Serving Washington
ADU Builder in Mountlake Terrace, Washington
Bayside Home Builders permits, designs, and builds accessory dwelling units in Mountlake Terrace, handling city approvals and construction so you get a finished unit without the runaround.
adu project · Mountlake TerraceThe Math on Mountlake Terrace ADUs Is Real, but So Are the Surprises
A one-bedroom detached ADU in Mountlake Terrace runs roughly 200,000 to 280,000 dollars to build. Two-bedroom units push into the 280,000 to 400,000 dollar range. Those numbers are real project costs, not marketing estimates, and they do not shrink just because your lot is small or your garage looks like it is in decent shape.
What you are living with
Homeowners who try to cut costs by hiring the lowest bidder usually end up paying for it twice. In Mountlake Terrace specifically, older utility connections sometimes need upgrading before a new dwelling unit can be connected. Drainage on smaller lots can require engineered solutions. And permit corrections that send you back to the start cost you months, not days. A 6 to 14 week review window means a bad first submission is an expensive mistake.
What you get instead
We do a real site assessment before we give you a number. We look at your lot dimensions, setbacks, existing utilities, and garage condition if conversion is on the table. We tell you what the permit process will actually cost in time and fees, and we give you a project cost range you can plan a budget around before you commit to anything. No inflated lowball to win the job and change order you later.
Our Recent Work
Accessory Dwelling Units Built to Code, Built to Last
An ADU adds livable square footage to your property without touching your primary residence. Whether you need a rental unit, a space for aging parents, or a home office with a bathroom and kitchenette, we design and build the structure from the ground up, handling permitting, utilities, and inspections so you do not have to coordinate between multiple contractors.
Site Evaluation and Feasibility
Before any plans are drawn, we walk your property and review zoning rules, setback requirements, lot coverage limits, and utility connection points. You get a clear yes or no on what is buildable before spending money on design.
Architectural Design and Permit Drawings
Our in-house design team produces permit-ready drawings sized and positioned to satisfy local zoning. We handle the permit application and communicate directly with the building department through review and approval.
Foundation and Structural Framing
We pour the foundation appropriate to your soil conditions and frame the structure to current residential building code. Every framing inspection is passed before we close up walls.
Mechanical, Electrical, and Plumbing Rough-In
Licensed subcontractors install the electrical panel, plumbing supply and drain lines, and HVAC or mini-split system. We coordinate the inspection schedule so each trade is signed off in sequence without delays.
Interior Finishes and Fixtures
Insulation, drywall, flooring, cabinetry, countertops, and fixtures are all included in our scope. You select finishes from our supplier network. We install and trim out everything to a move-in ready standard.
Final Inspections and Certificate of Occupancy
We schedule and pass every final inspection, including building, electrical, plumbing, and mechanical, and hand you the certificate of occupancy so the unit is legal to rent or occupy from day one.
Why Homeowners Choose Bayside for ADU Projects
ADUs require a contractor who can manage design, permitting, and construction as a single coordinated process. Here is what separates the way we work from hiring a general contractor who subs out the design.
Design and Construction Under One Roof
We employ our own designers and run our own crews. When a permit reviewer asks for a revision or a field condition changes the plan, the same team that drew the plans adjusts them the same week. There is no finger-pointing between a separate architect and a separate builder.
Licensed and Bonded, Washington L&I
We carry active WA L&I licensing and full bonding. You can verify our license number directly with the state before signing anything. We will not ask you to pull your own permits or list yourself as the owner-builder to cut costs.
Permit Experience Across Multiple Jurisdictions
ADU rules differ from one municipality to the next. We have navigated varying setback rules, owner-occupancy requirements, and utility connection standards across multiple jurisdictions. We know what reviewers flag and we write plans that pass on the first or second submission, not the fifth.
Fixed-Scope Contracts with Itemized Budgets
We provide a written contract with a line-item budget before work begins. Allowances for finishes are called out explicitly so you know exactly what is included. Change orders require your written approval before any additional work proceeds.
What our clients say
We hired Bayside for a full home remodel, and the results are absolutely breathtaking! Coral was our project manager and did an outstanding job coordinating the team and managing every aspect of the project. The new open-concept living space and…
Bayside transformed our entire house into something straight out of a magazine! Coral, our project manager, was an absolute gem, organized, communicative, and attentive to every detail. From the new flooring to the redesigned layout, everything was…
How an ADU Project Works with Bayside
Most ADU projects follow the same four-phase sequence from first conversation to move-in ready. Here is what to expect at each stage.
Discovery and Feasibility
We meet at your property, review your lot dimensions and zoning classification, and assess your utility stub locations. You leave that meeting knowing whether an ADU is feasible, what size is realistic, and what the permitting process will look like. No fee for this first conversation.
Design, Pricing, and Permitting
Once you decide to move forward, we produce a detailed scope, a fixed-price contract, and permit-ready drawings. We submit the permit application and manage the back-and-forth with the building department. This phase typically takes several weeks depending on local review times.
Construction
We break ground after permit approval is in hand. Our project manager updates you weekly and is reachable by phone or text throughout the build. We schedule each inspection proactively so the project does not sit idle waiting for a sign-off.
Final Walkthrough and Turnover
Before we hand over keys, we walk the completed unit with you and create a punch list of any items to address. You receive the certificate of occupancy, warranty documentation, and contact information for ongoing support. The unit is ready to occupy or rent.
What Adu Costs
ADU costs in Mountlake Terrace depend on which type you build and what your lot allows under city code.
Attached ADU
Converting or adding living space within the existing footprint.
Garage conversion
Turning an existing garage into a permitted dwelling.
Detached DADU
A standalone backyard cottage, built to code and permitted.
Mountlake Terrace processes ADU permits through its own building department at 6100 219th Street, and permit review typically runs 6 to 14 weeks, so budget that window into your project timeline before breaking ground. The city follows state law under HB 1337, which means most single-family lots can support two ADUs, but city setback, height, and size standards still apply and can shift your scope and cost. We pull those site-specific rules before we quote anything, so you know exactly what you can build.
ADU Contractors Serving Mountlake Terrace, WA
Mountlake Terrace sits in a dense, established corridor between Seattle and Lynnwood where lot sizes are modest and the city is actively processing ADU applications under Washington's updated statewide rules. We build detached and attached ADUs here, handle permits through the city's building department at 6100 219th Street, and know what the review process actually looks like from submission to final inspection.
Permits & review
Mountlake Terrace processes ADU permits through its own building department. Expect a permit review window in the range of 6 to 14 weeks depending on project complexity and current workload. Under HB 1337, the city must allow up to two ADUs on lots zoned single-family, so if your lot can accommodate a detached ADU plus an attached unit, that option is worth running through the numbers. The city requires owner or immediate family occupancy on the property, and any rental of the ADU must be for terms of 31 days or longer. We put together complete permit packages the first time so you are not losing weeks to correction requests.
Housing stock
Most Mountlake Terrace lots were built out in the 1950s through 1970s with single-story or split-level homes on smaller rectangular lots. That means we are frequently working around existing detached garages, mature trees, and setback constraints that limit where a detached ADU can land. Garage conversions are a cost-effective path here when the structure is sound. New detached builds are possible on many lots but require a careful site check before you commit to a budget. We walk the lot before we quote anything.
Areas we serve
We serve Mountlake Terrace and the surrounding Snohomish and King County communities along the I-5 corridor. If you are close to the Mountlake Terrace transit center area or near the 236th Street SW corridor, we are already familiar with the neighborhood lot patterns. Call us and we will tell you quickly whether your specific address and lot configuration make an ADU viable.
Common questions
What are the rules for ADUs in Mountlake Terrace under Washington state law?
Mountlake Terrace follows Washington state standards, including HB 1337, which now allows two ADUs on most single-family lots in cities over 25,000 people. A detached ADU can be up to 1,000 square feet on a lot with one ADU, or up to 1,600 square feet combined when you add a second. The city requires permits through its building department at 6100 219th Street. Short-term rentals under 31 days are not allowed in ADUs, and owner or immediate family occupancy of the primary home is required.
Can I build two ADUs on my Mountlake Terrace lot?
Yes, in most cases. HB 1337 requires Mountlake Terrace to permit two ADUs on single-family zoned lots. That can mean one attached or interior ADU plus one detached, or other combinations depending on your lot. We review your specific parcel before quoting anything, because setbacks, lot coverage, and existing structures all affect what is actually buildable.
How much does an ADU cost to build in Mountlake Terrace?
A one-bedroom detached ADU in the area typically runs $200,000 to $280,000 for construction. Two-bedroom units generally fall in the $280,000 to $400,000 range depending on size, finishes, and site conditions. Attached or garage-conversion ADUs usually cost less because the foundation and shell work is reduced. These ranges do not include soft costs like permits, engineering, or utility connections, which can add $15,000 to $40,000 depending on the scope. We give you an itemized estimate before you commit to anything.
How long does the ADU permit process take in Mountlake Terrace?
Plan on 6 to 14 weeks for permit processing through the city, depending on project complexity and current workload at the building department. Complete, clean permit packages move faster. We prepare your drawings and application documents to minimize back-and-forth with the city. Total project time from signed contract to a finished ADU is typically 9 to 14 months when you factor in design, permitting, and construction.
What are the real disadvantages of building an ADU?
The honest ones: upfront cost is significant and financing options are more limited than for a primary home purchase. Permitting and construction take most of a year. If you are adding a full kitchen and bathroom, utility connection fees and system upgrades can be a surprise cost. Renting an ADU also makes you a landlord, with the responsibilities that come with it. That said, for homeowners who want rental income, multigenerational living, or long-term property value, a well-built ADU typically pencils out over time.
Do I need to live on the property to have an ADU in Mountlake Terrace?
Yes. Mountlake Terrace requires the owner or an immediate family member to occupy either the primary home or the ADU. You or a qualifying family member must have resided on the property for at least three months before the ADU can be rented out. The city does not allow short-term rentals of 30 days or fewer in ADUs.
Why hire Bayside Home Builders for an ADU in Mountlake Terrace instead of a general contractor?
We are a design-build firm, meaning we handle design, engineering coordination, permitting, and construction under one roof. You deal with one team instead of managing an architect, a permit expeditor, and a builder separately. We know Mountlake Terrace permit requirements and have built ADUs throughout Seattle and the Eastside. That experience means fewer surprises on your budget and your timeline.
Keep exploring
Other services in Mountlake Terrace
Bathroom Remodeling→Kitchen Remodeling→Home Renovation→Home Addition→Home Builders→
Planning your remodel?
Bayside gives free, itemized estimates with no pressure to sign.