How to spot a converted garage in satellite imagery
A garage count mismatch is one of the quieter ways a listing record goes wrong. The tax roll says two-car garage. The MLS photo shows a converted den with a window where the door used to be. Nobody updated the field, because nobody updates that field. It just sits there, dragging the comp set in the wrong direction every time an AVM pulls it.
Converted garages are common enough in older housing stock that it's worth checking for them on a regular schedule, before a dispute forces the question. You don't need a site visit to catch most of them. The visual cues show up fine from directly overhead, if you know what you're looking at.
What a conversion looks like from above
A garage that's still a garage has a driveway running straight up to a door-sized opening, usually a shade darker or more reflective than the surrounding wall if it's a metal roll-up door. A converted garage breaks that pattern in one of a few ways:
- The driveway ends at a blank wall or a window instead of a door-width gap.
- The roofline over that section doesn't match the rest of the structure, because someone raised it, added a dormer, or re-pitched it during the conversion.
- The roofing material changes right at the garage footprint. A re-roof years later often misses the converted section if it was done separately, leaving a visible seam.
- A window sits where a garage door would be, especially one that's smaller and centered differently than the house's other windows.
- Cars are parked on the driveway or the apron, not in a bay. One parked car in front of a blank wall, every pass of imagery, is a pattern worth flagging.
None of these alone is proof. A driveway with no door could just mean the garage door happens to be closed and flush with the siding. But two or three of these together, especially the roofline break plus a parked car, is a strong signal that whatever the record says about garage count, the ground truth has changed.
Why the garage count field keeps drifting
Garage conversions rarely get permitted, and when they do, the permit rarely makes it back into the parcel record on any kind of schedule. An owner converts the garage into a home office, lists the house five years later, and the listing photos show the converted space while the public record still carries the original bedroom and garage count. A portal pulling specs straight from tax data inherits the stale number. An AVM comping against "similar 3BR/2-car" properties quietly includes a house that's actually a 4BR/0-car, which skews the comp even if the square footage is right.
This is a garage conversion property record problem more than an imagery problem. The imagery is just the fastest way to check it at scale, because photo review doesn't scale and manual QA on a portfolio of any real size means picking a sample and hoping the rest looks like the sample.
Checking it at scale instead of by sample
Running this check by eye, parcel by parcel, works for a handful of disputed listings. It doesn't work across a metro's worth of records, which is why most portals either leave the garage field untouched or flag it only when a listing agent happens to correct it. Property Attributes was built for exactly that gap: it reads visible lot and structure details from VHR satellite and aerial imagery, refreshed annually, and returns them as attribute fields keyed to your existing property IDs. Garage presence and condition is one of the fields in that set, alongside driveways, outbuildings, pools, and tree cover, the kind of detail a listing photo shows and a tabular database usually doesn't carry.
If garage count mismatches are costing you comp accuracy at any real volume, it's worth seeing what an attribute feed built for this would catch across your own portfolio.