FLYP builds home additions and accessory dwelling units across Seattle and the Puget Sound — room and bump-out additions, second stories, attached and detached ADUs (DADUs), and garage conversions. We handle design, permitting, foundation and framing, and the full managed build, and hand you a written fixed-scope quote first.
Adding on is the biggest way to change how a home lives without leaving the neighborhood you love. It's also the most structural work FLYP does — you're not refinishing a room, you're extending the foundation, framing, roofline, and mechanical systems of an existing house and tying new construction cleanly into old. On Seattle and Puget Sound housing stock, that "old" is usually a 1920s Craftsman, a mid-century rambler, or a 1970s split-level, and each brings its own quirks: undersized original footings, balloon framing, knob-and-tube or aluminum wiring, and floor and roof planes that were never quite level to begin with. We plan for that reality up front rather than discovering it after demo.
ADUs and DADUs are their own category. Seattle and many surrounding jurisdictions have opened up backyard cottages and in-home units considerably, and the rules — size caps, height limits, setbacks, parking, tree protection, and whether the unit can be sold or only rented — vary by city and even by lot. Whether you're after rental income, a place for aging parents or an adult kid, or a work-from-home studio that isn't the spare bedroom, the feasibility question comes before the design question. We start by pressure-testing what your specific lot and zoning actually allow, so you're not designing a dream that the code won't let you build.
Because additions break the weather envelope of a standing house, sequencing matters more here than in almost any other remodel — especially through a wet Pacific Northwest fall and winter. We stage foundation, framing, and dry-in so the existing home stays protected and the new structure gets weather-tight before the rain finds it. One project manager owns that schedule and stays your single point of contact from the first site walk through final inspection and punch-list.
What this service covers
Room & bump-out additions
Second-story additions
Detached & attached ADUs (DADU)
Garage conversions
Foundation & framing
Design & permitting
Why the plan matters more than the paint on an addition
With additions and ADUs, the value is made or lost long before finishes go in. The line items that actually drive cost are foundation and structural work, how far your utilities — sewer, water, power, and often a new panel — have to be extended, roofline complexity, and how much of the permitting and design phase your lot demands. Two additions of identical square footage can land at very different numbers depending on slope, soil, tree protection, and whether a second story requires reinforcing the structure below it. That's why we scope the hard, hidden parts honestly instead of quoting a pretty rendering and true-ing up the price later.
For most owners, the smartest dollars go into getting feasibility, design, and permitting right, and into a foundation and envelope that will never be the reason you regret the project. A well-built DADU or in-law suite can add durable living space, flexibility, and — where local rules allow rental — income, but only if it's designed to what your jurisdiction permits and built to last in this climate. We'll tell you plainly when a bump-out gets you 80 percent of what a full addition would at a fraction of the disruption, even when the bigger job would pay us more.
Frequently asked questions
What's the difference between an ADU and a DADU, and can I build one on my lot?
An ADU (accessory dwelling unit) is a second, self-contained living space on your property; an attached ADU shares a wall with the main house or is carved out of it (like a basement suite), while a DADU (detached accessory dwelling unit) is a standalone backyard cottage. Whether you can build one — and how big and how tall — depends on your city's zoning, your lot size, setbacks, tree protection, and parking rules, which differ across Seattle, Bellevue, Tacoma, and the smaller Puget Sound jurisdictions. Our first job is confirming what your specific lot actually allows before anyone draws a plan.
Do I need permits, and how long does the permitting take?
Yes — additions and ADUs are permitted work involving structural, electrical, plumbing, and often energy-code review, plus inspections along the way. Permitting is frequently the longest and least predictable phase of the whole project, and timelines vary by jurisdiction and how busy the department is; some cities have streamlined ADU review, others haven't. We handle design and permitting as part of the scope and give you a realistic schedule rather than a best-case guess, so the permit clock is planned for, not a surprise.
What drives the cost of an addition or ADU?
Cost is driven mainly by the structural and site work rather than the finishes: foundation type and soil conditions, how far utilities and the electrical panel have to be extended, roofline and second-story complexity, lot slope, and the design and permitting your jurisdiction requires. A garage conversion that reuses an existing slab and walls is a very different budget than a new-foundation DADU. We size it to your actual lot and goals at the consultation and put the number in a written, fixed-scope quote before work begins.
Can you build an addition onto an older Seattle home without it looking bolted on?
That's most of the craft. On Craftsman, mid-century, and split-level homes we match rooflines, siding, window proportions, and trim so the addition reads as part of the original house, not an afterthought — and we plan for the realities older homes hide, like undersized footings, out-of-level floors, and dated wiring that may need to be brought up to code where the new work ties in. The goal is that a year later a visitor can't tell where the old house stops and the new one starts.
Will my house be livable during the build, and how do you handle the rain?
For many additions you can stay in the home, though there will be stretches of noise, dust, and a temporarily opened wall or roof. Because breaking the weather envelope of a standing house is riskier in our wet season, we sequence foundation, framing, and dry-in so the existing home stays protected and the new structure is weather-tight before sustained rain arrives. Your project manager walks you through the disruption and the plan up front so you know what to expect week to week.
