Thoughts on flat roof detail? Protected membrane with gravel
brandons
| Posted in General Questions on
I came across this detail on Youtube. I’m developing infill townhomes with a low slope assembly in climate zone 5B. On past projects we’ve done flat roof deck using tapered insulation/densdeck/tpo. Have also done sloped deck, iso board, densdeck, then tpo. The assembly below at first glance seems costly, but there are no fasteners, plates, coverboard, or separate air barrier involved. The townhomes will be for sale perhaps this is a way to improve longevity.
What are your thoughts on the assembly?
(video)
https://www.youtube.com/watch?v=OC92wyzjT3o
Thank you,
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Replies
What you are describing is close to the perfect roof here:
https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall
I don't see why it would not work but there are a lot of small details that need to be worked out. All those drainage mats need to drain somewhere and you need a vapor control layer of the concrete (I think TPO will work, but something to watch).
Since the roof membrane is well protected, it should last a long time.
The one issue I can see is any leaks or additional roof penetrations down the road will be very big jobs compared to a standard roof. If under warrantee, that cost will be yours, something to watch.
I appreciate your response. The roof is monopitch. The footprint is 100'x36', maybe 5 scuppers would take care of the drainage? I try to do the best roof I can within reason. This assembly would cost slightly more, but I think it's worth the trade off for longevity. We're framing the roof with I-joists/osb . Was hoping to use EDPM instead of TPO.
We typically warranty roofs a few years here. It's a gamble, perhaps moreso with an exposed membrane.