Roof measurement from satellite, by address

When you tap Measure the roof, four things happen, and each one is listed under the answer.

• The address is placed on the map. Koira looks it up with OpenStreetMap's address search and keeps only an answer that is a door, not a street or a town. A pin on the street would measure the neighbour's roof, so a street-level answer is refused and you are asked to draw instead.
• Google's model is read. Koira asks Google's Solar API for the building closest to the pin. Google answers with the roof split into planes. For each plane: the area with its tilt included, the area of its footprint, the pitch in degrees and the compass direction it faces.
• The planes are added up. The roof area is the sum of the planes' sloped areas. The footprint is the sum of their ground areas.
• The order is worked out. Squares are the area over 100. Bundles are squares times 3, times one plus your waste, rounded up.

The table under the answer lists every plane: which way it faces, its pitch as x/12 and in degrees, its roof area and its footprint. That is the breakdown you need to price a tear-off by face, plan a solar layout, or see which side takes the weather.

Say Google's model splits a hip roof into four planes:

2,020 sq ft ÷ 100 = 20.2 squares. A hip roof has more cut pieces than a gable, so pick 15% waste: 20.2 × 3 × 1.15 = 69.7, rounded up to 70 bundles. At 10% it would be 66.7, so 67 bundles.

On top of the shingles, the order still needs starter, hip and ridge cap, underlayment, drip edge and flashing. Those run by the length of the edges and ridges, which this tool does not measure (see below), so take them off the roof itself or draw them with the Draw line tab.

Roofers say pitch as the rise in inches over a 12 inch run: a 6/12 roof climbs 6 inches for every foot across. Google gives pitch in degrees. The tool shows both: rise = 12 × tan(angle), so 26.6° is 6/12.

The pitch that covers the most roof area is named as the main pitch. On a roof with a low porch and a steep main roof, look at the plane table for the breakdown.

When you draw a roof yourself on the map, you are drawing its footprint, because the picture looks straight down. Pick the pitch under the map and the tool multiplies the footprint up to the roof area:

The multiplier is plain geometry: √(1 + (rise ÷ 12)²), the length of a rafter over the length of its run. The angle is the arctangent of rise ÷ 12.

Google grades every roof it models, and the answer shows the grade:

• HIGH: built from low-altitude aerial photos processed at 10 cm a pixel. The tool calls this high confidence when the roof has two or more planes.
• MEDIUM: built from high-altitude aerial photos at 25 cm a pixel.
• BASE: built from satellite pictures at 25 cm a pixel. The tool calls this low and asks you to check it on the map.

The answer also gives the month the picture was taken. A roof with an addition built since then, heavy tree cover, or a flat commercial roof with lots of equipment can come back wrong. Small planes such as dormers and bump-outs may be missed or merged.

Ridge, hip, valley, rake and eave lengths are not shown. Google's model gives each plane's area, pitch, direction and a box around it, but not the lines where the planes meet. A length worked out from the boxes would be a guess, and a guess on a materials order costs money, so the tool leaves those out.

It also does not measure walls, siding, windows or gutters. For gutters and edges, the Draw line tab gives you feet: tap along the eaves. For walls and siding, paid services sell exterior reports; the comparison page has what Hover, EagleView and QuoteIQ list and charge, with dates.

Measuring by address does not replace the visit. It changes what the visit is for.

• Before the visit: measure by address, get a price range from the calculator and give it on the first call. The homeowner knows whether you are in their budget before you drive out.
• At the visit: check what a picture cannot show. Decking, the number of layers, soft spots, ventilation, flashing, chimney and skylight condition. Confirm the plane count against the roof in front of you.
• Before the order: if the visit changed anything, adjust the waste or redraw the plane that was off, and re-run the bundles.

Two numbers from two methods that land close together are worth more than either one. If Google's model and your own drawing disagree by more than a few percent, find out why before you order: an addition, a covered porch that was missed, or a pin on the garage instead of the house.

The "Use in a calculator" button opens the roof replacement cost calculator with the footprint, the pitch and your waste filled in. Pick the shingle, the tear-off layers and your area, and it gives a price range with the math shown.

"Save to a Koira estimate" opens a free Koira office. In Koira, the same roof measuring sits on every estimate, so the square feet land on the line and the estimate goes to the customer from your phone. See how roofers run on Koira.