Whatcom County, WA Building Setbacks & Zoning: Lot Coverage Limits (2026)

450 governs lot coverage in the Residential Rural (RR) district, the base rural zoning that covers most of the unincorporated county outside the seven cities and the designated urban growth areas. The rule caps combined building footprint, meaning the house plus every accessory structure together, at whichever is greater of 5,000 square feet or 20 percent of total lot area, but total coverage may never exceed 25,000 square feet even on a very large parcel. Two carve-outs apply: public community facilities serving a predominantly rural area may cover up to 35 percent of the lot with no cap on individual building size, and any building used for livestock or agricultural products, such as a barn, milking parlor or hay shed, is entirely exempt from the coverage calculation, reflecting the county's dairy and berry-farming base.

97, defines 'lot coverage' as the percentage of a lot covered by structures measured at the weather-tight roofline, and for shoreline parcels under Title 23, submerged lands and tidelands waterward of the ordinary high-water mark are excluded from the calculation entirely. 450, a lower square-footage ceiling paired with a higher percentage than the RR district's formula. Violations of any Title 20 zoning standard, including lot coverage, are enforced under WCC ch. 94: the zoning administrator issues a notice of violation and may impose a civil penalty of up to $1,000 per day, with each day of continuing violation charged as a separate offense.

A property owner has 20 calendar days to apply in writing for remission or mitigation of the penalty, and the county's decision on that application can be appealed to the hearing examiner within 10 calendar days of issuance.