Home additions built for Hillsborough estates
Adding to a home in Hillsborough is rarely a simple matter of square footage. The town sits on steep, forested hills with deep setbacks and generous parcels, and its housing stock leans heavily on Tudor Revival, Mediterranean Revival, French Norman, Georgian Colonial, and Mid-Century Modern character that an addition has to respect rather than fight. New Key Construction builds home additions the way these properties deserve to be treated: as one continuous design-build process, with our designers and our construction team under one roof, priced options handed to you up front, and photoreal 3D renderings produced before any permit is ever pulled.
That single-team model matters here. When the people drawing your new primary suite, expanded kitchen wing, or second story are the same people pricing and building it, the design that gets approved is the design that actually gets constructed, on the number you agreed to. No handoff gap between an architect and a general contractor, no surprise value engineering after the drawings are already in front of the town. White-glove project management runs the whole thing, from the first measurement to the final walkthrough.
Designed for the way Hillsborough actually builds
Hillsborough is its own jurisdiction inside San Mateo County, with a Planning Division and an Architecture and Design Review Board that take neighborhood compatibility seriously. New houses, second-story additions, and ground-floor additions of roughly 500 square feet or larger trigger ADRB review, where the board weighs massing, scale, materials, and how the work reads against the surrounding street. Smaller, low-impact additions can often move through an administrative review path. Either way, the town's Residential Design Guidelines sit on top of the hard development standards for setbacks, height, and lot coverage, so an addition has to clear both.
We design to that reality from day one. Whether your home is in Hillsborough Heights, the older estates of Ryan Tract in lower Hillsborough, the one-to-two-acre parcels around Tobin Clark, or the larger traditional homes near Skyfarm and Carolands, the addition is shaped to your lot's slope, mature trees, and existing rooflines before it is ever drawn for the board. Because we produce photoreal 3D renderings of the finished result up front, you and the ADRB are looking at the same thing: how the new wing or upper floor meets the eave line, how the materials carry across the elevation, and how the massing settles into the hillside. That clarity tends to make the review conversation shorter and the outcome more predictable.
A process that protects the number and the timeline
Most addition projects in Hillsborough begin with structure that is decades old, sometimes from the 1920s through the 1940s in the older neighborhoods. Tying new framing, foundations, and systems into that original construction is where budgets usually slip. We investigate the existing conditions, design the addition to integrate cleanly, and put priced options in front of you before commitments are made, so decisions about scope, finish level, and structure happen on paper, not mid-construction.
From there the path is deliberate. Concept and 3D renderings come first, then the documentation and engineering needed for the town, then ADRB or administrative review, then permitting through the Hillsborough Building Division, then construction by the same team that designed it. Because design and build are one organization, the schedule is coordinated rather than negotiated between two firms. You get a single point of accountability for the kitchen expansion, the primary suite, the family room, the guest quarters, or the full second story, all of it designed to read as if it always belonged to the house and engineered for the town's hillside conditions and the Peninsula's seismic expectations.
Frequently Asked Questions
Does a home addition in Hillsborough require design review?
It depends on size and visibility. New houses, second-story additions, and ground-floor additions of roughly 500 square feet or larger are subject to Architecture and Design Review Board review against the town's Residential Design Guidelines. Smaller, low-impact additions can often qualify for an administrative review path. We confirm which applies to your property early and design accordingly.
How long does the design and permitting process take?
Timelines vary with scope, but the design, documentation, and town review phases typically run several months before construction starts, and ADRB-level projects take longer than administrative ones. Hillside conditions and integration with older original structures can add time. We build a realistic schedule into the project plan up front rather than promising a single fixed number.
What does a home addition in Hillsborough cost?
Cost is driven by size, finish level, structural integration with the existing home, and site conditions like slope and access, so ranges vary widely across the town's neighborhoods. Rather than quote a generic figure, we hand you priced options up front so you can weigh scope and materials against budget before anything is committed. The number you approve is the number we build to.
Will the addition match my home's original architecture?
That is the goal of designing and building under one roof. We study your home's existing massing, rooflines, and materials, whether Tudor, Mediterranean, French Norman, Colonial, or Mid-Century, and produce photoreal 3D renderings so you can see the match before any permit is pulled. The addition is shaped to read as part of the original house, not as something bolted on.
Can you handle the entire process, from design through construction?
Yes. New Key Construction is a design-build firm, so one team carries your project from first concept and 3D renderings through Hillsborough permitting and final construction. White-glove project management means a single point of accountability for both how the addition looks and how it is built.
If you are weighing an addition to your Hillsborough home, start with a conversation. We will walk your property, talk through what is possible within the town's review process, and show you priced options and renderings before any permit is pulled.
