Quartz Construction & Remodeling

Quick Answer: ADU construction in Belmont, San Mateo County costs $175,000–$410,000 for a detached ADU in 2025. Quartz Construction — CSLB #1003436, BBB A+, 4.9 stars (65+ reviews) — builds studio, 1-bedroom, and 2-bedroom ADUs serving Belmont with full permit management. Call (650) 749-7436.

ADU Construction in Belmont, San Mateo County

Adding an Accessory Dwelling Unit (ADU) to your Belmont property creates rental income, multigenerational housing, or home office space. Under California ADU law (AB 68/SB 13 and 2024 updates), all single-family lots in Belmont are eligible to add at least one detached ADU up to 1,200 sq ft with minimum 4-foot side/rear setbacks.

ADU Cost in Belmont 2025

• Studio ADU (300-500 sq ft): $175,000 – approximately $225,000
• 1-Bedroom ADU (500-800 sq ft): $205,000 – $410,000
• 2-Bedroom ADU (800-1,200 sq ft): $410,000 and up
• Garage conversion ADU: $80,000–$150,000 (most affordable option)

Quartz Construction manages the entire ADU process in Belmont: feasibility, design coordination, permitting, construction, and final inspection sign-off. CSLB #1003436 | BBB A+ | 4.9⭐ (65+ reviews). Call (650) 749-7436 or complete the form below for a free consultation.