We start with your design. Modular is how we build it, not what you settle for.
Shape Homes · Where we build · Monte Sereno
Monte Sereno has the most prescriptive design standards of any town on this list, and a sewer rule that decides where a detached unit can physically go.
Book a consultation
| Rule | What it says | Source |
|---|---|---|
| Size | 850 sq ft, or 1,000 sq ft with more than one bedroom | City ADU ordinance |
| Size by district | Varies across R-1-8, R-1-20 and R-1-44 | City ADU ordinance |
| JADU | 150 to 500 sq ft | City ADU ordinance |
| Height, detached | 16 ft maximum | City ADU ordinance |
| Setbacks, detached | 4 ft side and rear minimum | City ADU ordinance |
| Conversions | No setback required when converting existing living area | City ADU ordinance |
| Coverage | Must meet structural and impervious coverage limits | City ADU ordinance |
| Coverage exception | An 800 sq ft ADU is allowed even where coverage would be exceeded | City ADU ordinance |
| Design standards | Materials substantially identical in color, texture and appearance | City ADU ordinance |
| Sewer | Must connect to sanitary sewer. The main line may not pass through a building | City ADU ordinance |
Sources: City of Monte Sereno, Monte Sereno ADU Handbook, Monte Sereno Municipal Code, Pre-Approved ADU Plan Requirements, West Valley Sanitation District. Rules change often; we confirm them for your lot before design.
Size is rarely the constraint. These are.
Materials must be substantially identical in color, texture and appearance to the primary dwelling, and the roof must follow. That is not a design guideline, it is the standard your permit is measured against. In practice it means the second unit is specified off the main home's schedule, and if the main home is thirty years old that schedule has to be reconstructed before anything is ordered.
Monte Sereno requires connection to the sanitary sewer, and for a detached ADU the main sewer line may not pass through any existing building. On a deep lot with the home in the middle, that single sentence can decide which side of the property the unit goes on, and it is a trenching cost nobody includes in an early estimate.
Coverage limits apply, except that an ADU up to 800 square feet is allowed even where coverage would be exceeded. On a small Monte Sereno lot that exception is often the only thing that makes a second unit possible at all, and it caps the design at 800 square feet whether you like it or not.
Los Gatos and Monte Sereno are often grouped in regional guides, but their ADU standards and permit processes differ. We confirm the jurisdiction, zoning district and current City guidance for the address before applying a size or height figure. We then compare the proposed footprint with existing coverage and the appropriate approval path. A neighboring Los Gatos project is a design reference, rather than proof of what this lot allows.
Wooded and foothill properties can bring tree, slope and fire-access constraints to the same drawing. We check the mapped fire designation and the reviewing fire agency's requirements, including access and water supply where applicable. Services and construction staging are tested against the landscape too. That work helps identify a buildable position with a usable entry, before the exterior and interior choices are fixed.
Monte Sereno's pre-approved-plan route has eligibility restrictions, including exclusions for Wildland-Urban Interface areas in the City's published requirements. Site-specific geotechnical and fire review may still be needed. We check eligibility before treating prior plan approval as a schedule saving. Any permit-fee incentive is also confirmed directly with the City, including whether it remains available for a new application.
The connection to the sanitary sewer needs a clear route around the existing buildings. We establish the provider's requirements, trench length and restoration scope before completing the estimate. Exterior materials and roof choices are developed with the main home and the City's current standards in view. For a sloping site, drainage and foundation engineering are separate decisions that should be visible alongside the building package.
The parts of the process that decide whether the schedule holds.
State law, carried into Monte Sereno's ordinance, does not require the property owner to live in either the main home or the ADU while a standard ADU is rented out. A junior ADU is treated differently, since the owner generally must occupy one of the two units. We confirm the current occupancy rule for your unit type before the lease or family-use plan is finalized.
An ADU does not need to be sold or financed separately, and it cannot be subdivided onto its own parcel through the ADU process alone. It stays attached to the underlying property as an accessory use. Financing, insurance and resale planning should be built around that fact rather than around an assumption that the unit can later be split off.
Monte Sereno's handbook follows the state standard: an ADU is not required to have fire sprinklers if the primary residence does not have them. If the main home already has sprinklers, the ADU typically needs them too. We check the existing dwelling before pricing fire protection into the ADU scope.
An ADU under 750 sq ft is exempt from most impact fees under state law carried into the City's handbook. Above that threshold, fees are charged proportionately to the primary dwelling's fee, not at the full single-family rate. We confirm current fee schedules with the City before the fee line in your estimate is finalized, since schedules are updated periodically.
Under state law summarized by the Santa Clara County Assessor, adding an ADU triggers a reassessment of only the new construction itself, based on the building permit valuation. It does not reassess the land or the existing home. That keeps the property tax impact proportionate to what was actually built, which is worth confirming with the Assessor once your permit value is known.
A newly constructed detached ADU is treated as a new single-family building under California's Energy Code and must meet the current Title 24 standards; conversions of existing space follow the alteration standards instead. Solar PV requirements for new construction have specific exceptions. We confirm which path applies to your unit before the energy compliance documents are prepared.
Approximate, and dependent on your lot, the City's current workload and the sewer district's review.
| Step | Typical time |
|---|---|
| Feasibility and plan selection | 2 to 4 weeks |
| Design and engineering, including geotechnical where required | 4 to 10 weeks |
| West Valley Sanitation District permit review | Typically 3 business days once complete; 10 to 15 business days for an ADU scope |
| City building permit review | Varies by completeness and current queue; we confirm the City's posted turnaround |
| Site work, foundation and utility connection | Several weeks, longer where sewer trenching is required |
| Build, from permit | A few months; we confirm the schedule in your agreement |
Sources: West Valley Sanitation District permit process, City of Monte Sereno ADU Handbook. A range is not a schedule guarantee; we confirm dates in writing before construction starts.
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 Monte Sereno 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.
850 sq ft, or 1,000 sq ft with more than one bedroom, varying by district across R-1-8, R-1-20 and R-1-44. A junior ADU runs from 150 to 500 sq ft.
Prescriptive. Materials must be substantially identical in color, texture and appearance to the primary dwelling, and the roof must match. This is the most specific design requirement of any town we build in.
No. The parcel must connect to the sanitary sewer. For a detached ADU the main sewer line may not pass through any existing building, which frequently decides where the unit can be sited.
An ADU up to 800 sq ft is allowed even where structural and impervious coverage would otherwise be exceeded. Above 800 sq ft the coverage limits apply normally.
No. The cities have different development standards and approval processes. We confirm your jurisdiction, zoning district and current Monte Sereno requirements before selecting a plan. A shared regional guide should not be treated as a single ordinance.
The City's published pre-approved-plan requirements exclude Wildland-Urban Interface areas. We confirm the current eligibility rules and mapped designation for your parcel. A custom site-specific design may be needed, alongside geotechnical and fire review.
The City has offered an ADU permit-fee incentive, but availability and eligibility must be checked for a new application. We confirm the current program with the City before allowing for a discount in the estimate; it is not an assumed saving.
No. State law, reflected in the City's ADU handbook, does not require the owner to occupy either unit for a standard ADU. A junior ADU is different, since owner-occupancy typically applies to one of the two units. We confirm the current rule for your unit type before you plan to rent.
No. State law has the Assessor value only the new construction, based on the ADU's building permit value, not the land or the existing home. We confirm the approach with the Santa Clara County Assessor once your permit value is set.
Generally only if the primary residence already has them. The City's ADU handbook follows the state standard that an ADU is not required to have sprinklers if the main home does not. We check your existing home before pricing fire protection.
We pull your parcel, the Monte Sereno ordinance and a street view of the driveway before the call.
Book a consultation