Home Additions
Custom Home Additions in Redwood City & Silicon Valley
Add the space your family needs with a beautifully crafted home addition that feels like it’s always been part of your house.
When moving isn’t the right answer, a custom home addition can give you the space and functionality you’ve been missing. Calwest Builders designs and builds home additions that expand your footprint or living area while preserving—and often enhancing—your home’s character. In the space-constrained Bay Area, adding a new bedroom, enlarging your kitchen, or creating a second-story living level can unlock your property’s potential without changing your address. Serving Atherton, Menlo Park, Woodside, Redwood City, and surrounding Silicon Valley communities, we create room additions that feel seamless, intentional, and tailored to your lifestyle.
Types of Additions We Specialize In
First-Floor Room Additions
First-floor additions are a powerful way to gain livable space by building out into your yard. We frequently create new family rooms, expanded kitchens, guest suites, and larger primary suites that open onto patios or gardens. Every extension is carefully designed to match your existing home’s rooflines, exterior finishes, and architectural details so the final result looks original—not “tacked on.” From foundation work to final trim, we treat the new space with the same care as a ground-up custom home.
Second-Story Additions
When lot size is limited, going up may be the best solution. Second-story additions can double your usable space by adding bedrooms, bathrooms, and flexible living areas above the existing footprint. These projects require thoughtful structural design to ensure your foundation and framing can support the new level. Calwest coordinates structural engineering, seismic considerations, and load paths, then executes the build with precision so your expanded home is safe, comfortable, and visually cohesive.
ADU vs. Addition
Homeowners often weigh the benefits of an attached addition versus a detached Accessory Dwelling Unit (ADU). If your primary goal is expanding your main living areas—such as enlarging a great room or adding a primary suite—an attached addition usually makes the most sense. If you’re considering an in-law suite, rental unit, or private guest house, an ADU may be the better fit. We can help you compare both options and, if you opt for a detached unit, our dedicated ADU Construction services provide a complete design-build solution.
Specialty Additions
Beyond standard room additions, we also deliver specialty expansions tailored to your needs. This includes converting garages into livable space, bumping out specific rooms such as kitchens or primary baths, or adding sunrooms, home offices, gyms, and hobby spaces. These smaller or highly customized projects must still integrate structurally and visually with the home, and we approach them with the same level of care as larger additions. Whatever you envision, we’ll help you design a space that feels purposeful and well-integrated.
The Calwest Approach to Additions
Thoughtful Design Integration
Additions should feel like they were always part of the original design. We study your home’s architecture, roof pitches, window styles, trim profiles, and exterior materials to create a cohesive plan. Whether we’re working from your architect’s drawings or coordinating with designers and architects we trust, our focus is on continuity—inside and out. That means consistent ceiling heights, aligned floor levels, and transitions that feel natural rather than abrupt.
Handling Zoning & Permits
Every city on the Peninsula has its own zoning rules, setbacks, lot coverage limits, and height restrictions. In communities like Atherton and Woodside, neighborhood guidelines and design reviews can add extra layers of complexity. Calwest navigates these regulations on your behalf, preparing permit sets, coordinating with structural and energy consultants, and representing your project through city review. We manage the process end to end so you don’t have to become an expert in local codes.
Quality Construction & Structural Integrity
A home addition is essentially new construction attached to an existing structure. Our team focuses on making that tie-in as strong and safe as if it were originally built together. We use robust framing practices, appropriate insulation, and high-quality building envelope systems to protect against moisture and temperature fluctuations. Seismic performance is also top of mind, especially for second-story additions, and we coordinate with structural engineers to ensure your expanded home is built to last.
Minimizing Disruption to Daily Life
Building an addition is a significant project, but it doesn’t have to feel chaotic. We plan logistics carefully—choosing access points, staging materials, and sequencing work to reduce the impact on your daily routine. For first-floor wings, we often isolate the construction area so much of the existing home remains livable. For second-story work, we discuss safety and comfort, and when necessary, help you plan partial or full temporary relocation. Transparency about schedule and milestones helps you make informed decisions at every step.
Why Build Your Addition with Calwest Builders
Experience with Complex Builds
Large additions and structural expansions require a different level of expertise than surface-level remodels. Calwest’s background includes managing complex projects and working on high-end properties where quality expectations are extremely high. This experience translates into smoother coordination with engineers, architects, inspectors, and specialty trades, all of which are essential for a successful addition.
Project Management Excellence
Additions involve many moving parts—from planning and approvals to foundational work, framing, and interior finishes. We serve as your single point of contact, orchestrating all parties and keeping the project aligned with the agreed budget and timeline. Regular updates, clear communication, and detailed scheduling keep you informed and confident throughout the build.
Premium Materials & Methods
Because an addition is a long-term investment, we build with durability and performance in mind. That means high-quality framing lumber, energy-efficient windows and doors, robust roofing, and exterior finishes selected for both beauty and longevity. Inside, we apply the same premium standards to insulation, mechanical systems, and finishes so your new spaces feel as solid and refined as the rest of your home—or better.
Custom Touches for Your Lifestyle
A custom home addition is an opportunity to create exactly what your family needs. Vaulted ceilings in a new great room, expansive sliding doors to the backyard, a light-filled studio, or a luxurious new primary suite—the options are nearly endless. We work closely with you and your design team to incorporate the special touches that turn added square footage into spaces you truly love spending time in.
Let’s Expand Your Home
If you need more space—or have been imagining a new suite, great room, or upper level—now is the time to explore what’s possible. Contact Calwest Builders to schedule a consultation, and we’ll walk your property, listen to your ideas, and develop a plan to expand your home with precision and care.
How much does a home addition cost?
Costs depend on size, complexity, and finishes, but in this region a home addition might range from the mid hundreds of thousands upward, particularly for larger or second-story projects with high-end finishes. On a rough per-square-foot basis, addition projects often fall in a premium range appropriate to Silicon Valley’s construction market. Once we understand your goals and site conditions, we provide a detailed, tailored quote that breaks down major cost categories and helps you make informed decisions.
How long does it take to build an addition?
Timelines vary, but a moderate addition may take 4–6 months from the start of construction, while more extensive or second-story additions can span 6–12 months including design and permitting. Factors include the city’s review process, weather, complexity of structural work, and the level of interior finish you choose. Early in the process we’ll develop a realistic schedule and update it as milestones are reached so you always know where your project stands.
Do I need an architect for an addition?
Most additions require architectural plans and structural engineering, especially when expanding outward or building up a second level. We’re happy to work with your existing architect or introduce you to experienced residential architects and designers we collaborate with regularly. For more straightforward projects, we can often manage the design and engineering process for you as part of a design-build approach, ensuring that plans meet both your needs and local code requirements.
What about permits and inspections?
Home additions nearly always require permits for structural, mechanical, electrical, and plumbing work, as well as energy compliance documentation such as Title 24 in California. Calwest prepares the necessary drawings, coordinates with consultants, submits to the city, and schedules all required inspections. Our strong track record with jurisdictions like Menlo Park, Woodside, and other Peninsula cities reflects our commitment to quality and code adherence.
Can we live in the house during an addition build?
Often, yes—at least for part of the project. For first-floor additions that extend outward, we can usually isolate the work zone so you can remain in the existing portion of the home, albeit with some noise and temporary disruptions. For second-story additions or more invasive work, families sometimes choose to move out during heavy construction phases for comfort and safety. We’ll discuss options with you and help you plan the approach that works best for your household.
Will the new addition look like it was always part of the house?
That’s our goal. We match rooflines, exterior finishes, windows, trim, and interior details so the addition feels like a natural extension rather than an obvious afterthought. If you prefer a contrast—such as a modern addition on a more traditional home—we can design that with intention as well. Either way, continuity in quality and thoughtful transitions are central to our approach.
Can you build second stories on homes in my area?
In many local jurisdictions, second-story additions are allowed as long as zoning and design guidelines are met. Height limits, setbacks, and neighbor privacy rules may influence the final design. As part of our pre-construction process, we review applicable regulations, assess the structure, and help determine what is feasible on your property before moving into full design and permitting.