Hillsborough is a town of large estates, half-acre and larger minimum lots, winding roads with no sidewalks, and a deep architectural tradition that runs from period revival, Tudor, Mediterranean, and Colonial, through to confident contemporary work. Homeowners here do not want an accessory dwelling unit that reads as a prefab box dropped on the back lawn. They want a second structure that belongs to the main house, sits naturally in mature landscaping, and holds the same level of craft as everything else on the property. That is the exact problem ADU design and construction in Hillsborough has to solve, and it is the work New Key Construction is built for.
What a Hillsborough ADU actually has to do
On an estate lot, an ADU is rarely about squeezing in extra square footage. It is about purpose. A detached unit might be a guest house for visiting family, quarters for a caregiver or live-in help, a pool house with a kitchen and bath, a private home office set away from the main residence, or housing that lets adult children or aging parents stay close while keeping their own front door. Because the lots are generous, you usually have room to do it right, which means the design conversation is less about minimum dimensions and more about siting, sightlines, privacy, and how the new structure relates to the existing home and grounds.
That freedom comes with responsibility. A larger lot means more landscape to protect, more mature trees to design around, and more visible exterior that has to match the architecture you already love. This is where generic ADU plans fall apart and where considered design earns its keep.
The Hillsborough planning reality
Hillsborough has its own building and planning department, and it is known for a careful, design-conscious review process. Projects of any consequence are looked at closely for how they fit the neighborhood, the streetscape, and the character of the town. For an ADU that means setbacks, height, lot coverage, and the relationship to neighboring properties all matter, and the exterior design is not an afterthought. The town also layers in the practical realities of estate properties: grading on sloped sites, tree protection, driveway and access considerations on roads without sidewalks, and septic or sewer capacity depending on where the property sits.
California's statewide ADU rules set a baseline that local jurisdictions work within, but in a town like Hillsborough the smart move is to design with the local review process in mind from day one rather than fighting it later. We do not publish invented fee figures or permit timelines, because those change and should come straight from the town. What we do is build your project around the standards that apply to your specific lot, then carry the drawings through the town's process for you.
Why design-build is the right model here
New Key Construction is a design-build firm, which means one team handles both the design and the construction of your ADU. You are not hiring an architect, then separately bidding the work to a contractor, then refereeing between the two when the budget and the drawings disagree. Design and construction sit at the same table from the first sketch, so what we draw is what we can actually build, at a price we have already stood behind.
Three things make that concrete:
- One team for design and build. A single accountable group owns the outcome from concept through final walkthrough. There is no gap to fall through between the people who designed it and the people who built it.
- Priced options up front. Before you commit, you see real, costed choices, not a single take-it-or-leave-it number that balloons later. You can weigh a higher finish level against budget with actual figures in front of you.
- 3D renderings before permits. You see your ADU in photorealistic 3D, sited on your property and styled to match your home, before a single permit is filed. That means decisions get made on something you can see, and the design that goes to the town is the design you approved.
How a project runs
We start with discovery: your goals for the unit, how it will be used, and a real look at the lot, the existing home, and the constraints. From there we develop the design, bring it to life in 3D, and present priced options so you can choose with full information. Once you sign off, we prepare the permit set tailored to Hillsborough's requirements and manage the submittal and review. Then the same firm builds it, with the design intent intact because the people who drew it are the people delivering it. The result is an accessory dwelling unit that looks like it was always meant to be there, matched to a Tudor, a Mediterranean villa, a Colonial, or a clean modern home with equal seriousness.
FAQ
Do you match the ADU to the style of my existing Hillsborough home?
Yes. Matching the architecture is central to how we work, especially in Hillsborough where period revival and modern homes set a high bar. We design the ADU's massing, rooflines, materials, and details to read as a deliberate companion to the main house, and you approve that direction in 3D before anything is built.
Can you handle the design and the construction, or just one?
Both, under one roof. As a design-build firm we take the project from first concept through finished construction with a single accountable team. That removes the handoff between architect and builder and keeps your design, budget, and schedule aligned the whole way through.
What does the design-build process give me that hiring separately does not?
You get priced options before you commit and photorealistic 3D renderings before permits are filed, so you make decisions on real numbers and real images instead of assumptions. Because the team that designs it also builds it, the drawings reflect what we can actually deliver at the price we quoted.
How do you handle Hillsborough's planning and permit review?
We design with the town's review standards in mind from the start, prepare a permit set tailored to your lot, and manage the submittal through Hillsborough's building and planning department. Specific fees and timelines come from the town itself, and we guide your project through that process rather than leaving you to navigate it alone.
Are large Hillsborough lots better suited to detached ADUs?
Often, yes. The half-acre and larger lots common in Hillsborough usually give room for a detached unit with its own entrance and privacy, sited to protect mature trees, sightlines, and the relationship to the main home. We use that space to make the ADU feel like a natural extension of the estate rather than a structure squeezed onto it.
