Basement Conversion to a 1-Bedroom ADU in Belmont, CA
For this Belmont project, Design by M&M transformed an underused basement into a fully functional one-bedroom accessory dwelling unit (ADU) with a complete kitchen, a full bathroom, a comfortable living area, and a private bedroom. The result is a self-contained, livable space that adds real square footage and long-term value to the home — without changing the property’s footprint.
The homeowner’s long-term goal was to create a dedicated space for the kids, with room for a home cinema and a pool table play area. The key planning challenge was that, under local rules, the basement could only be legally converted into permitted, livable space by building it as an ADU. Finishing it as a standard “bonus room” wouldn’t have met code for a space meant to be lived in. Structuring the project as an ADU was what made the conversion both legal and genuinely usable.
What this project involved:
Converting an existing basement into permitted, code-compliant living space
Adding a full kitchen, full bathroom, living area, and one bedroom
Coordinating the design, permitting, and construction as a single managed process
Solving the layout and feasibility questions that come with finishing a below-grade space
Basement-to-ADU conversions are a smart option for Belmont homeowners who want more usable space — whether for family, guests, rental potential, or future flexibility — while staying in the neighborhood they already love. Because Belmont’s hillside lots and older homes often come with site-specific structural and access considerations, this kind of project benefits from a design-build team that handles feasibility, permitting, and construction together.
Planning a basement conversion or ADU in Belmont or the surrounding Peninsula? Contact Design by M&M to discuss what’s possible for your property.
