Woodside · San Mateo County
Custom Homes, Guest Houses & Estate ADUs in Woodside, California
Woodside's large parcels and rural character make it ideal for a detached ADU that feels like a small custom home, not an add-on.
Building custom homes and estate ADUs in Woodside, California
SHAPE designs and builds custom homes, guest houses, and estate ADUs for owners in Woodside, California , from Central Woodside, Woodside Heights, Skywood Acres, Kings Mountain, and the equestrian lots off Cañada Road.
Woodside's large parcels, horse properties, and privacy standards make a detached ADU the natural way to add a guest house or caretaker unit without disturbing the main compound.
We're a licensed California general contractor (CSLB #1158688) with an architect-led, design-build model. One team owns the drawings, the permits, and the field work, so a Woodside project moves without the usual finger-pointing between architect, contractor, and city.
Woodside Building Standards at a Glance
The ADU standards below apply to accessory dwelling units. A new primary residence or a different type of accessory building follows its own requirements.
- Setbacks: California state law caps rear and side setbacks for new ADUs at 4 feet, and Woodside follows that standard.
- Height: Detached ADUs can be 17 feet tall with an 11-foot plate, or 18 feet when built over a detached garage. Attached ADUs can match the main house.
- Maximum size: Woodside publishes a maximum ADU size of 1,500 square feet, subject to the applicable standards. An 800-square-foot limit applies to the portion allowed within the required basic setbacks. Total permitted floor area and site constraints must also be checked.
- JADUs: Junior ADUs (up to 500 sq ft) are allowed inside the existing footprint of the primary home, in addition to a detached ADU on most single-family lots.
- Lots over one acre: The Town's ADU handout allows up to three ADUs on lots of one acre or more, one of them a conversion of existing space, plus a junior ADU.
- Parking: Requirements for parking serving the ADU depend on the applicable local standards and state exemptions. Replacement of parking removed or converted for an ADU is a separate rule; proximity to transit is not a condition for that replacement-parking exemption.
Rules checked September 2026 against: Town of Woodside ADU page, Town ADU handout, San Mateo County ADU Resource Center, HCD ADU Handbook, California Energy Commission ADU guidance, San Mateo County Assessor, California Department of Insurance, Safer from Wildfires. Town rules change often. We confirm the rules for your lot before design.
SHAPE handles the full permit package with the Woodside planning department, zoning verification, building plans, Title 24 energy, and every correction cycle, so you don't have to learn the code.
Read the Woodside ADU planning notes for the property checks behind these rules.
Our Process
- Site assessment. We walk your Woodside lot, confirm setbacks and utility locations, and give you a feasibility read and an all-in price the same week.
- Design. Our in-house architects design the custom home or estate ADU around your lot, your family, and your budget, with fixed pricing before you sign.
- Permits. We submit, respond to every planning and building comment, and drive the file to permit issuance with Woodside.
- Build. Modules are fabricated in our facility while site work, foundation, utilities, landscaping, runs in parallel. Set and finish happen on site.
Planning a Woodside ADU alongside the main home
Separate the ADU decision from the custom-home decision
An independent family dwelling, a guest house, and a new primary residence are different projects. Start with the intended use, including whether the building needs its own permanent kitchen, bathroom, and sleeping space.
The Town's ADU guidance describes an ADU as a permanent dwelling with its own living facilities. A familiar label such as “guest cottage” does not establish the building's permitted use.
If the main home is also being rebuilt, identify which drawings and site works are shared and which approvals belong to each building. That gives the project a clearer sequence and prevents an ADU schedule from being mistaken for the schedule of the entire estate.
Test the larger option against setbacks and total floor area
Woodside's published maximum of 1,500 square feet is useful, but it is only one part of the siting decision. The Town's ADU zoning handout separately addresses the smaller allowance within required basic setbacks and how ADU area relates to the site's total permitted floor area.
Compare a compact family unit with a larger plan using the same survey. Show the existing house, accessory structures, driveway, trees, and the actual limits of the proposed building. Include decks and entry features in the review rather than drawing only the enclosed rooms.
A larger interior can be worthwhile. It should be a deliberate choice made alongside its effect on the garden, privacy, foundation, and service connections.
Resolve the rural site before selecting a standard plan
The Town identifies geotechnical and seismic hazards, steep slopes, stream corridors, easements, septic suitability, and Fire District standards as site-specific considerations, including for pre-approved plans. These conditions vary by parcel.
On a septic property, establish whether the system can serve the proposed use and bedroom count. On sloping ground, study a section through the building and the route from the main house. Where there is a creek or drainage corridor, confirm its location and applicable constraints before placing the foundation or service trench.
A pre-approved building design does not approve those site conditions. It is more useful to know which constraints control the location before spending time adapting the interior.
What those checks involve in Woodside:
- Septic: only about 28% of developed Woodside parcels are on sewer. San Mateo County sizes septic systems at 150 gallons a day per bedroom with a full reserve area. Sewered lots need a West Bay Sanitary District permit.
- Geology: the Town requires a geotechnical report for new living space and added bedrooms. The Town Geologist reviews it in about 20 working days.
- Grading: moving more than 100 cubic yards needs a site development permit. More than 1,500 cubic yards goes to the Planning Commission.
- Trees: significant trees are protected from 7.6 inches in diameter for blue oak and madrone, and 9.5 inches for coast live oak, valley oak and redwood.
- Fire: the Woodside Fire Protection District requires 100 feet of defensible space. In designated fire hazard areas, construction follows the 2025 California Wildland-Urban Interface Code.
Make the site-work budget and family brief agree
For a Woodside family ADU, discuss how people will arrive, carry groceries, reach the main house, and use the outdoor space. If convenient access without multiple steps matters, place that requirement in the brief at the start.
Then price the chosen location consistently. Distinguish foundation work, retaining or grading work, utility connections, wastewater work, and restoration of paths and planting. Ask where construction equipment will operate and what will protect the existing landscape.
The Town's permit information is a reference for coordinating the necessary approvals. The goal of the first site review is to connect the desired rooms with a workable location and a clearly defined construction scope.
Request a Woodside site assessment with the intended use and any survey, septic, or previous permit records available.
Guest house or ADU in Woodside?
Under Town rules, a detached building without a kitchen is an accessory building, and all of it counts against the lot's total floor area. Add a kitchen and it becomes an ADU, which can go 800 square feet past the floor area limit and is approved with a building permit.
| Guest house without a kitchen | ADU with a kitchen | |
|---|---|---|
| Floor area | Counts toward total floor area, and toward the house size cap if within 15 feet of the house (8 feet in R-1) | Can exceed total floor area by 800 sq ft |
| Size and height | Up to 1,500 sq ft, 17 feet | Up to 1,500 sq ft, 17 feet (18 over a garage) |
| Kitchen | A wet bar is fine (sink, fridge, dishwasher), no stove or oven | Full kitchen |
On most Woodside lots, building it as an ADU saves floor area and time, and you can still use it as a guest house.
Costs beyond the building on a Woodside lot
The building price is only part of a Woodside budget. These costs are set by the county and the utilities, not by the builder, and we price the ones your lot needs before you sign.
| Item | Amount |
|---|---|
| Septic site evaluation and perc test (San Mateo County, 2026) | $3,936 |
| County septic review with the building permit | $1,968 |
| New septic system permit | $3,773 to $6,559 |
| Sewer connection, West Bay Sanitary District (sewered lots) | $8,608 per equivalent dwelling unit |
| PG&E new electric service for an ADU (average, projects finished 2023 to August 2025) | $4,832 |
| PG&E new gas service for an ADU (same period) | $16,865 |
Sources: San Mateo County Environmental Health fees, West Bay Sanitary District, PG&E ADU service report
Timeline for a Woodside ADU
On a Woodside lot the permit is rarely the longest step. 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 |
| Town Geologist review of the geotechnical report | About 20 working days |
| PG&E new service | Averaged 118 days as of March 2026, by PG&E's count |
| Build, from permit | 2 to 4 months with our modular process |
We run design, the geotechnical report and the PG&E application side by side, so the longest item sets the schedule instead of the sum of all of them.
Sources: 2025 ADU law update (SB 543), PG&E new service times
Frequently asked
- How much does a custom home or estate ADU cost in Woodside?
- Custom homes and estate-caliber ADUs in Woodside typically start in the mid-seven figures for a full ground-up build and from the mid-$500ks for detached guest houses. SHAPE quotes a fixed all-in number after a site walk and a design brief.
- How long do permits take in Woodside?
- Woodside's design-review-heavy process usually runs 6–12 months for a full custom home, and 2–4 months for an ADU under California's ministerial review rules. SHAPE manages every submittal and correction cycle.
- Do I need to add parking?
- Woodside custom homes follow the local off-street parking standards. Check the ADU's approval path and the property-specific exemptions before adding a parking space to the plan. State exemptions include qualifying locations within a half-mile walking distance of public transit. Separately, parking removed or converted in connection with an ADU generally does not need to be replaced. Do not assume that a neighborhood name establishes a transit exemption.
- Can I build a guest house and an ADU on the same lot?
- The answer depends on the permitted use of each building, the existing structures, and the site's development limits. A guest house without independent living facilities is not automatically an ADU. Confirm the allowed combination and any conversion requirements before designing both buildings.
- Do you work with an existing architect?
- We do. SHAPE can execute a set of drawings your architect has already developed, or run the full design in-house. Either way, one contract and one fixed price.
- Can I build an ADU on any Woodside lot?
- Yes, on any lot with an existing or proposed single-family home. State law does not allow a minimum lot size for ADUs. On most Woodside parcels the real limits are septic capacity, slope, creek setbacks and fire access, which is why we start with a site walk.
- Do I need Architectural and Site Review Board approval for an ADU?
- Not for an ADU on its own. Woodside approves ADUs with a building permit. The ASRB reviews ADUs that are part of a larger project, such as a new main house, where grading, story poles and trees come up.
- Can I build the ADU and a new main house at the same time?
- Yes. State law lets the Town approve an ADU together with a new single-family home, and the ADU is still reviewed without discretionary review. One difference: when the ADU is built together with a new house, utilities can treat it as new residential use when they set connection fees.
- Can I turn my barn or stable into a guest house?
- Yes. Woodside allows barns and stables to be converted to ADUs. A barn ADU needs fire sprinklers and a fire wall. We check the structure, septic capacity and fire access before we price a conversion.
- How many bedrooms can a Woodside guest house have?
- State law does not let towns cap the number of bedrooms in an ADU. On a septic lot the system sets the practical limit, because the county sizes septic by bedroom count. We test capacity before the floor plan is fixed.
- Does a Woodside ADU need solar panels?
- A new detached ADU does. Under the 2025 California Energy Code it needs new solar panels, but they can be added to an existing solar system elsewhere on the property instead of the ADU roof. An attached ADU counts as an addition and does not need solar.
- Does the ADU need its own utility connections?
- Not always. State law bars a separate-connection requirement for ADUs built inside existing space. For a new detached ADU, PG&E, the water provider or the sewer district can require its own connection, with fees in proportion to the ADU's size. We settle this with each utility during design.
- Will a guest house raise my property taxes?
- Only on the new building. The San Mateo County Assessor does not reassess your existing home. It adds the ADU's market value at completion to your current assessed value. If construction is only partly done on January 1, a partial assessment appears on that year's bill.
- Do I have to live on the property?
- No. State law (AB 976) permanently bars towns from requiring the owner to live on a property with an ADU.
- Can I sell the ADU separately?
- Not today. State law (AB 1033) lets a city allow ADUs to be sold separately as condominiums, but only if it adopts its own ordinance. As of January 2026, Woodside had not.
- Can I legalize an older cottage built without permits?
- Often, yes. State law (AB 2533) covers ADUs built without permits before 2020. The Town cannot charge impact fees or penalties for them, but it can deny a unit that is substantially unsafe. We can assess what it would take to bring yours up to code.
- What are the permit fees for a Woodside ADU?
- The San Mateo County ADU Resource Center lists about $20,700 in fees for a 1,493 square foot detached ADU, with no Town building permit or inspection fees. ADUs of 750 square feet or less pay no impact fees under state law.
- What is the difference between an ADU and a junior ADU?
- A junior ADU is up to 500 square feet and sits inside the walls of the main house. It needs its own efficiency kitchen but can share a bathroom with the house. An ADU can be attached or detached, has its own full kitchen and bathroom, and can be much larger. A lot can have both.
- Will an ADU change my home insurance?
- 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.
- How long does PG&E take to connect an ADU in Woodside?
- PG&E reported ADU electric hookups averaging about 300 days from request for projects finished by August 2025, and says its times have improved since. Woodside also requires new utility lines to run underground. We file with PG&E when the permit goes in so power is not the last thing we wait on.
- Is the California $40,000 ADU grant still available?
- No. CalHFA's ADU Grant paid up to $40,000 toward predevelopment costs, and CalHFA says its latest round was fully allocated in December 2023. CalHFA warns that anyone offering to get you one is running a scam.
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