ADU Builders & Remodeling Contractor in Tumwater, WA

Tumwater’s Trusted Partner in ADU and Tiny Home Construction

Tumwater has been quietly rewriting its residential code. Between 2025 and 2026 the city amended its low-density residential zoning to permit duplexes, triplexes, quadplexes, cottage housing, and stacked flats alongside single-family homes. Accessory dwelling units are permitted across every residential district in the city.

For a homeowner on Littlerock Road or up near Black Lake, that means the options on your own property are broader than they’ve ever been.

Mallard Brothers Construction is a design-build general contractor based in Olympia. We build ADUs, additions, and whole-home remodels throughout Tumwater.

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Building an ADU in Tumwater

Tumwater governs accessory dwelling units under Tumwater Municipal Code 18.42.010, and the code’s stated purpose is worth reading, because it explains why permitting here tends to go more smoothly than people expect. The city’s explicit intent is to encourage small housing units in all residential districts, make more efficient use of the existing housing stock, and support resident families of limited income while protecting property values.

Two things make Tumwater genuinely distinctive. You can sell a Tumwater ADU separately from the main house. Under the city’s code, an accessory dwelling unit may be sold independently of the principal residence upon approval and completion of a condominium or unit lot subdivision. This changes how the project appraises.

HB 1337 sets your floor. Inside the urban growth area, Washington requires cities to allow at least two ADUs per lot, prohibits owner-occupancy conditions, and bars any floor-area cap below 1,000 square feet. Tumwater’s own code operates on that baseline.

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What we build in Tumwater

Mallard Brothers offers a variety of ADU types to fit your property and lifestyle.

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Attached ADUs

Connected to the main home but with private entrances, providing independence within proximity.

Detached ADUs (DADUs)

Stand-alone units that offer privacy and versatility for guests, rentals, or workspaces.

Garage Conversions

Transform your garage into a livable space while navigating Thurston County codes around wells and septic systems.

Custom Tiny Homes

Eco-friendly and efficient, designed for minimal living without sacrificing comfort.

Sewer, septic, and Tumwater’s water situation

Central Tumwater is well served by city utilities and permits cleanly. But the city’s southern and western reaches, out toward Bush Prairie, Littlerock Road, and the Black Lake area, include properties on septic and on private or shared wells, and that is where ADU projects get complicated.

On septic, a second dwelling means proving your existing system can handle additional bedrooms. That may require a site evaluation, a system design update, or replacement. On a well, you’re looking at capacity and potential water-rights questions. Either can incur significant expenses.

We run this check as the first stage of design. If your property can’t support what you have in mind, we want to be able to offer you alternatives as soon as possible.

Remodeling and Additions in Tumwater

We take on substantial remodels, whole-home renovations, structural additions, full-floor reconfigurations, generally starting around $100,000. That’s the scale where a design-build team genuinely earns its fee. Below it, a specialist trade will usually serve you better, and we’ll tell you so.

Tumwater’s housing stock runs in distinct eras, and each brings its own work. The older homes through the Tumwater Hill and Brewery District areas tend to need systems brought current alongside the cosmetic work. The 1980s and ’90s subdivisions off Israel Road and Linderson come to us for primary suite additions and kitchen reconfigurations. And the larger parcels toward Bush Prairie and Littlerock support real footprint expansion.

For reference, our 800-square-foot Olympia addition won the Olympia Master Builders 2026 REX Award for Addition Over $250,000.

What we remodel

  • Whole-home and multi-room renovations
  • Structural additions and second-story builds
  • Kitchens designed around how the room actually gets used. See our kitchen work
  • Full bathroom suites, including curbless and barrier-free showers. See our bathroom work
  • Accessibility and universal design retrofits
  • Decks, covered outdoor living, and site work

Types of ADUs

Mallard Brothers offers a variety of ADU types to fit your property and lifestyle.

Get a Custom Quote

Garage Conversions

Transform your garage into a livable space while navigating local codes around wells and septic systems.

Custom Tiny Homes

Eco-friendly and efficient, designed for minimal living without sacrificing comfort.

Attached ADUs

Connected to the main home but with private entrances, providing independence within proximity.

Detached ADUs (DADUs)

Stand-alone units that offer privacy and versatility for guests, rentals, or workspaces.

ADA-Accessible ADUs for Aging in Place

Our team is experienced in building ADA-accessible ADUs for aging in place, allowing loved ones to live comfortably and safely. From wider doorways and ramps to barrier-free showers, our ADUs can be tailored with accessible features to support a range of mobility needs.

Fast-Tracked ADU Design with Preapproved Plans

If your property is within Olympia city limits, our team can expedite your project using Olympia’s Preapproved ADU plan sets. By choosing from these four designs, you’ll reduce permitting time and bypass additional engineering costs, helping you realize your ADU faster.

CRAFTSMANSHIP REDEFINED

Why Choose Us?

With Mallard Brothers, you’ll experience quality craftsmanship, attention to detail, and a personalized approach to each project. We bring your vision to life with durable materials, thoughtful layouts, and seamless integration with your property’s existing style.

Whether you want to build from a pre-approved plan or need a fully customized ADU, our team works closely with you to ensure the final result fits your vision and lifestyle.

Key Steps in the ADU Building Process

Building an ADU with Mallard Brothers is collaborative process

1

Initial Consultation and Feasibility Study

We assess your property’s requirements, including zoning, sewer, and septic capacity, to determine the best path forward.

2

Design and Planning

Choose from pre-approved plans or work with our designers to create a custom layout that fits your unique needs.

3

Permits and Approvals

Our team handles all necessary permits and regulations, ensuring full compliance for a worry-free build.

4

Construction and Finalization

From utility connections to finishing touches, our skilled team completes your ADU with precision and quality, ready for move-in.

Customization Options

Our ADUs are designed with flexibility in mind, allowing you to customize features to suit your preferences and lifestyle

Interior and Exterior Design

Choose from vaulted ceilings, cedar details, or custom finishes for a truly unique look.

Outdoor Spaces

Add saunas, covered decks, or landscaped seating areas for added comfort.

Energy-Efficiency Features

Solar panels, sustainable materials, and eco-friendly choices available to meet your green goals.

  • From first contact through construction

    …and the final inspection, the Mallard Brothers (Kevin, Keenan & Tyler) were phenomenal. Their team approach with clients, great communication and collaboration skills in addition to exemplary design, carpentry and construction skills resulted in a studio/home that’s beautiful, friendly, welcoming and awesome! It was truly a pleasure working with them and I wouldn’t hesitate to recommend them.
    Dane Kirkendall

  • Positive, can-do attitudes!

    If you are looking for a company who is truly in tune with your needs then these guys are for you! The only thing that matches their high standards of building is there positive, can-do attitudes! Doing business with Mallard Brothers Construction is, has been, and always will be a pleasure!
    Joseph Z

Serving Tumwater and the Surrounding Area

We’re based in downtown Olympia, ten to fifteen minutes from most Tumwater addresses. We work throughout Tumwater and its urban growth area, including Tumwater Hill, the Brewery District, Bush Prairie, Littlerock Road, Black Lake, Linderson Way, Israel Road, and the neighborhoods south toward Trosper and Capitol Boulevard. We also build in Olympia, Lacey, Yelm, DuPont, and unincorporated Thurston County.

Tumwater ADU and Remodeling FAQs

Yes, and this sets Tumwater apart. City code allows an accessory dwelling unit to be sold independently of the principal residence upon approval and completion of a condominium or unit lot subdivision. It’s a real exit strategy, not just a rental. We can advise on designing and siting the unit so that option stays open to you.

No. HB 1337 prohibits Washington cities inside urban growth areas from imposing owner-occupancy requirements on ADUs.

Detached ground-up ADUs in Thurston County generally run $300,000 to $450,000, depending on size, finish level, site conditions, and utility work. Garage conversions typically land lower. The largest single swing factor is sewer versus septic. We give you a real number after walking the property.

Accessory dwelling units are permitted across Tumwater’s residential zone districts, including low density residential and residential/sensitive resource, subject to the requirements of TMC 18.42.010. Your specific district determines setbacks, height, and lot coverage — we confirm this during feasibility.

About seven months as a working baseline — roughly four months for design and permitting, three for construction. Septic or well complications, critical-area review, or heavy customization can extend it.

Yes. Design, engineering, submittal, inspections, and final sign-off with Tumwater Community Development are all in our scope.

Remodels generally start around $100,000, ADUs around $300,000, and custom homes around $500,000. We run a limited number of projects a year so each gets real attention.

Ready to Find Out What Your Tumwater Property Can Support?

Send us your address, lot size, whether you’re on sewer or septic, and what you’re picturing. We’ll walk the property and give you a straight answer on feasibility and budget — no charge. (360) 504-8918

Request Your Free Feasibility Consult