We start with your design. Modular is how we build it, not what you settle for.
Shape Homes · Where we build · Los Altos Hills
Los Altos Hills has no discretionary design review, which sounds permissive until you read the objective standards. Everything runs on two acronyms and a list of places you may not build.
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| Rule | What it says | Source |
|---|---|---|
| ADU, exempt from MDA and MFA | 800 sq ft | Town ADU handout |
| ADU with parking and 30 ft setbacks | Up to 1,200 sq ft | Town ADU handout |
| Counting against MDA/MFA | 850 sq ft studio or 1-bed, 1,000 sq ft 2-bed | Town ADU handout |
| JADU | 500 sq ft, 650 with parking | Town ADU handout |
| Height | 16 ft standard, up to 19 ft with parking and 30 ft setbacks | Town ADU handout |
| Front setback | At least 40 ft — the Town's signature rule | Town ADU handout |
| Side and rear setbacks | 4 ft minimum, or 30 ft to unlock the size and height bonuses | Town ADU handout |
| Minimum lot size | None. Permitted on any R-A property | Town ADU handout |
| Design review | None. Objective standards only | Town ADU handout |
| Light reflectivity | Exterior 50 or less, roof 40 or less | Town ADU handout |
Sources: Town of Los Altos Hills ADU page, Los Altos Hills ADU code, Los Altos Hills ADU pre-application checklist, Los Altos Hills septic requirements, Santa Clara County ADU Resource Center, Los Altos Hills. Rules change often; we confirm them for your lot before design.
Size is rarely the constraint. These are.
You may not build in a Heritage Oak zone, on slopes over 30%, within 25 feet of a creek bank, in an easement, or in a geotechnical or seismic hazard zone. On a large irregular Los Altos Hills parcel these overlap, and the buildable envelope that survives all five is often nothing like where the owner assumed the unit would go. This is the first thing we map.
The unit must use similar exterior wall materials, window types, trims, roofing materials and roof pitch to the primary residence. Exterior light reflectivity is capped at 50, roofs at 40, and exterior lighting must be shrouded or downward-facing. These are objective, which means they are checked rather than debated — and a material selected without them in mind gets rejected at the counter.
Los Altos Hills is largely unsewered and the Town's ADU material does not address septic. That gap is not reassurance. Capacity for a second unit has to be established before design, and on these lot sizes a leach field expansion can be the item that decides where the building sits.
A large Page Mill Road, Moody Road or Fremont Hills parcel can still have a tightly constrained building area. We compare alternative locations against slope, creeks, trees, easements and the Town's development-area and floor-area calculations. The remaining allowances matter for a larger ADU. Testing a compact layout alongside a larger one makes the trade-offs in garden space, access and site work visible before the plan is selected.
Los Altos Hills properties may use sewer or septic. For a septic-served lot, we confirm the existing system, proposed bedroom count, reserve area and environmental-health requirements before finalizing the brief. The available wastewater solution can influence the location and number of rooms. Any new system, upgrade, testing and seasonal installation restrictions need to be understood in the site scope and schedule.
Privacy and views are important on a hillside lot, but so is the daily walk between buildings. We use the survey to test the floor level, path gradient, landings and drainage, then coordinate them with fire access and any retaining work. For parents or long-term family use, the entrance route is part of the design brief. A distant corner may create more site work than its open space first suggests.
Underground services, long trenches, grading, retaining walls and landscape restoration can be substantial on a Los Altos Hills property. We separate those items from the building package when reviewing the estimate. The same comparison should identify survey work, geotechnical review and wastewater approvals where needed. Two proposals only give a useful price comparison when they assume the same location, utility solution and finished access route.
The numbers behind the septic and fire-access questions.
Roughly 41% of Los Altos Hills parcels use septic rather than sewer. The Town's rules require a separate system for each detached secondary dwelling, and no septic installation is allowed between November 1 and April 1, so a fall start on a septic lot usually means the system goes in first thing the following spring. Santa Clara County Environmental Health clears the system using a site plan and a pumper's report no more than three years old.
Santa Clara County Fire's access standard calls for a fire road within 150 feet of every part of the building, or 200 feet if it is sprinklered. A car reaching the proposed entrance does not establish that construction and emergency-access arrangements work. We check driveway width, slope and turning space against that standard before the floor plan is fixed, not after.
Planning, permitting and build, in sequence.
| Step | Typical time |
|---|---|
| Pre-application meeting | A few weeks to schedule |
| Planning and building permit | 10–16 weeks, longer on a septic lot |
| Septic design and county clearance (if applicable) | Adds several weeks, and no installation November 1 to April 1 |
| Build, from permit | A few months; we confirm the schedule in your agreement |
Sources: Los Altos Hills ADU pre-application checklist, Los Altos Hills septic requirements.
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 Los Altos Hills 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 Los Altos Hills 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 Los Altos Hills. 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 Los Altos Hills lot, so a pool house or in-law cottage designed as an ADU clears review sooner than the same building filed any other way.
| Guest house without a kitchen | ADU with a kitchen | |
|---|---|---|
| Floor area | Counts toward the maximum | 800 sq ft beyond the maximum |
| Development area | Counts toward the maximum | 800 sq ft beyond the maximum |
| Review | Planning Commission at 500 sq ft with height over 19 ft, or 1,500 sq ft total | Staff approval within 60 days |
On most Los Altos Hills lots, the ADU route is the one that fits. Source: Town of Los Altos Hills ADU page.
800 sq ft is exempt from your Maximum Development Area and Maximum Floor Area entirely. With parking and 30-foot setbacks you can reach 1,200 sq ft. If you go larger, 850 sq ft for a studio or one-bed and 1,000 for a two-bed counts against your MDA and MFA allowance, which is usually the more important number on a constrained parcel.
At least 40 feet. It is the single most distinctive placement rule in the Town and it removes the front third of many parcels from consideration before anything else is drawn.
No discretionary review. Objective standards only. But those standards require the unit to match the main home in wall material, window type, trim, roofing material and roof pitch, and they cap exterior light reflectivity at 50 and roof reflectivity at 40.
Not over 30%. Nor within 25 feet of a creek bank, nor in a Heritage Oak zone, nor in a mapped geotechnical or seismic hazard zone. On a hillside parcel these constraints stack, and mapping them is the first hour of work.
Yes. In Los Altos Hills 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.
Yes. On a septic-served Los Altos Hills lot, bedroom count and the wastewater review are connected. We confirm the system, reserve area and applicable environmental-health requirements before fixing the layout, and include any testing or upgrade in the site scope.
No. Slope, creek and tree constraints, easements and development-area or floor-area allowances can limit the usable envelope. We compare the proposed location with the applicable approval path and current Town calculations before selecting the footprint.
Long underground utility routes, wastewater work, grading, retaining structures, drainage and finished entry paths can all matter. Survey and specialist-review costs should also be identified where required. We price those items against the selected placement rather than assuming a typical flat lot.
Possibly. The Town's 2025 map puts 507 properties in Very High and 178 in High, about 50 more than the state required, weighing dead-end streets, escape routes and distance to open space. New ADUs in those zones are built to the 2025 Wildland-Urban Interface Code.
The Town code limits detached ADUs to one story at 16 feet, or 19 feet with 30-foot setbacks. In January 2026 the state housing department told the Town that parts of its ADU rules, including the one-story limit, conflict with state law. Ask us for the current status before you design.
A planner reviews your site plan against setbacks, slope, trees, floor area and septic before you apply. We bring a draft plan and two possible locations so the meeting settles real questions instead of raising new ones later.
Tell your insurer before the ADU is occupied, since 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 Los Altos Hills ordinance and a street view of the driveway before the call.
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