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Room Addition Contractor in the Bay Area
Hamilton Exteriors is a room addition contractor. We plan and build the addition: foundation, structural opening, roof tie-in, utilities, permit, and final inspection. Serving the Bay Area and Northern California.
500+ projects
Since 2018
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A ground-floor room addition can expand a kitchen, add a bedroom suite, or create a family room or office. The new footprint should improve circulation and daylight without taking more yard than the room needs.
The site and the existing home set the design limits. Setbacks, lot coverage, foundation conditions, roof shape, utilities, windows, and access all affect the new footprint. We measure those conditions before fixing the room size or exterior form.
The connection to the existing home decides whether a room addition feels intentional. Floor levels, the structural opening, roof drainage, exterior materials, and utility paths must meet at that joint. We resolve those details in the plans before the crew opens the original wall.
How We Plan and Build a Room Addition
The new room must work with both the property and the existing floor plan.
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Evaluate the Footprint
We measure the home and review setbacks, yard use, access, soil, roof shape, utilities, and the proposed interior connection.
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Design and Permit the Addition
The plans coordinate the room layout, foundation, structural opening, roof tie-in, building systems, exterior, and permit documents.
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Build and Connect the New Room
The crew builds the exterior shell before completing the structural opening, utility connections, finishes, inspections, and closeout.
Room Addition Planning Check
| Item | What We Review | Design Effect |
|---|---|---|
| Footprint | Setbacks, lot coverage, yard, and access | Sets size and placement |
| Foundation | Soil, loads, levels, and existing structure | Sets support and floor height |
| Roof and exterior | Roof shape, drainage, windows, and cladding | Connects new and existing work |
| Utilities | Electrical, plumbing, HVAC, and ventilation | Supports the room's use |
| Interior opening | Walls, beams, finishes, and circulation | Controls how the rooms connect |
Plan the New Footprint
A larger room is useful only when the path through the home still works. We study the connection between existing rooms, doors, windows, outdoor space, and the new footprint. This keeps the addition from creating a dark interior room or an awkward circulation path.
Connect New and Existing Construction
The foundation, floor, walls, roof, and weather barrier must join the original home correctly. The visible work matters too. Window proportions, trim, cladding, roof edges, and interior finishes should form one clear design rather than look added later.
Manage the Final Tie-In
Much of the addition can be built before opening the existing exterior wall. We plan temporary protection, structural support, utility changes, and finish repairs before that tie-in begins. This reduces disruption and keeps the home protected while the two spaces become one.
Room Addition Financing Options
Room addition costs can include design, engineering, permit fees, foundation work, the structural opening, roof tie-in, utilities, and construction. Financing is available with approved credit for eligible project costs. During your consultation, we explain available terms, payment timing, and which parts of your room addition can be financed.
Ask about room addition financing during your consultation.
Call Now (650) 977-3351 Room Addition Reviews
Homeowner feedback from addition and remodeling projects.
Kevin L
via Google
We hired them for a bigger renovation. Alex was very responsive, which I appreciated. We changed a couple requirements during the job and they worked with us on it without making it complicated. Overall, everything went pretty smooth and their quality of work is solid. I recommend them highly!
Jacob Rothwell
via Google
Alex Li helped me with my basement remodeling, they were super efficient, and the work came out better than I could’ve ever imagined! Thank me later!
Maan D
via Google
Had Hamilton Exteriors do a full kitchen renovation. Natasha helped a lot with scheduling and coordination which made things easier on our end. We got regular updates and didn’t feel left in the dark at any point. The team paid attention to details and made sure everything was installed properly. the whole process felt pretty smooth and the kitchen came out really clean. happy with the final result
Lekan Ajayi
via Google
This service was good and very efficient, all remodeling was done to liking. Jacob was a great worker and helped with answering questions that was needed. Would recommend to others.
Frequently Asked Questions
Didn't find the answer to your question? Call Now (650) 977-3351
What rooms can a ground-floor addition create?
Common projects include kitchen expansions, bedroom suites, family rooms, offices, and enclosed living areas. The right type depends on the existing floor plan, yard, setbacks, and how your household uses the home.
Does a room addition need a new foundation?
Most ground-floor additions need a new foundation connected to the existing structure. The engineer sets the footing or pier design from the soil, loads, floor system, and existing foundation.
How much does a room addition cost?
Our current planning range is $250 to $525 per square foot. Kitchens, bathrooms, structural openings, utility moves, site access, finishes, and agency conditions shape the final price. We price the work after measured design and feasibility review.
Can the new room match the existing home?
Yes. We study the roof shape, windows, siding or stucco, trim, floor levels, and interior details. Some original materials cannot be matched exactly, so the design may use a compatible transition instead of a false match.
How long does room addition construction take?
After permits are approved and materials are ready, a straightforward build often takes eight to twelve weeks. Kitchens, bathrooms, major structural openings, difficult access, or custom finishes can extend the schedule.
How do you limit disruption inside the home?
We phase the exterior work before opening the existing wall when the design allows it. Temporary barriers, structural support, utility planning, dust control, and weather protection help manage the final connection.
Get Your Room Addition Quote
Tell us about your project. We usually call within 3–5 minutes.
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21634 Redwood Rd Unit F, Castro Valley, CA 94546
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