PE-stamped
4.9/5 rating
WA Licensed
Engineering on every build
Google Reviews
#ALEXHHQ785QQ
Structural + permit-approved
UBI #604988178
150+
Projects across Puget Sound
Every project PE-engineered
Why homeowners build ADUs in Seattle
— Why Build an ADU in Seattle
Multi-generational Living & Flexibility
Keep aging parents or adult children close while everyone maintains independence. A DADU offers a full kitchen, bathroom, and separate entrance. Today a family suite, tomorrow a rental — your DADU adapts to your life stage.
ADU permits in Seattle have grown 4x in recent years
$30,000/year in rental income
A one-bedroom ADU in Seattle rents for $2,000–$2,600/month — that's $30,000/year toward your mortgage, retirement, or your next investment. With no owner-occupancy requirement, you can rent both your main home and ADU simultaneously.
ROI: 5.2% annually · Break-even: 8–12 years
Add $200K-$350K in Property Value
Properties with ADUs sell for 20–30% more than comparable homes without one, and sell 26% faster. A $300K DADU investment can add $350K+ to your property value. Under 2025 rules, DADUs can now be subdivided and sold as separate parcels.
Avg. property value increase: 20–30%
Seattle’s housing market makes ADUs one of the smartest investments a homeowner can make.
With median home prices near $ 1,050,000 and rental demand at 94%+ occupancy, your backyard is an untapped asset.
Browse completed projects across Seattle, Bellevue, and King County
— Our Work
Recent ADU & DADU Projects
DADU · Detached ADU
$285,000
Two-Bedroom Rental Cottage
DADU · Detached ADU
Est. $155K–$195K
Compact One-Bedroom Backyard Cottage
DADU · Detached ADU
$312,000
Modern Backyard Cottage
DADU · Detached ADU
$465,500
Two-Story Cottage with Storage Loft
DADU · Detached ADU
$298,000
Open-Plan Two-Bedroom Cottage
DADU · Detached ADU
$220,000
Backyard Cottage with Wraparound Deck
What we promise — in writing
— Why Evercrest
Your price locks after engineering.
It doesn’t move.
Most Seattle contractors give you an estimate. We give you a guarantee. Once engineering is finalized, the number in your contract is the number you pay. Any changes are agreed before engineering closes — after that, nothing shifts.
Architecture, engineering, construction. One team. One contract.
No separate architect. No separate contractor. No gaps in accountability when scope changes. Design, engineering, and build are sold as a single package — one point of responsibility, start to finish.
One project manager.
The whole way through.
One person who knows your project inside out — from design sign-off to final city inspection. Same-day response during business hours. No departments. No repeating yourself halfway through the build.
10-year warranty.
In writing. In your contract.
Every project is backed by a 10-year workmanship warranty, documented in the contract. If anything fails due to our work, we fix it at no cost. Not a verbal promise — a contractual obligation.
Extension, ADU & DADU — What’s the Difference?
All three are ways to add independent living space to your property. The right choice depends on your goals, lot, and budget.
$285,000
Home Extension
Expand your existing home by adding a new wing, level, or attached addition. Ideal if you want more space within the main structure — extra bedrooms, a sunroom, or an expanded living area that becomes part of the primary residence.
From $350 / sq ft
ADU — Attached Unit
A fully self-contained secondary dwelling attached to or inside your home — basement apartment, garage conversion, or side addition with its own entrance, kitchen, and bathroom. Legal to rent out long-term or short-term in Seattle.
From $380 / sq ft
DADU — Detached Backyard Home
A completely standalone cottage or home built in your backyard with no shared walls. Maximum privacy for tenants or family. Adds the most equity and rental income potential of all three options — and qualifies as a separate legal dwelling unit under Seattle zoning.
From $350 / sq ft
- Becomes part of primary residence — not a separate dwelling
- No separate utility connections needed — ties into existing systems
- Seamless architectural integration: roofline, siding, trim matching
- Foundation tie-in engineering for structural additions included
- Sewer work typically not required for extensions
- Best for: Growing families needing more bedrooms, living space, or a master suite
- Cannot be rented out as a separate unit
- Typical projects: Second-story addition ($180K–$280K for 1,000 sq ft), rear extension ($80K–$150K for 400 sq ft), master suite ($120K–$180K for 500 sq ft)
- Fully independent unit: own entrance, kitchen, bathroom, and living area
- Shares at least one wall (or is within) the main house
- Up to 1,000 sq ft in most Seattle NR zones (conversions may exceed)
- Shares existing utility connections — lower infrastructure cost than DADU
- Legal to rent out in Seattle — no owner-occupancy requirement since 2019
- Types: Basement ADU ($120K–$180K), Garage Conversion ($150K–$200K), Attached addition ($160K–$220K)
- Rental income: $1,600–$2,600/month depending on size and neighborhood
- Best for: Budget-conscious owners wanting rental income or a family suite with lower construction cost
- Completely independent standalone structure — no shared walls
- Up to 1,000 sq ft · Up to 32 ft height in NR zones (2-story possible)
- 5 ft side/rear setbacks (0 ft if rear borders an alley)
- Requires separate utility connections: water, sewer, electrical ($ 18K-$ 35K)
- Separate foundation and full site work required ($ 35K-$ 110K depending on slope)
- Highest rental income: $ 2,000-$ 3,500/month · Adds $ 200K-$ 350K property value
- Can be subdivided and sold separately under 2025 HB 1337 rules
- Two DADUs now allowed per lot — can be in the same or separate structures
- Typical cost: $ 250K-$ 400K for 600−1,000 sq ft · Premium builds: $ 400K-$ 600K
- Best for: Maximum rental income, long-term investment, complete privacy for family
$193K
how much will your ADU cost — and earn?
ADU construction starting cost
$2,300/mo
Average rental income (1-bed)
+$250K
Average property value increase
7 years
Average break-even
Get a personalized estimate in 2 minutes. Construction cost, monthly rent, property value increase, and break-even timeline - based on real Seattle data.
— Investment Calculator
Seattle adopted permanent Neighborhood Residential zoning in February 2026 (Council Bill 120993), building on HB 1337 and HB 1110. Here are the key rules for your property.
What You Can Build Right Now
— Seattle ADU Regulations 2025–2026
Units Per Lot
Up to 4
Up to 4 total dwelling units on any Neighborhood Residential (NR) lot — configured as detached cottages, townhouses, stacked flats, or any combination. Up to 6 units if the lot is within ¼ mile of a major transit stop or includes 2 affordable units.
Both primary units and ADUs count toward density limits
Max ADU Size
1,000 sq ft
Maximum gross floor area per ADU in NR zones. Actual buildable size also depends on your lot’s Floor Area Ratio (FAR) and lot coverage — on smaller lots, these limits may restrict you below 1,000 sq ft.
Conversions of existing structures may exceed this limit
Height Limit
Up to 32 ft
In NR zones — same as principal dwelling. Up to 40 ft+ in other zones. Pitched roof ridge can extend an additional 5 ft within a 4:12 sloped envelope (effectively ~37 ft). Two-story DADUs are now fully possible.
Side / Rear Setback
5 feet
Standard minimum from side and rear property lines. Zero setback where rear yard abuts an alley. Front setbacks follow standard zoning rules for the lot.
DADUs exceeding 18 ft in height require increased setbacks
Owner Occupancy
Not required
You can rent out both your main home and ADU/DADU without living on the property. Owner-occupancy requirement was eliminated by 2019 reforms and reinforced by HB 1337 in 2025.
Parking Required
No
Off-street parking requirements eliminated for ADUs. You can include parking based on your needs, but the code does not require it. Reduces cost and enables projects on smaller lots.
Lot Coverage
Up to 50%
For lots with multiple dwelling units, maximum lot coverage increased from 35% to 50%. On a typical 5,000 sq ft lot, this means 2,500 sq ft of building footprint — enough for a primary home plus additional units.
Was 35% under old SF zoning — a major increase
Impact Fees
Waived
Impact fees waived for ADUs under 1,000 sq ft. ADUs are also exempt from street improvement requirements regardless of zone. Saves thousands in permitting costs.
Every project type follows a proven 7-step process — from first consultation to your final walkthrough.
Our 7-Step Build Process
Private meeting at your home to review goals, lifestyle needs, and structural feasibility of the addition.
1
step
Our architect confirms buildable scope, setback requirements, and zoning compliance. Sewer work is typically not required for extensions.
2
step
We prepare a structural phase plan covering excavation, foundation, framing, roofing, and exterior shell with preliminary pricing.
3
step
Formal agreement with fixed pricing, timeline reservation, and team assignment. Your start date is locked in.
4
step
Layout, exterior integration, windows, and doors — all designed for seamless flow with your existing home. Homeowner approval required before permitting.
5
step
Structural calculations, foundation requirements, framing and roof systems. We handle full permit submission with the City of Seattle.
6
step
from first call to keys in hand: 8–14 months
Excavation → foundation inspection → framing → roofing & enclosure → MEP inspections → drywall, paint, flooring → final city inspection → walkthrough → 10-year warranty.
7
step
We define the ADU purpose (rental, family suite, office) and evaluate existing utility connections and structural feasibility.
1
step
We verify square footage allowances, height limits, setback requirements, and Seattle ADU-specific zoning rules for your property.
2
step
Cost estimate covering excavation (if needed), foundation, framing, roofing, and exterior build-out with finish-level options.
3
step
Fixed-price agreement, timeline confirmation, design phase kickoff, and team assignment.
4
step
Bedroom and bathroom placement, kitchen zone design, private entry, and flow — optimized for both comfort and rental appeal.
5
step
Foundation design, structural framing, roof load specs, sewer and plumbing planning. Full permit package submitted to the City of Seattle.
6
step
from first call to keys in hand: 8–14 months
Full build including framing, MEP rough-ins and inspections, drywall, flooring, cabinetry, tile, fixtures, appliances → final inspection → walkthrough → 10-year warranty.
7
step
We assess backyard placement, privacy, access routes, slope, and discuss your goals — rental income, multi-gen living, or long-term investment.
1
step
We verify setbacks, height limits, parking requirements, utility access, and DADU-specific Seattle zoning rules for your lot.
2
step
Full cost breakdown covering excavation, foundation, framing, roofing, and enclosure — with site-specific adjustments for slope and soil conditions.
3
step
Fixed-price agreement with secured start date and dedicated project team. Your slot in our schedule is confirmed.
4
step
Complete layout, exterior style selection, kitchen and bathroom placement, and living flow design — with homeowner sign-off before permitting begins.
5
step
Structural calculations, foundation design, roof systems, dedicated sewer trenching, and utility connections. Full permit package submitted and managed.
6
step
from first call to keys in hand: 8–14 months
Excavation → utilities & sewer inspection → foundation → framing → enclosure → MEP inspections → drywall, paint, flooring → full kitchen & bathrooms → final city inspection → walkthrough → 10-year warranty.
7
step
Not sure how to finance your project?
We work with trusted local lenders who specialize in ADU and home improvement financing — including home equity loans, construction loans, and cash-out refinancing. We’ll connect you with the right person based on your situation.
ADU & DADU
FAQ
FAQ
In the greater Seattle area, the typical cost to build an ADU is approximately $ 350 to $ 450 per square foot. This price includes construction labor and rough materials — framing, structural work, and core building systems. It does not include finish materials like flooring, paint, kitchen and bathroom materials, fixtures, or appliances. The total cost depends on size, site conditions, permit requirements, and the level of finishes chosen.
An ADU (Accessory Dwelling Unit) is a secondary living unit on the same property as the main house — it can be attached, built inside the home (such as a basement unit), or detached. A DADU (Detached Accessory Dwelling Unit) is a specific type of ADU that is completely separate from the primary residence, typically built as a standalone backyard cottage or small independent structure with no shared walls.
In the Seattle area, building a backyard cottage typically takes about 8 to 14 months from start to finish. This includes permitting, site preparation, construction, and final inspections. For a standard DADU around 1,000−1,500 sq ft, the construction timeline is usually around 8 months. A larger project of around 3,000−3,500 square feet can take closer to 14 months, because it would need to be permitted not as a DADU, but more like a townhouse-type structure. The permitting process for that typically takes longer, and of course the construction itself also takes additional timeand in addtion all this depending on design complexity, site conditions, and city permit review timelines.
Yes — in Seattle you can legally rent out your ADU (long-term or short-term), as long as it is properly permitted and registered. ADUs are allowed as rental units under Seattle zoning and building codes. There is no owner-occupancy requirement, meaning you do not need to live in the main house or the ADU in order to rent it out
Yes — building an ADU typically increases property value because it adds additional livable square footage, creates a rental income stream, and makes the property more attractive to buyers looking for multi-generational housing or investment opportunities. In high-demand markets like Seattle, an ADU can significantly improve resale value by turning a single-family lot into a more flexible, income-producing property.
Yes — we manage the full permitting and city approval process for ADU, DADU, and extension projects. This includes preparing all required documentation, coordinating with architects and engineers, submitting plans to the City of Seattle, and guiding the project through plan review, inspections, and final approval to ensure full compliance with building codes and regulations.
There are several financing options commonly used for ADU and DADU projects in Seattle — including home equity loans (HELOC), cash-out refinancing, and construction loans. The right option depends on your current equity, credit profile, and how you plan to use the unit. We work with trusted local lenders who specialize in ADU and home improvement financing and can connect you with the right person based on your situation. Just bring it up during your free consultation and we’ll point you in the right direction.
Yes — in many cases, you can legally convert an existing garage into an ADU in Seattle, as long as the structure meets current zoning, building code, and safety requirements. The garage must be permitted, upgraded for insulation, plumbing, electrical, and egress, and approved through the city’s plan review and inspection process. Feasibility depends on property layout, utility access, and Seattle ADU regulations. We assess this during your free consultation.
Under Seattle’s 2025 zoning updates (HB 1337 and HB 1110 compliance), you can build up to two ADUs per lot that contains a principal dwelling unit. Both can be detached (two DADUs), or any combination of attached and detached. Some lots near major transit stops can accommodate up to 6 total units. Two DADUs can even be located in the same structure. ADUs count toward overall density limits.
Standard: 5-foot setback from side and rear property lines. If your property borders a back alley, you can build with zero setback on the alley side. Front setbacks follow standard zoning rules. When a DADU exceeds 18 feet in height, Seattle requires increased setbacks from property lines. These requirements apply across all NR zones (NR1, NR2, NR3, and RSL zones).
No. Seattle eliminated off-street parking requirements for ADUs in both the 2019 reforms and 2025 updates. You can choose to include parking, but the code doesn’t require it. This reduces construction costs, makes projects feasible on smaller lots, and promotes transit-oriented development.
Each ADU can be up to 1,000 sq ft of gross floor area in most NR zones. The actual buildable size also depends on your lot’s Floor Area Ratio (FAR up to 1.2 depending on zone) and lot coverage limits. Conversions of existing structures (basements, garages) may exceed the 1,000 sq ft limit. Minimum lot sizes no longer apply for ADUs
Yes. Under the 2025 rules, DADUs can be up to 32 feet tall in Neighborhood Residential zones and up to 40 feet in other areas. The ridge of a pitched roof can extend an additional 5 feet above the height limit within a 4:12 sloped envelope. This means two-story DADUs are now fully possible and increasingly popular for maximizing space on smaller lots.
