Felt is not roofing, it's roofing underlayment.

>>2999181
Because in 15-20 years you can apply another coating of the elastomeric layer only which is significantly cheaper than the original installation. A double layer of felt for a 0/12 pitch flat roof under any type of shingles would be inappropriate because of the low slope itself: water can pool under certain conditions such as up-slope wind and a heavy downpour.

Alternatives for a flat roof is a modified bitumen and glass felt layer, or a multi-ply TPO roof. However for homewoners, they're not likely to spend even more than an elestomeric roof coating that lasts 20 years and is easily repairable and "refeshable" when necessary.

I hope this helps :)

23 years in residential remodeling, I'd say like 90% of the flat roofs we've done have been TPO.

>>2999181
flat roofs can't be used in areas with heavy rainfall, the water pools on top and will add so much weight the roof will cave-in
you can't live in a home with a flat roof

>>2999275
>flat roofs can't be used in areas with heavy rainfall, the water pools on top and will add so much weight the roof will cave-in
That is simply incorrect. Next time you drive by an industrial park, a grocery store, a strip mall, literally any of the billions of flat roof buildings aren't caving in every time it rains. Same for snow, but thats a slightly different issue to deal with.

>>2999276
> industrial park, a grocery store, a strip mall, literally any of the billions of flat roof buildings
these have a gentle slope and aren't flat
https://www.slideshare.net/slideshow/commercial-roof-systems/10647635

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You can see in the pic these arent flat roofs they are all sloped slightly

>>2999278
>these have a gentle slope and aren't flat
Do you think a "flat" roof is genuinely 0-degree flat?

>>2999280
in the olden days when they were building condos in Sun City AZ, they left the roofs flat intentionally so that water would pool on top of them and cool the buildings. Was a huge pain in the ass.

>>2999275
no one has a totally flat roof.

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>>2999286

>>2999279
go up on any old roof and the slopes are all fucked with massive puddles

>>2999276
The real problem is with snow build up, that shit will pile up several feet high

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>>2999293
Sometimes the old BUR with gravel flood are totally flat. I've actually seen a bunch of totally flat roofs. We are doing one in two weeks that if I took the taper system off, it would be 0/12 pitch. If the building is old as fuck, solid chance the roof is indeed totally flat. Not that can't be changed with polyiso or EPS.
>>2999227
TPO roof is great because of the gadgets. You don't need any cool gadgets for EPDM. I guess Rapid Lock membrane is gadget like and is definitely cool. I'm start a couple hundred squares of it 7/20.

>>2999275
Bro... flat roofs aren't actually flat. They are built with a very low slope (I think it's 1/4" per foot minimum per IRC code) so that water drains off.

" they left the roofs flat intentionally so that water would pool on top of them and cool the buildings."
It's called an irrigated roof & it's not to cool the building it's to cool the roof. It goes back to using asphalt as a roofing material. Asphalt gets hot it can bubble & crack. irrigating prolongs the life almost indefinitely . Best practice would be to looselay a couple of inches of granite chips over the asphalt & the water pools in that. Periodically, requires raking to keep it level & remove leaves etc.

>>2999313
uh huh, its why they build the structure in general to sustain likely loads with a safety margin. Do you think everywhere it snows no large building is 'flat'?