Flat roof materials questions

i am a homeowner in the northeast seeking to repair our old and leaking flat roof and hoping to educate myself a bit during the estimate process.

of the two contractors so far, one would prefer to overlay with Firestone APP 160 cool process and aluminized coating. he said it would need recoating in about 8 years.

the other suggested a white granulated surface (Firestone APP 180 i think) and no additional surface treatment. he suggested this should be more or less maintenance free and warranted for 12 years. this estimate is almost 50% above the quote from the contractor using aluminum coated smooth modified bitumen.

i believe the current roofing material is a smooth modified bitumen with aluminized coating, definitely showing its age.

my questions are:
which material reflects a better choice for me, the homeowner ?
i am interested in a durable and trouble free roof, energy efficiency would be a bonus as well.
are there distinct advantages to one material over the other ?
is the difference in prices due to a large difference in materials cost ?

thanks for any help

You need to at least do spot tear off to make sure the leaking areas are dried out and solid. If you go over the existing, make sure the aluminum coating is removed first, or you will have disbonding problems. Since you have moisture in the system, you’ll need 2-way breather vents. Mod-bit and TPO are good for 10 years or so, EPDM will last at least 20 years. You can add insulation board to decrease the heat loss. With ALL roofing jobs your main cost is in the labor, it’s prudent to pay for quality materials

A good mod bit roof lasts as long or longer than EPDM. Of course the standard should be multiply roofs and not single layers of mod bit, which should be avoided IMO.

If you are in the northeast then you will probably get more energy efficiency from a darker roof.

The purpose of aluminum coating and granules on asphalt roofs is to protect the sheets from the sun. UV light does most of the damage to your roof.

The material cost and labor of a ply of APP160 smooth cap sheet plus aluminum coat is more than the cost of APP180 Granulated Cap sheet. There is probably another reason for the price difference.

If one is a tear off and the other a lay over, or does one use a single ply of new roofing and the other a base ply and cap ply, or is one also replacing edge metals and the other not would be my guesses.

If you have evidence of wet wood deck or water trapped in the roof you would be better just tearing it off. At a minimum you would need to listen to Darkthirty for venting and removing coating if you insist on a layover.

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What are the specs for a 30 year warranted MB roof system? I’ve seen excellent older modified roofs, but the norm is sloppy work. I’ve done a lot of repairs and coatings but the largest torch repair was only 35 SQ.

If they are not flood coated then they usually need at least a ply of minimum 120 mil base sheet and 220 mil cap sheet. Usually hot mopped but can be cold adhesive, torch, or a combination depending on the manufacturer. Siplast and Soprema want all their mod bit systems to be a combination. It is also common now to use a robot for the laps on the cap sheet.

The other common spec if for 80 mil base, 220 mil cap, and a flood coat and gravel. In either case all vertical laps get 3 coursed and usually aluminum coated.

I have bid a 40 year system using modified coal tar products but didn’t get that one. Otherwise longest warranted system we did was a 35 year. That one was 3 ply of Type IV, a 120 mil base sheet, and 220 mil cap cap sheet.

That’s a robust system, with maintenance it could last forever. I’ve worked on old coal tar BURs and was very impressed with them. What is a ballpark material and labor cost on that system?