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doingygirl 12-16-2007 02:13 PM

Modified bitumen vs 60 mil EPDM membrane Flat Roof
My husband and I have received two estimates to replace our flat roofs(lower roof 14'x171/2' upper roof 34 1/2'x17'). We are now trying to decide which roofing co. we should hire to replace our two flat roofs on our 1890 brownstone.

The first estimate proposes to install the following for $11,960.00 (Firestone 60 mil EPDM membrane):
-Install 1/4" Dens deck Prime roof insulation mechanically fastened to the roof deck.
-Install Firestone 60 mil EPDM membrane, fully adhered to insulation in accordance with the manufacturers 20 year specifications.
-Install new flashing at all perimeters, curbs, and all roof penetrations.
-Install shop fabricated .032 brown aluminum coping, drip edge, and counter flashings and terminations.
-Install 6" ogee brown aluminum gutter and 4" aluminum downspout to replace existing at rear.
0Workmanship guranteed against leakage for two years.

The second estimate proposes the following for $16,491.00 (3 ply modified
bitumen roof system):
-Provide and install new perimeter edge metal.
-Provide and install 3 squares of fiberglass base sheet.
-Provide and install 3 squares of SBS modified bitumen smooth surface modified bitumen roofing installed in a cold applied fashion.
-provide and install 3 squares of SBS granular surface modified bitumen roofing installed in a cold applied fashion.
-Provide and install 14 feet new SBS modified bitumen granular sufaced wall flashing.
-Provide and install all new base flashings to the roof curbs and chimneys.
-Provide and install .032 aluminum counter flashing where needed.
-Provide and install new pitch pocket flashing to the conduit lines.
-Provide and install loose granules to the bleed out of all seams.
-Provide an exclusive lifetime guarantee/warranty for manufacturing defects and misapplication.

I'm not sure if one product is superior to the other (3 ply modified bitumen vs/ 60 mil EPDM membrane) to justify the difference in price or if one company's proposal is superior to the other? We live in D.C. so the weather is not too extreme. We do have a large tree in the rear of our yard but it doesn't hang directly over the roof so it really shouldn't be a problem (unless lightening strikes it or some other act of nature). -Are there any other questions I might want to ask either company when comparing their bids? Each company has a very good reputation and have both been around for a long time. -Any advice or insight is greatly appreciated since I've never owned a house with a flat roof before.


tinner666 12-16-2007 03:24 PM

Is either certified by the manufacturer of the material spec'd by the specific roofer? Will the ma nufacturer be offering an extended workmanship/material warranty? DO a bit of research on the manufacturer's site to learn more about the installer(s).

SBS needs a bit of slope to work well Does water remain more than 24-36 hours in cool weather? If so, I would avoid the SBS.

My personal preference would be the EPDM with 6" seam tapes instead of 3".

BTW- I and many other roofers will install these and other products even though we are NOT certified by the manufacturer! Keep that in mind. I do it on a case by case scenario.

Ed the Roofer 12-16-2007 03:30 PM

The purpose of installing multi-ply roof systems would be to have redundancy in the event that the top ply failed and leaked.

I would have to know what they mean by cold applying the 1st and 2nd layer of modified bitumen sheets.

Does that mean with an adhesive?

Or, does that mean that they are just flopping the materials down in place without any adhesion at all. Most modifieds are torch weled, but their are cold process adhesion products available.

Get a clarification, because if it is not a true roofing system on its own merits before the next layer is applied, it would be useless.

Plus, they are only covering 3 squares? That would only be 300 square feet.

The smaller roof surface is about 2 1/2 squares by itself and the larger one is about 5 3/4 squares and these figures do not accouunt for a waste factor of at least 10 % to 15 %.

You have at least 8 1/4 squares of actual measurements, which should be rounded up to at least 10 squares needing to be covered.

Did the modified bitumen company include both roof sections?


tinner666 12-16-2007 03:56 PM

Neither company mentioned removing the existing roof(s). How many layers on there now, and what are they composed of? Tear-off of existing would be preferable. IMO.

the roofing god 12-16-2007 10:02 PM

I would tear it off,and install IB roofing,you can check their website for an installer,the warranty is lifetime on the IB with removal of the old,and the seams are hot air welded,better than epdm glue or modified bitumen adhesive in my opinion

doingygirl 12-17-2007 10:51 AM

Ed, the cold application modified bitumen applies an adhesive (1 1/2 gal. per square) between each of the 3-plys. The bid did include both roofs to be done as well as a tear off of the existing roofs.

Roofing God, I don't know if the IB roofing system is recommended for our house since it is an adjoining row house and was built in 1890 due to the potential fire hazard in using an open flame with the hot air welding. Some of the roofers that gave us estimates did mention the hot air welded application but all shyed away from it citing the increased risk of fire in a closed area ( our house is connected to two other houses) since our house is a row house and all of the houses are quite old (late 1800's) . I did contact IB roofers anyway to see what they had to say and am awaiting a phone call from one of their local reps..

-Thanks everyone for all your advise and suggestions!! I greatly appreciate it.

Ed the Roofer 12-17-2007 11:06 AM

Hot air welding is different than open flame torch down roofing.

The heat from a glorified hair dryer actually melts and molecularly fuses the two lap joint seams together.

If you had suggested that one of the installers had recommended that type of membrane, I would have said that would be the preferable choice.

In the other forum where you have this posted, at roofing dot com, you mentioned this was a row house.

Are there fire-walls built between the seperate units? If so, and if they are like the Chicago row houses, this would be a great alternative.


the roofing god 12-17-2007 05:06 PM

Ed is exactly right,the IB is well worth it

ncgrogan 12-27-2007 03:32 PM

I would go with the second one as they IMO have listed a better system and have enough detail in their proposal to give some confidence they know what they are doing. The modified system is going to typically be more expensive than a single ply. The cold adhesives of today are much better than previous years setup a lot quicker. Once setup its adhered just as well if not better than a hot system. You just want to make sure once the cold plys are down there is not a lot of traffic on it as it tends to "float". I dont see any mention of insulation. You typically need a minimum of 2" of polyisocyanurate in a tapered system to meet the energy code. If you have structural slope youll need a thicker minimum. Go with a minimum of two layers of insulation so they can be staggered in at least one direction.

rodeo 12-27-2007 05:13 PM

I like the EPDM better. I also like heat welded seams better that glued.
Didnt hear much about the tearoff.
You might want to investigate what to expect for a tearoff.
There could be an unknown roof structure/insulation/ventilation
design defect that is best solved at the time of tearoff.
Flat roofs are especially notorious for this.
Dont trust that the contractor would correct a design defect on his own.
Most would be more inclined to rebuild your deck the same way
(at best) as before, damn the defects.

TomBrooklyn 01-07-2008 05:50 AM


Originally Posted by tinner666 (Post 81060)
Is either certified by the manufacturer of the material spec'd by the specific roofer? Will the ma nufacturer be offering an extended workmanship/material warranty?

Firestone doesn't warantee residential jobs. I don't think any of the other mfgs do either.

the roofing god 01-07-2008 08:41 AM

Ib Does With A Lifetime Warranty

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