ROOFTAP

Data sources & accuracy

Where the numbers come from

Aerial LiDAR

Roof slopes are measured from public airborne LiDAR: the USGS 3D Elevation Program (3DEP), NOAA Digital Coast and state programs. Before a survey is used for paid reports it passes a validation run on at least 100 houses. Of the 372 city pages on this site, 293 use a survey flown in 2018 or later.

Building outlines

Building footprints come from county and city GIS data and Microsoft’s open building footprints (CDLA-Permissive-2.0), registered to the LiDAR so the outline sits on the roof the laser actually saw.

Material prices

Typical U.S. material-only prices per roofing square, adjusted by state using the Bureau of Economic Analysis Regional Price Parities for goods. They are planning values, not supplier quotes.

What a free estimate can and can’t tell you

  • It measures the predominant pitch from the laser points on the roof.
  • Roof area is the building outline times the slope factor, with a likely range because overhangs may extend past the outline.
  • It does not see changes made after the survey, roofs hidden by trees, or details like skylights and vents.
  • It is not a surveyed measurement and does not replace an on-site inspection.