By Harmony Cooper, AIA | Harmony Architecture Studio, Everett WA
A lot of the calls I have been taking lately start the same way. A homeowner in Everett, or somewhere else across Snohomish County, has an idea. Maybe a parent moving closer. Maybe a rental that could help carry the mortgage. Maybe a teenager who wants a little space of their own before leaving for college. Washington state recently opened the door wider than ever, and accessory dwelling units are suddenly on everyone’s mind.
Then comes the second part of the conversation, which is usually the more interesting one. They have already looked at the prefab options. They have seen the prices. They know they could have something in their backyard in a few months. And something is still holding them back.
Usually what is holding them back is the same instinct that made them fall in love with their house in the first place. Their home was built with care. They chose it because it feels like something, not just because it functions. And the idea of setting a generic, production-line box next to it feels wrong, even if they cannot quite put their finger on why.
This post is for those homeowners. I am an AIA-licensed architect based in Everett, and I design custom homes across the Pacific Northwest. Here is what I have learned about building ADUs in this city: how the rules actually work, what the real trade-off between custom and prefab looks like, and why I almost always recommend a custom, architect-led approach for homeowners who care about how their property ages.
What an ADU Is, and Why Everett Is Building Them
An accessory dwelling unit is a secondary living space on a single-family lot. It has its own kitchen, bathroom, and sleeping area, and functions as a complete small home. Two configurations are common. An attached ADU shares at least one wall with the primary residence, often carved out of a basement, garage, or existing addition. A detached ADU, sometimes called a DADU, sits as its own structure in the yard.
Everett has a few specific reasons for the sudden momentum. Multi-generational living has become more common as aging parents move closer to adult children and housing costs make shared property arrangements appealing. Long-term rental income from a well-designed ADU in this area typically lands somewhere between $1,800 and $2,800 per month depending on finish level, size, and neighborhood. And property values tend to rise meaningfully when a legal ADU is added, particularly one that reads as part of the original architecture rather than an afterthought.
The state of Washington also changed its ADU laws recently. House Bill 1337, codified in RCW 36.70A, opened up allowances across most cities, and Everett has implemented those changes through its Municipal Code, Title 19.
What You Can Actually Build in Everett
The short version: most Everett homeowners can now build up to two ADUs on a single residential lot. Both can be attached, both can be detached, or you can mix one of each. This applies across nearly every residential zone in the city, with a few exceptions in heavy industrial areas and certain overlay districts.
A few key rules worth understanding before you start sketching ideas.
Each ADU is capped at 1,000 square feet of habitable space. That is a real constraint, and it shapes design decisions from day one. A well-designed 900-square-foot ADU can feel generous. A poorly designed one can feel cramped at the same size.
Setbacks, height, and lot coverage follow the standards for your underlying zone. Most residential zones allow a detached ADU up to 24 feet in height, though this can vary. I always encourage homeowners to pull their site’s zoning before any design work begins. It changes what is possible.
Design standards do apply. Everett requires a street-facing entrance or porch for street-visible ADUs, along with private or shared yard space. If your property sits within a historic overlay, there is an additional review process. None of this is prohibitive, but it does require planning.
Parking requirements have relaxed considerably. Many lots no longer require additional off-street parking for an ADU under 1,000 square feet, which frees up design possibilities significantly.
Impact fees are where Everett has gone out of its way to be friendly. Many park, transportation, and school impact fees are reduced by 50 percent or fully waived for the first one or two ADUs on a property. Over the course of a project, this can mean tens of thousands of dollars. Check your specific situation with the city, because the incentives are genuinely worth factoring into the feasibility math.
Permits run through the city’s online portal. For most projects, expect the full review process to take several months, though this depends on complexity and current review volume.
The Real Question Most Homeowners Are Actually Asking
Once a homeowner understands what is allowed, the question almost always narrows to this: should I go with a prefab ADU to save time and lock in the cost, or should I have something designed specifically for my property?
It is a fair question, and I want to answer it honestly before I argue my position.
Prefab has real advantages. The timeline is faster. A prefab unit can often be delivered and set on a prepared foundation in a matter of weeks, compared to six months to a year or more for a custom build. The pricing is more predictable upfront, since you are buying a known product rather than pricing a design. And there is less decision-making fatigue, which matters for some homeowners.
What prefab typically gives up, though, is specificity. The unit is designed to work on a generic site, not yours. It comes in a limited set of finishes, dimensions, and layouts. It is designed to look acceptable next to any primary residence, which in practice often means it does not look quite right next to yours. And the long-term flexibility is limited. Modifying a prefab structure later is harder than modifying a site-built one.
The honest cost picture is also more complicated than the sticker price suggests. Prefab quotes rarely include the full site work: foundation, utility connections, permit fees, landscape restoration, grading, drainage solutions. Once those are layered in, the total installed cost of a prefab ADU in the Everett market often ends up similar to a modest custom ADU.
So the question is not really about money, even though it often gets framed that way. It is about what you want the finished property to look like and feel like, five, ten, twenty years from now.
Why I Argue for Custom
I design homes across the Pacific Northwest, and the projects I am most proud of share one quality: they feel like they belong to the land they sit on. The materials, the proportions, the way light enters, all of it emerges from a specific site and the specific people who will live there. That is the core of what architects do, and it is the main thing a prefab cannot offer.
An ADU designed with the same care as your primary residence reads as part of the property, not as something that landed there. The siding can match the main house. The roof pitch can echo it. Window placement can respect the views and privacy patterns of the existing home. The entry sequence can be considered, with a sense of arrival that ties the two structures together rather than making them compete.
On sites where the topography or the surroundings demand something specific, this matters even more. A sloped Everett lot with view corridors or mature trees is not a setting where a standard prefab model will do its best work. The site deserves a design that responds to it.
There is also the long-term value question. In my experience, homeowners who invest in a custom, architect-designed ADU tend to see a higher return when they eventually sell, and they command higher rental premiums in the meantime. Buyers notice when an accessory structure feels considered. Renters pay more to live in something that feels like a real home.
One of the recent projects I have worked on in the Methow Valley involved a main residence with a detached garage, a workout studio, a sauna outbuilding, and a dog run, all arranged on the site as part of a single architectural conversation. Every structure had its own purpose, but none of them felt separate. They shared materials, proportions, and a relationship to the land. That is the principle I try to bring to every ADU project, whether the detached structure is 500 square feet or something larger. It should feel like part of the same story.
How the Process Actually Goes
Every ADU project I take on moves through the same five phases, though the pace and emphasis change depending on the site and the client.
The first phase is site analysis and feasibility. Before I put pencil to paper, I spend time on the property. I look at topography, sun angles across the day and the seasons, prevailing winds, existing trees, views in and views out, privacy to and from neighbors, access routes, and where utilities enter the property. I also review zoning, setbacks, allowable height, lot coverage, and any overlay conditions. This phase answers one question: what is this site actually asking for?
The second phase is concept design. I sketch by hand first. I find that working with paper keeps ideas loose and flexible in a way that software does not. From those sketches, I develop early three-dimensional models that let a client see the shape and scale of a design before any decisions feel permanent. This is the phase where the big moves are made: where the ADU sits on the lot, how it relates to the main house, where the light enters, where the views are framed.
The third phase is design development. The concept deepens. Materials are studied. Structural systems are resolved. Consultants come in. Early cost estimates get real. This is where the design takes on the specificity that separates architecture from drafting.
The fourth phase is construction documents and permitting. Every detail gets drawn and specified so a contractor can build the design precisely and the city can issue permits with confidence. The quality of this document set is what protects the budget and the schedule once construction begins.
The fifth phase is construction administration. I stay involved through the build. Site visits, quick responses to contractor questions, resolving field conditions that inevitably arise. The goal is to protect the design intent through the part of the project that happens after the drawings are done.
What a Custom ADU Actually Costs
Transparent cost conversations help everyone, so here is the picture as I see it in the current Everett market.
Construction costs for a custom-designed ADU generally fall between $180,000 and $350,000 all-in, depending on size, finish level, and site complexity. A straightforward 600-square-foot DADU with quality but not luxury finishes tends to land toward the lower end. A highly finished 1,000-square-foot unit on a complicated site tends to land higher.
Design fees for architect-led residential work typically run between 8 and 15 percent of construction cost. On an ADU project, expect to be in that range. What you are paying for is a design tuned to your specific site, a complete set of drawings that protects you during construction, and an architect who stays engaged through the build.
Permit fees, impact fees where applicable, utility connection charges, and site-specific items like drainage or grading round out the total. I always advise clients to plan a 10 to 15 percent contingency on top of hard costs, especially on sites with unknowns.
Compared to the all-in cost of a fully installed prefab, the numbers are often closer than the sticker prices suggest. The real differentiation is not in cost. It is in what you get for the money.
Mistakes I See Often
A few patterns come up repeatedly with ADU projects that were not designed well.
The ADU looks nothing like the main house. This is the most common and the most damaging over time. Whatever you saved on speed or cost gets eroded by a permanent visual mismatch.
The site costs were underestimated. A beautiful unit set on a site that could not support it without major grading, drainage, or utility work can blow a budget fast. Good site analysis early prevents this.
The interior was designed without thinking about how the space actually lives. A 900-square-foot unit can feel like a well-proportioned small home or like a cramped apartment, depending on how the plan is organized.
The project started without understanding the overlay conditions. Historic district properties, critical area buffers, and certain zoning overlays add review layers that catch unprepared homeowners off guard.
All of these are avoidable with an experienced architect on the team from the beginning.
What to Look for in an Architect
Not every architect is the right fit for every ADU project, and it is worth spending a little time on this before committing.
Look for someone who designs residential work primarily, not occasionally. Residential architecture is its own craft, and experience matters.
Ask to see projects that are similar in scale and context to what you are considering. Look for work that seems rooted in its site, not imposed on it.
Make sure the architect is AIA-licensed and in good standing. The credential matters. It represents a level of training, accountability, and continuing education that unlicensed designers cannot claim.
Pay attention to how they talk about process. A good architect will be curious about you and your site before they start suggesting solutions.
Finally, trust your read on whether the person is someone you can work with over the course of a year or more. The ADU project itself is a partnership. Choose someone you want to partner with.
Questions I Get Asked Most
How many ADUs can I build on my Everett lot?
In most residential zones, up to two ADUs per lot. The specific allowance depends on your zoning designation, but the state’s recent expansion through HB 1337 opened up capacity significantly. Verify with the city for your specific parcel.
Do I actually need an architect, or can a builder handle this?
A builder can build. An architect designs. For a simple prefab unit on a flat lot, a design-build contractor may be sufficient. For a custom unit that integrates with your property, holds its value, and reads as architecture, an architect is worth the investment.
How long does a custom ADU take, start to finish?
Most custom ADU projects take between nine and eighteen months from first site visit to move-in, depending on permitting, design complexity, and construction schedule.
Will an ADU raise my property taxes?
Usually yes. The county assessor will reassess your property to include the value of the new structure. The increase is typically proportional to the added value.
Does an ADU affect my primary residence’s design?
A well-designed ADU enhances the main property without altering the primary residence. A poorly placed ADU can disrupt views, sight lines, and yard function. This is one of the reasons site analysis matters so much upfront.
Can I rent out an ADU in Everett?
Yes. Long-term rentals are widely permitted. Short-term rental rules can vary, so confirm current city regulations for your specific zone.
What happens if my property sits in a historic overlay?
An additional review process applies. The Everett Historic Preservation Commission reviews projects in overlay districts for compatibility with the historic character. An architect familiar with this process can guide you through it without significant added cost.
A Final Thought
At some point in every ADU conversation I have, the homeowner and I land on a version of the same question. Do they want a finished project that looks like something belonging to the property, or something that looks like something that landed there? Both paths lead to a habitable structure. Only one of them produces a property that feels considered.
If you are in Everett or the surrounding Snohomish County area and thinking about an ADU on your property, I am happy to have a conversation about your site, your goals, and whether a custom, architect-led approach fits what you are trying to build. The first conversation is straightforward. We talk about the lot, the constraints, what you imagine, and whether we are the right match for each other.
Good architecture does not need to be loud. An ADU that belongs on your property should feel, from the street, like it has always been there.
Harmony Cooper, AIA
Harmony Architecture Studio | Everett, WA | Pacific Northwest