MEP Plans in San Mateo County, CA

San Mateo County project facts we design around

County seat	Redwood City
Population	742,893 (Census 2024 estimate)
Incorporated cities	20
Unincorporated residents	About 60,985 (8% of the county)
Permits in unincorporated areas	San Mateo County Planning and Building Department – Building
Title 24 climate zones	CZ 3 (about 96% of residents), CZ 4 (about 4% of residents). Confirmed by ZIP for every project
ADU approval timeline	Approve or deny within 60 days of a complete application (state law)

HVAC design across San Mateo County

Climate Zone 3 and 4: mild Bay Area climate.

Mild temperatures mean small loads, and many Bay Area ADUs are heated with a single heat pump while cooling is a secondary concern. The harder problems here are usually in the existing house: older homes often have 100-amp (or smaller) services, aging panels and original sewer laterals, which is why the electrical load calculation and the sewer connection deserve attention early.

• Load calculation on an older service before you assume a panel upgrade (or skip one)
• Sewer lateral condition and connection route — some Bay Area cities have lateral inspection rules
• Compact heat pump design for a heating-dominated, low-load unit

Unincorporated San Mateo County

Unincorporated communities are permitted by the county, not by a city. County plan check reviews MEP drawings against the same California Mechanical, Electrical and Plumbing Codes and the Title 24 Energy Code as any city, but the submittal checklist, forms and fees are the county's own, so we prepare the set to match. In rural areas, parcels outside a sewer district often rely on a private septic system; adding an ADU can require the county's environmental health division to confirm the system has capacity, and the plumbing plan then shows the connection to the septic tank instead of a sewer lateral.

What's in a San Mateo County MEP set

• Mechanical: HVAC layout, Manual J load calculation, equipment schedule, exhaust and whole-unit ventilation
• Electrical: power and lighting plan, panel schedule, NEC 220 load calculation, single-line diagram
• Plumbing: supply and DWV layout, fixture units, water heater, gas (if any), sewer or septic connection
• Title 24 (add-on): energy compliance for your address's climate zone, coordinated with the MEP design so the two documents agree

Pricing is flat statewide: ADU plans from $995, full ADU MEP package from $2,295, Title 24 add-on $240. Standard turnaround is 5 business days with two revisions and corrections included.

San Mateo County cities and communities

Place	Climate zone	Electric utility
Atherton	CZ 3	Pacific Gas and Electric (PG&E)
Belmont	CZ 3	Pacific Gas and Electric (PG&E)
Brisbane	CZ 3	Pacific Gas and Electric (PG&E)
Burlingame	CZ 3	Pacific Gas and Electric (PG&E)
Daly City	CZ 3	Pacific Gas and Electric (PG&E)
East Palo Alto	CZ 4	Pacific Gas and Electric (PG&E)
El Granada (unincorporated)	CZ 3	Pacific Gas and Electric (PG&E)
Foster City	CZ 3	Pacific Gas and Electric (PG&E)
Half Moon Bay	CZ 3	Pacific Gas and Electric (PG&E)
Hillsborough	CZ 3	Pacific Gas and Electric (PG&E)
Menlo Park	CZ 3	Pacific Gas and Electric (PG&E)
Millbrae	CZ 3	Pacific Gas and Electric (PG&E)
Montara (unincorporated)	CZ 3	Pacific Gas and Electric (PG&E)
Moss Beach (unincorporated)	CZ 3	Pacific Gas and Electric (PG&E)
Pacifica	CZ 3	Pacific Gas and Electric (PG&E)
Portola Valley	CZ 3	Pacific Gas and Electric (PG&E)
Redwood City	CZ 3	Pacific Gas and Electric (PG&E)
San Bruno	CZ 3	Pacific Gas and Electric (PG&E)
San Carlos	CZ 3	Pacific Gas and Electric (PG&E)
San Mateo	CZ 3	Pacific Gas and Electric (PG&E)
South San Francisco	CZ 3	Pacific Gas and Electric (PG&E)
Woodside	CZ 3	Pacific Gas and Electric (PG&E)

Shown for most addresses in each city. We also serve San Mateo County's other 1 city and every unincorporated community.

San Mateo County ADU MEP questions

Who issues building permits for an ADU in unincorporated San Mateo County?

In unincorporated areas, home to about 60,985 residents (8% of the county), ADU and residential permits go through San Mateo County Planning and Building Department – Building. Inside the county's 20 incorporated cities, that city's own building department reviews the plans instead. We prepare the MEP set for whichever office has jurisdiction over your address.

What Title 24 climate zones are in San Mateo County?

San Mateo County spans 2 Title 24 climate zones: CZ 3 (about 96% of residents), CZ 4 (about 4% of residents). Zones follow ZIP-code boundaries, so we confirm the zone from your project address before sizing the HVAC or running the Title 24 report.

Who provides electric service in San Mateo County?

It depends on the address. In the San Mateo County places listed on this page, most addresses are served by Pacific Gas and Electric (PG&E). We confirm the serving utility for every project, because service upgrades and new meters are requested from the utility, separately from the building permit.

How much do ADU MEP plans cost in San Mateo County?

Our pricing is flat across California: single-discipline ADU plans start at $995, a full MEP package for an ADU up to 600 SF is $2,295, and a Title 24 report can be added for $240. Residential (single-family) full MEP packages start at $3,495. Standard turnaround is 5 business days, and corrections are included.

How long does ADU approval take in San Mateo County?

California law requires local agencies, counties included, to approve or deny a complete ADU permit application within 60 days. Incomplete or inconsistent drawings are the most common reason the clock restarts, which is why MEP plans that match the architectural set, and a Title 24 report that matches the MEP design, matter.