Additions
Home additions and room additions across the Bay Area
More house without moving house. We add the room you need, tied into the structure, the roofline and the systems so it never reads as an add on.
The short version
Home additions across the Bay Area that look like they were always there.
In the Bay Area, adding to the house you own is usually cheaper than buying the house you want. The hard part is not the framing. It is the setbacks, the lot coverage, the foundation tie in, and whether the existing panel and ducting can carry more house.
We answer all of that before you spend money on drawings. If the addition you want will not clear planning, you will hear it in the first week rather than the fourth month.
Scope
What a home addition includes
Foundation to roof tie-in under one contract, so the addition has one owner from day one.
- Feasibility review Setbacks, lot coverage, height limits and easements checked before you commit.
- Design and engineering Architectural drawings, structural calculations and Title 24 compliance.
- Foundation New footings poured and tied to the existing foundation so nothing settles apart.
- Framing and roof Framed to match, with the roofline blended so it reads as one house.
- Systems extension Electrical, plumbing and HVAC extended, with panel or unit upgrades if needed.
- Exterior match Siding, stucco, trim and roofing matched to the existing house, then painted whole.
- Interior finish Insulation, drywall, flooring, trim and paint continuous with the rooms it joins.
- Final inspections Every sign off through to the certificate of completion.
Honest numbers
Home additions costs in the Bay Area.
Most contractors will not put a number on a web page. Here is ours, so you can find out whether we are in your range before you spend an afternoon on a consultation.
$400 to $650 per square foot
Single story additions on a simple lot sit at the low end. Second story additions cost more because the existing foundation and framing usually need reinforcing.
Single story addition
New footprint on grade, tied to the existing house and roofline.
Primary suite addition
Bedroom and bathroom, which carries plumbing and finish costs.
Second story addition
New floor above, with foundation and framing reinforcement below.
These are typical ranges for completed Bay Area projects, not quotes. Costs move with the city and the age of the house, so your fixed price comes after we walk the space.
How it works
Five steps, start to finish.
The walkthrough
We come to you, look at the space, and talk about what you actually want. It is free, it takes about an hour, and there is no sales pitch at the end of it.
The contract and your price
An itemized breakdown of what every part of your project costs, a schedule for how long the work will take, and a clear payment structure, all in writing before anything begins. Read it closely and ask us anything. A contract you fully understand on day one is why the project ends with no surprises on the final bill.
Design and drawings
Measured plans and elevations of your space, drawn with you, so you can review the finished design before a single wall is touched. You approve it, and only then does the build begin.
Permits and build
We pull the permits, meet the inspectors and build it. You get a weekly update and a site we sweep every evening.
Walkthrough and warranty
We walk the finished job with you, clear the punch list, and hand over the warranty. And if you ever need us afterward, we will be right here, as we have been since 1989.
What clients say
300+ five star reviews from Bay Area homeowners.
I love the way my finished room looks! We started with an unfinished basement covered almost entirely in cement and now I have my dream room.
I ended up choosing Clarity out of 3 bids because I thought they were the most detailed and Daniel was actually the one who suggested we adjust the layout to get more room out of our bathroom… The team was done with everything ahead of schedule… I'd highly recommend Clarity to everyone I know and seriously LOVE the final results.
They guided me through what initially felt like an overwhelming project - transforming my small, outdated bathroom into a clean, functional walk-in shower… Every member of their team was punctual, professional, and efficient… Choosing Clarity was the best decision for my bathroom renovation!
We added onto our old 1970s home, and in just about six months, Clarity Construction completely transformed it. The house feels open, bright, and brand new again… Clarity truly lives up to their name - clear communication, great workmanship, and a beautiful result. Highly recommend them.
Recent reviews, copied word for word from our Thumbtack profile. Updated September 2026.
Straight answers
Worth knowing before you start.
What the code asks of new space.
A new bedroom must be able to get you out: an egress window with at least five point seven square feet of clear opening, sized and silled so an adult can climb through and a firefighter can climb in. New envelope meets today's insulation and glazing standards under the state energy code, smoke and carbon monoxide protection comes up to standard through the house, and the addition's foundation and framing are engineered, stamped and inspected. This is all ordinary for us, and all invisible in the finished room except as comfort.
Your lot writes the first draft.
Setbacks, floor area limits, height rules and protected trees vary city by city, and sometimes block by block: Sunnyvale has single-story districts where the second floor is simply off the table, Campbell's San Tomas area carries its own setback rules, and most cities protect mature trees with permits and replacement requirements. We read your parcel's rules before we sketch, which is why our first drawing is one the city will actually approve. See our city pages for what your town requires.
Tie-in is the craft.
Anyone can build a box. The craft is making the addition read as original: matching foundation heights, roof pitches and eave details, weaving new siding into old, and running the flooring through without a threshold that announces where the house used to end. That is carpenter work, our carpenters, and it is the difference between an addition and a bigger house.
Home Additions questions
What people ask us about home additions.
How much does a room addition cost in the Bay Area?
Budget $400 to $650 per square foot. A 400 square foot single story family room addition typically runs $160,000 to $200,000. A primary suite addition of the same size runs higher because of the bathroom. A second story costs the most because the structure below has to be reinforced.
How do I know if I am allowed to add on?
It comes down to setbacks, lot coverage and height limits for your specific parcel. We pull your property information and check it before you pay for any drawings. If what you want will not clear planning, we tell you in the first week and show you what will.
How long does a home addition take?
The honest answer is that approval, not construction, is what people are surprised by, and approval times differ by city and by month. We will not print a number that turns out to be wrong for your address. Once the permit is issued our crews build quickly, because framing through finish is all in house. Call us with the address and we will tell you what your city has actually been doing lately.
Will the addition look like an addition?
Not when it is done right. Matching the roofline, the siding profile, the window style and the trim is what separates an addition that reads as part of the house from one that reads as a box on the back. We repaint the whole exterior at the end so nothing shows a seam.
Can I stay in the house during an addition?
Usually yes, because most of the work happens outside the existing walls until the tie in. There is a period of a few weeks when we open the house to join the two structures, and we seal that off and schedule it tightly.
Also worth a look
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Let us price your home additions properly.
Tell us what you are planning. We will walk the space, talk through what it really takes, and put a fixed price in writing.