EPDM is a better product IMO.
Fit as many layers of felt as you want, But over time it will fail and leak because of the joins and over time the expansion and contraction will eventually see them joins fail.
EPDM however wont fail IMO, As there is no joins on most flat roofs, It expands, and contracts without splitting.
No brainer really.
And there are the words of a man that know absolutely nothing about felt.
As previously, what cast iron insurance backed single point guarantees do you get with EPDM? How many times is it inspected by manufacturers tech dept during installation? What license do you need from the manufacturer to install it?
Its a single answer....None. Its loved by those looking for cheap installation giving maximum profit, and anyone can install it with minimal plant.
So your honestly saying felt will outlast EPDM??
How long does a felt roof last?? Does it split/crack after so many years? Does rubber??
HT felts don't split/crack. Do you know anything about elastomeric membranes? Have a google.
EPDM is only as good as its bonding agent. It will last as long as it lasts, but the bond will not. Constant expansion and contraction see the membrane ripple, which begins the de bonding process. Then the laps will fail and combined with wind it will let go.
We ripped 16000m2 of it off Brent Cross. We've ripped 1000's of M2 off various other roofs, especially schools in Surrey/Kent. As a single sheet with no joins on someones back addition, it will be fine, except every tom dick or harry is slinging it down, without the faintest idea what they're doing.
We get roughly 100 tenders a month come in, and do you know how many of them have been EPDM specs over the last 20 odd years? None, because people who know what they're doing in the professional world of roofing know its limitations.
We do £3 million a year in single ply, but its in proper stuff, Sana/Trocal etc tc with manufacturer support and genuine warranty.
We could probably buy EPDM in at £5-£6 a M2 if we wanted, that gives you an idea of its value.
You don't spend a day on a training course to lay felt, you spend 4 years as an improver, then work your way up to to the premium systems. Asphalt installers used to have to go to college and be certified too. But since the demise of Asphalt due to cost and availability, good ones are hard to find. As the comments above, EPDM is getting banged on about quite a bit here, but not by Proper Roofers, because they know its s**t.
And finally, we do a lot of green roofing, this involves felting the roof then putting tons of growing medium on top , you wouldn't do that with EPDM.