Home Additions in Gilroy & South Bay
Expert room additions, second stories, and ADUs in Gilroy, Morgan Hill, and throughout the South Bay.
Expand your living space with D One Builders, the premier home addition contractor serving Gilroy, Morgan Hill, and the South Bay. With CSLB license #1028049 and decades of experience, we transform homes with seamless room additions, second story expansions, and profitable ADU construction that enhances your lifestyle and property value.
Types of Home Additions We Build
Room Additions
- Master bedroom suites
- Family rooms & great rooms
- Home offices & studies
- Guest bedrooms
Starting at: $300/sq ft
Second Story Additions
- Full second story construction
- Partial second story additions
- Master suite above garage
- Multi-room expansions
Starting at: $400/sq ft
ADUs & In-Law Units
- Detached ADU construction
- Garage conversions
- Attached in-law units
- Junior ADUs (JADUs)
Investment return: $2,500-$4,000/month rental income
Our Addition Construction Process
Design & Engineering
Our architects and engineers create detailed plans that seamlessly integrate with your existing home. We analyze structural requirements, setback restrictions, and maximize square footage within zoning limits.
Permits & Approvals
We navigate complex permitting requirements in Gilroy, Morgan Hill, and throughout the South Bay. Our team handles building permits, planning approvals, and utility connections to keep your project moving forward.
Foundation & Structural Work
Professional excavation, foundation pouring, and structural framing ensure your addition is built to last. We match existing foundation systems and ensure proper integration with your home's structure.
Systems Integration
We extend electrical, plumbing, and HVAC systems to your new space. Our licensed professionals ensure all connections meet current codes and provide efficient operation.
Finishing & Integration
Expert finishing work ensures your addition looks like original construction. We match siding, roofing, windows, and interior finishes for seamless integration with your existing home.
Addition Investment & Timeline
Transparent pricing and realistic timelines for your South Bay home addition
Single Room Addition
- 400 sq ft bedroom or office
- Includes bathroom if needed
- Foundation to finish
- Quality materials and fixtures
Timeline: 3-4 months
ADU Construction
- 500-1200 sq ft living space
- Full kitchen and bathroom
- Separate entrance and utilities
- Rental income potential
Timeline: 4-6 months
Second Story Addition
- 800+ sq ft of new space
- Multiple bedrooms and bathrooms
- Structural reinforcement
- New staircase construction
Timeline: 6-8 months
What Our Customers Say
"D One Builders added a beautiful 600 sq ft master suite to our Gilroy home. The addition looks like it was always part of the original house. They handled everything from permits to finishing touches, and we're generating $3,200 monthly income from the ADU they built last year. Excellent craftsmanship and project management."— Tom & Maria Rodriguez, Gilroy
Frequently Asked Questions
How much does a home addition cost in Gilroy?
Home additions in Gilroy typically cost $300-$500 per square foot. A 400 sq ft bedroom addition ranges from $120,000-$200,000. Second story additions cost $400-$600 per square foot. ADU construction ranges from $180,000-$350,000 depending on size and finishes.
How long does a room addition take to build?
Room additions typically take 3-6 months from start to finish. Simple single-room additions take 3-4 months, while second story additions can take 6-8 months. Timeline includes design, permitting, construction, and final inspection phases.
Do you handle permits for home additions in the South Bay?
Yes, D One Builders handles all permitting for home additions in Gilroy, Morgan Hill, San Jose, and throughout the South Bay. We work directly with city planning departments and ensure compliance with local building codes and zoning requirements.
Can you build ADUs (Accessory Dwelling Units) in Gilroy?
Yes, we specialize in ADU construction throughout the South Bay. ADUs are an excellent investment, often generating $2,500-$4,000 monthly rental income. We handle design, permits, and construction for detached ADUs, garage conversions, and attached units.
Will a home addition increase my property value?
Well-designed home additions typically return 60-80% of their cost in increased home value. Master suite additions, family rooms, and ADUs provide the best returns in the South Bay market. We design additions that maximize both functionality and resale value.
Can you match existing architectural styles in additions?
Absolutely. Our design team excels at seamlessly blending new additions with existing home architecture. We match materials, rooflines, windows, and exterior finishes to ensure additions look like original construction, not afterthoughts.
Ready to Expand Your Home?
Get a free consultation and detailed estimate for your home addition in Gilroy or the South Bay.