Short answer: aerial measurement is accurate for roof area on simple roofs and is a legitimate tool. What it cannot do is assess condition, layers, decking, ventilation or flashing, and it frequently misreads pitch and small planes on complex roofs.
What aerial measurement does well
- Calculates roof area quickly and usually within a few percent on simple roofs
- Identifies major planes, ridges, hips and valleys
- Produces a diagram that is genuinely useful for material ordering
- Lets a contractor give a ballpark without a site visit
We are not against it. It is a reasonable first step.
What it misses
- Number of existing layers. Invisible from above, and it changes tear-off cost substantially.
- Decking type and condition, including plank decking on older homes.
- Flashing condition at chimneys, walls and skylights.
- Ventilation, especially whether soffit intake exists and is unblocked.
- Actual damage, since hail bruising and broken seal strips cannot be seen from imagery.
- Access and staging, which on steep Helotes or west Austin lots is a real cost line.
- Pitch accuracy on complex roofs, where aerial estimates are least reliable.
- Small planes, dormers and additions that imagery resolution can smooth over.
Why this produces wrong quotes
A quote built entirely from imagery is a material estimate with assumptions about everything else. When the crew arrives and finds two old layers, soft decking and no soffit intake, the number moves. That is the conversation nobody wants to have with the roof already open.
This is also how a suspiciously low quote happens honestly. The contractor was not lying, they just priced a roof they had not looked at.
What a proper inspection adds
- Walking the roof where it is safe, and assessing by feel as well as sight
- Checking the attic for daylight, staining, moisture and ventilation
- Looking at the rake and eave edges to count layers
- Photographing every penetration and flashing detail
- Noting access and staging constraints before pricing them
The practical rule
Aerial measurement for a ballpark is fine. A contract number should come from someone who has been on or at your roof. If a contractor wants to sign you without having visited, that is worth questioning.
For understanding roof area yourself, see how many squares is my roof.
Get a measured, inspected written estimate free, or call (210) 245-4125.
