For land outside the 18 cities, the County's Planning & Development Services issues the building permit and its Building Division runs plan check. Many lots here depend on septic and wells, which the Department of Environmental Health and Quality should sign off before you apply, and fire review goes to the fire authority for your area; 12 fire protection districts share the County's 2026 wildfire code. Since April 4, 2026 a house and its ADU can also become condominiums and be sold separately, under conditions the County added on September 18, 2026.
Who issues permits in the unincorporated County, and how plan check runs
Start by confirming the County is your permit authority. The County's ADU page links a map of the unincorporated area, and its list of communities runs from Alpine, Fallbrook and Ramona to Spring Valley and Valley Center, with unincorporated pockets listed under El Cajon and Escondido. A city name in your mailing address does not settle it. The Property Summary Report in the County's online records, run with your assessor's parcel number, shows your zoning.
The Building Division of Planning & Development Services issues building permits for homes and other buildings across the unincorporated area. It checks plans against the state building codes with the County's amendments, its grading and zoning ordinances, and the County's consolidated fire and wildland-urban interface codes.
Small jobs such as a window replacement, a water heater or rooftop solar can be applied for online in Accela Citizen Access. An ADU, a new house or an addition goes through the Permit Center in Kearny Mesa, which takes new projects and resubmittals without an appointment. Before you submit, staff run a pre-review with zoning, building engineering, land development and, when needed, electrical, plumbing and mechanical review. You certify there whether the lot is on public sewer or septic and whether water comes from a district or a well.
Plan check fees are due when you submit, and the County opens a permit record listing your conditions of approval. Structural, planning and electrical, plumbing and mechanical reviewers send correction lists, and you resubmit until each one is cleared. A plan check stays open for one year. The County's permit summary, revised in 2013 and still linked from its ADU page, says about half of projects need more than two plan check cycles.
State law sets the County two deadlines on an ADU: 15 business days to say whether your application is complete, and once it is, 60 days to decide when a home already stands on the lot.
- Environmental Health and Quality (DEHQ) reviews septic systems and wells. On a septic lot it wants an approved septic layout before you apply for the building permit, and the County rejects site plans that leave out the well and septic locations.
- Your fire authority reviews the plans too. County Fire reviews them in the San Diego County Fire Protection District and the Deer Springs district, and the Building Division notifies it when you submit. In other districts you take the plans to that district's fire authority, which stamps them and completes the fire mitigation form.
- Land Development checks flood review, drainage, work on County roads and transportation impact fees. The County names fire district approval, flood control, septic review and driveway review as conditions that may take longer, so start them early.
Since July 1, 2024 the County has offered set review times for some housing. A home in an area the County maps as VMT efficient or infill gets 15 days of building plan check and 15 days of septic review, but only after a third-party building official certified by the ICC confirms the plans meet the codes.
Once issued, a permit has to show progress. Work must start and pass an inspection within two years, pass another inspection at least every 180 days, and finish within three years.
- A remodel or addition. Altering, enlarging or converting a building needs a County permit; the County's exempt list covers small items such as a one-story shed up to 120 square feet or a fence up to six feet. The wildfire code exempts additions to and remodels of buildings first built before July 1, 2008.
- A custom home on raw land. You show the County the parcel was legally created, get DEHQ's septic and well approvals, and add a grading permit once you move 200 cubic yards of earth or cut or fill 8 feet or more. Where no adequate public or private water supply exists for firefighting, the fire code official can accept a water tank on site built to County Fire's standards.
County ADU rules that differ from state law
State law sets the floor every authority must allow. The County writes its own rules in section 6156.x of its zoning ordinance, summarizes them in a handout, PDS-611, and has said in writing that where its zoning ordinance and mandatory state housing law conflict, staff follow state law.
| Rule | In the unincorporated County |
|---|---|
| Where you can add one | A lot zoned for residential or mixed use with an existing or planned house or apartment building. You need a County building permit. |
| How many on a house lot | You can combine a converted ADU, a junior ADU and a new detached ADU of up to 800 square feet. The state housing department says the County must also let you add one ADU built under the general rules, such as a new attached ADU or a detached ADU over 800 square feet, in any order. The ordinance hasn't caught up, so raise it with the County before you design. |
| Detached ADU size | Up to 1,200 square feet, whatever the size of the house. State law also requires the County to allow an 800-square-foot ADU with 4-foot side and rear setbacks wherever its other limits would block one. |
| Attached ADU size | Up to half the house's floor area and no more than 1,200 square feet. If half your house is less, you can still build up to 850 square feet, or up to 1,000 square feet if the ADU has more than one bedroom. With a 1,200 square foot house, for example, half is 600, but an 850 square foot one-bedroom ADU is still allowed. |
| How size is measured | State law sizes ADUs by interior livable space, and the County's current handout measures from the inside face of the outside walls. The zoning ordinance still says outside dimensions, and the state has told the County to change it. It matters near a limit: a 30 by 40 foot room inside is 1,200 square feet, but about 1,271 measured outside 6-inch walls. |
| Converting existing space | A permitted accessory building of any size, even a large barn, can become an ADU if it stays within its walls, with up to 150 square feet added for a way in and out. Part of the house can convert, but never all of it. |
| Height | A detached ADU can reach 25 feet, more than the 16 feet state law makes the County allow. A detached ADU of 800 square feet or less built under the state's streamlined path is held to 18 feet, as are detached ADUs beside an existing apartment building. An attached ADU can be at least 25 feet tall, or as tall as the zone allows the house if that is lower, and need not go past two stories. |
| Side and rear setbacks | At least 4 feet for a new ADU, including one built above a permitted garage, unless your fire authority requires more. A converted building needs no setback except for fire safety, private wells and septic systems. |
| Front setback | A new detached ADU of 800 square feet or less, with 4-foot side and rear setbacks, can sit in the front setback. An attached or larger ADU meets the front setback, unless that would leave no room for an ADU of up to 800 square feet. An ADU in the front setback cannot block the driveway or the house's two parking spaces unless you replace them. |
| Parking | One space, which can sit in a setback or behind another car in the driveway. None within half a mile of public transit, in a historic district, for an ADU inside the house or an accessory building, where on-street permits are not offered to the tenant, within one block of a car share vehicle, or when you apply with a new house. A garage you convert or tear down need not be replaced. The handout adds that an ADU under 800 square feet needs no space. |
| Fire sprinklers | Not required in the ADU when the house does not need them, and an ADU does not trigger sprinklers in an existing apartment building. |
| Owner occupancy | None for an ADU. For a junior ADU, only when it shares a bathroom with the house, and then you live in the rest of the house or the junior ADU. |
| Short-term rental | Not allowed. Each rental of an ADU or a junior ADU runs at least 31 days. |
| Junior ADU | Up to 500 square feet inside the house, an attached garage included, with its own entrance and an efficiency kitchen. No separate electric meter, and a recorded deed restriction bars selling it apart from the house. Turning a garage into a junior ADU doesn't mean replacing its parking, and a junior ADU can sit beside an attached ADU as long as it stays inside the house's walls. |
| Separate sale | Since April 4, 2026 the house and ADU can become condominiums through a tentative parcel map or tentative map, and since September 18, 2026 each sale carries a right of first refusal, a buyer's occupancy affidavit and a 30-day public listing. |
| Septic and wells | On a lot with a septic system or a well, DEHQ must find that the system serves both the house and the ADU to current standards. If it falls short, you upgrade it or plan fewer bedrooms. |
| ADUs built without permits before 2020 | The County cannot deny a permit over building standards or its ADU rules unless a fix is needed for septic standards, health and safety, or a building found substandard. Impact fees and connection charges are waived unless new utility work is needed for health and safety. |
| Design and community areas | Section 6156.x sets no design or style rules for ADUs. Separately, land carrying the County's design review designator, including village zones in Fallbrook, Ramona and Alpine, needs a site plan permit or an exemption before a building permit, and the Julian Historic District has its own review board. The County's ADU page and handout do not say how this applies to an ADU, so ask the Zoning counter early. |
| Lots with an apartment building | Up to eight detached ADUs beside an existing building, never more than its unit count, or two beside a planned one. Unused space such as storage rooms or garages can become ADUs up to a quarter of the existing units. The County's 2024 Handbook still says two; the law changed in 2025. |
State law sets the floors in this table, and the County's own 2025 Director's Determination says state law wins where its zoning ordinance conflicts. In July 2026 the state housing department told the County that five parts of its ordinance fall short of state law. As of October 19, 2026 the County had not amended them.
Some County documents haven't caught up, so you may read something different from what this table says:
- The 2024 ADU Handbook keeps an attached ADU to the house's height or 16 feet. State law sets the 25-foot floor.
- The County's ADU web page ties the attached ADU size floor to the house's bedrooms. The ordinance and the handout count the ADU's bedrooms, so plan on the ADU's.
- The PDS-611 handout allows rentals of 30 days. The ordinance says 31, so use 31.
- The ordinance and PDS-611 still show the older junior ADU rules on owner occupancy, ADUs next door and parking. State law changed on January 1, 2026.
- The 2024 Handbook says an ADU can't be sold separately and that an apartment lot gets only two detached ADUs, and PDS-611 leaves out the condominium route. All three are out of date.
If your design sits close to a size limit or depends on one of these points, ask Planning & Development Services at intake how plan check will apply it.
The County's standard ADU plans
The County has published free standard plans since 2019, checked by its staff against the building code and meant to work anywhere in the unincorporated communities. Six can be built as an ADU or as a house, and two more are for houses only.
- Plan A: 1,200 square feet, three bedrooms, one bath.
- Plan B: 1,200 square feet, two bedrooms, one bath.
- Plan C: 1,200 square feet, two bedrooms, two baths.
- Plan D: 1,000 square feet, one bedroom, one and a half baths.
- Plan E: 800 square feet, one bedroom, one bath.
- Plan F: 600 square feet, one bedroom, one bath.
Each set comes as a PDF in two sheet sizes and as a CAD file. The sets carry a January 1, 2026 revision and list the 2025 California codes, which took effect that day. That matters because state law requires a decision within 30 days on a complete application for a detached ADU drawn from a plan pre-approved in the current code cycle.
The County calls the plans about 85 percent complete. Its checklist asks for a plot plan and vicinity map, owner and parcel details, the stormwater plan and impervious area figures before plan check, and lists energy calculations, truss calculations from a truss maker and your fire district's approval as items that may follow the submittal. If the Property Summary Report puts your lot in any fire hazard zone other than urban unzoned, the plot plan also shows fuel modification.
A standard plan does not change what your lot needs. Septic layout approval, grading, energy calculations for your site and fire review still apply. State law has required every agency to accept ADU plans from anyone for pre-approval since January 1, 2025; the County's project page says that law prompted no change to its program, so ask PDS how it handles a plan your designer submits.
Fire districts, septic and wells, the San Dieguito coast, historic sites and slopes
Most of the county is unincorporated, about 2.3 million of its 2.9 million acres, but tribal land, state and federal land and military bases such as Camp Pendleton leave the County land-use authority over 772,239 acres. Lot sizes vary widely: the zoning ordinance scales how much accessory building you may add by lot size, in steps from under half an acre to 16 acres or more. The 2011 General Plan placed 80 percent of future housing capacity where the County Water Authority can deliver imported water.
- Fire districts. Twelve fire protection districts share the County's 2026 wildland-urban interface code, in effect since April 2, 2026: Alpine, Bonita-Sunnyside, Deer Springs, Lakeside, North County, Rancho Santa Fe, Rincon Del Diablo, San Diego County Fire, San Marcos, San Miguel, Valley Center and Vista. County Fire was formed in 2008 to unify the support of 15 rural fire agencies and extend around-the-clock protection to about 1.5 million acres.
- State Responsibility Area. The code reaches new buildings on all unincorporated State Responsibility Area land at moderate, high or very high hazard, and the Alpine, Bonita-Sunnyside, Lakeside and San Miguel districts treat all such land as very high. The state's hazard maps for that land took effect on April 1, 2024.
- The 2025 local maps. The state released new maps for Local Responsibility Areas on March 24, 2025. County Fire says zones inside its district's local area may have changed and points you to the State Fire Marshal's viewer to compare the 2007 and 2025 designations.
- Fuel modification. The County asks for 100 feet of fuel modification around a building, or to the property line if that is closer: the first 50 feet cleared, planted with fire-resistant plants and irrigated, the rest thinned by half.
- Fire setbacks. The wildfire code sets buildings at least 30 feet from property lines, unless the building official and the fire authority find the wildfire hazard not significant or the lot's terrain or size makes that infeasible, and 100 feet from a line next to a national forest, state park or open space preserve. Nine districts add a setback from the top of a slope, 15 feet for one story and 30 feet for two. The County's ADU rules keep 4-foot setbacks except where fire setbacks require more, so call your fire district before you design.
- Water for firefighting. Where no adequate public or private water supply exists, the fire code official can accept a tank, with its fire department connection 50 to 150 feet from the building.
- Zone 0. The state's ember-resistant rules for the first five feet around a building cover State Responsibility Area land and Very High Fire Hazard Severity Zones in Local Responsibility Areas. The Board of Forestry adopted them on August 19, 2026 and says they are still under final review by the Office of Administrative Law.
- Septic. Where there is no public sewer, a septic professional designs the system and files a layout application with DEHQ, which inspects the site. Tank size follows the bedrooms in each dwelling, the disposal field is sized from percolation tests run where it will go, and the plan has to set aside a full reserve area for a future replacement. An approved layout lasts one year.
- An existing system. DEHQ says an ADU almost always exceeds the capacity of the existing tank and disposal field, though a large enough tank may be reused and the field expanded.
- Groundwater and wells. Groundwater is the only drinking water in many rural communities, so a conventional system needs at least 5 feet of soil above the highest expected groundwater, or 2 feet with a supplemental treatment system. Drilling a well takes a DEHQ well permit.
Coastal land. The unincorporated County does have Coastal Zone land: about two square miles in the San Dieguito community, San Dieguito Park included. The Coastal Commission certified the County's Local Coastal Program on February 10, 2021, and the County has issued coastal permits there since March 15, 2021. A form lets you ask PDS whether your project is exempt.
Historic sites. On a property carrying the County's historic landmark or district designator, no permit issues for new construction or alterations until a site plan is approved. In the Julian Historic District, buildings are to look like Julian's buildings of 1870 to 1913, and a district review board advises on each site plan. An ADU in an architecturally and historically significant historic district needs no parking space.
Steep slopes. The Resource Protection Ordinance protects steep slopes, defined as ground sloping 25 percent or steeper that climbs at least 50 feet, along with wetlands, floodplains, sensitive habitat and significant prehistoric or historic sites. It applies to discretionary applications such as tentative maps, site plans and administrative permits, not to an existing single-family parcel otherwise. The County's ADU Handbook advises against grading on slopes over 25 percent.
County fees and where their schedules live
The County's trial waiver of ADU impact fees ran from January 9, 2019 to January 9, 2024. A project started before the end date skipped the plan check fee, but if its permit was not issued by then, every fee due at issuance applies.
- Plan check and permit fees. PDS sets them in its building fee schedule, PDS 613, which has its own line for an ADU and a lower one for an ADU simple enough for counter review, each a base amount plus a rate per square foot. A fee estimator spreadsheet sits on the Online Services page. You pay plan check at submittal and the rest at issuance.
- Impact fees. Transportation impact and drainage fees come from a County calculator. Park fees come from the Park Land Dedication Ordinance, which the Parks department prices for each of 24 local park planning areas with a separate ADU rate, and PDS collects them when the permit issues. Under state law an ADU with 750 square feet or less of interior livable space pays no impact fees, and a larger one pays only in proportion to the size of the house.
- School fees. Your school district charges them and gives you a clearance letter the County needs before issuance. State law treats an ADU under 500 square feet of interior livable space as too small for them.
- Fire fees. Where County Fire reviews your plans, its fees are in the County's fee ordinance, and the Board revised the County Fire fee schedule on May 6, 2025. Fire mitigation fees are collected with the other agency fees before the permit issues.
- Septic and well fees. DEHQ sets them in section 65.107 of the County code and posts its current fees and the approved fees for fiscal year 2026-27: separate fees for reviewing percolation tests, for a layout report, for an installation permit, and for a domestic well permit.
- Water and sewer. Water and sewer districts charge their own connection fees. State law bars requiring a new connection, or charging for one, for an ADU or junior ADU made inside the house or an existing accessory building, unless it comes with a new house or the ADU is sold as a condominium.
- Selling an ADU as a condominium. The map runs through the County's discretionary process, whose costs are set out in the Discretionary Permit Cost Guide on the Online Services page.
ADUs permitted in the unincorporated County
Every California city and county reports its housing permits to HCD each year. These are the ADUs the County reported permitting in the unincorporated area.
- 792018
- 1372019
- 1422020
- 2992021
- 3382022
- 4262023
- 4892024
- 4032025
Units in HCD's ADU category that the County, reporting for the unincorporated area only, listed as issued a building permit during each calendar year; the 18 cities report their own. HCD's instructions count junior ADUs as housing units yet give the County's report no junior ADU category, so these County figures cannot split the two.
What changed in the County, 2024 to 2026
The dated changes that shape an ADU or a new home in the unincorporated County today.
Unincorporated lots still pay the County's transportation, drainage and park impact fees, so SB 1117 is felt here: where a lot holds no more than two ADUs, a unit past 750 square feet is charged only for the area beyond 750. Details in our state law guide.
New conditions on selling an ADU condominium took effect: a right of first refusal, an affidavit that the buyer or a family member will live there for at least a year, and a 30-day public listing. The Board, which adopted them on August 19, also asked staff to report within 180 days on enforcement, deed restrictions and larger ADU sizes.
The state Board of Forestry adopted emergency Zone 0 rules covering all State Responsibility Area land; they still await final review.
HCD found five points where the County's ADU rules do not comply with state law, from how floor area is measured to junior ADU owner occupancy and parking, and asked the County to reply in writing by August 6, 2026 with a plan to amend its ordinance or adopt findings.
The reorganized ADU section of the zoning ordinance and the separate-sale program took effect, after the Board of Supervisors adopted them unanimously on March 4, 2026.
The 2026 County wildland-urban interface code, shared by the 12 fire protection districts, took effect.
The County's standard plan sets were revised to the 2025 California codes.
The Building Division's simplified permitting under the Homeowner's and Business Owner's Relief Acts ended, apart from solar.
The state released its revised fire hazard maps for Local Responsibility Areas; County Fire says zones in its district's local area may have changed.
The PDS director confirmed in writing that where the zoning ordinance and mandatory state housing law conflict, staff follow state law.
HCD found that the County's 2023 ADU ordinance did not comply with state law on several points, among them how ADU types can be combined on one lot, and asked for a response by October 24, 2024.
Set review times for some housing took effect, including 15 days of building plan check for homes in VMT efficient or infill areas with a third-party code certification.
The State Fire Marshal's new hazard zone maps for State Responsibility Area land took effect.
The County's trial ADU impact fee waiver, in place since January 9, 2019, ended. Permits issued after this date pay every fee due at issuance.
How BHI approaches a County project
What we look at first on unincorporated land.
On unincorporated land we start with three questions the County's own rules leave to others: which fire district reviews the plans, whether the lot runs on septic, and which water district serves it, since each can add its own conditions. Our own County ADUs near Escondido show the spread: a garage conversion cleared plan check in roughly five weeks, while a two-story detached unit took about seven and a half months. Book a call to talk through yours.
Next steps
Confirm the County is your permit authority, check what your lot allows, then price the work.