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Tapered Insulation on a Commercial Roofing Takeoff: What to Take Off, What the Quote Covers, and How Board Feet Work
Disclosure: Sharp Pencil sells commercial roofing takeoffs, so we have a stake in this topic.
On most commercial bids, the tapered insulation number comes from a manufacturer's tapered quote, not your own measurement. Your takeoff supplies what the quote needs: roof areas, slope, minimum thickness, R-value basis, drains, crickets and sumps. Then check the quote: board feet equal area times average thickness. Carry the lines taper moves yourself: edge blocking height, fastener lengths, flashing heights and freight.
Note: The example roof below is made up to show the method. It is not a real job. Panel sizes and thicknesses come from one manufacturer's published data sheet. Check the data sheet for the product your spec names.
Who designs the taper on a commercial bid?
Usually the insulation manufacturer, through its tapered design department or a distributor, from the drawings and spec you send. The estimator does not design the layout.
Atlas Tapered Services asks for quote requests at least 48 hours before the bid date, with bid date, project name, location, specification, and a dimensioned or scalable roof plan. Quotes come back for review. After award, a purchase order starts shop drawings, which the contractor signs. Atlas notes that shop drawing amendments may result in price revisions to the original quote. Atlas says quote requests come from distributors and private label partners, and there is no fee if the job is bought through Atlas.
That matches the line on our roofing RFI register: "Taper is nearly always a quote, not a calculation, because the manufacturer designs the layout." Put the taper question there when ownership or layout is open.
Sometimes the architect already shows a full tapered plan (designers can get manufacturer design assistance, which Atlas offers to architects and specifiers). Then the quote prices that plan rather than designing one. When the set says "tapered insulation by others" or shows slope arrows with no layout, that is a question for the GC, not an assumption.
What to pull from the drawings before you request a tapered quote
Pull these items from the set before you fill a manufacturer or distributor tapered quote request.
| Item | Where to find it | Why it matters |
|---|---|---|
| Taper slope (1/8, 1/4, 3/8 or 1/2 in. per ft) | Roof plan slope arrows, plus spec Division 07 insulation | Sets panel series and how fast thickness builds. The 2021 IBC requires a design slope of not less than 1/4 unit vertical in 12 units horizontal (2 percent) for single-ply and modified bitumen (Sections 1507.12.1 and 1507.11.1, as printed in the 2021 Seattle Building Code, which follows the IBC numbering). Check the code your jurisdiction adopted. |
| Minimum thickness at the drains | Spec or roof plan note | Sets the starting panel. One manufacturer's tapered design guide says the thinnest available thickness for tapered polyiso is 0.5 in. and that the minimum thickness should be clearly specified. |
| R-value, minimum or average | Spec | Carlisle's form asks you to choose minimum or average. The same design guide says to specify minimum or average, NOT both. One choice only. No energy-code math on this page. |
| Cricket slope | Roof plan or spec | Carlisle's form asks for cricket slope separately from taper slope. |
| Drains, overflow drains and scuppers | Roof plan plus plumbing sheets | Each is a low point in the layout. See the sheets a takeoff reads besides the roof plan. |
| Sumps | Roof plan or drain detail | Carlisle's form offers 8 x 8 or 4 x 4 sumps and omits the unit. Write them as 8 ft by 8 ft or 4 ft by 4 ft (the design guide shows sumps in feet). |
| Slope in the deck | Structural sheets | Carlisle asks Slope in Deck: Yes / No. The design guide says to note structurally sloped areas and the net slope wanted. |
| Curbs and penetrations | Mechanical sheets | The design guide asks for major penetrations and the support type on the roof plan and says to avoid curbs in drain valleys or low points. |
| Attachment, cover board, compressive strength, facer | Spec | Carlisle's form asks fully adhered yes or no, HD cover board yes or no, 20 or 25 psi, and facer type. |
| Drawing file | Your set | Carlisle accepts JPG, PNG, PDF, TIFF, PLN, DWG, ZIP and RVT uploads on its quote form. |
Anything the set leaves open goes on the request as a stated assumption and on the Questions tab as a question.
How board feet and average thickness work
One board foot is one square foot of board one inch thick. Board feet for a tapered area equal its plan area times its average thickness in inches. For a straight taper the average is the thinnest point plus the thickest point, divided by two.
GAF's EnergyGuard NH Tapered Polyiso data sheet (COMGN753) lists each 4 ft by 4 ft panel with its thickness range, average thickness and board feet per panel. At 1/4 in. per ft, panel X runs 0.5 to 1.5 in., average 1.0 in., 16 board feet. Panel Y runs 1.5 to 2.5 in., average 2.0 in., 32 board feet. Panel Z runs 2.5 to 3.5 in., average 3.0 in., 48 board feet. Panel ZZ runs 3.5 to 4.5 in., average 4.0 in., 64 board feet. That is 16 SF times the average thickness each time. At 1/4 in. per ft, a 4 ft panel gains 1 in. Above the thickest tapered panel, flat fill goes under the next series.
Insulation ships and is priced by volume, so the quote's board feet are the number to check. Our TPO pricing page already notes that taper changes truck count. See how fastener length and freight follow the stack.
The quick check does not catch crickets, sumps, and the cut panels at drains, curbs and edges. Board waste comes from the board layout. See single-ply waste factors and roll layout. This page does not invent a waste percent.
When the spec states a minimum or average R-value, the stack and board count can change. See tapered insulation R-value.
Example: checking a tapered quote on one roof area (made up, not a real job)
This example is invented. Use it only to see the arithmetic. Crickets are still needed along the valley between drains. Their board feet come from the quote.
Assumptions (invented): roof area 96 ft by 48 ft, 4,608 SF, flat structural deck. A line of drains runs down the middle along the 96 ft length. Taper slopes both ways to the drain line at 1/4 in. per ft, 0.5 in. minimum at the drains. Each side runs 24 ft from drain line to high edge.
- Thickness: 24 ft at 1/4 in. per ft adds 6 in., so 0.5 in. at the drains and 6.5 in. at both high edges. Average thickness 3.5 in.
- Quick check: 4,608 SF times 3.5 in. = 16,128 board feet, before crickets, sumps and waste.
- Panel rows, each side (6 rows of 4 ft): X, Y, Z, ZZ, then 4 in. of flat fill under X, then 4 in. of flat fill under Y. Row averages 1, 2, 3, 4, 5 and 6 in. (mean 3.5 in., which matches). 24 panels per row along 96 ft.
| Row | Panels (both sides) | Board feet per panel | Board feet |
|---|---|---|---|
| X (tapered) | 96 | 16 | 1,536 |
| Y (tapered) | 96 | 32 | 3,072 |
| Z (tapered) | 48 | 48 | 2,304 |
| ZZ (tapered) | 48 | 64 | 3,072 |
| Tapered subtotal | 9,984 | ||
| Flat fill (4 in. under outer two rows, both sides) | 1,536 SF at 4 in. | 6,144 | |
| Total | 16,128 |
Tapered panels: 96 X, 96 Y, 48 Z and 48 ZZ. Tapered board feet: (96 × 16) + (96 × 32) + (48 × 48) + (48 × 64) = 1,536 + 3,072 + 2,304 + 3,072 = 9,984. Flat fill: 4 in. under the outer two rows on each side, 96 ft × 8 ft × 2 sides = 1,536 SF at 4 in. = 6,144 board feet. Spec decides whether that is one layer or two. Total: 9,984 + 6,144 = 16,128 board feet, which matches the quick check.
With drains in a line, the layout needs crickets between drains along the valley line. Count and locate them on the takeoff. The quote carries their board feet.
Lines taper moves on this roof: the high edges sit at 6.5 in. of insulation plus any cover board, so the takeoff checks that edge blocking and nailer height on the details suit the finished height at the high edges, not the 0.5 in. at the drains. Fastener lengths step up across the roof. Drain flashings sit at the thin end.
How crickets and sumps work at bid time
A cricket is a raised, sloped area that turns water toward a drain, built from steeper tapered panels. A sump is a small recessed area at a drain. The manufacturer sizes them. The estimator counts and locates them so nothing gets missed in the quote.
Atlas's cricket design sheet says cricket panel slope is typically double the roof surface slope. Its table: at 1/8 in. roof slope, 1/4 in. cricket panels, 3:1 maximum length to width, cricket valley slope 0.040 in. per ft. At 1/4 in. roof slope, 1/2 in. cricket panels, 3:1, 0.080 in. per ft. At 1/2 in. roof slope, 1/2 in. cricket panels, 4:1, 0.121 in. per ft. Atlas notes that the functionality of the cricket is determined by the cricket valley slope, and points to PIMA Technical Bulletin 108 and the NRCA Roofing Manual.
One manufacturer's tapered design guide says cricket material slope should be greater than the roof surface slope. Its example is a 1/2 in. per ft roof slope with crickets no less than 3/4 in. per ft, for a 1/4 in. net positive slope.
Takeoff lines: crickets behind every curb that blocks flow (the RFI register asks whether crickets behind curbs are included), crickets between drains, and sumps at drains by size. Their board feet come from the quote. Their count and locations come from you.
What tapered insulation changes elsewhere on the bid
- Edge blocking and nailers sized to the finished height at each edge, which changes along a sloped edge.
- Exposed parapet height gets shorter where taper builds up. See parapet membrane wrap.
- Fastener lengths step up with stack thickness across the roof.
- Curb and penetration flashing heights measured from the finished surface at that spot.
- Drain flashings and any sumps at the thin end, including overflow drains from the plumbing sheets.
- Freight and staging by volume, not square feet.
- Two layers, staggered joints, if the spec or code requires them. PIMA Technical Bulletin 118 says that under the IECC, continuous roof insulation is generally required to be installed in two or more layers (see C402.2.1).
- Shop drawing changes after award can change the price (Atlas). Carry the quote date and number on the bid.
Mod bit and BUR over taper follow the same quote-and-check habit. See modified bitumen and built-up roof takeoff.
When slope is shaped in spray polyurethane foam rather than sheet polyiso, see SPF roof takeoff for foam board feet and cricket volume. Sheet taper method stays on this page.
When the set says "tapered insulation by others" or shows no layout
Write it as an open question to the GC: who designs, who furnishes, who installs, whether the slope shown meets the code minimum, and whether crickets behind curbs are included. Mirror the wording on the RFI register. Bid it as a stated assumption, never a silent exclusion. Put the item on the Questions tab with that default stated.
See a sample takeoff to check how a carried default shows up on the Questions tab.
Get your first takeoff free
One per contractor, on a job you're bidding or quoting. Upload the plan set and you get quantities you can check against the sheets.
Usually within one business day. Delivered within 48 hours*.
*Clock starts once any questions we send you are answered.
FAQ
How do you calculate board feet of tapered insulation?
One board foot is one square foot of board one inch thick. Board feet for a tapered area equal its plan area times its average thickness in inches. For a straight taper, average thickness is the thinnest point plus the thickest point, divided by two.
What information does a manufacturer need for a tapered insulation quote?
Slope, minimum thickness, whether R-value is minimum or average (not both), cricket slope, drains and overflows, sumps, slope in the deck, curbs and penetrations, attachment, cover board, compressive strength, facer, and a dimensioned or scalable roof plan.
What slope do crickets use?
Cricket panel slope is typically double the roof surface slope. Atlas publishes length-to-width limits and valley slopes for common roof slopes. One manufacturer's tapered design guide says cricket material slope should be greater than the roof surface slope.
Does tapered insulation change the edge blocking on a bid?
Yes. Edge blocking and nailers are sized to the finished height at each edge, which changes along a sloped edge. Fastener lengths, flashing heights, and freight also move with stack thickness.
Does Sharp Pencil take off tapered insulation?
Yes. We read the plan set for the job you're bidding: tapered layouts, detail callouts, edge conditions, structural notes, spec references. The takeoff workbook lists field area, tapered, edge metal by profile, penetrations, drains, blocking, and flashing. Open items go on the Questions tab. We do not design tapered layouts or produce shop drawings.
Why send your takeoffs to Sharp Pencil
If your problem is hours, not skill, here's what to look for when you hand takeoffs off.
- Usually within one business day. Delivered within 48 hours*. A takeoff stuck in a week-long queue does you no good when the bid is due sooner.
- Every page gets read. Send the full set: architectural, structural, mechanical, plumbing, and the spec book if you have it.
- Every quantity names its sheet. Every quantity carries its source sheet and its basis, so you can check it against the drawings.
- Questions instead of guesses. If the set leaves something open, like a taper layout marked "by others," it goes on the Questions tab in Takeoff.xlsx, not into the number as a guess.
- Checked before it goes out. Every paid takeoff is checked before delivery. A person reviews every takeoff before it reaches you.
- Four files, one package. START HERE, marked-up drawings PDF, Takeoff.xlsx with a Questions tab, and the material order list.
- Your plans stay yours. A plan set you send us will never be used to compete with you, and plan sets are deleted whenever you ask. See what happens to your plans.
- First takeoff free, one per contractor, on a job you're bidding or quoting. After that, $395 per new set of drawings, or monthly Shop plans. See what a takeoff costs and how it works.
Commercial roofing takeoffs for low-slope (TPO, EPDM, PVC, mod bit and BUR), standing seam and shingle roofs. Residential is not our focus today, but ask if you have a job in mind. See our commercial roofing takeoff services and where every number comes from.
Get your first takeoff free · See full pricing and plan terms · Or email [email protected]
*Clock starts once any questions we send you are answered.
The Sharp Pencil team
Sources
- GAF, EnergyGuard NH Tapered Polyiso Insulation data sheet COMGN753: gaf.com data sheet
- A roofing manufacturer's tapered polyiso design guide (Feb. 2019), hosted at prarfg.com
- Atlas Roofing, Did You Know? Atlas Tapered Polyiso Cricket Design (2017): atlasrwi.com cricket PDF
- Atlas Tapered Services: atlasrwi.com/about-polyiso/tapered-services
- Carlisle SynTec, Tapered Quote Request form: forms.carlislesyntec.com
- 2021 Seattle Building Code Chapter 15 (IBC 1507.11.1 / 1507.12.1 minimum slope): seattle.gov PDF
- PIMA Technical Bulletin 118: polyiso.org TB 118
- Sharp Pencil, Roofing RFI register: getsharppencil.com/roofing-rfi-register