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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*. A takeoff that sits in a week-long queue is no help when the bid is due sooner. *Clock starts once any questions we send you are answered.
• 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.
• 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.
• Every takeoff is reviewed before delivery. The review is included in the price, not sold 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 for your takeoff, never shared or pooled, and deleted whenever you ask (automatic deletion after 90 days is being rolled out). See what happens to your plans.
• Monthly plans, with your first takeoff free. Our monthly plans are the main way to buy, and $395 is the price per single takeoff. Either way, try your first one free 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, canopy, or mansard, or a new 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 the square foot of plan area. Standing seam goes by slope-adjusted area plus linear feet of trim, and shingles by the square. One total cannot feed all three material lists, and a plan-view number undercounts the sloped areas.
• Different crews or subs. GAF Detail 601 says "Shingles, tile, or metal panels by others", and JM T-TI-02 shows "Ice and water guard (by others)". If the metal or shingle work is subbed, the sub needs its own quantity, and the transition needs a clear owner.
• Different edge metal and warranty terms. 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 edge metal testing page explains, so keep low-slope edge metal apart from steep-slope drip edge and rake trim. Each detail also carries its own manufacturer terms; the JM T-TI-02 title block lists a maximum guarantee term of 20 years for that detail.
• 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

Outline each area on the roof plan, then confirm its system from the notes, details, sections, elevations, and spec book; a roof plan hatch alone can be wrong. Label each area with its system and slope, such as "Area A, TPO, low-slope" and "Area B, standing seam, 4:12".

Check heights where the systems meet. They are often missing from plan views and belong in a roofing RFI register. The details set minimums of their own: JM T-TI-02 shows 8 inches (203 mm) minimum of coated metal up the slope and 12 inches (300 mm) minimum total vertical height, and the MetalMax detail shows 8 inches minimum vertical. If the set does not show the height, it is an RFI.

Step 2: Take off each assembly on its own

• Low-slope membrane (TPO, PVC, or EPDM): field area, insulation and cover board, taper (flagged for a tapered quote), attachment, edge metal by type, drains, penetrations, curbs, walls, and parapets. See pricing a TPO roof line by line.
• Standing seam metal: slope-adjusted area by plane, panel type, underlayment, clips, and eave, rake, ridge, hip, valley, and wall trim as linear lines.
• Asphalt shingle: slope-adjusted area, underlayment, ice and water barrier where specified, starter, ridge and hip, drip edge and rake, wall flashing, and valleys.

Apply your own waste factors and prices to each; they differ by system.

Step 3: Carry every transition as its own linear line

Take each line where two systems meet as its own item, not inside either system's eave, edge metal, or flashing totals, and name it by its detail, such as "TPO to standing seam transition, per detail 5/A-501". The line carries the transition flashing or coated metal, its end laps, sealant, fasteners at the detail's spacing, and the tie-in strip. The MetalMax detail shows "Transition flashing with 12" end laps", and laps change the piece count. Carry the ends of each transition at walls, rakes, or parapets as separate items; they are often not detailed, so they go on the RFI list.

Step 4: Decide which assembly owns the overlap

In the cited details, both systems are present in the overlap strip. GAF Detail 601 shows an 18 inch minimum overlap and says "Continue underlayment over EverGuard membrane or metal". The MetalMax detail says "Membrane roofing, extend under roof panels min. 24"". JM T-TI-02 shows TPO coated metal up the slope with ice and water guard by others lapping over it.

In the details we cite, the membrane that runs up the slope is membrane material and membrane labor, so it usually belongs in the membrane assembly, with the underlayment and roofing over it in the steep-slope assembly. The project details and the bid documents' scope split decide this; follow them. 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 the systems added together should match the building's roof outline on the roof plan, give or take what you can explain.
• Label slope-adjusted areas as slope-adjusted on the line, so nobody adds them to plan area later.

What the manufacturer transition details show

Each manufacturer details the tie-in differently, which is why the material on the transition line depends on the specified detail, not on a rule of thumb.

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.

Assumptions:

• A one-story commercial building with three roof systems. All dimensions are invented for the example.
• Area A: TPO low-slope field, 150 ft by 120 ft in plan, taken at plan area.
• Area B: standing seam metal entry roof, one plane, 40 ft wide, 12 ft horizontal run (480 SF, 4.8 squares, in plan), slope 4:12. Its low eave meets Area A along the full 40 ft.
• Area C: 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 outline, so nothing is subtracted from Area A.
• The metal transition detail follows a pattern like the MetalMax detail: membrane 24 inches under the panels, transition flashing with 12 inch end laps.
• The shingle transition detail calls for an 18 inch overlap, the minimum GAF Detail 601 shows.
• Transition flashing comes in 10 ft pieces. 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 membrane total before waste and laps is 18,000 + 80 + 60 = 18,140 SF, and each 10 ft flashing piece covers 9 ft once the 12 inch end lap comes out, so 40 / 9 = 4.4, rounded up to 5 pieces.

What a blended number would have hidden: 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. These are worth copying into your register:

• 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?

For how to keep and send these, 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 our monthly plans, a mixed-system building counts as one takeoff; bought on its own, it is one single takeoff at $395 for the whole mixed set. Price goes by new set of drawings or new address, not by the number of roof systems.

What you get back:

• Each system as its own lines in the takeoff workbook, with separate area, edge, and detail lines, and standing seam and shingle areas in SF with the sheet each quantity came from.
• Transitions as their own linear lines when the set shows a transition or tie-in detail, with open transition questions as drafted RFIs on the Questions tab and your job page.
• A material order list when the takeoff supports one, with every takeoff reviewed before delivery, delivered within 48 hours*.

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, architectural and three-tab); insulation and taper, with taper flagged for quote; and sheet metal (coping, drip edge, gravel stop, gutters, downspouts, scuppers). For the full list, see what an outsourced commercial roofing takeoff includes, and for prices across the market, see what commercial roofing takeoffs cost across the market.

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 included 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, one panel manufacturer's detail, shows 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?

In your own takeoff, 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, and on a monthly plan a mixed-system building counts as one takeoff; bought on its own, it is one single takeoff at $395 for the whole mixed set. 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 is delivered within 48 hours once any questions we send you are answered, and the first takeoff is free on a live bid.