect).

Observation: butterfly roof with a single drain.
Potential issue: if the drain clogs, water backs up 3" and gets under the shingles.
Recommendation: refer to qualified roofer for installation of an emergency overflow “scupper” drain or equivalent, limiting ponding in the case of a drain failure.


Thank you Bryce, that’s very helpful


From a design standpoint this is pretty common - steeper than 3:12 generally get shingles but lower slope areas need membranes, etc. I often find membrane/flat sections when “crawling” around on roofs with lots of pitch changes and varying roof lines.

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Morning, Chris.
Hope this post finds you well and in good spirits today.
Chris, are those (2 intersecting parallel gable roofs), with a sloped butterfly intersection?
What is under the center of the butterfly section? A partial open breezeway?
Any pictures from the front or sides of the residence?
Looking forward to your answers.

Thanks for the reply Robert. Unfortunately I didn’t get a good pic depicting that area from the outside but under the butterfly is an add-on game room built up to the original exterior wall, there is no breezeway between the two. We had solid showers for about 12 hours prior to the inspection and there were no signs of leakage but I got the client up on a ladder and showed him where the potential for future problems lie. Turns out the re-model was unpermitted and the client/seller are dealing with that issue now.

Thank you everybody for the shared expertise

Hey, Guys, It was framed kind of like this, the two roofs shared the same common wall, and a cricket was built on top.
images (15)


That’s it right there Scott. I hadn’t seen that before and wasn’t sure what I was looking at but your pic makes it clear. Thank you so much…you guys have been great