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Shape Homes · Where we build · Hillsborough
Hillsborough is the one town on this list where the rules themselves are unsettled. The State issued eleven findings against the Town's ADU ordinance in 2024. Anyone quoting you confident numbers here should be showing you their source.
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| Rule | What it says | Source |
|---|---|---|
| JADU | 500 sq ft maximum | hillsborough.net ADU page |
| Efficiency kitchen | Cooking equipment, 15 sq ft counter, 30 sq ft cabinet | hillsborough.net ADU page |
| Conversion ADU | Existing footprint may expand up to 150 sq ft | hillsborough.net ADU page |
| Conversion setbacks | Sufficient for safety, per building and fire codes | hillsborough.net ADU page |
| Maximum size | 850 sq ft studio or one bedroom; 1,000 sq ft two or more bedrooms | HMC Ch. 17.52 |
| State-exempt ADU | Up to 800 sq ft, 4 ft side and rear setbacks, Building Division only | HMC Ch. 17.52 |
| Height, detached | 16 ft on the state-exempt path | HMC 17.52.020.E.6 |
| Side and rear setbacks | 4 ft | State law, HCD ADU Handbook |
| Governing ordinances | ADU chapter replaced April 2026 (HMC Ch. 17.52) | hillsborough.net ADU page |
Sources: Town of Hillsborough ADU page, Hillsborough Municipal Code, Title 17, HCD findings on Hillsborough's ADU ordinance, May 2024, Town landscape requirements, HCD ADU Handbook. Rules change often; we confirm them for your lot before design.
Size is rarely the constraint. These are.
In May 2024 the California Department of Housing and Community Development issued eleven non-compliance findings against Hillsborough Municipal Code 17.52.020 and required a response by 30 June 2024. Flagged provisions included the 25-foot front setback, owner-occupancy after January 2025, the 30-day minimum applied to junior units, deed restrictions, income reporting and neighbor notice. Some of these may no longer be enforceable. Some may have been amended since. We confirm the current position with the Town before design, every time.
Hillsborough runs an ADRB with its own application and checklist. Where a project goes in front of it, the schedule is set by hearing calendars rather than plan check. Getting that answer early is the difference between a nine-month project and a fourteen-month one.
A Hillsborough ADU, a guest house without a kitchen and a new custom home can require different reviews. We establish the intended use and compare the applicable state-standard and local ADU paths before developing the drawing. Current Town guidance needs to be confirmed because the ordinance has been subject to state compliance review. The path determines which coverage, height, setback and design checks apply.
Lower Hillsborough, Country Club Manor, Tobin Clark, Skyfarm and Ridgeway have different combinations of grade, mature landscaping and existing development. We put the main home, accessory structures, easements and proposed ADU on the survey together. The coverage and floor-area review should account for the whole parcel. A large garden can conceal a constrained location once trees, utility easements and access are drawn accurately.
Established trees and terraced gardens help a second dwelling feel private, but they also shape construction and emergency access. We confirm the applicable tree and fire review, then coordinate service trenches, staging and the exterior specification. Windows, outdoor seating and paths are placed with neighboring sightlines in view. The landscape plan should show both what is protected during work and what will be restored afterward.
On a sloping Hillsborough site, the floor elevation influences foundation cost, retaining work, drainage and the entrance route. We draw those elements together before deciding the finish package. For parents or visiting family, a comfortable route from the home to the ADU may influence which location works best. Surveying, engineering, utility extensions and site restoration then become explicit parts of the project estimate.
The property checks behind the standards above.
Any tree 18 inches or more in diameter, of any species, has been protected under a Town ordinance adopted March 13, 2023. On a mature Hillsborough lot that reaches further than people expect, and it is worth surveying before a footprint is fixed rather than after.
Many Hillsborough properties fall inside Central County Fire's Wildland-Urban Interface program, which adds vegetation management and fire-resistant construction requirements on top of the base building code. We confirm whether a given parcel is inside the program before pricing the exterior specification.
The Town's landscape requirements identify public-utility easements and water-efficient landscape standards that can apply on a given lot. We pull the actual easement, not the assumed one, before placing a permanent structure or a replacement planting bed anywhere near it.
If mapping or a survey identifies a flood-related constraint on a parcel, we confirm the requirement with the Town directly. We do not assume every Hillsborough property shares it, and we do not assume a hillside location rules it out automatically.
In May 2024 the state housing department reviewed Hillsborough's ADU ordinance and told the Town to change it. The findings required the Town to allow every ADU combination state law allows on a single-family lot, drop the owner-occupancy rule planned for 2025, stop requiring deed restrictions, income reporting and neighbor notice as conditions of approval, revisit a 25-foot front setback, and approve or deny complete applications in writing within 60 days. Hillsborough replaced its ADU chapter in April 2026. If a neighbor's approval or an older handout says something different, it may reflect the old rules, so we check every project against the current chapter before design starts.
On the state-exempt path, a Hillsborough ADU goes straight to the Building Division. Here is how the clocks line up.
| Step | Typical time |
|---|---|
| Town completeness check | 15 days under state law (2026) |
| Town decision on a complete application | Within 60 days under state law |
| PG&E new service | Averaged 118 days as of March 2026, by PG&E's count |
| Build, from permit | A few months; we confirm the schedule in your agreement |
Planning Permit and Exception ADUs add planning review before the building permit, so we choose the path before design is final. Sources: 2025 ADU law update (SB 543), PG&E new service times.
Three from the library, chosen against this town's rules rather than its postcode.
Planning ranges, all in: factory package, delivery, foundation, utilities, permits and site work.
What moves a project inside its range is the lot, not the home. On Hillsborough parcels the items above are what usually decide it. A range is not a bid; a fixed price applies only as written in an executed construction agreement. See the plans or how the build works.
Most of our Hillsborough projects are called guest houses by the people who own them. A few are called pool houses, and one or two are called in-law cottages. Legally they are the same thing: an accessory dwelling unit. There is no separate guest house permit in Hillsborough. The rules described on this page, the size caps, the setbacks, the review path, apply to all of them, whatever the drawings call the building. That is good news. The ADU path is the fastest approval route available on a Hillsborough lot, so a pool house or in-law cottage designed as an ADU clears review sooner than the same building filed any other way.
Hillsborough allows any number of accessory buildings, each up to 1,000 square feet. Without a kitchen, a guest house must stay out of the 20-foot side and rear and 25-foot street setback areas, and at 500 square feet or more it goes to the Architecture and Design Review Board. An ADU on the state-exempt path can sit 4 feet from side and rear lines and goes straight to the Building Division.
| Guest house without a kitchen | ADU with a kitchen (state-exempt path) | |
|---|---|---|
| Size | Up to 1,000 sq ft per building | Up to 800 sq ft |
| Side and rear setbacks | 20 feet | 4 feet |
| Review | Architecture and Design Review Board at 500 sq ft | Building Division only |
An ADU is the faster path, and a separate accessory building can still hold a pool house or studio.
Parts of it are under State challenge. HCD issued eleven non-compliance findings in May 2024 covering the front setback, owner occupancy, minimum tenancy, deed restrictions, income reporting and neighbor notice. Where state law and a local ordinance conflict, state law generally governs, but the practical answer for your parcel comes from the Town's planning counter and it changes. We check it at lot check.
Under the current local standards, up to 850 sq ft for a studio or one bedroom and 1,000 sq ft for two or more bedrooms. A state-exempt ADU can be up to 800 sq ft with 4 ft side and rear setbacks. A junior ADU can be up to 500 sq ft inside the main home.
The Town operates an Architectural Design Review Board with a published application and checklist. Whether your project needs it depends on scope and siting, and that answer drives the schedule more than anything else in Hillsborough.
Because the long pole here is approval, not construction. When the shell goes up in a week and the components are already state approved, an extra month at the counter costs you a month, not a season of exposed framing through a wet winter.
Yes. In Hillsborough a guest house, pool house or in-law cottage is permitted as an accessory dwelling unit, so the size caps, setbacks and review steps described above apply exactly as written. The label on the drawings does not change the path. What changes the answer is the lot: its size, its slope, and what is already built on it.
The Town's ordinance has been subject to state compliance review, and the applicable state-standard or local path can change the development checks. We confirm the current requirements with the Town for the proposed ADU before treating a published local standard as final.
Yes. Trees, terracing and narrow routes can limit where equipment, deliveries and service trenches can go. We map the working area alongside tree protection, fire access and landscape restoration before finalizing the building location and site-work budget.
It should identify foundation engineering, drainage, retaining work, utility routes, entry paths, required specialist review and restoration, as applicable to the chosen location. Those items are considered alongside the building and permit scope so the estimate reflects the actual property.
A new detached ADU does. Under the 2025 California Energy Code it needs new solar panels, which can be added to an existing system elsewhere on the property instead of the ADU roof. An attached ADU counts as an addition and does not need solar.
Usually, yes. State law (Government Code 66323) allows an ADU inside an existing accessory building, such as a pool house or studio, with up to 150 square feet added for access. Hillsborough asks that conversions keep side and rear setbacks sufficient for safety. We check the structure and utilities before pricing the conversion.
Often, yes, if it was built before 2020. State law (AB 2533) bars impact fees and penalties for those units, though the Town can deny one that is substantially unsafe. We can assess what it would take to bring yours up to code.
Tell your insurer before the ADU is occupied, because it adds value to cover. In fire hazard areas, California's Safer from Wildfires program requires insurers to offer discounts for measures such as a Class A roof and ember-resistant vents, and a new ADU built to the 2025 Wildland-Urban Interface Code already has both.
We pull your parcel, the Hillsborough ordinance and a street view of the driveway before the call.
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