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Roof penetrations and curb flashing on a commercial takeoff
What does a roof penetration takeoff count?
Pipe and vent flashings by type, pitch pans, curbs for rooftop units, skylights and hatches measured by perimeter, and equipment and pipe supports, each with its unit and source sheet. Any count that differs between the roof plan and the mechanical, plumbing or electrical sheets goes on the Questions tab.
Disclosure: Sharp Pencil sells commercial roofing takeoffs, so we have a stake in this topic.
This is a takeoff checklist, not mechanical, code, structural or warranty advice. The design professional, the manufacturer and your bid documents decide the details.
Short answer
A penetration takeoff counts every pipe, vent, conduit and support that goes through the roof, sorted by flashing type, and measures every curb by its perimeter for the curb flashing. Skylights, hatches and rooftop units sit on curbs, so they count the same way. Each count carries the sheet it came from. Check the mechanical, plumbing and electrical sheets against the roof plan, because they can differ. What the drawings leave open goes on the Questions tab.
What penetration and curb lines does a commercial takeoff carry?
A rooftop unit is not one line. The curb, its flashing and the pipes and conduit around it are each a line.
| Line | Unit | Where it usually comes from |
|---|---|---|
| Pipe and vent flashings, by size range | EA | Plumbing and mechanical sheets, roof plan |
| Pitch pans or sealant pockets | EA | Roof details, Division 07 |
| Conduit and cable penetrations | EA | Electrical sheets |
| Gas piping penetrations | EA | Plumbing or mechanical sheets |
| Rooftop unit and fan curbs, by size | EA with size | Mechanical sheets, roof plan |
| Curb flashing | LF of curb perimeter, as detailed | Curb size from the mechanical sheets, curb detail |
| Skylights | EA with size, curb flashing LF | Roof plan, architectural details |
| Roof hatches | EA with size, curb flashing LF | Roof plan, architectural details |
| Equipment supports and rails | EA | Mechanical and structural sheets |
| Pipe supports and pads | EA | Mechanical and plumbing sheets, Division 07 |
| Crickets behind curbs | Flagged for the taper quote | Taper layout or roof plan |
For where each count lives in the set, see the sheets a roofing takeoff has to read. For crickets behind curbs, see tapered insulation takeoff.
What does each flashing type add?
The detail sheet decides how each penetration is flashed. The takeoff counts it that way.
| Flashing type | Lines it adds | Where to confirm |
|---|---|---|
| Prefabricated pipe boot | One boot per pipe, clamp and sealant as detailed | Penetration detail, Division 07 |
| Field wrapped flashing | Flashing membrane and clamp as detailed, where the detail calls for it | Penetration detail |
| Pitch pan or sealant pocket | One pan per penetration or cluster, with sealant as detailed | Penetration detail |
| Curb flashing | Membrane up the curb by perimeter, termination and curb cap or counterflashing as detailed | Curb detail |
On re-roofs, ask whether existing curbs, pans and flashings are removed or reused, and who raises curbs if the new roof is thicker. See commercial re-roof takeoff.
Measure curbs by perimeter
A curb is counted once and flashed all the way around.
- Curb flashing is the perimeter of each curb, from the curb size on the mechanical sheets.
- Count rooftop units, fans, skylights and hatches the same way.
- When the mechanical sheets give the unit size but not the curb size, that goes on the Questions tab.
The takeoff counts what the drawings show. It does not size curbs or decide flashing heights. That is the design professional's and the manufacturer's call.
Supports, conduit and gas lines
The items that fill a roof after the units go in can be missing from the roof plan.
- Equipment supports and rails by EA from the mechanical and structural sheets.
- Pipe supports and pads by EA from the mechanical and plumbing sheets.
- Conduit and gas piping penetrations by EA from the electrical, plumbing or mechanical sheets.
See roofing bid items that are not on the roof plan.
When the roof plan and the MEP sheets disagree
Count the penetrations twice, once on the roof plan and once on the trade sheets.
Carry the higher count with its source and put the difference on the Questions tab.
- Curb or penetration count differs between the roof plan and the mechanical, plumbing or electrical sheets
- Curb size not shown, only the unit size
- Flashing type for a penetration not detailed
- Existing curbs and flashings removed or reused on a re-roof
- Equipment or pipe supports shown on mechanical sheets but not on the roof plan
- Skylight or hatch size not dimensioned
Worked example
Example data, not a real job.
Assume a 200 ft by 150 ft low slope roof, TPO. The mechanical sheets show 5 rooftop unit curbs, each 8 ft by 6 ft. The roof plan shows 2 skylights, each 4 ft by 4 ft, and 1 roof hatch, 3 ft by 4 ft. The plumbing and mechanical sheets show 18 pipe penetrations with prefabricated boots and 4 irregular penetrations detailed as pitch pans. The electrical sheets show 6 conduit penetrations, and the roof plan shows 4. The mechanical sheets show 10 pipe supports.
- Curbs: 5 rooftop units at 2 x (8 + 6) = 28 LF each is 140 LF of curb flashing.
- Skylights: 2 at 2 x (4 + 4) = 16 LF each is 32 LF.
- Hatch: 1 at 2 x (3 + 4) = 14 LF.
- Curb flashing total: 140 + 32 + 14 = 186 LF.
- Pipe boots: 18. Pitch pans: 4. Conduit penetrations: 6, carried from the electrical sheets. Pipe supports: 10.
| Line | Quantity | Basis |
|---|---|---|
| Rooftop unit curbs | 5 EA, 8 ft by 6 ft | Drawings, mechanical sheets |
| Skylights | 2 EA, 4 ft by 4 ft | Drawings, roof plan |
| Roof hatch | 1 EA, 3 ft by 4 ft | Drawings, roof plan |
| Curb flashing | 186 LF | Curb perimeters |
| Pipe boots | 18 EA | Drawings, plumbing and mechanical sheets |
| Pitch pans | 4 EA | Drawings, penetration detail |
| Conduit penetrations | 6 EA | Drawings, electrical sheets |
| Pipe supports | 10 EA | Drawings, mechanical sheets |
This set would raise one question: the roof plan shows 4 conduit penetrations and the electrical sheets show 6.
Sources: manufacturer installation guides and published roofing detail guidance.
What you get back from Sharp Pencil
The same penetrations and curbs, counted for you from the full set.
Every quantity carries its source sheet and its basis.
Four files: START HERE, marked-up drawings PDF, Takeoff.xlsx with a Questions tab, and the material order list.
Pricing is optional. Send your cost data and we apply your prices to the quantities. Any line you have not priced comes back marked UNPRICED.
We take off steep slope (standing seam, shingle) and commercial low slope (TPO, EPDM, PVC, mod bit, BUR) from the full set. For the rest of the roof, see TPO roofing takeoff, modified bitumen and built-up roof takeoff and roof drainage takeoff.
See commercial roofing takeoff services and a sample takeoff.
FAQ
What is a roof penetration takeoff?
The part of a roofing takeoff that counts every pipe, vent, conduit, curb, skylight, hatch and support that goes through or sits on the roof, with the flashing lines each one adds, tied to the sheet each count came from.
How is curb flashing measured on a takeoff?
By the perimeter of each curb, in linear feet, from the curb size on the mechanical sheets or the roof plan. If only the unit size is shown, the curb size goes on the Questions tab.
Where do I find the penetration count?
On the mechanical, plumbing and electrical sheets, then the roof plan. The roof plan may show fewer, so a count that differs goes on the Questions tab.
Does the takeoff decide how each penetration is flashed?
No. The details, the design professional and the manufacturer decide the flashing. The takeoff counts each penetration the way the drawings detail it and lists what they leave open.
What does a takeoff from Sharp Pencil cost?
$395 per takeoff. $395 covers a new set of drawings, or a new address. Your first takeoff is free, one per contractor, on a job you're bidding or quoting.
What does Sharp Pencil send back?
Four files: START HERE, marked-up drawings PDF, Takeoff.xlsx with a Questions tab, and the material order list. Every quantity carries its source sheet and its basis. Usually within one business day. Delivered within 48 hours*.
*Clock starts once any questions we send you are answered.
Why send it to us
- We take off steep slope (standing seam, shingle) and commercial low slope (TPO, EPDM, PVC, mod bit, BUR) from the full set.
- Every quantity carries its source sheet and its basis.
- Four files: START HERE, marked-up drawings PDF, Takeoff.xlsx with a Questions tab, and the material order list.
- Pricing is optional. Send your cost data and we apply your prices to the quantities. Any line you have not priced comes back marked UNPRICED.
- Usually within one business day. Delivered within 48 hours*.
- A plan set you send us will never be used to compete with you, and plan sets are deleted whenever you ask.
- First takeoff free, one per contractor, on a job you're bidding or quoting.
Residential is not our focus today, but ask if you have a job in mind.
*Clock starts once any questions we send you are answered.
Try it on a job you are bidding
Get your first takeoff free · $395 per takeoff · See a sample takeoff
The Sharp Pencil team