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G_05 / New Construction

Small Residential Development contractor —
Seattle & Puget Sound.

HB 1110 unlocked middle-housing density across Washington. We build townhomes, cottage clusters, and missing-middle infill for owners turning single lots into small developments.

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Group
New Construction
Timeline
14–24 months
Range
$1.8M – $8M+
OVERVIEW

Small residential development is the work of turning one parcel of land into more than one home. In the Puget Sound that universe now includes duplexes, triplexes, fourplexes, townhomes (attached or detached), cottage clusters, courtyard apartments, and the occasional sixplex on transit-adjacent parcels. It is where owner-developers, family-owned land, and savvy single-family lot owners are spending the most effort right now — and it is also where the most expensive mistakes are made when feasibility is skipped.

Washington House Bill 1110, signed in 2023, requires most cities of 25,000 or more residents to allow at least four units per lot on what used to be single-family parcels, and at least six units on lots within roughly one-quarter mile of a major transit stop, subject to local implementation. This was a structural change to residential land use in Washington. Cities are still actively rolling out their implementation — Seattle through the One Seattle Plan and SMC Title 23 amendments, Bellevue through its Middle Housing Code Update, and the Department of Commerce maintains a statewide implementation hub at commerce.wa.gov that tracks city-by-city status.

Critically, HB 1110 set a floor, not a guarantee. Whether your specific parcel can actually deliver four or six units depends on its size, shape, zoning overlay, design standards in the local code, parking requirements, fire-access requirements, utility capacity, stormwater obligations, critical-area buffers, and frontage improvements. We have walked owners through parcels where HB 1110 ostensibly allows four units but where civil cost, fire access, and stormwater detention make three units the realistic outcome — and others where the parcel comfortably supports the full middle-housing density. Feasibility is a parcel-specific analysis, not a code-citation exercise.

Golden State ADU Builders builds small residential developments across Seattle and the Eastside for two main client profiles. The first is the owner-developer building two to six units on a parcel they already own or are acquiring, for sale, long-term rental, or family use. The second is the existing single-family owner who realizes — often after an inheritance or a refinance — that their parcel is now zoned for more density than the existing house represents, and wants a credible read on whether to redevelop. We start every conversation with a parcel screen before any architectural fee is paid.

Construction-wise, small residential development uses much of the same engineering and trades as single-family new construction (see /services/new-construction). What separates it is the regulatory layer: site planning, civil engineering, fire access, stormwater detention, condominium or unit-lot subdivision platting where individual ownership is the exit strategy, and the cash-flow modeling that comes with multi-unit construction draws. We staff the construction with a single project manager and we coordinate the platting, civil, and permit work with the appropriate specialists; the buck stops in one place.

What we build

SCOPE
  • 01HB 1110 middle housing
  • 02Townhome + cottage clusters
  • 03Site planning + civil
  • 04Permitting + condo platting
  • 05Marketing-ready finishes
  • 06Phased turnover

Phased process

PROCESS
  1. 01

    Parcel screen & HB 1110 eligibility

    Read the parcel against the current city zoning code and the local middle-housing implementation. Check transit overlay, design standards, lot dimensional requirements, parking, fire-access path, and known utility constraints. Output: a one-page memo with realistic unit-count range.

  2. 02

    Pro forma & target program

    Back-of-envelope budget and revenue model based on the realistic unit count, exit strategy (sale vs hold vs hybrid), and current market rents and comps. If the project does not pencil at the parcel screen, we tell you here, before you spend on architect fees.

  3. 03

    Architect & civil engagement

    Site plan, building plans, civil drawings (utilities, fire access, stormwater), and landscape coordination. On cluster and townhome projects the site plan often consumes more design hours than the buildings themselves.

  4. 04

    Survey, geotech, & critical-area review

    Boundary and topographic survey, geotechnical report, critical-area screen (steep slope, wetland, stream, shoreline). On Eastside parcels with mature trees, an arborist letter and tree-protection plan are typically required.

  5. 05

    Stormwater & frontage strategy

    Multi-unit projects routinely cross impervious-surface thresholds in the WA Ecology Stormwater Manual for Western WA, triggering detention vaults, dispersion systems, or infiltration trenches. Frontage improvements (curb, gutter, sidewalk, ADA ramps) are often required by the local AHJ.

  6. 06

    Permit strategy & submittal

    Building permit(s), site/civil permit, side-sewer permits per unit, electrical service permits, demolition permit where applicable, fire-marshal review. Submitted via SDCI in Seattle or MyBuildingPermit on the Eastside. Active correction-cycle management.

  7. 07

    Platting decision — condo vs unit-lot subdivision

    If individual sale is the exit, decide between condominium platting (RCW 64.34, most flexible, more legal cost) and unit-lot subdivision (SDCI Tip 207 in Seattle — simpler but limits unit configuration). Decided early so it does not constrain design or permit later.

  8. 08

    Demolition & site work

    Demolition of any existing structure, mass grading, retaining walls, utility trunk installation, stormwater infrastructure, fire-access surface, and frontage improvements.

  9. 09

    Foundations & vertical construction

    Phased by building where it helps the schedule and the cash draw. Foundations, framing, MEP rough, envelope dry-in, finishes, and unit-by-unit punch and inspection.

  10. 10

    Final inspections, occupancy, & sale-ready

    Final building, mechanical, plumbing, electrical, and fire-marshal inspections. Certificate of Occupancy per unit. Condo or unit-lot recording where applicable. Owner / broker walkthroughs, warranty package, marketing-ready finishes.

Spec sheet

SPEC
  • +Attached townhome or detached cottage configurations, fire-rated wall assemblies per IBC where attached
  • +Marketing-grade finishes (mid- to upper-mid-range) for resale-driven projects; durable rental-grade specs for long-term hold
  • +Shared or individual utility services depending on platting strategy and code requirements
  • +EV-ready electrical pre-wire to every unit
  • +Heat-pump primary heat per unit, sized via Manual J
  • +Common open space and amenity areas per cluster and townhouse ordinances
  • +Fire-access surface, hydrant location, and turning radius per local Fire Code Official requirements
  • +Stormwater detention or dispersion system sized per WA Ecology Stormwater Manual for Western WA
  • +Frontage improvements (curb, gutter, sidewalk, ADA ramps) where required by the AHJ

Cost drivers

COST
  • Realistic unit count vs theoretical maximumPer-unit cost typically drops with scale, but only if the parcel can physically deliver the theoretical maximum. Civil cost and design constraints often pull realistic count below code maximum.
  • Attached townhomes vs detached cottagesAttached townhomes generally save on foundation and roof area per unit; detached cottages can command rental and resale premiums in certain markets. The choice is market-driven as much as cost-driven.
  • Site conditions (slope, rock, soils)Sloped, rocky, or constrained lots add meaningfully to site-work, retaining, and foundation budgets. A geotechnical report at parcel screen is the cheapest insurance.
  • Stormwater detention & frontage improvementsCrossing impervious-surface thresholds triggers detention infrastructure, and frontage improvements (sidewalk, curb, ADA ramps) can each add five- to six-figure line items that do not show in vertical building cost.
  • Platting strategy (condo vs unit-lot vs apartment)Condo platting adds legal, survey, and HOA-formation cost but enables maximum flexibility on unit configuration. Unit-lot subdivision is simpler but constrains design. Apartment / rental-only avoids platting cost but locks the exit strategy.
  • Permit and carrying-cost timelineMulti-unit reviews typically run 8–14 months in Seattle and 6–12 months on the Eastside. Land carrying cost and debt service during review are real and should be modeled into the pro forma.
  • Fire access and utility upsizeCluster developments often trigger fire-marshal access requirements (turning radius, hydrant location, all-weather surface) and utility upsize on the public main; both can change project economics.
  • Construction financing draw structureMulti-unit construction draws are more complex than single-family; coordinating with the lender's inspector and managing draw timing matters more here than on a single house.

Codes & permits

COMPLIANCE
  • Washington HB 1110 (Session Law, 2023)

    Statewide middle-housing law: most cities of 25K+ must allow at least 4 units per lot in single-family zones, and at least 6 units within ~1/4 mile of a major transit stop, subject to local implementation. The statute is binding on cities; the specific code amendments are city-by-city.

  • WA Department of Commerce — Middle Housing resource hub

    Authoritative state-level explainer of HB 1110, transit overlays, and city implementation status. The first source we cite on every middle-housing question.

  • Seattle One Plan & SMC Title 23 amendments

    Seattle's local implementation of state middle-housing requirements (densities by neighborhood, design standards, parking, and tree-protection rules). Read alongside the state law for any Seattle parcel.

  • SDCI Tip 207 — Unit Lot Subdivision (Seattle)

    Defines the process for converting attached townhome units into individually-saleable fee-simple lots without condo platting. Path of choice on many attached townhome projects.

  • Washington Condominium Act — RCW 64.34

    Legal framework for condo platting when individual unit sale is the exit strategy. Adds legal and HOA-formation cost but enables maximum flexibility on unit configuration.

  • WA Ecology Stormwater Manual for Western Washington

    Governs new and replaced impervious surface thresholds and required stormwater BMPs on redevelopment parcels. Multi-unit projects routinely cross these thresholds.

  • Local Fire Code — fire-marshal access requirements

    Cluster and townhome developments commonly trigger fire-truck access standards (turning radius, hydrant location, all-weather surface) that materially affect site plan and budget.

WHEN_YOU_NEED

Is small residential development the right call?

  • →You own a single-family parcel that the local code (after HB 1110 implementation) now allows to host four or more units
  • →You are an owner-developer building two to six units on an infill lot for sale, long-term rental, or hybrid
  • →You inherited or are acquiring family land and want a credible feasibility read before deciding to develop, sell, or hold
  • →You are evaluating cottage cluster, townhome, or stacked-flat infill on a parcel near transit
  • →You want one accountable contractor across feasibility, civil coordination, vertical construction, and turnover
  • →You need a builder who will tell you 'this parcel does not pencil at the unit count you hoped for' instead of selling you on the project

Development questions

FAQ
  • Q.01

    How many units can I build on my lot under HB 1110?

    It depends on the specific parcel, the local city's implementation of HB 1110, transit overlays, lot dimensions, design standards, parking, fire access, stormwater obligations, and critical-area buffers. The state law sets a floor of four units (six near major transit) for most cities of 25,000+ residents, but actual realistic unit count is parcel-specific. We do this analysis as a paid feasibility memo before any architectural fee is incurred. The authoritative state-level explainer is the WA Department of Commerce Middle Housing resource hub linked in our official sources below.
  • Q.02

    Can I sell the units individually, or only as one apartment building?

    Both are options. If you want to sell unit by unit, the two main paths are condominium platting (RCW 64.34 — most flexible, more legal cost) and unit-lot subdivision (SDCI Tip 207 in Seattle — simpler but more constrained). If you plan to hold and rent, you can build as an apartment without platting. The decision is best made early because it affects design and permitting.
  • Q.03

    What is the realistic timeline for a three- or four-unit cottage cluster?

    Allow roughly 16–24 months total: 6–10 months for design, feasibility, civil, and permit review, then 10–14 months for construction, depending on phasing and weather. Multi-unit reviews typically run longer than single-family reviews in the same jurisdiction.
  • Q.04

    Do you handle the platting and HOA formation yourselves?

    We coordinate with the appropriate specialists — land-use attorney for condo or unit-lot platting, civil engineer for the site work, surveyor for legal descriptions. We do not practice law. We manage the construction and the cross-disciplinary timeline so the platting work lands when it needs to without delaying construction.
  • Q.05

    What does middle-housing implementation look like outside Seattle?

    Bellevue is rolling out its Middle Housing Code Update; Kirkland, Redmond, and Sammamish are at different stages of code amendment work, often consolidating around the MyBuildingPermit.com regional portal for submittals. The Department of Commerce tracks city status. Your feasibility memo includes the current implementation status for your specific parcel's jurisdiction.
  • Q.06

    Will HB 1110 guarantee that my project gets approved?

    No. The statute requires cities to allow middle housing by-right in single-family zones, but the city's design standards, parking rules, stormwater obligations, and fire-access requirements still apply. We can give you a realistic read on what the parcel will actually support, but we will not promise outcomes that depend on AHJ review or third-party utility decisions.
  • Q.07

    Do you do small-multifamily ground-up construction (4–6 units) in one stand-alone building?

    We build attached townhomes, cottage clusters, and small stacked-flat projects where local code allows. Larger multifamily buildings (high-rise wood-frame or concrete) are outside our current self-perform scope; we recommend specialized multifamily GCs for those projects and are happy to make the introduction.
  • Q.08

    Is this legal advice?

    No. The content on this page summarizes our experience as a Washington general contractor and links to the official state and city sources. Specific legal questions about ownership structure, condo declarations, lender requirements, or land-use appeals should be directed to a Washington-licensed real-estate attorney.

SOURCE_LAYER / Official citations

Where these claims come from

Permit, code, and middle-housing statements on this page are sourced to the official publishers below. Click any title to read the primary document. Dates indicate when each URL was last hand-verified by an editor.

This page is informational, not legal advice. Specific land-use, permit, or HB 1110 questions about a particular parcel should be directed to the appropriate AHJ or a Washington-licensed attorney.

AUTHORITY / Verify the spec

Official resources & sources

COVERAGE / Available in
SeattleBellevueKirklandRedmondTacomaSammamishIssaquahRentonMercer IslandShorelineEverettMukilteoLynnwoodEdmondsMountlake TerraceMill CreekBothellWoodinvilleBurienSeaTacTukwilaDes MoinesFederal WayKentAuburnUniversity PlaceLakewoodDuPontPuyallupLaceyTumwaterOlympia
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