Now Booking Fall 2026 Additions: Schedule Your Consultation
Bay Area Home Addition Contractor From Design to Final Inspection
We assess the existing structure, design the added space, and coordinate engineering, permits, construction, and final inspection.
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Since 2018
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A home addition creates new living space connected to an existing residence. It can extend the ground floor or add another story. The work starts with an assessment of the existing foundation and framing, then moves through design, engineering, permits, construction, inspections, and integration with the original home.
For second-story pricing factors, use our Bay Area second story addition cost guide.
Reviewed by Alexander Hamilton Li, Architect & General Contractor · CSLB #1078806 · Updated August 2026
Your next step
Start Your Home Addition Consultation Online
Share your property and expansion goals. We will discuss the existing home, feasibility, design, permits, and the next planning step.
Start With the Home Expansion Path You Need
Second-Story Additions
Vertical expansion planned around the existing foundation, framing, stair location, roof changes, seismic work, utilities, and occupied-home logistics.
Room Extensions
Attached ground-floor space coordinated with the existing plan, foundation, roof, openings, drainage, building systems, and architectural character.
Guest Houses and Detached Living Space
A separate project path for detached guest space. Independent dwelling units also require ADU-specific feasibility and permit review.
Whole-House Remodels
Coordinated work across most rooms and building systems when the project changes the home beyond one added space.
Homeowner Reviews of Our Construction Work
Public feedback from remodeling and related construction 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.
How Hamilton Exteriors
Manages Your Home Addition
Existing-Home Assessment
We review the foundation, framing, roof, utilities, drainage, access, and likely connection points before the addition design advances.
Design and Permit Coordination
Our team coordinates the layout, architecture, structural engineering, energy documents, permits, comments, revisions, and approved plans.
Addition Construction
We manage site protection, structural connections, foundation, framing, weatherproofing, building systems, finishes, inspections, and documented changes.
Integration and Closeout
We check connections between new and existing work, complete final inspections and the punch list, and review applicable warranty terms.
Compare Broad Home Expansion Paths
Swipe to compare all options.
| Feature | Second Story | Room Extension | Guest House | Whole-House Remodel |
|---|---|---|---|---|
| Relationship to home | New level above | Attached ground-floor space | Detached structure | Existing home transformed |
| Main structural focus | Foundation capacity, framing, and roof | New foundation and connection | New foundation and separate structure | Existing framing and building systems |
| Site impact | Keeps most yard area | Uses ground-floor footprint | Uses a separate site area | Usually stays within the home footprint |
| Early planning focus | Stairs, structure, roof, and occupancy | Layout, setback, roof, and drainage | Access, utilities, setbacks, and use | Phasing, systems, structure, and relocation |
| Dedicated guide | Second story | Room extension | Guest house | Whole-house remodel |
Plan Your Home Addition With Approved Credit
Financing may be available for eligible room extensions, second-story additions, and larger remodeling projects with approved credit. During planning, we review the scope and explain current lender programs, terms, amounts, and payment timing.
Ask which current options fit your home addition project.
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Frequently Asked Questions
Didn't find the answer to your question? Call Now (650) 977-3351
What counts as a home addition?
A home addition creates new living space connected to the existing residence. Common paths add a floor above or extend a room outward. Detached guest houses and ADUs use a separate project path because their site, utility, access, and permit needs differ.
Should I add a second story or extend the ground floor?
The choice depends on yard space, setbacks, foundation capacity, stair placement, roof changes, accessibility, drainage, budget, and how the home will function during construction. Feasibility compares these constraints before detailed design begins.
How do you assess the existing home before design?
We review available plans, field conditions, foundation and framing access, roof geometry, utilities, drainage, code triggers, and likely connection points. Engineers provide final technical recommendations where the addition affects structural systems.
Do you handle design, engineering, and permits?
Yes. Our architect-led team coordinates design, required engineering, energy documents, permit submittals, agency comments, revisions, inspections, and closeout. The exact consultant team and permit path depend on the existing home and scope.
Can I stay in my home during addition construction?
Occupancy depends on the scope, utility shutdowns, structural work, dust control, access, and local safety requirements. We discuss phasing early and identify when temporary relocation is practical or required before the construction schedule is finalized.
Plan Your Project With a Clear Scope
Financing may be available with approved credit for eligible projects.
Tell us about your project. We usually call within 3–5 minutes to schedule the next step.
21634 Redwood Rd Unit F, Castro Valley, CA 94546
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