Home additions
Home Addition Services
Room additions, bump-outs, sunrooms, and second stories. We check what your lot and house can carry first, then design and build an addition that looks like it was always there.
An addition is decided by what your lot and house can carry. Setbacks and coverage cap the size; the foundation and framing decide whether you can build up. Get the tie-in and the structure right and the addition disappears into the home. Get them wrong and it leaks, sags, or looks bolted on, which is exactly what a specialist gets right the first time.
Why choose us
Why choose us for your home addition
01
We check what your lot and house can carry first
Setbacks and lot coverage decide how much you can add. The existing foundation and framing decide whether you can build up. We check both before you spend on design, so the plan starts on something that will actually permit and stand.
02
The number is settled before demo day
Additions hide their cost in the foundation and the tie-in, the parts a quick quote skims over. We itemize the whole scope, put real allowances on selections, and lock it before we start, so the estimate is the number, not the opening bid.
03
It looks like it was always there
A good addition disappears. We match the roofline, siding, windows, and proportions so it reads as part of the house instead of a box bolted onto the side. Where an exact match is impossible, we design a deliberate transition rather than a mismatch.
04
One contract, one point of contact
Design, engineering, permits, foundation, framing, the tie-in, and finishes under one roof. Nothing falls through the gap between an architect, an engineer, a GC, and the subs. You call one number, and the person who answers owns the whole project.
Avoid these
Common home addition mistakes to avoid
Six ways additions go wrong, most of them in the foundation, the structure, and the seam where new meets old.
The lot cannot legally take the square footage
Setbacks and lot coverage cap how much you can add, and finding the limit after design is wasted money. We confirm what your lot allows first, before anyone draws a plan.
The existing foundation is assumed to be fine
Tying a new addition, especially a second story, onto an old foundation without checking capacity is a structural gamble. We assess the foundation and framing before pricing.
The tie-in leaks
Where new construction meets the old house is where water gets in when the flashing and transitions are careless. We detail the tie-in to stay watertight, because the seam is the risk.
The addition looks bolted on
A mismatched roofline, siding, or window style makes an addition scream addition. We match the existing house so the finished home reads as one.
The systems cannot handle more house
More square footage can outrun the existing furnace, panel, or sewer. We check capacity and plan upgrades where the bigger house needs them.
Structural engineering is skipped or rushed
Additions almost always need engineering for load paths and seismic. We build from stamped plans, not a guess about what the framing will hold.
Quality
What quality home additions look like
The new room gets the attention. These are the things that make an addition sound, dry, and part of the house.
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A foundation matched to the house
Footings and foundation tied in and sized for the soil and the load, not just poured to the property line.
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Structural tie-in done right
New roof and floor framing connected into the existing structure with engineered load paths and seismic detailing.
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A watertight transition
Flashing and weatherproofing where new meets old, so the seam does not become the leak two winters later.
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Rooflines and siding that match
Pitch, materials, and trim chosen to blend, so the addition disappears into the house.
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Insulation and envelope to code
New conditioned space built to Washington energy code, comfortable and efficient year round.
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Systems sized for the bigger house
HVAC, electrical, and plumbing extended and upgraded to carry the added square footage.
Options
Types of home additions
Most additions are one of these three. Which one fits depends on your lot, your house, and your budget.
Level 01
Bump-out or room addition
Extending the footprint on the ground floor to add a room or two.
- New foundation
- Single-story tie-in
- Matched roof and siding
- One or two new rooms
What moves the price: the foundation and how far the footprint extends.
Level 02
Sunroom or enclosed porch
Adding light-filled or three-season living space.
- Foundation or slab
- Generous glazing
- Insulation for year-round use
- Roof and wall tie-in
What moves the price: whether it is conditioned for year-round use and the amount of glazing.
Level 03
Second-story addition
Building up instead of out, when the lot is tight.
- Foundation and framing reinforcement
- A whole new floor
- Roof rebuilt
- Living arrangements during work
What moves the price: whether the existing structure can carry it and the reinforcement needed.
Permits & code
Home addition permits and code in Washington
An addition here is shaped by zoning, structural engineering, and a permit process with several inspections along the way.
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Setbacks and lot coverage
Zoning caps how close to the line and how much of the lot you can build on. We confirm what your lot allows before design. TKTK specifics by city.
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Structural engineering and seismic
Additions here need engineered load paths and seismic detailing, especially second stories. We build from stamped plans, not assumptions.
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Washington energy code
New conditioned space triggers insulation, air-sealing, and ventilation requirements. We build to current code so it passes and performs.
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Permits and inspections
Additions need a permit, engineering review, and several inspections. We pull it and manage the schedule. TKTK typical review windows by city.
Service areas
Home additions by city
Zoning, permit offices, and local pricing change by city. Pick yours for the details that apply to your lot.
FAQ
Home addition FAQs
Can I add on to my house?
Usually, within limits. Setbacks and lot coverage cap how much you can add, and your foundation and framing decide whether you can build up. We check both before you spend on design, so you are not paying to draw something the lot or the house cannot support.
Is it cheaper to build up or out?
It depends on your house and lot. Building out needs new foundation; building up may need to reinforce the existing foundation and framing but does not use more yard. We will price both against your actual home rather than a rule of thumb.
Do additions need a permit?
Yes, and usually structural engineering and several inspections. We pull the permit and manage the process, including the engineering review. Specifics vary by city, so check your city page.
Will the addition match my house?
That is the goal. We match roofline, siding, windows, and proportions so it reads as part of the home, not an add-on. Where an exact match is impossible, we design a deliberate transition instead of a mismatch.
Can I live in my home during an addition?
Often yes, since the existing house usually stays intact until the tie-in, though a second story is more disruptive. We plan the phasing with you up front so you know what to expect.
How much does a home addition cost?
It depends on type, size, foundation, and structural scope, so we price against your real conditions rather than a national average. See your city page for local ranges, or send the form for a free written estimate. TKTK local cost bands by city.
Ready when you are
Get a free home addition estimate
Tell us what you want to add and where. We will check what your lot and house can carry, call within one business day, and put a written estimate together with no pressure to sign.