Polyiso over old bitumen flat roof
We have a NYC rowhouse with a flat roof and we are putting on a new surface in preparation for solar panels. We want to also add 2″ polyiso while we are at it. The old surface is a sloppy bitumen with lots of air bubbles and pooling.
One contractor said he can slash open all the air bubbles, make the roof flat and put the polyiso on top of that without going down to the cladding. This is obviously a much cheaper solution than ripping off old layers of bitumen and we do not have to deal with possibility of encountering asbestos felt. I am asking because he is the only roofer who is offering this option. Is there any drawbacks from going this direction? My main concern is durability and future pooling, etc. And the fact that adding more layers will bring the surface approximately to the height of the parapet wall. Thanks!!
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Replies
Knowing the actual condition of the roof deck is a reason to strip
if you go down to the deck then the NYC energy code requires you to go up to R25 or R30 which is really thick, especially given that your parapet is relatively low.
however, putting solar panels onto a roof where you don't know the condition of the framing or the sheathing can lead to roof failure later.
the ponding of the roof is likely due to deflection of the framing members. if they are undersized now with only the roof load, then imagine how they will be with the added load of solar panels.
also, dealing with asbestos in NYC is run-of-the-mill work compared with some other jurisdictions. many contractors to do this work.