Do you need a flat roof Poly Iso Tapered System? • ASAP Roofing Do you need a flat roof Poly Iso Tapered System? • ASAP Roofing
On March 10, 2013

Do you need a flat roof Poly Iso Tapered System?


Flat roofs…the eternal headache for almost everyone who has one. One in three residential property owners asks us, “Why are flat roofs used?” The answer, building a home without a roof line is much cheaper, for the builder that is!

The inherent flaw with a flat roof, is the “flatness” of it. Poor drainage, leads to standing water, which leads to leaks. Often times a bit of pitch is built into these flat roof structures, somewhere about 1/8th inch pitch per foot of run. This pitch, while it seems so slight, is often times enough to keep pooling from occurring. To help understand what qualifies at pooling, or standing water: water that remains on the roof for over 24 hours after the precipitation event has ended.

Connecticut building codes follow the standard set by the International Building Codes. International Building Code is thus, there must be 1/4 inch of pitch for every 1 foot in rise. When a building is already in existence, this would be quite hard, and expensive, to accomplish with traditional stick framing. The solution is a polyisocyanurate taped system. We will refer to these as poly ISO or ISO systems.

Another interesting roofing code in Connecticut, a roof system must be installed to manufacturer specifications. Basically, do it how it is supposed to be done! We will examine 2 very commonly used flat roofing systems to help you determine if you are in need of an tapered ISO system. We will also make a whole hearted attempt to layout materials and labor costs associated with each of these systems in regards to your needs for your roofing project.

Above is the rough sketch of the roof that we requested a tapered ISO system for. For demonstration purposes this flat roof in Wolcott CT is a great example. The roof is 2800 square feet, dimensions are 40 feet by 70 feet.

We priced this roof out 2 different ways for the customer. The first way as an 045 mil reinforced EPDM black rubber roof manufactured by Carlisle, the second way as a 50 mil white reinforced PVC roof, manufacturer IB roof systems.

In order to get an accurate comparison of the two roofing systems we need to first compare material costs. Here is a breakdown roughly of materials required with cost for each different type of roof.

Carlisle 045 EPDM Rubber Roofing Materials List with prices.

1. EPDM Membrane per square foot $0.65, total cost $1,182

2. Perimeter Metal 230 lf, $14.23 per 10 feet $328.00

3. 6 inch cover tape, $1.90 lf, $437.00

4. 6 inch seam tape $65.00 a roll, 7 needed $455.00

5. Primer Low VOC $55.00 a can, 3 needed, $165.00

6. “T” Joints, $17.00 each, need 6, $102.00

IB 50 mil White PVC.

1. 50 mil membrane, $0.74 a square foot, $2,072

2. Perimeter Metal, white, PVC coated galvanized steel, $17.02 per 10 feet, 230 lf $391.46

3. There will be no cover tapes or seam tapes, or even primers, PVC is heat welded.

4. “T” Joints will be made from 50 mil non reinforced 12 inch by 50 ft roll, need 1 roll, could do this job 4 times from the same roll, cost $147.00

If you are a professional roofer reading this your shaking your head, your thinking that I didn’t include screws, plates, substrate, seam cleaner. Your correct, I did not account for those items, they are needed no matter which system we install.

Here we are, total cost for the materials not carried by both systems, 045 EPDM costs $2,669.00. Total cost for 50 mil white IB PVC, $2,610.00. An EPDM system actually costs more to install by $59.00.

Comparing the two different roof systems. EPDM is a solid product. 5 years ago, you could get a new EPDM system for 85% the cost of PVC or TPO. When gas and oil prices rise, so do the cost of petroleum based rubber products. Both of these systems are mechanically attached. Both are eligible for 15 year NDL warranties from their manufacturers. SO now you might be wondering why “tapered roof systems” were the topic of this blog post?

Remember earlier in the post I had mentioned that International Building Code was for 1/4 inch pitch for every foot of run? I had also mentioned that code also stipulates that a roofing system must be installed in accordance to manufacturer specifications. All EPDM manufacturers stipulate that ponding must not occur on their roof systems longer than 24 hours. On a true flat roof you are stuck, in order to get a manufacturers’ NDL warranty, and also not break the law and be within the local building code ordinances, you must install a tapered ISO system. The cost of the tapered system, not including materials for additional wood nailers, RUSS strip from proper membrane securement, additional plates and screws of greater length, an additional $2,435.00

Often times when doing an estimate for a customer we ask to price the roof in IB PVC. Anyone who has done a bit of homework knows that IB membranes are a top notch product. They are definitely not the cheapest material out there. However IB membranes are not void of warranty if there is ponding water. Therefore you do not need a tapered roof system. You can now rest assured that you have saved yourself at least $4,500 additional by not being stuck with the added cost, that since IB does not require a pitch system, neither will your building department.


This article was written by Marcus Bernice Keilche ( of Marcus Anthony Construction LLC, CT Roofing Contractor.

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  • By kirk  2 Comments 

    Posted by Alison Turner on
    • Mar 11 2013
    Great comparison article! The more I learn about PVC, the bigger fan of the material I become.
    Posted by HVAC Repair Simi Valley on
    • Aug 4 2015
    This is the perfect web site for anybody who would like to find out about this topic. You know a whole lot its almost hard to argue with you (not that I personally would want to…HaHa). You certainly put a brand new spin on a subject that's been discussed for a long time. Excellent stuff, just excellent!

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