Satellite roof measurement takes a street address, finds the building in aerial imagery, traces its outline and turns that outline into square footage you can price. In RoofSell it happens inside the estimate widget on your website, while the homeowner is still on the page. This post walks through each step, explains why a footprint is not the same thing as a roof, and gives you a short routine for checking a measurement before your name goes on a number.
What happens when a homeowner enters an address
The homeowner starts typing in the widget and picks their address from the suggestions. From there, the steps run in this order.
- The address is turned into map coordinates, and the map zooms to the property in satellite view.
- RoofSell looks for the building outline. Outlines come from OpenStreetMap building data, read from Mapbox's building map layer and from the Overpass API. Overpass also carries street address tags, which helps pick the right building when several sit close together.
- Google's Solar API is asked about the same building. It reports the pitch of each roof plane and a measured roof area. RoofSell uses that answer to pre-fill the slope and to throw out an outline that's far too big or far too small for the roof Google sees, such as a whole row of townhouses mapped as one shape.
- The outline appears on the map. Nearby outbuildings, like a detached garage, can be picked up as extra structures, and the homeowner can leave out any that aren't part of the job.
- The homeowner confirms the slope for each structure (Flat, Shallow, Medium or Steep), can drag the corners of the outline with Edit Roof, and can draw another structure with Add Roof.
The homeowner never sees the square footage. That number stays on your side, in the lead.
If nothing reliable is found, the widget shows "Building not found at this address" instead of guessing. A wrong roof is worse than no roof, because it puts a bad price in front of a homeowner on your own website.
Footprint vs roof area: the number that trips people up
An outline traced from above gives you the footprint. That's the flat area the roof covers when you look straight down. A pitched roof has more surface than its footprint, because each plane is tilted, and the steeper the pitch, the bigger the gap.
The standard pitch multiplier is the square root of (12 squared plus the rise squared), divided by 12. For common pitches it works out to:
- 4/12: about 1.054
- 6/12: about 1.118
- 8/12: about 1.202
- 10/12: about 1.302
- 12/12: about 1.414
A worked example
Here's an example with round numbers. A house has a 2,000 sq ft footprint and a 6/12 roof.
- Roof surface: 2,000 x 1.118 = 2,236 sq ft
- Squares: 2,236 / 100 = about 22.4 squares
- With a 10% waste factor: 2,236 x 1.10 = 2,460 sq ft, or about 24.6 squares
Price the footprint as if it were the roof and you'd quote 20 squares instead of almost 25. On a steep roof the miss gets bigger.
How RoofSell turns the outline into a price
Each structure (main house, garage, addition) is stored with its own footprint, slope and waste factor. Open the quote in your dashboard and the Quote Info panel shows the Footprint, the slope adjustment for each roof and an Adjusted Total, worked out as footprint x slope x (1 + waste%).
The slope adjustment is a set percentage for each slope category (Flat, Shallow, Medium and Steep), and Quote Info shows the multiplier next to each roof, so you can always see where the adjusted number came from.
Every product you've selected on the Products page is then priced from that adjusted figure: adjusted square feet divided by 100, times that product's price per square. That's why the homeowner sees a price for each of your options instead of one number.
Two inputs are yours to set. Your default waste factor lives under Settings (anywhere from 0% to 12%), and each product's price per square is set on the Products page. For a longer explanation of the math, see how roof area detection works.
Where satellite roof measurement falls short
Satellite data is a fast first pass. It doesn't replace a tape measure or a drone before you sign a contract. These are the cases where you should expect to adjust:
- New construction. Map data lags behind building. A house finished last year may not have an outline yet, and the closest outline may belong to the neighbor.
- Heavy tree cover. Trees hide roof edges in imagery, which affects how buildings were traced in the first place.
- Outlines traced at the walls. Some building outlines follow the walls rather than the eaves, so overhangs can be missing from the area.
- Cut-up roofs. One slope can't describe a steep main roof with a low porch and three dormers. RoofSell uses an area-weighted average of the planes Google reports, which is close on simple roofs and rougher on complicated ones.
- Attached and multi-unit buildings. Townhouses and duplexes are often mapped as one shape. The size check against Google's data catches the worst of these, but not every one.
- No Solar data. Google's Solar API doesn't cover every address. When it has nothing, the slope starts at Medium and the homeowner picks it.
The help center lists these in more detail in accuracy and limitations of automatic measurement.
Why it matters for contractor quoting
The goal isn't to skip the inspection. It's to show up to the inspection with a homeowner who has already seen a price and still wants to talk.
A homeowner who finds your site at 9 p.m. gets a number that night, instead of waiting two days for a callback to learn roughly what a new roof costs. The ones who book a visit after that are past the sticker shock.
You get the lead with the address, the outline, the slope for each structure and the price range already attached. Before you pick up the phone, you know roughly how big the job is.
And every rep quotes from the same starting point, because the math comes from one outline and your prices, not from whoever happened to measure that day.
How to check a satellite measurement in 2 minutes
Run this routine on every new widget lead before you call:
- Open the lead and look at the outline on the satellite map. Is it on the right building? Does it cover the whole roof, including attached garages and porches?
- Count the structures. If a detached garage or shop belongs in the job and isn't there, add it with Add Roof and draw it. If one doesn't belong, remove it.
- Check the slope on each structure against what you see in the imagery. Homeowners guess, and Google's average can be off on cut-up roofs.
- Look at the Adjusted Total in Quote Info. If it's far from what you'd expect for a house that size, find out why before you send anything.
- Change the waste factor on any roof that's more cut up than your default.
- Click Save, then send the quote once you're happy with it.
On a typical single-family home this takes a couple of minutes. To see the whole process from the homeowner's side, read how RoofSell works.