Roof Replacement Estimating Basics

Measure the roof in squares, add waste for its shape, and price every line the crew will touch. That is the whole method. The rest of this guide is the detail.

A square is 100 square feet of roof. The floor area of the house is not the area of the roof. Pitch adds area, overhangs add area, and every dormer, valley and hip adds cutting.

Measure from the roof itself, from a satellite measurement report, or from the footprint times a pitch multiplier. Then say which method you used, so you can defend the number.

A steep or complex roof changes labor too, not just material:

• Price per square goes up with pitch. The crew moves slower and needs more safety gear.
• It goes up with complexity. Cuts and flashing are where the hours hide.

Write the pitch and the number of roof faces next to the square count. For example: "28 squares, 8/12 pitch, 4 valleys, 2 dormers." The customer cannot see the roof from the ground the way you can. That line explains your price before they ask, and it protects you when the crew arrives.

Shingles come in bundles. A roof with hips and valleys throws away more of each bundle than a simple gable roof.

A common rule of thumb:

• About 10 percent waste on a simple roof.
• 15 percent or more on a cut-up one.

The waste goes into ridge caps, starter strips and the cuts along valleys.

Put the waste on the estimate as a percentage, not a mystery. A customer who reads "plus 12 percent for cuts and starter" believes the material line.

Find out how many layers are on the roof. A second layer means more tear-off labor and more dumpster weight. In many places, it is also why the roof cannot be layered over again. Price tear-off per square, per layer.

Then price what you cannot see: the decking, the boards under the shingles. Put 3 things on the estimate:

• A price per sheet for replacing rotten decking.
• An allowance for the number of sheets you expect.
• A note that anything past the allowance is billed at that rate, with photos.

That one note prevents most roof-job disputes.

Give each of these its own line, with a quantity:

• Tear-off and disposal, by square and by layer.
• Decking repair allowance, with the per-sheet rate.
• Underlayment for the field. Add ice-and-water barrier at eaves, valleys and roof openings where the climate or the code calls for it.
• Drip edge, starter strip, the shingle by product and color, and ridge cap.
• Flashing: step flashing at walls, new pipe boots, and chimney and skylight flashing. Say whether old metal is reused or replaced.
• Ventilation: ridge vent or roof vents, plus intake vents at the soffit, sized to the attic.
• Fasteners and sealants.
• Dumpster, delivery, and the magnet sweep for nails.
• Permit, passed through at cost, and the inspection visit.

A one-number estimate with a shingle color loses to the one that shows its work.

Roof material is a big cost before the crew starts, so a deposit is normal.

A schedule tied to milestones is clearer for both sides than one large deposit:

• A deposit when the customer signs.
• A payment when the material is delivered.
• The balance when the job is done.

Some states cap deposits on home improvement contracts. Check your state's rule before you print the schedule on the quote.