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Takeoff vs What Got Installed: How to Check a Closed Roofing Job and Fix Your Waste Factors

By The Sharp Pencil team

Disclosure: Sharp Pencil sells commercial roofing takeoffs, so we have a stake in this topic. The worked example is arithmetic on stated assumptions, not an actual job.

For each material line on a closed job, line up four numbers: the takeoff quantity, what was delivered, what came back or was left over, and the as-built quantity after approved changes. Delivered minus returned is what the job actually used. Measure waste against the as-built quantity, not the original takeoff, or a change order ends up looking like waste. Only touch next bid's waste factor when the same pattern shows up across several similar jobs.

What do you need to pull from a closed roofing job?

Four numbers for every material line, and each one comes from its own paperwork. Pull them while the job is fresh, before the tickets and credit memos get scattered.

Table 1. The four numbers per material line
NumberWhere it comes fromCommon trap
Takeoff quantityThe takeoff workbook and the bid, in the same unit the bid used (SF, SQ, LF, EA)Comparing a gross bid quantity (waste already in) to a net installed quantity
DeliveredSupplier delivery tickets and invoices, in purchase units (rolls, pallets, pails, boxes)Counting what was ordered instead of what arrived; missing shorts and backorders
Returned or left overReturn tickets and credit memos, plus anything moved to the shop or the next jobLeftovers that leave the job without paperwork get counted as waste
As-built quantityThe takeoff plus approved change orders, checked against the redlines or as-built drawings if the project produced themMeasuring waste against the original takeoff, so every added area shows up as waste

The as-built number is easiest to trust when change orders get tied to the as-built record as they happen. Do that during the job and the drawings and the cost record should already agree at closeout.

Why separate takeoff error, scope change, and waste?

Quantity variance. The takeoff was off, or the drawings did not show what got built. Fix it at the takeoff. Tighten the method, or ask the question on the next similar set (more on turning gaps into RFIs). Don't pad waste to cover it.

Scope variance. Approved changes, owner adds, and substitutions. That belongs on the change order, not in the waste factor. A substitution can also change the purchase unit (a different roll width, say), so write substitutions down.

Consumption variance. Cut-up, laps, offcuts, damage, spills, and rework. This is the only part a waste factor should carry. For why that number moves with roof cut-up and roll width, see where single-ply waste comes from.

Lump all three into one waste percentage and the next bid inherits the last job's change orders.

How do you calculate what a roof actually consumed?

Here are three examples of where to find the unit. They show where the number lives. Use the data sheet for the product on your job, and don't treat these as typical figures for every product.

Membrane trap. If wall and curb flashing came out of the same field rolls, take that area out using the takeoff's flashing quantities. If you don't, the field waste number soaks it up.

Worked example (an example, not a real job)

Assumptions: adhered TPO re-roof. Takeoff net field area 30,000 SF (300 SQ). One approved change order added a 1,000 SF canopy roof, so the as-built net field area is 31,000 SF. Field membrane in 10 ft by 100 ft rolls (1,000 SF gross each). One layer of 2.0 in. flat polyiso, 4x8, at 768 SF per pallet. Bonding adhesive at the published 60 SF per gallon in 5 gal pails, which is 300 SF per pail at that rate. Flashing membrane is tracked as its own line and left out of these numbers.

Table 2. Worked example closeout (example only, not a real job)
LineTakeoff or bidDeliveredReturnedConsumedAs-built netPercent over net
Field membrane36 rolls bid on 30,000 SF (20% over net), plus 2 rolls on the change order38 rolls3 rolls unopened35 rolls (35,000 SF gross)31,000 SFAbout 12.9%
Polyiso, 2.0 in.About 40.4 pallets needed on 31,000 SF, so 41 minimum42 pallets1 pallet41 pallets (31,488 SF)31,000 SFAbout 1.6%
Bonding adhesiveAbout 103.3 pails at the published rate118 pailsNone118 pails (590 gal), about 52.5 SF per gallon31,000 SFAbout 14% more adhesive than the published rate

Against the original 30,000 SF takeoff, the same 35 rolls would look like about 16.7% over net. That gap is the change order dressed up as waste. The bid carried 20% over net and the job used about 12.9%, roughly 7 points less.

So one closeout gives three different answers. Membrane waste may be too fat on the bid, insulation is tight, and adhesive is running over the data sheet. Check the cause on the adhesive first (substrate porosity, weather, application) before changing anything, since the data sheet itself says porous substrates may need more.

What should change on the next bid?

Change a waste factor only when the same direction of variance repeats across several similar jobs: same system, attachment, roll width, and roof cut-up. One job is a data point, not a rule. How many jobs is enough is your call as the estimator.

Once the quantities are right, pricing them is a separate job. See how to price a TPO roof.

What about labor?

The same routine works for labor hours by task. Professional Roofing, NRCA's magazine, reported in June 2019 on a labor study commissioned by CertainTeed: estimators' numbers for flashing drains and hot stacks ran longer than the timed field data, while termination bar into concrete was consistently underestimated (Professional Roofing, "Getting labor data to work for you"). Comparing by task catches misses in both directions. Sharp Pencil does takeoffs and does not set labor rates.

Common mistakes when checking a takeoff against the job

FAQ

How do I calculate actual waste on a roofing job?

Take what was delivered, subtract what was returned or documented as moved to another job, and that is what the job consumed. Divide it by the as-built net quantity and report the result as percent over net.

Should returned material count as waste?

No. Unopened returns and documented leftovers moved to another job were not consumed, so they stay out of the waste number.

Why measure against the as-built quantity instead of the takeoff?

So approved changes do not show up as waste. In our worked example, the same membrane comes out about 12.9% over the as-built quantity but about 16.7% over the original takeoff, and the difference is the change order.

When should I change my waste factor?

When the same pattern repeats across several similar jobs with the same system, attachment, roll width, and roof cut-up. One job is a data point, not a rule.

Does Sharp Pencil's takeoff help with this?

Sharp Pencil's takeoff workbook cites the sheet behind every quantity, so after the job you can check each line against what was installed. Gaps the drawings can't settle go on the open questions (RFI) list instead of into the number. We don't do your job costing; your actuals stay yours.

Why send your takeoffs to Sharp Pencil

A takeoff backlog hurts most on the jobs you pass on because nobody has the hours. Here's what to look for when you hand takeoffs off.

Our focus is commercial low-slope roofing. Residential is not our focus today, but ask if you have a job in mind. See our commercial roofing takeoff services.

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The Sharp Pencil team

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