Sharp Pencil › Guides

How to Take Off a Mixed-System Commercial Roof: TPO or EPDM Next to Metal or Shingle

By The Sharp Pencil team

Take off each roof system as its own assembly, with its own area, edges, and details, and never fold sloped metal or shingle area into the membrane square footage. Then carry every place where two systems meet as a separate linear line priced from the specified tie-in detail, because in the manufacturer details the membrane or a coated metal flashing runs up under the steep-slope roofing, so both layers exist in that strip.

Why send your takeoffs to Sharp Pencil

The expensive part of a takeoff backlog is the jobs you no-bid because nobody has the hours. Each point below answers a specific way a takeoff costs you time or trust.

• Delivered within 48 hours, often sooner. 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 are never stuck with a number you cannot check.
• Measurements marked up on your own sheets. Your job page shows the measurements drawn on your own sheets, and you can open and zoom them to check the numbers.
• 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 comes back as a drafted RFI you can copy and send to your architect. Paste the answers into your job page and the takeoff is updated; one re-run is included when you answer the questions.
• Priced with your numbers. Send us your costs once in a simple price book, and each takeoff also comes back with a client-ready proposal and a re-price sheet, and the workbook adds a Pricing tab.
• UNPRICED instead of a guessed number. Where a cost is missing, the line says UNPRICED and shows the quantity, so nothing is hidden inside the total.
• A roofing professional reviews every paid job before it goes out. The review comes with every paid takeoff, not as 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. They are used only for your takeoff, never shared or pooled, and deleted automatically after 90 days.
• First takeoff free on a live bid, then $395 per set. Try it on a job you are actually bidding before you pay anything.

What counts as a mixed-system commercial roof?

Any building where more than one roof assembly is bid in the same job. Most often that is a low-slope membrane field next to a sloped standing seam, metal panel, or shingle area: a flat main roof with a sloped entry roof or mansard, or a low-slope addition tied into an existing sloped roof.

The same building can have more than one of these, and each meeting line is its own detail.

Why blending the assemblies costs you

One roof area number hides differences in material, labor, attachment, and responsibility that each system carries on its own.

• Different materials and units. Membrane, insulation, and cover board go by plan square feet; standing seam panels, clips, and trim by slope-adjusted area and linear feet; shingles, underlayment, and starter by the square. One total cannot feed all three material lists.
• Slope adjustment. Steep-slope areas have to be taken at slope-adjusted area. A plan-view number undercounts them.
• Different crews or subs. Manufacturer transition details mark the steep-slope roofing as work by others. GAF Detail 601 says "Shingles, tile, or metal panels by others", and JM T-TI-02 shows the ice and water guard by others. A subbed metal or shingle scope needs its own quantity, and the transition needs a clear owner.
• Warranty boundaries. Each detail carries its own manufacturer terms. JM's T-TI-02 title block lists a maximum guarantee term of 20 years for that detail. Do not assume one warranty covers the whole roof.
• Edge metal requirements differ. On low-slope roofs, metal edge systems must be tested to ANSI/SPRI/FM 4435/ES-1 under IBC 2024 section 1504.6, as NRCA's page on shop-fabricated edge metal testing explains. Keep low-slope edge metal on its own lines, separate from steep-slope drip edge and rake trim.
• Missed lines and change orders. The transition is where the two scopes overlap, so it is the line most likely to be left out by both. As our guide on how long a commercial roof takeoff really takes puts it: "Every unique edge, transition, and termination is a separate assembly to quantify."

How to take off a mixed-system roof, step by step

Mark the boundaries, take off each system on its own, carry the transitions as linear lines, decide who owns the overlap, then check the totals.

Step 1: Mark the system boundaries before you take off anything

Use the roof plan for the outline, then confirm each area's system from the plan notes, details, sections, elevations, and spec book; a roof plan hatch alone can be wrong or generic. Label each area with its system and slope, for example "Area A, TPO, low-slope" and "Area B, standing seam, 4:12".

Then check elevations and sections for heights where the systems meet. They are often missing from plan views, which is why they sit on almost every list of what belongs in a roofing RFI register. JM T-TI-02 shows the TPO coated metal running at least 8 inches (203 mm) up the slope and a minimum total vertical height of 12 inches (300 mm). The MetalMax standing seam detail, which is one panel manufacturer's detail, shows an 8 inch minimum vertical dimension. Those are each maker's figures for its own detail, not code. If your set does not show the height at a transition, it is an RFI.

Step 2: Take off each assembly on its own

• Low-slope membrane (TPO, PVC, or EPDM): field area, insulation layers and cover board, taper (flag it for a tapered quote where the set calls for it), attachment type, edge metal by type, drains, penetrations, curbs, walls, and parapets. For pricing, see our guide on pricing a TPO roof line by line.
• Standing seam metal: slope-adjusted area by roof plane, panel type, underlayment, and clips; eave, rake, ridge, hip, valley, and wall trim as linear lines; closures; and penetrations through the panels.
• Asphalt shingle: slope-adjusted area (the worked example shows the slope factor), underlayment, ice and water barrier where specified, starter, ridge and hip, drip edge and rake, step and counterflashing at walls, and valleys.

Apply your own waste factors and prices to each assembly; this guide does not give them.

Step 3: Carry every transition as its own linear line

Measure each line where two systems meet as its own item, not inside the eave, edge metal, or flashing totals of either system. Name it by its detail, for example "TPO to standing seam transition, per detail 5/A-501".

What goes on that line comes from the detail: the transition flashing or coated metal, its end laps, sealant, fasteners at the spacing shown, and the membrane strip or cover strip that ties it in. The MetalMax detail shows 12 inch end laps on the transition flashing, which changes your piece count, plus a continuous bead of sealant and #10-9 x 1 inch pancake head wood screws at 12 inches on center. JM T-TI-02 shows fasteners at 6 inches (152 mm) on center on the coated metal and a 1 1/2 inch (38 mm) minimum continuous weld. Use the spacing and laps on your project's detail.

Count the ends of each transition as separate items where the transition meets a wall, a rake, or a parapet. Those corners are often not detailed and belong on the RFI list.

Step 4: Decide which assembly owns the overlap

In the published details, both systems are present in the overlap strip: membrane or coated metal runs up the slope, and the steep-slope roofing laps over it. GAF Detail 601 shows an 18 inch (457 mm) minimum overlap and says "Continue underlayment over EverGuard membrane or metal". The MetalMax detail shows the membrane extending at least 24 inches under the roof panels. JM T-TI-02 shows TPO coated metal up the slope with ice and water guard by others lapping over it at least 3 inches, and notes "Do not install shingles with nails penetrating into coated metal", which belongs in the shingle scope.

Carry the membrane that runs up the slope in the membrane assembly, since it is membrane material and labor, and the underlayment and roofing over it in the steep-slope assembly. The project details and the scope split in the bid documents decide this, so follow them over this guide. If two contractors are involved, write the split into your bid clarifications.

Step 5: Check the totals for double counting

• The plan area of the steep-slope sections should not also sit inside the membrane field area.
• The plan areas of all systems should add up to the roof outline on the roof plan, give or take what you can explain.
• Carry slope-adjusted area for the steep-slope sections in your own takeoff, and say so on the line.

What the manufacturer transition details show

Each manufacturer details the tie-in differently, so the transition line's material depends on the specified detail, not on a rule of thumb. These four are published examples; the details in your project documents govern, and none of these dimensions is a code requirement or an industry standard.

For a wider library, NRCA publishes The NRCA Roofing Manual: Membrane Roof Systems, 2023, which its store page says includes 210 construction details for BUR, polymer-modified bitumen, liquid-applied, EPDM, and thermoplastic systems, and The NRCA Roofing Manual: Metal Panel and SPF Roof Systems, 2024, which covers low- and steep-slope applications.

Worked example: one building, three systems (an example, not a real job)

This is an example with made-up dimensions to show the method. It is not a Sharp Pencil job or a customer project, and it uses no prices.

The assumptions:

• A one-story commercial building with three roof systems. All dimensions are invented.
• Area A: a TPO low-slope field, 150 ft by 120 ft in plan. The example takes the low-slope field at plan area.
• Area B: a standing seam metal entry roof, one plane, 40 ft wide, 12 ft horizontal run, slope 4:12. Its low eave meets Area A along the full 40 ft.
• Area C: an asphalt shingle roof on a wing, one plane, 40 ft wide, 16 ft horizontal run, slope 6:12. Its low eave meets Area A along the full 40 ft.
• Areas B and C sit outside Area A's 150 ft by 120 ft outline, so nothing is subtracted from Area A.
• The project detail at the metal transition follows a pattern like the MetalMax detail: membrane extends 24 inches under the panels, with transition flashing at 12 inch end laps.
• The project detail at the shingle transition calls for an 18 inch overlap, the minimum GAF Detail 601 shows.
• Transition flashing comes in 10 ft pieces. That is an assumption for the example; use the length your supplier furnishes.
• Slope factor = square root of (1 + (rise / 12) squared). 4:12 gives about 1.0541; 6:12 gives about 1.1180.

The arithmetic:

• Area A: 150 x 120 = 18,000 SF (180 squares) of membrane field.
• Area B: plan area 40 x 12 = 480 SF; 480 x 1.0541 = 506.0 SF slope-adjusted of standing seam.
• Area C: plan area 40 x 16 = 640 SF; 640 x 1.1180 = 715.5 SF slope-adjusted, or about 7.2 squares of shingles.
• Transition at metal: 40 LF. Membrane strip under the panels: 40 x 2 ft = 80 SF, carried in the membrane assembly.
• Transition at shingle: 40 LF. Membrane or coated metal strip under the shingles: 40 x 1.5 ft = 60 SF, carried in the membrane assembly.
• Transition flashing pieces at metal: each 10 ft piece covers 9 ft once a 12 inch end lap is taken out, so 40 / 9 = 4.4, rounded up to 5 pieces.
• Membrane before waste and laps: 18,000 + 80 + 60 = 18,140 SF.
• Ends of each transition where it meets a wall or rake: 2 per transition, 4 in total, each flagged for a detail check.

The blended version: 18,000 + 506.0 + 715.5 = 19,221.5 SF of "roof". That one figure mixes plan and slope-adjusted area, cannot feed a membrane, panel, or shingle order, has no transition lines, and misses the 140 SF of membrane that runs up under the steep-slope roofing.

RFI questions a mixed-system set usually raises

The transition is where the drawings most often leave things open, so expect questions there:

• Which detail applies at each transition, and does it match the manufacturer of the specified membrane?
• What is the height of the steep-slope roofing above the low roof at each transition?
• How far does the membrane extend under the steep-slope roofing, and who installs the underlayment over it?
• Who furnishes and installs the transition flashing: the membrane contractor or the metal or shingle contractor?
• How are the ends of each transition flashed where they meet walls, rakes, or parapets?
• Is the steep-slope roofing new work, or existing work by others that the new membrane ties into?
• Which warranty covers the transition?

See what belongs in a roofing RFI register.

How Sharp Pencil handles mixed-system jobs

Commercial low-slope is the core, and we also cover standing seam metal and shingle scopes when they're part of the job. On a mixed-system set you get:

• Each system as its own lines in the takeoff workbook, with separate area, edge, and detail lines. Systems are not blended. The sample takeoff on our homepage lists each quantity on its own line with the sheet it came from; it is a fictional sample, not a customer job.
• Transitions as their own linear lines when the set shows a transition or tie-in detail.
• Standing seam and shingle areas reported in SF, each with its sheet cite.
• Open transition questions as drafted RFIs on the Questions tab and on your job page.
• A material order list when the takeoff supports one.
• A roofing professional reviews every paid job.
• The takeoff comes back within 48 hours, often sooner.

What we cover: TPO, PVC, and EPDM (adhered, mechanically attached, induction welded, ballasted); standing seam metal (snap-lock and mechanical seam, new construction and retrofit); metal panel retrofit; asphalt shingle (new and tear-off); insulation and taper (taper flagged for quote); and sheet metal, from coping and drip edge to gutters, downspouts, and scuppers. See what an outsourced commercial roofing takeoff includes.

The first takeoff is free on a live bid, then $395 per set. A mixed-system building is still one set at $395. Price goes by new set of drawings or new address, not by the number of roof systems. For how that compares, see what commercial roofing takeoffs cost across the market.

Still deciding where takeoff hours come from? Read whether to hire an estimator or outsource the takeoffs, or software, aerial reports, and services compared.

FAQ

How do you take off a commercial roof with more than one roof system?

Take off each system as its own assembly with its own area, edges, and details, and carry every place where two systems meet as a separate linear line. Then check that no area is counted in two systems.

Should transition flashing be its own line in a roofing takeoff?

Yes. The transition uses its own detail, with its own flashing, laps, sealant, and fasteners, and it is the line most likely to be left out when two scopes overlap.

How far does TPO or EPDM run under a metal or shingle roof at a transition?

It depends on the detail in the project documents. GAF's Detail 601 shows an 18 inch minimum overlap, and the MetalMax standing seam detail, which is one panel manufacturer's detail, shows the membrane extended at least 24 inches under the panels. If the set does not say, put it on the RFI list.

Do I use slope-adjusted area for the metal and shingle sections?

For your own takeoff method, yes: multiply the plan area of each steep-slope plane by its slope factor (about 1.054 at 4:12 and 1.118 at 6:12), and keep those areas separate from the low-slope membrane area.

Who covers the transition between a membrane roof and a shingle or metal roof?

The details and the bid documents decide it. GAF's and JM's transition details mark the shingles, metal panels, or ice and water guard as "by others", so write the split into your bid clarifications and check each manufacturer's warranty terms for that detail.

What should go on the RFI list for a mixed-system roof?

Which detail applies at each transition, the height of the steep-slope roofing above the low roof, how far the membrane extends under it, who furnishes the transition flashing, how the transition ends are flashed, and which warranty covers the transition.

Can Sharp Pencil take off a job with TPO or EPDM plus standing seam or shingle?

Yes. Commercial low-slope is the core, and standing seam metal and shingle scopes are covered when they are part of the job. Each system comes back as its own lines, transitions as their own linear lines when the set shows a transition or tie-in detail, and open transition questions as drafted RFIs on the Questions tab. Standing-seam and shingle areas are reported in SF with sheet cites. The takeoff comes back within 48 hours, often sooner, and the first takeoff is free on a live bid. A mixed-system building is still one set at $395.