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Roof drainage on a commercial takeoff: drains, overflows, scuppers and gutters
What does a roof drainage takeoff count?
Primary and overflow drains, the flashing lines each drain adds, scuppers, conductor heads, downspouts and gutters, each with its unit and source sheet. Sumps go to the taper quote, and any count that differs between the roof plan and the plumbing 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 plumbing, code, structural or warranty advice. The plumbing engineer, the design professional and your bid documents decide the drainage.
Short answer
A roof drainage takeoff counts every primary and overflow drain, every scupper, conductor head and downspout, and every run of gutter, each tied to the sheet it came from. Each drain also brings its own flashing lines, and any sump goes to the taper quote. Check the roof plan count against the plumbing sheets, because they can differ. Sizing stays with the plumbing engineer. What the drawings leave open goes on the Questions tab.
What drainage lines does a commercial takeoff carry?
Drainage is more than a drain count. Each drain, scupper and gutter run brings lines of its own.
So the takeoff carries every drain, overflow, scupper, conductor head, downspout and gutter, each with its unit and the sheet it came from.
| Line | Unit | Where it usually comes from |
|---|---|---|
| Primary roof drains | EA | Plumbing sheets and drain schedule, roof plan |
| Overflow (secondary) drains | EA | Plumbing sheets and drain schedule |
| Drain flashing, one set per drain | EA, one set per drain, as detailed | Roof details, Division 07 |
| Drain sumps | EA, flagged for the taper quote | Roof plan, drain detail, taper layout |
| Through-wall and overflow scuppers | EA with size | Elevations, roof plan, scupper detail |
| Conductor heads | EA | Elevations, scupper detail |
| Downspouts | EA and LF | Elevations |
| Gutters | LF by size | Roof plan, edge details, elevations |
| Gutter outlets, end caps and hangers | EA, or by the gutter detail | Gutter detail |
| Crickets and saddles | 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 sumps and crickets, see tapered insulation takeoff.
What does each drain add to the roof side of the takeoff?
The plumber usually sets the drain body. The roofer flashes it, and that is where the lines come from.
| Membrane | Drain lines | Scupper lines |
|---|---|---|
| TPO or PVC | Membrane target sheet at each drain as detailed, sealant under the clamping ring, clamping ring and strainer reused or replaced as the spec says | Scupper sleeve or box, membrane wrap into the opening, edge metal at the face |
| EPDM | Drain flashing as detailed, clamping ring and strainer as the spec says | Scupper box, flashing into the opening, edge metal at the face |
| Mod bit or BUR | Drain flashing as detailed, clamping ring and strainer as the spec says | Scupper box, plies and cap sheet into the opening, edge metal at the face |
On re-roofs, ask whether the drain bodies, clamping rings and strainers are reused, and who replaces broken ones. See commercial re-roof takeoff.
Overflow drains and scuppers are their own lines
An overflow drain is not a spare. It is a second drain location with its own flashing.
- When the design calls for secondary (overflow) drainage, the drawings show overflow drains or overflow scuppers. Count each one as its own location.
- An overflow drain may sit next to the primary drain, sometimes in the same sump. Each still gets its own flashing.
- Overflow scuppers through a parapet add the scupper, the wrap and the edge metal at the face, plus a conductor head and downspout if the elevations show one.
The takeoff counts what the drawings show. It does not decide whether the roof needs more. That is the design professional's call.
Gutters, downspouts and conductor heads
On steep slope, or a low slope roof with a gravel stop, the water comes off at the edge.
- Gutters by LF and size, from the roof plan and edge details.
- Downspouts by LF from the elevations, with a count.
- Conductor heads by EA at each scupper that has one.
Steep slope gutters belong to the full linear list on standing seam metal roof takeoff and asphalt shingle roof takeoff. For edge profiles, see edge metal takeoff.
When the roof plan and the plumbing sheets disagree
Count the drains twice, once on each sheet.
The roof plan may show primary drains only, while the plumbing sheets show primary and overflow. Carry the higher count with its source and put the difference on the Questions tab.
- Drain count differs between the roof plan and the plumbing sheets
- Overflow drain or overflow scupper type not shown
- Drain body, clamping ring and strainer: new or reused on a re-roof
- Sump shown on the roof plan but not on the taper layout
- Scupper, conductor head or downspout on the elevations but not on the roof plan
- Gutter size or hanger detail not shown
Worked example
Example data, not a real job.
Assume a 200 ft by 150 ft low slope roof, TPO, with a parapet on three sides and a gravel stop with a gutter on one 150 ft side. The plumbing sheets show 4 primary drains and 4 overflow drains. The roof plan shows the 4 primary drains only. The elevations show 3 overflow scuppers through the parapet, each with a conductor head, and 3 downspouts on the gutter side, each 20 ft long. One sump at each drain (example assumption).
- Drains: 4 primary plus 4 overflow is 8 drain locations, so 8 sets of drain flashing.
- Sumps: 8, one at each drain (example assumption), flagged for the taper quote.
- Overflow scuppers: 3, with 3 conductor heads.
- Gutter: 150 LF on the gravel stop side.
- Downspouts: 3 at 20 ft is 60 LF.
| Line | Quantity | Basis |
|---|---|---|
| Primary roof drains | 4 EA | Drawings, plumbing sheets |
| Overflow drains | 4 EA | Drawings, plumbing sheets |
| Drain flashing | 8 EA | One set per drain |
| Drain sumps | 8 EA, flagged for the taper quote | Example assumption |
| Overflow scuppers | 3 EA | Drawings, elevations |
| Conductor heads | 3 EA | Drawings, elevations |
| Gutter | 150 LF | Example assumption |
| Downspouts | 3 EA, 60 LF | Drawings, elevations |
This set would raise two questions: the roof plan shows 4 drains and the plumbing sheets show 8, and the overflow scuppers have no downspouts shown.
Sources: manufacturer drain details and published drain sump guidance.
What you get back from Sharp Pencil
The same drainage lines, done 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 and modified bitumen and built-up roof takeoff.
See commercial roofing takeoff services and a sample takeoff.
FAQ
What is a roof drain takeoff?
The part of a roofing takeoff that counts every primary and overflow drain, scupper, conductor head, downspout and gutter, with the flashing lines each one adds, tied to the sheet each count came from.
Are overflow drains a separate line on the takeoff?
Yes. Each overflow drain is its own drain location with its own flashing, even when it sits next to the primary drain.
Where do I find the drain count?
On the plumbing sheets and drain schedule first, then the roof plan. The roof plan may show primary drains only, so a count that differs goes on the Questions tab.
Does the takeoff size the drains or scuppers?
No. The plumbing engineer and the design professional size the drainage. The takeoff counts what the drawings show 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