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Parapet Membrane Wrap on a Commercial Roofing Takeoff: Vertical Area, Termination Bar, and Nailer Coverage

By The Sharp Pencil team

Coping linear feet are not the parapet takeoff. On a low-slope roof with parapets, take off the membrane that turns up the inside face of each wall as its own square foot line, add the membrane that continues over the top of the wall and the wood nailer when the detail calls for it, and carry termination bar, counterflashing, and coping as separate linear foot lines. Each line comes from the wall detail on the drawings and the specified manufacturer's details, not from a habit.

Why send your takeoffs to Sharp Pencil

The real cost of a takeoff backlog is the jobs you no-bid because nobody has the hours. Here is how we handle the ways a takeoff costs you time or trust.

• Delivered within 48 hours*. A takeoff that sits in a week-long queue is no help when the bid is due sooner.
• Every quantity names its sheet. Each quantity carries the sheet it came from and a confidence grade, so you can check any number.
• No silent blanks. Any checklist line the drawings could not settle carries a written reason, not a blank or a guess.
• Questions instead of guesses. Anything the set leaves open, such as an undimensioned parapet height or an unclear coping scope, comes back as a drafted RFI you can copy and send to your architect. Paste the answers into your job page and we update the takeoff. One re-run is included when you answer the questions.
• Priced with your numbers. Send us your costs once in a simple price book. Each takeoff then comes back with a client-ready proposal and a re-price sheet, and the workbook gets a Pricing tab.
• UNPRICED instead of a guessed number. If a cost is missing, the line says UNPRICED and shows the quantity. Nothing gets hidden in the total.
• A roofing professional reviews every paid job before it goes out. The review comes with every paid takeoff. It is not an upgrade.
• Answers in one thread, not an email chain. Ask about your job in a thread on your job page. If a question needs a roofing estimator on our team, the answer comes back in the same thread.
• Your plans stay yours. Nothing is shared or sold. See what happens to your plans.
• Monthly plans, with your first takeoff free. Our monthly plans are the main way to buy: Shop 12 at $2,750 a month, Shop 25 at $5,500 a month, and Shop 60 at $11,000 a month. $395 is the price per single takeoff. Either way, your first one is free on a job you are actually bidding, before you pay anything.

Why parapet membrane goes missing

A deck plan shows the roof as a flat outline. The parapet walls around it are drawn as a line or a thin double line, so the vertical membrane on the inside face of each wall does not show up as area. Stop the takeoff at the deck outline and a coping linear foot count, and the wall flashing gets left out.

The gap adds up fast. As simple arithmetic, a roof with 1,200 linear feet of 36 inch parapet has 3,600 square feet of membrane on the inside face of the walls alone, which is 36 squares that never appear on the deck outline. The worked example below shows that math and labels every input as assumed.

What makes up the parapet wrap

A parapet on a single-ply roof usually carries several separate quantities. Keep them apart so you can price and check each one on its own.

Sources for the rules behind these lines are in the sections below.

How to set the flashing height

Use the height on the drawings first. Where the wall detail does not dimension it, the manufacturer's details give a minimum:

• IKO's detail T-T-2 for its TPO system, termination with termination bar and surface mounted counterflashing, states a minimum flashing height of 8 inches above the roof surface (IKO, detail T-T-2).
• Duro-Last's detail T6110, a TPO parapet wall detail for mechanically fastened systems, notes a minimum termination height of 8 inches above the finished deck (Duro-Last, detail T6110).
• The RCABC Roofing Practices Manual detail for TPO membrane termination at a wall calls for the membrane to be carried at least 8 inches above the finished roof system surface, plus at least 3 inches for wall control layer overlap, and at least 12 inches where heavy snow is possible or to allow for future membrane replacement (RCABC, TPO Membrane Termination A). RCABC is a Canadian standard, so treat it as a reference point, not a rule for a US job.

These are minimums, not the takeoff height. On a parapet where the detail runs the membrane to the top of the wall, the flashing height is the full parapet height.

Parapet height is the structural wall, not the nailer

Take the parapet height from the finished roof surface to the top of the structural wall. Do not add the nailer to that height. Where a parapet slopes along its length, count that run at its high end. The nailer, and any membrane the detail carries over it, is its own line in Table 1. Keep the two apart. Otherwise the nailer gets carried twice, once inside a taller wall height and again as nailer coverage. Kept separate, the nailer line can be checked against the carpentry detail.

Remember that the finished roof surface is above the deck. Where tapered insulation builds up toward the parapet, the exposed wall height gets shorter as the insulation gets thicker. Use the heights the drawings give for each wall, and send an RFI when they are not given.

Termination bar, counterflashing, and coping

Termination details change the linear foot lines. Read them wall by wall:

• Termination bar fastening. IKO's T-T-2 calls for termination bar fastened 12 inches on center maximum, with a 1/4 inch gap between sections, cut at inside and outside corners rather than bent around them, and terminated within 1 inch of all section ends. Duro-Last's T6110 shows termination bar with fasteners spaced 6 inches on center. The specified system sets the spacing, which drives the fastener count per linear foot.
• Counterflashing. IKO's T-T-2 shows one or two piece surface mounted counterflashing by others over the bar, 24 gauge prefinished steel or 0.032 inch minimum aluminum. Decide whether that metal is in your scope and carry it as its own line either way.
• Bonding adhesive on the wall. This rule is system specific. WeatherBond's mechanically attached TPO guide specification says bonding adhesive is not required on vertical surfaces when the flashing height is 12 inches or less and the membrane is terminated under a nailed metal counterflashing, and that when a coping or termination bar is used for vertical terminations, bonding adhesive may be eliminated for flashing heights of 18 inches or less (WeatherBond, TPO Mechanically Attached Guide Specification, January 2024). Versico's VersiWeld TPO mechanically attached guide specification carries the same 12 inch and 18 inch thresholds (Versico, VersiWeld Mechanically Attached Guide Specification). Both brands are part of the same manufacturer family, so treat these thresholds as rules for those systems, not an industry rule. In those systems, taller walls need adhesive, so the wall height decides whether an adhesive line exists. Other systems have their own rules, so check the specified manufacturer.
• Coping. Coping is a linear foot line for the wall top. It does not replace the membrane lines under it. Our wind uplift zones guide covers why perimeter areas also change fastening in the field membrane next to the wall.

How to take off parapet membrane, step by step

1. List every parapet segment. Use the roof plan and building sections to list each wall run with its length. Note where the parapet height changes, where the roof meets a taller wall, and where the edge has no parapet at all and gets edge metal instead.
2. Get the wall height for each segment. Take it from the sections or the wall details, from the finished roof surface to the top of the structural wall, not including the nailer. Count a sloped parapet run at its high end. Where it is not dimensioned, list it as an RFI rather than assuming a number.
3. Read the wall detail for each segment. Does the membrane stop at a termination bar, run to the top of the wall, or wrap over the top and the nailer? Is there counterflashing, a reglet, or a coping? Each answer adds or removes a line from Table 1.
4. Compute the vertical SF. Multiply each segment's length by its flashing height. Add the top of wall and nailer coverage lines where the detail shows them. Keep inside face, top of wall, nailer, and any outside face turn down on separate lines.
5. Add the linear foot lines. Termination bar, counterflashing, coping, and cleat each get their own length, with corners and splices from the details.
6. Apply the system rules. Check whether the wall height triggers bonding adhesive, and add the corner and splice accessories the manufacturer's details call for.
7. List what is still open. Missing wall heights, an undimensioned flashing height, an unclear coping scope, or a wall detail that does not match the roof plan all go on the RFI list.

Worked example: how much membrane is on the walls

This is arithmetic only, on an assumed building. Every input is assumed for the example and is not a recommendation: 1,200 linear feet of parapet (assumed), a 36 inch structural wall height measured from the finished roof surface to the top of the structural wall, not including the nailer (assumed), and an 8 inch wide wall top (assumed).

On this assumed building, with flashing assumed to run the full wall height, the 36 inch inside face alone is 3,600 SF, or 36 squares. If the detail also wraps an 8 inch wall top, that adds about 800 SF more, before any nailer line. That wall area sits on top of whatever the deck plan shows. Corners, splices, and the overlap onto the field membrane come from the manufacturer's details and are added on top of the arithmetic.

Common mistakes

• Counting coping LF and calling the parapet done.
• Adding the nailer into the parapet height and then counting nailer coverage again.
• Using the deck to wall height when tapered insulation has raised the finished roof surface.
• Using one parapet height for the whole roof when the sections show different heights.
• Leaving out termination bar, counterflashing, or the bar fasteners.
• Forgetting bonding adhesive on walls tall enough to need it.
• Treating a manufacturer's 8 inch minimum as the takeoff height on a wall where the membrane runs to the top.

FAQ

How do I calculate parapet membrane square footage?

Multiply the length of each parapet segment by its flashing height on the inside face, taken from the finished roof surface to the top of the structural wall or to the termination point shown in the detail. Add separate lines for the top of wall wrap and the nailer coverage when the detail calls for them.

Is the nailer part of the parapet height?

No. Take the parapet height to the top of the structural wall only. The nailer and the membrane that covers it go on their own line, so nothing is carried twice. Where a parapet slopes, count that run at its high end.

What is the minimum flashing height for TPO at a parapet?

Several manufacturer details state 8 inches above the roof surface as the minimum, including IKO detail T-T-2 and Duro-Last detail T6110. The project details and the specified system govern, and many walls are flashed higher than the minimum.

Do I need bonding adhesive on the parapet wall?

It depends on the system and the wall height. WeatherBond's and Versico's mechanically attached TPO guide specifications allow adhesive to be left off at 12 inches or less under nailed counterflashing, and at 18 inches or less with a coping or termination bar. Those are rules for those systems, so check the specified manufacturer's rules for the job.

How many termination bar fasteners should I take off?

Divide the termination bar length by the fastener spacing in the specified detail. IKO detail T-T-2 shows 12 inches on center maximum, and Duro-Last detail T6110 shows 6 inches on center, so the system you are bidding sets the count.

Can Sharp Pencil take off parapet membrane and terminations?

Yes. Wall flashing, top of wall wrap, nailer coverage, termination bar, counterflashing, and coping come back as separate lines with sheet cites, and missing wall heights or unclear details come back as drafted RFIs on the Questions tab. Delivered within 48 hours*. The first takeoff is free on a live bid.