Diagrams and aerial reports
Drawings of the roof from above with areas, pitches and edge lengths, measured on site or from aircraft, satellite or drone imagery.
A free reference for homeowners
Read your roof measurements before you compare quotes.
Roofing Diagram is an independent guide to the drawings, measurement reports and quotes that homeowners receive when a roof needs work. It explains what the numbers mean, where they come from, and what to ask when two of them disagree. It sells nothing and is not a roofing company.
- Planes
- 4
- Pitch
- 6/12
- Footprint
- 1,700 sq ft
- Surface
- 1,901 sq ft
- Squares
- 19.0
The worked example in how to read a roof diagram, measured line by line.
The basics
What a roof diagram is
A roof diagram is a scaled drawing of a roof seen from directly above. Each flat section of roof, called a plane, is labeled with its pitch and its surface area. The lines between planes are the ridges, hips, valleys, eaves and rakes, each with a length in feet. A table adds everything up in squares, the unit roofers use to price a job and order materials.
Diagrams come from roofers measuring on site, from measurement services working with aircraft or satellite imagery, and from drone flights. A diagram describes the size and shape of a roof. It says nothing about condition, which is the job of an inspection report.
Roof documents
Contractor measurement takeoffs
The list of squares, edge lengths, flashing and materials a roofer prices a job from, and the questions to ask about it.
Insurance and pre-purchase inspections
Dated observations about the condition of a roof after a storm or before a sale, and what such a report cannot promise.
Different numbers
Why one roof gets different sizes on different quotes
Two quotes often disagree about the size of the same roof by a few squares. That does not mean anyone is being dishonest. Most gaps come down to scope, method or waste. Asking which one applies usually clears the difference up.
When you compare prices, divide every quote's total by the same trusted square count, not by each quote's own figure. The quote comparison guide shows why.
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Scope
What is included
One quote counts the detached garage and the porch roof. Another leaves them out.
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Method
How it was measured
Tape and pitch gauge on site, aerial imagery and drone photos each have different blind spots, from tree cover to old images.
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Waste
What was added
One figure is bare surface area. Another already includes 10 or 15 percent for cutting.
Never climb onto a roof to check a measurement
Roofs are steeper, more slippery and higher than they look from below, and a storm-damaged roof can give way underfoot. Everything on this site can be followed from the ground, from a window or with binoculars. For anything closer, hire a qualified professional.
Resources
Five guides for homeowners
Free to read, with no account and nothing to sign up for.
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Reading drawings
How to read a roof diagram
Planes, pitches, ridges, hips and valleys, and what a diagram cannot show.
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Measurement
Roof pitch and roofing squares explained
Pitch factors, waste and a worked example you can check with a calculator.
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Flashing and leaks
What flashing is, and why leaks often start there
Water tends to get in where the roof meets something else. What to look for from the ground.
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Decisions
Repair or replace: how to decide
Five questions that settle the choice for most roofs, taken in order.
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Quotes
How to compare roofing quotes line by line
One trusted square count, then every line item side by side.
Getting ready to hire someone?
Before anyone sets a ladder against your house, check their license and insurance, get the quote in writing, and agree on a payment schedule that never asks for the full price upfront.
