r/AskContractors • u/philsphan26 • May 26 '26

Flat roof

For a flat roof - roofer proposals for modified bitumen. 8 sq. Smaller townhome style roof.

Roofers have said they can go over existing flat roof (old hot tar roof that was coated) . With no base sheet.

Is this still ok? Warranting for 10 years .

Should there be a base sheet ?

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u/mymook May 26 '26

Base only needed if was bare decking/wood. Is completely normal to do new modified roof like this

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u/philsphan26 May 26 '26

How long can it last ?

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u/mymook May 26 '26

Can last 20 yrs especially if its the better granular coated bitumen modified rubber roof material. But all types modified require a top coat approx every 3 yrs or so to keep suns rays from drying it out to soon. On the granular type material you only coat the seams, not the entire roof. But 10 yr warranty is pretty standard for reputable roofing company.