TL;DR: Three rules mostly decide how much house you can build on a lot: lot coverage (how much of the ground the building can cover), setbacks (how far the building must stay from property lines), and FAR / floor area ratio (how much total floor area you get relative to lot size). Together they form a buildable “envelope.” Check all three before you fall in love with a design.
Homeowners often arrive with a design in mind, only to learn the city’s rules won’t allow it. Understanding three numbers up front saves heartbreak and money. Here’s what each means, in plain language, for Seattle and the Eastside.
Lot coverage: how much ground you can build on
Lot coverage is the percentage of your lot that structures can cover, measured as the building footprint (and often decks, garages, and other structures) divided by total lot area. If your zone allows 35% coverage on a 7,000 sq ft lot, your structures can cover up to about 2,450 sq ft of ground.
Coverage limits keep neighborhoods from being fully paved over and preserve yard, drainage, and tree space. On a lot with large trees, the protected ground around them can take more of the buildable area than the coverage limit does, which is covered in building around Seattle’s tree code. Note that lot coverage counts footprint, not total floor area, a two-story home and a one-story home with the same footprint use the same coverage.
Setbacks: how far from the property lines
Setbacks are the minimum distances a building must stay from each property line, front, rear, and sides. A zone might require a 20-foot front setback, 5-foot side setbacks, and a 25-foot rear setback. Subtract those from your lot and what’s left is the area where you can actually build.
Setbacks vary by city and zone, and special conditions (corner lots, shoreline, critical areas) can add more. On waterfront Eastside lots, shoreline setbacks can be the single biggest constraint on design.
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FAR: how much total floor area you get
Floor area ratio (FAR) caps total building floor area relative to lot size. An FAR of 0.5 on a 7,000 sq ft lot allows roughly 3,500 sq ft of countable floor area. Unlike lot coverage, FAR counts all floors, so it directly limits how big the finished house can be, including a second story.
Not every Seattle-area zone uses FAR the same way, and some use other tools (like maximum unit size) instead. Garages, basements, and unfinished space may be counted, partially counted, or exempt depending on the municipality, the details matter.
How the three work together: an example
Picture a 7,000 sq ft Bellevue lot zoned for 35% coverage, 0.45 FAR, and standard setbacks:
Setbacks
carve out the buildable area, say a 45 ft × 70 ft zone after front, side, and rear setbacks.
Lot coverage
caps the footprint at ~2,450 sq ft, so your ground-floor footprint can’t exceed that even if the setback zone is larger.
FAR
caps total floor area at ~3,150 sq ft across all levels.
The most restrictive rule wins at each step. Designing within all three from the start is exactly what an architect does in early site analysis.
Why check before you buy or design
If you’re evaluating a lot, these three numbers tell you how much house it can hold, crucial before purchase. See our guide to choosing a lot for a custom home. If you already own, they define what’s possible for an addition or rebuild.
Where to find your numbers
Each city publishes zoning by parcel, Seattle (SDCI), Bellevue, Kirkland, and Redmond all have online tools. Your zone designation links to the specific coverage, setback, and FAR rules. Because exceptions are common, confirming with the city or an architect before designing is worth the time.
Want to know what your lot can actually hold? Piper Cole Architects can run a quick feasibility check against your zoning before you invest in design, see our custom home design services.
FAQ
What’s the difference between lot coverage and FAR?
Lot coverage limits the building footprint on the ground; FAR limits total floor area across all stories. A lot can hit its coverage limit while still having FAR available for a second story, or vice versa.
Do setbacks include decks and garages?
Often yes, many cities count attached garages, and sometimes decks, within setback and coverage rules. Check your municipality’s definitions.
How do I find my lot’s zoning?
Use your city’s online zoning or permit portal by address or parcel number; the zone links to its coverage, setback, and FAR standards.
Does a basement count toward FAR?
It depends on the city and whether the space is finished or below grade. Some exempt basements, others count them partially. Confirm locally.
What is the difference between lot coverage and FAR?
Lot coverage limits the building footprint on the ground; FAR limits total floor area across all stories. A lot can hit its coverage limit while still having FAR available for a second story, or vice versa.
Do setbacks include decks and garages?
Often yes. Many cities count attached garages, and sometimes decks, within setback and coverage rules. Check your municipality’s definitions.
How do I find my lot’s zoning?
Use your city’s online zoning or permit portal by address or parcel number; the zone links to its coverage, setback, and FAR standards.
Does a basement count toward FAR?
It depends on the city and whether the space is finished or below grade. Some exempt basements, others count them partially. Confirm locally.
Sources consulted: Seattle SDCI zoning and development standards; City of Bellevue and City of Kirkland land use codes; general planning definitions of FAR, setbacks, and lot coverage; Piper Cole Architects feasibility practice.
Authoritative sources
Regulatory requirements referenced in this guide are set by the official agencies below. Rules change, always confirm current requirements with the source:
