Why two reports can disagree
Different imagery dates, building selections, roof-plane interpretations and included structures can produce different totals. One report may include a garage or porch that another omits. A footprint measurement is also not comparable to a slope-corrected surface measurement.
First compare the same building and included planes. Then compare surface area before waste, predominant pitch and edge lengths. An area-only percentage comparison can hide the reason for the difference.
Review the satellite data
Tree cover, shadows, complex junctions, small additions and outdated imagery deserve extra attention. Google Solar supplies building insights and raster data where available; a returned dataset is not a guarantee that every roof detail is correct.
RoofSnap derives refined outlines from building-mask data and internal boundaries from elevation data when available. Missing elevation detail can mean that the internal trace is unavailable, not that a roof is geometrically simple.
Check low-confidence facets and adjustments
Review a facet with a pitch that differs substantially from the rest of the roof. Keep, remove and snap actions can change totals, so check that a real low-slope porch has not been mistaken for noise.
Automatic artifact exclusion starts on; the optional area calibration starts off. A blanket area increase cannot correct every property because errors can go in either direction. Do not use an adjustment just to force agreement with another report.
What the report cannot establish
Satellite geometry cannot establish concealed decking condition, the number of roofing layers, current leaks or installation quality. Some flashing and penetration details may also be obscured.
Use the report for planning and quantity review. Confirm roof condition, uncertain dimensions and current property changes on site before a final contract or order. RoofSnap is a measurement tool, not an inspection or engineering service.
Sources & further reading
Product details reflect RoofSnap’s current measurement and report workflow. Geometry examples are rounded illustrations, not measurements of the pictured property.
Google Solar API documentation