Home Additions in Seattle
More room for your family without moving: room additions and attic conversions built by one team.
- We check zoning and structure before you commit to a design.
- We draw the plans and file the permits the city requires.
- You approve an itemized, written price before work starts.
By appointment. Limited start dates.
- Over 200 projects
- 4.9 on Google
- 20+ years building
- WA license VOLCABI792C6
When the house you love runs out of room
Most families who call us about an addition like their street, their school and their neighbors. The house is the part that no longer fits.
Everyone is sharing everything
A new baby, a parent moving in, two people working from home. One bathroom for five people and no quiet room to take a call.
Moving is expensive and uncertain
Selling means agent fees, excise tax, moving costs and a bidding war for a bigger house nearby. An addition keeps the address and puts the money into the home you already own.
The hard questions come first
Can the lot take a bigger footprint? Will the foundation carry a second floor? Is the attic tall enough to count as a room? You should have those answers before paying for drawings, so that is where we start.
What we build to add space
An addition is new structure tied into an old house, so the framing, roof, foundation and every trade have to meet in the middle. One team plans and builds all of it, and one project manager answers for it.
Room additions
A family room, bedroom suite or larger kitchen built out from the back or side of the house on a new foundation, with the roof, siding and windows matched to what is there so the addition looks like it was always part of the home.
Attic conversions
Turning attic storage into a bedroom, office or playroom inside the roof you already have. A habitable room needs a 7 foot ceiling over at least half its required floor area, a code stair and an emergency escape window, so we measure all three at the first visit.
Bathroom and bedroom additions
Adding a bathroom or bedroom inside the existing footprint, often in a basement or a lower floor. New walls, drains, venting and a fan tie into the house, and a new bedroom gets its own egress window.
Plumbing, electrical and heat
New circuits and panel capacity, supply and drain lines, and heating for the new rooms. In Seattle a new addition also needs interconnected, hardwired smoke alarms with battery backup and whole house ventilation sized to the Seattle Residential Code.
Design and drawings
Our designer lays out the new space with you and shows it in 3D, and the permit drawings show the existing framing the addition touches, as SDCI asks for on residential plans.
Permits and zoning
Any work that enlarges a house needs a building permit. We check setbacks, lot coverage and height against the zoning code, file the application and book each inspection.
Updating the rest of the house while you add on? Window Replacement in Seattle covers new windows for the existing rooms, and Foundation Repair in Seattle covers an older foundation that needs work before it carries more load.
Additions and conversions we have built
Real jobs, each captioned with the city on its project page. The Kirkland attic took 6 weeks on site; the Seattle bathroom addition took 8. Open a project to see the before and after photos and the full scope.
What homeowners say about working with us
Bar and the team at Volcano Builders did a great job! Professional service, great communication throughout the whole process, and everything was done with care and attention to detail. Highly recommend!
We were nervous about hiring a contractor because we were first-time homeowners, but Volcano Builders made it easy to understand. They made everything clear and helped us stick to our budget. I'm very happy with how everything turned out.
Just completed my inital meeting with Volcano Builders about my bathroom remodels and couldn't be happier with the interaction. On time, professional and extremely knowledge. Highly recommend you invite them out to see your next home improvement project!
Volcano did a master bath remodel for us. The project was completed efficiently and on time. All of their workman were courteous and hard working. When we had a couple of material delivery delays they kindly adjusted their schedules. Their pricing was fine and the terms of the contract were fulfilled. We highly recommend Volcano Building.
Overall, we had a great time with Volcano Builders. There were a few small delays, but they were clear in their communication and kept things moving. The last kitchen remodel turned out great, and the quality seems like it will last for a long time.
I recently hired Bar from Volcano Builders to remodel my bathroom. Overall, the experience was satisfactory. Bar was professional and communicated well throughout the project. The work was completed on time and within budget. The quality of the remodel met my expectations, though there were a few minor details that could have been improved. I would recommend Bar for anyone looking for a reliable contractor for bathroom renovations.
How your home addition works
Three steps, one team, and a written price before anyone picks up a tool.
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Site visit and feasibility
We visit, measure the house and the lot, look at the foundation and the attic, and tell you which kinds of addition the site can take.
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Design, price and permit
We design the addition, show it to you in 3D, price it in writing line by line and file the permit drawings with the city.
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Build and hand over
One project manager runs the foundation, framing, trades and finishes through each inspection and walks the new rooms with you at handover.
What drives the cost of a home addition in Seattle
Four things set most of the price of an addition. Your written estimate prices each one on its own line, so you can see where the money goes and adjust the plan before anything is built.
Out, up or in
Building out needs a foundation and a new roof. Building up needs the existing walls and footings checked, and often reinforced, to carry the new floor. Converting an attic or a basement reuses the shell, which usually means less new structure.
Size and roof shape
Every square foot of floor brings wall, roof and finish with it. A simple shed or gable roof tied into the existing one is less work than a complex roof line or a new dormer.
Plumbing and systems
A bedroom or office needs power, heat and light. A bathroom adds supply, drain and vent lines, a fan and waterproofing, and the more new rooms the house has, the more likely the panel and heating need an upgrade.
Site, code and finishes
Slopes, trees, equipment access and how close the addition sits to the property line all affect the work, and so do the windows, flooring, tile and fixtures you pick.
Three habits keep an addition on budget. Settle the zoning and structural questions before design, so the drawings never have to be redone. Match the existing roof pitch and siding where you can, because matching is simpler than inventing a new look. And choose finishes before the permit is issued, so the schedule is set when the build begins.
Seattle and Bellevue Remodeling Cost Guide
Financing is available: Home Renovation Financing in Seattle.
Homeowners on camera
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Yoshio Inoue
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Stephanie
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Clinton & Joan
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Teresa
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Rebecca
Home additions across Greater Seattle
Our main office is in Bellevue, and we build additions and attic conversions across King and Snohomish counties, from Seattle to Kirkland and the rest of the Eastside.
Permits come from the city the house is in. In Seattle, building permits come from the Seattle Department of Construction and Inspections, and the zoning code sets how close an addition can sit to the property line and how much of the lot it can cover. In Bellevue they come from Development Services, and in Kirkland from Planning and Building. We work with each one, so the permit plan in your estimate matches your address.
Planning more than an addition? See our remodeling pages for Seattle and Bellevue, or all 132+ cities we serve.
Home addition questions
Do I need a permit for a home addition in Seattle?
Yes. The Seattle Residential Code (R105.1) requires a building permit to construct, enlarge or alter a house, and every addition enlarges it. SDCI checks the plans against the building code, the Seattle Energy Code and the zoning rules for your lot. We prepare the drawings, file the permit and book the inspections. See Do You Need a Permit to Remodel in Seattle and Bellevue?
Can my attic become a bedroom?
Often, if three things line up. The ceiling must reach 7 feet over at least half of the room's required floor area, and floor where the ceiling is under 5 feet does not count. The room needs a stair built to code: in Seattle at least 36 inches wide with 6 feet 8 inches of headroom. And it needs an emergency escape window. We measure all three at the first visit, before any design work.
How long does a home addition take?
The jobs on our project pages took 6 weeks on site for the Kirkland attic conversion and 8 weeks for the Seattle bathroom addition. An addition on a new foundation takes longer, and design and permit review come first. How Long Does a Remodel Take in Seattle and Bellevue? covers each phase.
Is it better to build out or build up?
It depends on the lot and the house. Building out keeps the work on one level but uses yard, and the addition has to fit the setbacks and lot coverage limits. Building up keeps the yard but needs the walls and footings to carry the new floor, and a stair takes space on the floor below. For single story homes, Ranch Style House Addition Plans walks through the options.
Is an addition, an ADU or a garage conversion right for us?
It depends on who the space is for. An addition or attic conversion makes the house itself bigger and shares its kitchen and entry. An ADU or a DADU is a separate home on the lot with its own kitchen and bath, suited to a parent, an adult child or a renter. A garage conversion turns an existing structure into living space. We build all three. See ADU and DADU Builders and Garage Conversion.
How do I get a price?
Book a consultation. We visit, measure the house and the lot, and talk through the space you need, then send a written, itemized price before any work starts. For background, read the Seattle and Bellevue Remodeling Cost Guide.
Book your home addition consultation
Four quick steps. Tell us about your project and we’ll reach out to discuss it and see if we’re the right fit.