Confirm setbacks, lot coverage, and FAR for your lot

Good news: this is the cheapest step in the whole project, and it tells you whether to keep going. An afternoon at your laptop and you'll know if your addition idea is realistic for your specific lot. The Seattle Department of Construction and Inspections (SDCI) publishes everything you need for free.

Start here

For a single-story addition, the binding zoning constraints aren't height or FAR (floor-area ratio) — they're setbacks (how far the building has to sit from each property line) and lot coverage (footprint as a percentage of lot area). Both are public, both are tied to your specific zone, and both are looked up in the same place.

How to do it

1. Open SDCI's Research a Project, Permit, or Property page and follow the link to the GIS property lookup.
2. Enter your address.
3. Note the zone designation (most older houses are Neighborhood Residential — NR — under the One Seattle Plan rules that took effect 2026-01-21).
4. Open SMC 23.44 and look up the dimensional rules for that zone.

What you're looking for

• Front setback. NR zones typically require 20 ft from the front property line, with allowances tied to the average front setback on your block. A front addition is the most setback-sensitive geometry; if you're at 20 ft already, you can't push out front.
• Side setbacks. NR zones typically require 5 ft minimum on each side. Many older bungalows are non-conforming on one side (built before the current setback rules). A side addition that stacks on a non-conforming wall may need an "adjustment" or design departure.
• Rear setback. Typically 25 ft, with reductions allowed for shed-roof or low-profile additions. Most flexible direction for most lots.
• Lot coverage. Footprint as a percentage of lot area. NR zones cap at around 35% for the principal structure. Adding 300 sf to a 1,500 sf footprint on a 5,000 sf lot moves you from 30% → 36% — over the cap.
• FAR. Above-grade floor area divided by lot area. Less binding for single-story additions but still relevant if your house has a finished basement or partial second floor.

What this tells you

• Headroom on all four numbers? The addition is feasible from a zoning standpoint. Move on to the permit-history check.
• At lot-coverage cap already? The addition is not realistic without a variance. The realistic alternative is an interior-only remodel.
• One non-conforming side? Plan around it. Push the addition the other direction, or take a design departure path (more time, more cost).

A quick note on the One Seattle Plan

Phase One of the One Seattle Plan took effect 2026-01-21 and folded the older NR1 / NR2 / NR3 designators into a single NR zone. Older blog posts and even some city documents still reference the old zones — trust the current GIS lookup, which reflects the post-2026 rules.