Expand Your Home Without Moving
Second-story additions, room expansions, and more. Designed in 3D before we build.
Love your neighborhood but need more space? Custom Home designs and builds home additions that blend seamlessly with your existing structure. From second-story additions to ground-floor expansions, we bring deep structural engineering expertise to every project.
Why Choose Custom Home for Home Additions
Second-Story Additions
Double your living space by building up. Our structural engineers ensure your existing foundation can support the addition.
Room Additions
Expand your footprint with new bedrooms, family rooms, or home offices that integrate with your existing layout.
Bump-Outs & Extensions
Smaller expansions that make a big difference: extend kitchens, enlarge bathrooms, or add a sunroom.
Master Suite Additions
Add a primary bedroom with en-suite bathroom and walk-in closet. Whether on the ground floor or as part of a second-story addition, we design master suites that feel like a retreat.
Structural Expertise
Load-bearing wall modifications, foundation work, and seismic considerations handled by experienced engineers.
Years in the Bay Area
Licensed since 2005. 162+ projects completed across the South Bay, Peninsula, and beyond.
BuildZoom Rated
Ranked in the top 1% of Bay Area contractors based on qualifications, performance, and reliability.
Design-First Process
See every detail in 3D before construction. Our two-phase approach separates design from build so you never commit blind.
Change Orders
When you follow our full two-phase process from A to Z, every decision is locked in during design. No mid-project surprises.
Itemized Pricing
Every material, every line item, visible before you sign. No allowances, no hidden fees.
Second Story vs. Ground Floor Addition
| Factor | Second Story Addition | Ground Floor Addition |
|---|---|---|
| Yard Impact | No loss of yard space | Reduces lot footprint |
| Structural Work | Foundation reinforcement often required | New foundation for addition only |
| Cost per Sqft | Typically higher due to structural requirements | Comparable to new construction costs |
| Living Disruption | May require temporary relocation | Often can remain in home during build |
| Views & Light | Better views, more natural light on upper floor | Ground-level light, easier outdoor access |
| Permitting | Height restrictions and setback reviews apply | Lot coverage limits may restrict size |
What to Expect
Every addition is different. Cost varies based on structural requirements, finishes, and whether the addition is ground-floor or second-story.
Key Cost Factors
- Addition type (ground floor vs second story)
- Structural reinforcement needs
- Material and finish selections
- Permit and engineering requirements
- Square footage
All pricing is approximate and subject to change. Every project is unique, and final costs are determined on a project-by-project basis during our design phase.
Ready to discuss your home additions project? Call (888) 306-1688 or schedule a consultation.
What We Promise on Every Project
You'll Hear from Us Every Week
Weekly progress updates with photos and milestone reports. A dedicated project manager as your single point of contact. We respond to questions within 24 hours.
Every Subcontractor Is Licensed and Supervised
We maintain long-term relationships with licensed, insured trade partners. Our project managers directly supervise all work on your property. No unsupervised labor.
We Prioritize What's Behind the Walls
Foundation, framing, waterproofing, electrical, and plumbing are engineered and inspected before any finish work begins. Structural integrity always comes first.
We've Never Walked Away from a Project
162+ projects completed across the Bay Area since 2005. Every one delivered. When you hire Custom Home, your project gets finished.
Frequently Asked Questions
How much does a home addition cost in the Bay Area?
Home addition costs are a real concern for Bay Area homeowners. Additions typically range from $250 to $500 per square foot, similar to new construction costs. Second-story additions may cost more due to structural requirements. Our design phase locks in your exact cost before we start, so there are no surprises.
Can my home support a second-story addition?
Most homes can be structurally reinforced for a second story. Our engineering team evaluates your foundation and framing during the design phase to determine what modifications are needed.
How long does a home addition take?
Most home additions take 6-12 months from design to completion. Second-story additions typically require 8-14 months due to additional structural work and permitting.
How do you handle the structural engineering for additions?
Every addition project begins with a thorough structural evaluation of your existing home. Our engineering team assesses your foundation, framing, and load paths to determine exactly what reinforcement is needed. This analysis happens during the design phase, and all structural costs are included in your itemized scope before construction starts.
Can I stay in my home during the addition?
In most cases, yes. Ground-floor additions and bump-outs typically allow you to remain in the home with minimal disruption. Second-story additions may require temporary relocation during certain phases for safety. We discuss livability planning during the design phase so you know exactly what to expect.
How much does a master suite addition cost?
Master suite additions in the Bay Area typically cost $250 to $500 per square foot, consistent with other home additions. A master suite includes a primary bedroom, en-suite bathroom, and walk-in closet. Second-story master suites may cost more due to structural reinforcement requirements. Our design phase provides exact, line-item pricing before construction begins so you know the full cost upfront.
How do you keep me informed during construction?
You receive weekly progress updates with photos and milestone reports. A dedicated project manager serves as your single point of contact throughout the build. If questions come up between updates, we respond within 24 hours. You will never wonder what is happening on your project.
Where We Offer Home Additions
South Bay
Peninsula
East Bay
Tri-Valley
San Francisco
Coastal
Monterey Bay
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Read articleLast updated: April 2026