How to estimate a roofing job

Roofing is measured in squares — one hundred square feet of finished roof — and almost every other figure on the estimate is a multiplier applied to that count. Getting the square count and the pitch right is most of the work; the rest is deciding in advance what happens when the old roof comes off and the deck underneath is not what anybody assumed.

Count squares, not the building's footprint

  1. Measure each roof plane separately

    A roof is a set of rectangles and triangles, and every hip, valley and dormer starts another plane. A satellite measurement is fine for a first pass and unreliable on anything cut up.

  2. Apply the pitch multiplier

    The plan area of the building is not the area of the roof over it. A 6/12 roof is roughly a tenth larger than its footprint and a 12/12 is over forty per cent larger, and the multiplier is applied before anything else is.

  3. Divide by one hundred to get squares

    Material, labour and disposal are all quoted per square, so this is the figure the whole estimate is built on.

  4. Add waste for cuts and starter course

    Hips and valleys eat shingle. A simple gable wastes little and a cut-up roof wastes a great deal, so the waste percentage is a judgement about the shape rather than a constant you carry between jobs.

Tear-off is priced by the layer

Stripping one layer of asphalt is a different job from stripping three, and stripping cedar shake or slate is different again. Count the layers at a rake edge before quoting, write on the estimate how many the price assumes, and price an additional layer as its own line — so that finding one is an item the homeowner was warned about rather than an argument held on a driveway.

The decking is the figure you cannot know

What moves a roofing number up

  • Steepness past roughly 7/12, where staging and harnesses slow a crew down for the whole job
  • A second or third storey, which changes how material reaches the roof and how debris leaves it
  • Many hips, valleys, dormers, chimneys or skylights, each of which has to be flashed
  • Landscaping, a pool or a narrow drive, which decide where the dumpster can stand and how far material is carried
  • Ventilation, drip edge, ice-and-water membrane and flashing that current code requires and the old roof does not have

Hold the price for thirty days

Valid for 30 days is the working convention here, and it is a supply-house figure rather than a courtesy: shingle and underlayment are held at a quoted price for about that long, and a bundle price that moves after the homeowner has accepted is a loss taken on your own paperwork. Say what the price is held against, so that an extension is a conversation rather than an assumption, and settle how long an estimate should stand before you are asked rather than after.

Start from the roofing estimate template

Common questions

What is a roofing square?
One hundred square feet of finished roof surface. Material, labour and disposal are all quoted against it, which is why the square count is the first figure to get right and the one every other figure inherits.
Should the estimate include deck replacement?
As a rate per sheet charged only where it is used, never inside the per-square price. Nobody can see the deck until the old roof is off, so pricing it blind means either padding every job or absorbing the bad ones.
Does pitch really change the price that much?
Twice over. It increases the actual roof area against the building's footprint, and past roughly 7/12 it also slows the crew and adds staging — so it moves the material side and the labour side of the estimate independently.

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