Go Far®The realistic range
In Snohomish and King County, most additions price out at roughly $300–$550 per square foot, and a primary suite sits at the upper half of that band because of the plumbing, tile, and finish work packed into its bathroom. For a typical 350–500 square foot suite — bedroom, full bath, and walk-in closet — that means most projects here land between about $150,000 and $275,000, with larger suites, second-story builds, and premium finishes going beyond that. A suite carved out of existing space (a converted garage, bonus room, or two small bedrooms combined) is the lowest-cost path, because you are remodeling rather than building new house.
Why the bathroom sets the budget
A plain bedroom addition is framing, roof, windows, and drywall. A suite adds a wet room: new supply and drain lines, venting, waterproofing, tile, glass, a vanity with stone, and often a freestanding tub or curbless shower. That bathroom is regularly a third or more of the whole suite’s cost, and its position matters — a bath placed close to the home’s existing plumbing stack is far cheaper to connect than one at the far end of a new wing. Our bathroom cost guide covers the fixtures and finishes that move that number most.
Up, out, or convert
- Ground-floor addition. The most common route on Puget Sound lots with yard to spare. Money goes into excavation and foundation, and the payoff is a first-floor suite that works for every stage of life — the single most requested feature in aging-in-place remodels.
- Second-story suite. Building up keeps the yard and can add views, but requires engineering, a new roof structure, and a stair. See our second-story addition guide for how that pricing differs.
- Suite over the garage. A middle path: the foundation already exists, so cost goes into beefing up the garage structure, insulating properly, and tying the roofline in so it looks original.
- Convert existing space. Combining two bedrooms, or finishing an attic or bonus room, avoids foundation and envelope work entirely. It costs the least but gives up a room somewhere else.
What moves the number most
Site conditions — slopes, drainage, and tight setbacks are where Puget Sound lots vary most. Roofline and siding match — blending the addition so it reads as original takes craftsmanship and sometimes hunting down discontinued materials. Mechanical capacity — an older electrical panel or a furnace already at its limit may need upgrading, or a ductless mini-split for the new suite. Closet and finish level — a built-out walk-in closet, radiant floor heat, and premium tile each add their own line. And design and permits — additions need drawings, structural engineering, and city permits, a process measured in months around here, so we start it early. For the full picture of how additions price, read our home addition cost guide.
Is a primary suite worth it?
A suite is usually a lifestyle-first investment: it fixes a floor plan that no longer fits, and it is one of the few projects that can make a “we need to move” conversation go away. Resale return is strongest when the addition solves a real shortfall compared to neighboring homes — a three-bedroom, one-bath house in a neighborhood of four-bed, two-and-a-half-bath homes gains far more than a house that already has a suite. We ran the improve-versus-move math in our addition vs. moving guide; with today’s interest rates, adding on usually wins.
Get an itemized number for your suite
Go Far Construction designs and builds home additions across Snohomish and King County — free, no-obligation estimates with itemized written pricing, design and structural engineering coordinated for you, and permits handled start to finish. Tell us where the suite should go and how you want it to feel, and we will tell you exactly what it costs to build it right.