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stubits 06-26-2009 08:48 PM

Flat Roof Leak
I just discovered a relatively small leak in my asphalt roll flat roof. From what I can ascertain, it seems like there must be a break in the flashing around the house's main stack (3" cast iron), allowing a small amount of water to trickle in and run straight down the stack and into the attic. If necessary I can make my way up onto the roof tomorrow and take some photos (it's currently raining), but from previous visits to the roof I know that the flashing is not one of those preformed rubber or metal ones, rather, it looks as though some pliable metal (perhaps lead) was used and then coated with roofing cement.

So, how do I go about fixing this? The roof is in otherwise great shape.


Ed the Roofer 06-27-2009 03:16 AM

Read through these threads for similar advice on how to properly patch a flat roofing material and any flashings, looking for the terms, "Dope And Minnie", which is a Chicago terminology, but it is described succinctly in those various posts.


stubits 06-27-2009 07:12 AM

Ed- I hope you don't mind if I ask some follow-on questions. Specifically, I just want to confirm that the procedures you described in the past are appropriate given that this leak involves the flashing around the base of a vent pipe. Currently the shroud or flashing is a flexible material of some sort (hard to tell as it it coated in roofing cement). So, will this work?

There is no pipe boot, would it make sense to try and install one at this point? Is that even possible?

Also, it sounds like the choice of cement is dependent on the roofing material. How can I be certain what I have? It is obviously a roll roofing materially and looks like long and wide sheets of asphalt shingles. It is relatively light in color.


Ed the Roofer 06-27-2009 03:30 PM

Any asphaltic based flat roofing material will bind properly with a good grade Plastic Roofing Cement.

If there is No Boot flashing on it now, why did you describe the Lead covering in your first post?

I think possibly you Do have a lead boot flashings, but that does not matter for the repair aspect.

Get a new pipe boot flashing. Remove the old one carefully, so as not to damage the roofing material it is bonded to.

Install the new one. Under the flanges, trowel apply a thin layer of plastic roofing cement. Set the new boots flanges into this roofing cement. (Use some chalk to outline the perimeter edges of the boot flashing first, so you do not go overboard and get the area all messy. Tap the flanges into the bed of roofing cement. Now, apply the layer or roof cement, membrane fabric and then a top skin coat of roofing cement as described in the other posts I pointed out to you in my other reply.


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