Add Modified Bitumen on top of a Faulty Modified Bitumen Roof?

My condo is planning to replace our roof because the original was installed entirely incorrectly. The original roof appears to be a single layer modified bitumen roof, but it began to fail within 6 months causing dozens of leaks into the units. We have a flat roof (with a slope for water runoff) and wooden roof decks on top. Photos at the link below:

Our roofer recommended adding another layer of modified bitumen on top of the existing faulty layer, and he says that this will create a 2 layer modified bitumen roof that should last for 20+ years. Specifically, we are looking at adding Firestone APP UltraWhite cap sheet.

So, my question: Is it a good idea to just add a second layer of modified bitumen to an existing faulty layer and expect it to have the life of a 2 layer modified bitumen roof? Do we need to ensure that there is some sort of protective liner underneath the original layer to ensure the new roof will be properly installed?

Thanks in advance for any feedback!

Mod Bit isn’t my gig, but when there is water in the system, you’re better tearing it off and doing it right. With the existing roof open and wet, you’ll have vapor drive attempting to disbond the system from day 1.

Thanks, Darkthirty. I was kind of wondering about that. We definitely have some open seams that could be letting water in. Just based on where we have the leaks, it seems like the lack of proper flashing, collars, and pitch pockets is a bigger issue for us (at least for right now).

We did a lot of research and have confidence in our roof contractor. He seems to think that if they re-do all the flashing, add proper collars around all the pipes, and fix the penetration points that it shouldn’t be necessary to tear up the whole roof to do modified bitumen.

I should also say that the building is only about 2 years old, so the water damage has only been noticeable for about 1 year. Not sure whether that is enough time for the material under the membrane to deteriorate or rot.

Yes, because as you said, it was installed improperly and leaked immediately.

The perimeter eve drip metal should be
26 galvanized steel ( NEVER aluminum as he installed).
The proper heat to adhere warps and distorts aluminum.
He also didnt use primer.
He also didnt install a perimeter starter strip before he started his main rolls.
You can see the rust under the material indicating leaking.
I suspect the entire perimeter to be the same.

This is a very expensive roof
With two story porches with walls and entry ways, air conditioners on roof,
All siding to be removed and replaced.
Do NOT pick the cheapest guy.
Do Not.
You need the very best roofer in the area.
Probably should cost double what mister
I can go over this terrible mess roofer is asking.

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Pic 12 .53 says it all. Do not use the same roofer either…There are also probably carpenter ants working on the framing now, they can smell wet wood.

Your roofer mentioned making the flashing and penetrations “new” but he didnt mention making the perimeter new.
The most important part.

Choose another contractor.
He doesnt know what hes doing on the most basic. Or he could just be a salesman and the roofers would do it right.

On the other hand, roofers will take short cuts
If they dont have good leadership directions.
When you tell the roofers you are going over it,
They go over it, unless you TELL them to remove and replace the perimeter.

Soo, honestly i would choose a different contractor.

If the previous contractor knew what he was doing, then i would say yes, i could make it work.
But we both know he didnt and we cant ignore this just because fixing it the right way seems unfathomable financially.

Someone made a bad decision on choosing the last contractor. Dont do it again.


As mentioned by these previous roofers with much more flat experience than I have, you got hosed by the first roofing contractors, spent a bunch of money and now have water intrusion. What could you possibly be thinking by agreeing to an overlay over a shitty job that has possibly already compromised the decking? Some people never learn! The recent contractor led you to a conclusion which was pleasing to hear. The legit guy would tell you things that hurt but are necessary and cost more. You choose and hopefully you’re not back in two years for another go-round.

Thanks for all the feedback everyone. First, I should point out that the roofer we are working with is definitely NOT the original roofer. So the new proposal is from a roofer who is trying to go back and fix the problems with old roof.

We’ve done a ton of research on businesses and received over 5 quotes. Honestly, no option seems perfect. But we are going with someone who has a good reputation, provided references (we called people), and is the highest rated flat roofer in our area from online ratings.

Not knowing much about roofs, the technical research on the roof itself has been a lot harder. So, I guess I’m just trying to figure out what are critical questions we should ask to make sure there aren’t any surprises (and extra $$) later.

Here are the questions I have based on the feedback I’ve received here:

  • We know that the original roofer did virtually everything wrong. What assumptions are you making about existing roof if we add another membrane over the top without installing an entirely new roof?
  • Will your proposed solution work if the layers below were not installed properly, or not installed at all? (e.g. decking, insulation, base sheet, etc)
  • Will your proposed solution work if the layers below have become damaged due to improper installation and/or prolonged water exposure? (e.g. decking, insulation, base sheet, etc.)
  • The fasteners and plates under the corner of the penthouse roof are showing rust or corrosion. We don’t know whether this is true in other places as well. Does this need to be fixed and, if so, does your proposal address this problem?
  • Does your proposal include replacing the existing perimeter?

Any suggestions on other specific questions I should ask?

The roofer is not fixing the original problems by covering potentially water damaged decking. He may stop progression but he is not curing what has happened.

Online ratings are garbage. Some of the biggest hacks in our area are somehow rated highly.

References provided are cherry picked by the contractor and WILL NOT include people they have upset.

What does over 5 quotes mean; 6 or 10?

I think all of your other questions have already been answered by knowledgeable roofers and you’re holding out for an answer that justifies an overlay.

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