Looking for a home addition contractor in Antioch? Hamilton Exteriors is an architect-led design-build firm serving Antioch and all of Contra Costa County. We build second-story additions, room extensions, and ADUs that add real living space to your home.
A home addition in Antioch typically costs $120,000 to $300,000 depending on the scope, size, and finishes (Hamilton Exteriors 2024-2026 project data). Every project includes a fully itemized estimate, a dedicated project manager, and a 50-year manufacturer-backed warranty.
Get Your Free Quote or call (650) 977-3351.
Why Choose Hamilton Exteriors for Your Antioch Home Addition?
Most Antioch home addition contractors are tradesmen-only. Hamilton Exteriors is different. We are led by Alexander Hamilton Li, a licensed architect and general contractor (CSLB #1078806). That means every addition we build is designed with an architect's eye for proportion, flow, and natural light — not just square footage added to a floor plan.
Here is what sets us apart:
- Architect-led design-build. We handle the architectural drawings, structural engineering, and construction under one roof. No handoffs between an architect and a builder who have never worked together.
- Fully itemized estimates. Every cost is broken out: materials, labor, permits, structural engineering, and cleanup. You see exactly where your money goes.
- Dedicated project manager. One person is your point of contact from the first call through the final walkthrough. You will always know who to reach.
- 50-year manufacturer warranty. Our GAF Master Elite and James Hardie Elite Preferred certifications allow us to offer the strongest warranties in the industry.
- Financing available. $0-down options with approved credit, 12-month same-as-cash plans, and extended terms up to 15 years (Hamilton Exteriors 2024-2026 project data).
Home Addition Types We Build in Antioch
Second Story Additions
Add 800 to 1,500 square feet of living space without losing any yard. Second-story additions in Antioch typically cost $200 to $400 per square foot and take 16 to 24 weeks to complete (Hamilton Exteriors 2024-2026 project data). They are ideal for homeowners who want more space but do not want to move or give up their backyard.
Room Extensions
Expand a kitchen, living room, or primary bedroom outward. Room extensions cost $175 to $350 per square foot and complete in 8 to 12 weeks (Hamilton Exteriors 2024-2026 project data). They work well on Antioch's ranch-style homes from the 1950s through 1970s, which often sit on larger lots with room to expand.
ADUs and Guest Houses
Detached backyard ADUs, garage conversions, and junior ADUs add living space and generate rental income. ADUs in Antioch typically cost $150 to $350 per square foot and take 4 to 6 months (Hamilton Exteriors 2024-2026 project data). They are a strong option for multigenerational living or passive income.
Full Remodels
Transform your entire home while preserving its character. Full remodels cost $150 to $400 per square foot and take 4 to 7 months (Hamilton Exteriors 2024-2026 project data). We handle everything from kitchen and bathroom renovations to whole-home reconfigurations.
Antioch Home Addition Cost Guide
Here is what you can expect to pay for a home addition in Antioch in 2026:. Pricing reflects Hamilton Exteriors 2024-2026 project data.
| Addition Type | Cost per Square Foot | Typical Size | Total Cost Range | Build Time |
|---|---|---|---|---|
| Second story addition | $200 – $400 | 800 – 1,500 sq ft | $160,000 – $300,000 | 16 – 24 weeks |
| Room extension | $175 – $350 | 200 – 600 sq ft | $120,000 – $200,000 | 8 – 12 weeks |
| ADU / guest house | $150 – $350 | 400 – 1,200 sq ft | $120,000 – $250,000 | 4 – 6 months |
| Full remodel | $150 – $400 | Entire home | $150,000 – $400,000 | 4 – 7 months |
Sources: Remodeling Magazine 2024 Cost vs. Value Report (Pacific West region), Hamilton Exteriors project data 2024 – 2026.
What is included in these estimates: Structural engineering, architectural plans, building permits, foundation work (where needed), framing, roofing, siding, windows, insulation, drywall, interior finishes, electrical, plumbing, HVAC, and final cleanup.
What is not included: Seismic retrofitting of the existing structure (typically $10,000 – $25,000 if required), landscaping, driveway work, and furniture (Hamilton Exteriors 2024-2026 project data).
Antioch-Specific Considerations for Your Home Addition
Climate and Material Choices
Antioch sits in the inland East Bay, where summer temperatures regularly exceed 100°F. This drives two important considerations for your addition:
- Thermal cycling. The extreme temperature swings between hot days and cooler nights cause building materials to expand and contract. We specify materials rated for this environment — premium architectural shingles with Class A fire ratings, fiber cement siding that resists warping, and double-pane low-E windows that reduce heat gain.
- Cool roof requirements. Contra Costa County and many East Bay jurisdictions require roofing materials that meet minimum solar reflectance standards (Title 24, Part 6). We handle all Title 24 energy compliance documentation as part of your permit package.
Seismic Considerations
Antioch sits near the Concord Fault and within the broader Hayward Fault zone. The delta areas of Antioch and Pittsburg also have higher liquefaction risk. Every addition we build includes a structural engineer's assessment of your existing foundation. If reinforcement is needed — foundation bolting, cripple wall bracing, or moment frame installation — we include that in your estimate. This brings your entire home up to current California Building Code seismic standards (CBC Section 1613).
Fire Risk
While Antioch itself is not in a designated Very High Fire Hazard Severity Zone (VHFHSZ), parts of eastern Contra Costa County — including the Diablo Range — are classified as State Responsibility Area Very High FHSZ by CAL FIRE. If your property is in a WUI zone, we ensure full compliance with Chapter 7A fire-rated material requirements.
Permitting in Antioch
All home additions in Antioch require building permits from the Antioch Building Inspection Division. Permit fees for additions typically range from $5,000 to $15,000 depending on the scope. Plan review takes 4 to 8 weeks for most projects. We handle the entire process: architectural drawings, structural engineering, Title 24 energy calculations, plan submission, and inspection scheduling.
How We Price Home Additions in Antioch
We believe pricing should be transparent. Every estimate includes:
- Per-square-foot pricing for each material and finish option
- Separate line items for structural engineering, permits, and contingency
- A per-sheet price for any decking or sheathing replacement discovered during construction (so there are every cost itemized)
- A detailed scope of work that lists exactly what is included and what is not
We do not use lump-sum bids that hide markups. You will see every dollar before you sign.
Financing Your Antioch Home Addition
Most Antioch home additions range from $120,000 to $300,000 (Hamilton Exteriors 2024-2026 project data). Paying out of pocket is not your only option. We partner with multiple lending providers to offer:
- $0-down financing with approved credit
- 12-month same-as-cash plans
- Extended terms up to 15 years for larger projects
You only pay for completed, inspected work. We never ask for full payment before the job is done. Your project manager will walk you through every option during your estimate.
Get Your Free Quote for Your Antioch Home Addition
Ready to add space to your Antioch home? We will visit your property, measure, and provide a fully itemized estimate — at no cost.
Get Your Free Quote or call (650) 977-3351.
Hamilton Exteriors is a licensed California general contractor (CSLB #1078806), serving Antioch and the entire Bay Area since 2018.
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