shinnslist · Boulder County · listing check
Does this listing match the county record? Unpermitted additions in Boulder County
Bottom line: of 76 Boulder County homes listed October 16, 2026 to October 22, 2026, 18 (24%) showed more bedrooms or baths than the county building record, and 12 of those had no building permit on file since the last sale. A possible unpermitted addition is a question to ask before an offer, not a verdict.
The check
How shinnslist checks a listing against the county record
- Take the bedrooms and bathrooms the listing prints.
- Read the county assessor’s building record for the same home: bedrooms, full, three-quarter and half baths.
- Flag the home when the listing shows at least one more bedroom, or a whole bath more (half baths count as half). Square feet alone never flags it, because listings often count an unfinished basement.
- Look for a county or city building permit since the last recorded sale (no sale on record: the last 20 years) for new construction, an addition, a remodel, a basement finish, a bathroom, an enclosed porch or a garage.
- If the listing shows more and no such permit exists, the home is marked Possible unpermitted addition.
Where no permit file is available the answer is “unknown”, never “no”. Today the permit check covers Boulder County’s own permit file and the City of Boulder’s.
By the numbers
Boulder County, listings of October 16, 2026 to October 22, 2026
| Town | Homes checked | Listing shows more beds or baths | …and no permit since the last sale |
|---|---|---|---|
| Boulder | 24 | 5 (21%) | 2 (8% of homes checked) |
| Longmont | 19 | 4 (21%) | 3 (16% of homes checked) |
| Other Boulder County towns | 33 | 9 (27%) | 7 (21% of homes checked) |
| All of Boulder County | 76 | 18 (24%) | 12 (16% of homes checked) |
Source: listing alerts shinnslist receives, checked against the Boulder County Assessor building and sales records, the Boulder County permit file and the City of Boulder construction permits, read October 23, 2026. Towns with fewer than 10 homes checked are grouped. Counts only: no addresses or owners.
Read this first
What a flag does not mean
A flag is not a finding that anything is illegal, and it says nothing about the owner. County records lag: a finished basement or an added bathroom may be real, permitted and simply not yet in the assessor’s record. Treat a flag as a prompt to ask the seller for permits and to ask the building department.
See your own homes
See which homes, before you make an offer
Signed in, each flagged home shows what the listing says, what the county record says and the permit check, next to its other signals. The beta is free.
Questions
Questions people ask
What does "possible unpermitted addition" mean?
The listing shows more bedrooms or more bathrooms than the county assessor’s building record, and the county’s permit files show no permit for new construction, an addition, a remodel, a basement finish, a bathroom, an enclosed porch or a garage since the home last sold.
Does it mean the owner built something without a permit?
No. It is a reason to ask. The county record may be out of date, the work may have been permitted under another address, or it may predate the last sale. Only the county can say.
Why not compare square feet?
Listing sites often count an unfinished basement in the square feet. A bedroom or bath count that is higher than the record is a stronger sign that something changed.
How are half baths counted?
A half bath counts as half. A listing that rounds 2.5 baths up to 3 is not flagged; 3 baths over a record of 2 full baths is.
Can I see which homes?
Yes, signed in. Each flagged home shows what the listing says, what the county record says and the permit check, so you see it before you make an offer. This page shows counts only.