Decking on a Bitumen Roof - A detriment?

Hello Everyone, and thank you in advance for any advice you can give me. I live in a 6-unit, 3-floor condo building with a flat bitumen covered roof. I should also mention that I live in Chicago - with a wide variety of crappy weather.

The building is 2 years old, and recently we had been seeing evidence of water intrusion in the form of split window moulding, and baseboards pulling away from the wall. We had a professional and highly recommended inspector come out for a consultation. The consensus is that the masonry on the parapet walls needs to be patched and sealed…As well as scupper flashing replaced (was not installed correctly).

My question is in regards to roof decks. Like most new condo buildings in Chicago, ours has a roof decks on each side (accessed through internal stairways for the 3rd floor units). The inspector told us that we really should not have a roof deck on a bitumen surface, particularly in our climate. He says the “floating” of the deck could compromise the membrane, and overall said that it would greatly reduce the life of the bitumen.

I’ve not heard this before, but want to do what is best for our building. As of now, the roofs are technically a ‘common area’ – and their repair is the responsibility of the association. So you can see where this is going – why should we be responsible for damage of a roof due to a deck that can only be accessed by two people!

I would like to offer the upper residents an option: either take the roof decks down, or become liable for any roof repairs. Before I light the fuse to this bomb, I would like to get some more professional opinions.

Thank you so much, James

I would suspect this building has masonry coping (cap blocks) that are porous, cracked, or installed wrong and allowing water intrusion into the exterior walls. A leaky scupper drain will usually cause a lot of water in a small area, not all over the wall as you described.

This is common on old buildings as the coping ages, but on this building, it was probably installed poorly. We generally remove the blocks and cap the wall with metal parapet coping. Metal doesn’t leak, but masonry coping is notorious for leaking.

If the roof was failing, it would be leaking into the ceilings of the upstairs apartments.

Advice is generally worth what you pay for it.

You’ve already paid a highly recommended professional good money for his consulting services and he has personally inspected the building and has the opinion that traffic on the roof is going to tear it up. Why would you want to ask people on the internet that have never even seen your roof? But more importantly, how much credance are you going to lend to their opinions?

Go with what your inspector says, but have a roofing contractor look at it… there may be a workmanship issue. While he’s there, see if he’ll chime in on the roof traffic issue.

I don’t think you should make a big deal about it, unless they are moving furniture or playing basketball up there. Time and weather are the enemies of a roof. Light foot traffic isn’t going to hurt it that bad.

And think about it this way… the roof might last 20 years without foot traffic and 18 years with foot traffic. So the other tennants have reduced its utility by 10%, make the case that costs should be payed on a pro-rata basis.

I posted this because the website is called “” … so naturally I felt that people who have an idea about roofs read and respond to posts.

The inspector does recommend that decking should not be on a bitumen roof. But- many many condos in Chicago have decking on bitumen roofs, so I just wanted to put “feelers” out here to see if other roofing professionals concurred with this. I would like to gather more opinions before I have the conversation with the residents with the roof decks. I do trust my inspector’s advice, but being that so many roof decks exist atop bitumens - I wanted to see what the consensus was.

i was a roofing contractor in chicago for 30 yrs. your "consultant failed to tell you why it is not good for modified bitumin roofs to have decks built on them did he? he probably doesnt know why. i have done hundreds of mod roofs on condos like yours.
now for the big ?. what is under the deck?

  1. is it assembled on the roof itself?
  2. is there some type of slip sheet or padding under the deck?
  3. who built the decks on these roofs owners or the builder?
  4. is it a smooth surfaced or granulated roof?
  5. can you post any pics? especially of the scupper.

Hey Roofboss.

The inspector said that as the decks are “floating” (not nailed down or in any way attached to the roof) that they can cause wear in the bitumen membrane. He also says a roof deck voids any manufacturer warranty, and would reduce the life of the bitumen by 25%.

To answer your questions:

  1. No, it is not attached to the roof.
  2. Yes, there are pads under the feet that rest on the roof.
  3. The builder built one, and the resident on the other side had some Polish guys build his.
  4. It is a smooth surface.
  5. I will work on getting some pictures for you. Don’t have any at the moment.

Thanks for any advice you can give me. I realize having a deck on a bitumen may not be ideal, but given the amount of roofs with decks on condo buildings, it is hard for me to imagine that it is such a terrible idea. Just trying to gather information and have other opinions.

Jebber45 - You came to the right place. People come here all the time and ask questions like you did.

your worst worry for this is not the floating deck. its cigarettes. they will melt the top layer of the modified and cause it to eventually wear open and leak. since you stated it has pads under it i honestly wouldnt be to worried about it “rubbing” 25% of its lifespan out.the fact it has a deck over it is actually going to give it some protection from uv rays(sun light)
heres round 2

  1. is the roof coated with aluminum coating?
  2. how thick is the pads between the deck and roof?

scupper neads replaced? much bigger concern than a deck.
remove deck(s), fix roof(s) , do not replace decks until a few rains pass and you know its fixed.

hard rains.


Polyurea over your bitumen can serve a a hardcoat and waterproofing system, protecting your existing roofing from all of the above issues.

I was on a roof with exactly the same issues earlier this year. It was on the North side, of course. Same issues.

Was I at your building? New building, sustected leaky masonry, repairs work done to new roof by a drunken roofer that never finished?