Building Your Backyard Cottage in Tacoma Clear Process.

In Tacoma, an accessory dwelling unit (ADU) is a secondary living space on the same lot as a primary residence. A detached ADU is often referred to as a backyard cottage. The primary difference is simply the location; a detached unit is a separate structure, while an attached ADU shares a wall with the main house.

Regardless of the term, both are subject to the same strict zoning and building codes. You must ensure your lot meets the criteria for detached units, including setback requirements and utility connection standards. Always confirm your specific property's zoning classification with the City of Tacoma before proceeding with any construction plans.

Yes. Even if you are using the City of Tacoma's pre-approved detached plan program, you are required to obtain a building permit. A pre-approved plan is not a permit; it is merely a set of architectural drawings that have already been reviewed for compliance with building codes.

Once you choose a plan, you must submit it for site-specific review. This process ensures that the design works for your particular lot, taking into account things like utility connections, setbacks, and site drainage. Do not assume that a pre-approved plan means you can bypass the permit office. Always budget time and money for the full permitting cycle.

Finding ADU builders near Tacoma requires due diligence. Start by asking for their Washington L&I registration number, which you can verify yourself on the Washington State L&I website. Ask specifically how they handle detached structures and separate utility connections, because those are more involved than a simple renovation.

We recommend interviewing at least three contractors. Ask each one how they handle site-specific conditions and how they communicate during the build. Since we do not provide architectural or design services, make sure your chosen builder is willing to work alongside your designer so the construction matches the permitted plans.

Using a pre-approved plan is often considered streamlined rather than strictly cheaper. While you might save on initial architectural design fees, you will still pay for site-specific modifications, permit application fees, and engineering reviews. If you decide to change anything in the pre-approved set, you will incur separate designer fees for those revisions.

Additionally, the pre-approved plans belong to the City of Tacoma, not to the builder. This means the design is fixed unless you pay for professional adjustments. Always calculate the total cost, including these potential designer fees, when comparing your options against a custom-designed ADU.

Detached units in Tacoma may require separate utility connections, with external sewer and water service outside each unit. This often means running new sewer and water lines from the street to your backyard cottage, and depending on your lot layout it can be one of the larger items in the construction phase.

You must also consider electrical service. Some units may need a sub-panel or an upgrade to the main panel of the primary house to carry the additional load. During a site visit we can walk through the practical difficulties of connecting your new unit to existing infrastructure, and the final connection work should be done by a utility contractor registered for it.

The timeline for building an ADU is split into two major phases: permitting and construction. The permitting phase can take several months, depending on the City's workload and the complexity of your site-specific review. We cannot control this timeline, and it varies significantly from one property to the next.

Once the permit is issued and we begin the physical build, the construction phase typically takes several months depending on the size and complexity of the unit. Factors like weather, material availability, and the speed of required inspections can influence the actual completion date. We provide a construction schedule once we have an approved, permitted set of plans.

In Tacoma, a detached ADU must generally be at least five feet from a side property line. If the main entrance of the unit faces the side property line, that setback increases to eight feet. For the rear property line, the unit must be at least fifteen feet away, though no setback is required if the property abuts an alley.

These rules are strictly enforced to ensure fire safety and property access. During the pre-application process, the City will verify your site plan against these requirements. It is critical that your site survey is accurate, as any encroachment on these setbacks will result in a rejected permit application.

We do not offer fixed or flat-rate pricing before a site visit. The total cost to build a detached ADU depends on many factors, including the square footage, the cost of utility extensions, site preparation requirements, and the level of interior finishes you select.

Because every lot in Tacoma has unique characteristics—such as soil conditions, slope, and existing tree coverage—we need to conduct a thorough site assessment before providing a construction estimate. We recommend setting aside a contingency budget of at least 15-20% to account for unforeseen site conditions that may arise once construction begins, such as plumbing or electrical challenges.