Room Additions in San Mateo, CA
Design by M&M helps San Mateo homeowners expand their living space through carefully planned additions — managing design, permits, and construction from concept to completion.
Home Additions
Bedroom Additions
Add more sleeping capacity to the family or guests.
Dining Room Additions
Increase or develop classy eating and entertaining areas.
Family Room Additions
Make living spaces in the middle comfortable and cohesive.
Second Story Additions
Add a second story to maximize your living space
Home Office Additions
Special work areas to get work done.
Living Room Additions
More welcoming spaces to have in day-to-day life.
Bathroom Additions
Additional bathrooms as an addition to enhance convenience.
Kitchen Additions
increases or redesigns kitchen area to cook and hold meetings.
Mudroom Additions
These are practical entryways that are used to control clutter and storage.
Master suite Additions
Private, lavish retreats combined with your house.
Sunroom Additions
Well-lit areas of recreation and relaxation.
Laundry Room Additions
Roomy and neat areas to do laundry.
Home Additions
Design by M&M helps San Mateo homeowners create more functional living space through carefully planned room additions. As a design-build contractor serving San Mateo, San Mateo County, and the greater Bay Area, we manage the entire process — from early design and feasibility through permitting, construction, and final walkthrough.
On an San Mateo property, an addition is rarely just about square footage — it’s about how the home functions as a whole. As an experienced room addition contractor, Design by M&M helps homeowners expand your living space in a way that complements the existing architecture and takes full advantage of the lot.
Common addition projects we take on in San Mateo include:
- Rear additions — expanding living, kitchen, and entertaining spaces toward the garden and outdoor areas
- Primary suite additions — creating a true retreat with the space San Mateo lots allow
- Second story additions — adding an upper level, which triggers Single-Family Dwelling Design Review and 500-foot neighbor noticing
- Side additions — extending wings for guest quarters, offices, or family space where setbacks allow
- Full-home expansion projects — comprehensive additions that rework the entire footprint
Accessory Dwelling Units (ADU)
San Mateo lots are generous enough for a detached ADU on many properties, which makes it a practical way to add housing for a parent, an adult child, or a long-term tenant without giving up the neighborhood. As an experienced ADU builder in San Mateo, Design by M&M guides homeowners through every stage, from confirming what the lot can support to final inspection.
We design and build all types of ADUs, including:
- Detached ADUs and guest houses — standalone units designed to complement the main residence and landscape
- Attached ADUs — connected living quarters with independent access and privacy
- Junior ADUs and in-law suites — self-contained space within the existing home, ideal for multigenerational living
ADUs avoid the design review path entirely. State law makes the review ministerial — no public hearing, no 500-foot noticing — with a decision required within 60 days of a complete application. Cities cannot demand replacement parking when you convert a garage, and impact fees are waived on units under 750 square feet. That contrast matters: an ADU can be a materially faster route to added space in San Mateo than a second-story addition. What still needs establishing is what your property can support — setbacks, lot coverage, electrical panel capacity, sewer condition, and whether the parcel sits in a hillside or flood-hazard area. We work that out before design begins.
Garage Conversions
We specialize in turning underused garages and outbuildings into comfortable, fully permitted living space. Serving San Mateo and nearby communities, our team helps homeowners expand what their property can do — without adding new structures to the lot.
Popular garage conversion projects include:
- Converting a detached garage to an ADU or guest quarters
- Creating a home office, studio, or gym
- Transforming an outbuilding into flexible bonus space
Garage conversions often look simple from the outside, but they involve real construction and compliance work: insulation, electrical upgrades, plumbing (for ADU conversions), egress requirements, and city permitting. We manage those details from the start, so the finished space is safe, legal, and built to the same standard as the main home.
Design Build
Design by M&M is a design build contractor, which means one team manages your project from concept to completion. Instead of coordinating separate architects, designers, engineers, and builders, you work with a single team responsible for the entire outcome.
Our design-build approach includes:
- Consultation and property review
- Custom designs shaped around your goals, property, and budget
- Architectural planning and engineering coordination
- Town permitting and approvals
- Construction scheduling and project management
- The build phase, through final walkthrough
San Mateo asks more of homeowners than most cities, and it catches people off guard. Adding a second story to an existing single-story house triggers Single-Family Dwelling Design Review, and under the municipal code the applicant is responsible for noticing every property owner within a 500-foot radius — offering them the chance to discuss the project and review the plans — then filing a statement under penalty of perjury confirming it was done. That is a far wider net than most Peninsula cities cast, and it means neighbor relations are part of the project, not an afterthought. We plan for that from the beginning, and when one team owns both design and building, nothing gets lost between the drawing and the finished result.
Home Remodeling
As a remodeling company serving San Mateo, we focus on substantial renovation projects that bring mid-century homes up to modern standards of comfort, efficiency, and function. Much of San Mateo was built between the 1940s and 1960s, and those homes were designed for how families lived then — closed-off kitchens, small bathrooms, modest bedrooms, and electrical and plumbing systems near the end of their service life.
Our remodeling services include:
- Whole house renovation — comprehensive updates to layout, systems, and finishes across the residence
- Kitchen remodels — typically as part of larger layout improvements or expansions of the home’s main living areas
- Major renovations — reworking floor plans, modernizing structural and mechanical systems, and restoring older homes to their potential
- Renovation paired with additions — improving the existing home while expanding its footprint
Our remodeling process follows the same design-build structure as our additions and ADU work: feasibility first, then design, budget alignment, permitting, and construction — all managed by one team with clear communication throughout.
Design in 3 simple steps
Consult & Design
We start with a thorough consultation, creating custom designs tailored to your style and needs.
Expert Construction
Our skilled team manages every detail, from demolition to installation, ensuring precision and quality.
Enjoyment
We complete your project with meticulous attention, ensuring your complete satisfaction and a stunning new kitchen.
Frequently Asked Questions
If you don’t see your question answered here, please don’t hesitate to contact us directly – we’re always happy to help!”