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Bellevue & the Eastside · Design-build ADU and addition contractor
Backyard cottages, garage and basement conversions, and room or second-story additions. We check what your lot allows, design it in 3D, handle the permit and build it with our own crew, for one fixed price.
In-house crews · Licensed, bonded & insured in WA · Permits handled for you
ADU & addition at a glance
Typical cost
$60k – $350k+
Start to finish
6–18 months
Permit review
10–16 weeks for a DADU
Design
Lot check + 3D design
Licensed
Bonded & insured in WA
In-house
Crews for the core trades
3D design
See it before we build it
Permits
Filed and managed by us
The short answer
An ADU or home addition on the Eastside usually costs $60,000 to $350,000 or more. An interior or basement ADU runs $60k–$120k, a garage conversion $90k–$160k, a detached backyard ADU (DADU) $180k–$320k+, and a home addition $150k–$350k+. Most projects take 6 to 18 months from first consult to move-in, including 10 to 16 weeks of city permit review for a new DADU. Under Washington's HB 1337, most Eastside lots can now hold up to two ADUs, with no owner-occupancy rule.
Reviewed by John, project lead · Prices from our 2026 Eastside ADU and addition projects · Updated October 2026
ADU & addition services
Every project starts with a free lot and zoning check, so you know what your property allows before you pay for design.
A stand-alone backyard cottage with its own kitchen, bath and entrance, 400 to 1,200 sq ft.
$180k – $320k+
12–18 months
Detached ADUs →
Turn an attached or detached garage into a legal studio or one-bedroom unit, 400 to 700 sq ft.
$90k – $160k
8–14 months
Garage conversions →
Convert a basement or part of the house into a separate unit with its own exterior entrance, up to 500 sq ft.
$60k – $120k
6–10 months
Basement ADUs →
A new family room, primary suite or kitchen bump-out that adds 300 to 1,500 sq ft to the main house.
$150k – $350k+
10–16 months
Home additions →
Add a full or partial upper floor when your lot can't spare the yard space, after a structural check of the house below.
Quoted per home
Structural check first
Second-story additions →
Lot feasibility, zoning check, 3D design, structural engineering and a permit-ready drawing set.
Design-only available
8–14 weeks
Plans & design →
ADUs and additions on the Eastside
One team runs the whole project: a lot and zoning check, 3D design, structural engineering, permit drawings, the city submittal, site work and foundation, framing, utility hookups, finishes and the final inspection that gets you a certificate of occupancy. You get one fixed price and one project lead from the first visit to move-in.
Washington's HB 1337 changed what Eastside lots can hold. Cities must now allow at least two ADUs per lot, can't require the owner to live on site, must allow detached ADUs of at least 1,000 sq ft, and can charge no more than 50% of the impact fees for a new house. We check how your city has written those rules before you spend anything on design.
When the designer and the builder are the same company, the drawings are priced as they're drawn. You never pay for an ADU design you can't afford to build, and the crew that frames it helped plan the foundation and utility runs.
✓
Free lot and zoning check before design
✓
3D design and permit-ready drawings
✓
Engineering and city submittal handled
✓
Fixed price before ground breaks
✓
In-house crews, one project lead
Rules and timelines
DADU · 400–1,200 sq ft · 12–18 months
Garage conversion · 400–700 sq ft
Basement ADU · up to 500 sq ft
Addition · 300–1,500 sq ft
Up to 2 ADUs per lot (HB 1337)
No owner-occupancy requirement
Impact fees capped at 50%
Certificate of occupancy before renting
How it works
01
Week 1
We visit, look at access, slope, setbacks and utilities, and check what your city allows on your lot.
02
Weeks 2–10
We design the unit in 3D, size the utilities and complete the structural engineering, then lock in a fixed price.
03
Weeks 10–14
We prepare the full permit set and submit it to your city.
04
Months 3–7
The city reviews the plans, usually 10 to 16 weeks for a DADU. We answer every correction notice for you.
05
Months 7–18
Our crew builds it in 16 to 24 weeks, and we take the final inspection through to a certificate of occupancy.
Typical projects
Detached ADU
A one-bedroom DADU with its own entry and path. Renting at $2,200 a month brings in about $26,400 a year, paying back a $220k build in about 8.3 years.
$180k – $320k+
12–18 months
Garage conversion
Garage door replaced with windows and an entry, new insulation, kitchenette and bath. A $110k conversion renting at $1,800 a month pays back in about 5 years.
$90k – $160k
8–14 months
Interior ADU
A basement turned into a separate unit with a kitchenette, bathroom, egress windows and its own exterior door.
$60k – $120k
6–10 months
Reviews
Real Google reviews from homeowners we've built for across Bellevue and the Eastside.
FAQ
Straight answers on cost, timelines, rules and rental income. Ask us anything else at the free lot check.
How much does an ADU cost in Bellevue?
Most Eastside ADUs cost $60,000 to $320,000 or more. An interior or basement ADU runs $60k–$120k, a garage conversion $90k–$160k, and a detached ADU $180k–$320k+. Site work, slope and utility hookups move the number most.
How long does it take to build an ADU?
A detached ADU usually takes 12 to 18 months from first consult to move-in: 6–10 weeks of design and engineering, 2–4 weeks of permit drawings, 10–16 weeks of city review and 16–24 weeks of construction. Garage conversions take 8–14 months and basement ADUs 6–10 months.
What did Washington's HB 1337 change for ADUs?
HB 1337, passed in 2023, requires Eastside cities to allow at least two ADUs per lot, drop owner-occupancy rules, cap ADU impact fees at 50% of a new house's, and allow detached ADUs of at least 1,000 sq ft. Cities had to update their codes by 2025, so details still vary a little by city. We check yours at the lot check.
Can I rent out my ADU?
Yes. With no owner-occupancy rule, you can rent the ADU or the main house. You need a certificate of occupancy first, which we get at final inspection. Eastside rental vacancy runs under 5%, and a DADU renting at $2,200 a month pays back a $220k build in about 8.3 years.
Does an ADU add value to my home?
Usually, yes. A permitted, well-built ADU on the Eastside typically adds $150,000 to $280,000 in appraised value, on top of the rent it can bring in.
Should I build an ADU or a home addition?
Build an ADU if you want a separate unit with its own kitchen and entrance for rent, family or guests. Build an addition if you want more room in the main house, like a bigger kitchen, a family room or a primary suite. We'll sketch both on your lot at the free consult.
What if my lot is sloped?
Lots steeper than about 15–20% need a geotechnical report before the design is final. Plan on $3,000–$6,000 and 4–6 extra weeks. We order it and design the foundation around what it finds.
Start your ADU or addition
Tell us about your property. We'll visit, check zoning, slope and utilities, talk through what you want to build, then send you a fixed price.
Renovision Design & Build LLC
1400 112th Ave NE, Bellevue, WA 98004
(425) 276-6501 · Mon–Fri 8–5
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