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Shape Homes · Where we build · Woodside
Woodside allows a larger ADU than any of its neighbors and will let it reach nearly full home height if you site it conventionally. What constrains a Woodside project is almost never the unit. It is earth, trees and fire.
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| Rule | What it says | Source |
|---|---|---|
| Detached ADU, maximum | 1,500 sq ft — the most generous cap in this set | Town ADU Zoning Requirements handout |
| Attached ADU | Lesser of 50% of the home or 1,500 sq ft | Town handout |
| JADU | 500 sq ft | Town handout |
| Height, meeting full setbacks | 28 ft in R-1, 30 ft in other zones | Town handout |
| Height, encroaching setbacks | 17 ft overall, 11 ft plate | Town handout |
| Height, above a garage | 18 ft overall, 12 ft plate | Town handout |
| Setbacks | 4 ft side and rear, but only 800 sq ft may sit inside that zone | Town handout |
| Foundation and utilities | Permanent, required for every ADU | Town handout |
| Parking | One space with a bedroom. None for a studio | Town handout |
| Minimum tenancy | 30 days | Town handout |
Sources: Town of Woodside ADU page, Town ADU handout, Town permit information, San Mateo County ADU Resource Center, HCD ADU Handbook. Rules change often; we confirm them for your lot before design.
Size is rarely the constraint. These are.
Total project grading over 1,500 cubic yards, or any single cut or fill deeper than eight feet, triggers a Planning Commission Grading Exception. On a sloping Woodside parcel that is reached far more easily than people expect, and it converts a ministerial project into a hearing. We test the earthwork volume during the lot check, before design commits to a bench.
Site plans must show the surveyed location, trunk circumference measured four feet above grade, species, and field-determined dripline of every Significant Tree. Protection extends wherever the dripline crosses a structure, cut, fill, driveway, path, patio, deck, pool, wall or fence. Not the trunk. The dripline. It routinely relocates a building.
Woodside Fire Protection District reviews the project, and design review routes through the Fire District portal. Where the parcel is on septic, San Mateo County Environmental Health reviews capacity, and the Town notes plainly that limits on septic installation may apply. Slopes over 35% need a stamped geotechnical or civil report.
An ADU beside the main home has a different review path from a new custom home or an accessory building without a kitchen. We confirm the intended use first, then compare the applicable ADU provisions with the parcel's remaining floor-area capacity. A larger property or a larger published size allowance does not settle the location. Setbacks, trees, terrain and access still need to work on the actual survey.
Central Woodside, equestrian properties along Cañada Road and wooded hillside parcels can have very different service arrangements. We identify whether the property uses sewer or septic and confirm the relevant provider or environmental-health review. Wastewater capacity, bedroom count and utility routes are considered together. Existing septic records, well information where applicable and prior service drawings can make the first feasibility review more useful.
A wooded or sloping Woodside site may need geotechnical information, tree protection, grading review and fire-agency coordination. We confirm which reports and permits apply rather than assuming every property needs the same package. Foundation design, construction access and defensible-space work are checked together. The site plan should show where materials and equipment can go while maintaining the required tree-protection and emergency-access areas.
A private ADU at the back of an estate still needs a comfortable route to the main home, parking and garden. We draw that route with the floor level and drainage, including any steps, landings or retaining structures. The estimate then identifies wastewater work, utility extensions, foundation engineering and landscape restoration. Those choices should match the intended occupants and the way the new space will be used every day.
The property checks behind the standards above.
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, and sewered lots need a West Bay Sanitary District permit. We confirm which applies before the bedroom count is set.
The Town requires a geotechnical report for new living space and added bedrooms, and the Town Geologist reviews it in about 20 working days. We run that review alongside design rather than after it, so it does not become the last thing standing between you and a permit.
Moving more than 100 cubic yards needs a site development permit. More than 1,500 cubic yards goes to the Planning Commission. On a sloping lot those numbers arrive faster than most homeowners expect, which is why we test earthwork volume at the lot check.
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. The Woodside Fire Protection District also requires 100 feet of defensible space, and in designated fire hazard areas construction follows the 2025 California Wildland-Urban Interface Code.
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.
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 | A few months; we confirm the schedule in your agreement |
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.
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 Woodside 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 Woodside 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 Woodside. 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 Woodside lot, so a pool house or in-law cottage designed as an ADU clears review sooner than the same building filed any other way.
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 home size cap if within 15 feet of the home (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.
Up to 1,500 sq ft detached, which is above the state default of 1,200 and above every neighboring town. An attached unit is the lesser of 1,500 sq ft or 50% of the main residence. At least one ADU up to 800 sq ft does not count toward your floor-area limit.
This is where Woodside is genuinely unusual. If the unit meets full setbacks it may reach 28 ft in R-1 and 30 ft in other zones — effectively full home height. If it encroaches into a setback it drops to 17 ft overall with an 11 ft plate. Siting decides height here, not unit type.
More than 1,500 cubic yards of total project grading, or any single cut or fill over eight feet. It requires Planning Commission approval, which adds a hearing and months. It is the single most common reason a Woodside schedule slips.
Much of it is. Where it is sewered, West Bay Sanitary District issues the permit. Where it is not, San Mateo County Environmental Health reviews whether the system has capacity for the new unit. Either way it is confirmed before design, not after.
Yes. In Woodside 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.
Not necessarily. ADUs, new custom homes and accessory buildings without kitchens use different provisions. We confirm the intended use and applicable approval path before applying floor-area, setback and review requirements to the design.
Bring the address and any survey, septic or sewer records, prior permit plans, geotechnical information and tree reports you have. We use them to identify service capacity, potential locations and the specialist checks needed for the proposed ADU.
The applicable fire designation and agency requirements can affect access, water supply, materials and landscape management. We coordinate those findings with tree protection and the construction route, then include the resulting work in the site plan and estimate.
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.
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.
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.
We pull your parcel, the Woodside ordinance and a street view of the driveway before the call.
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