MEP Plans in Marin County, CA

Marin County project facts we design around

County seat	San Rafael
Population	256,400 (Census 2024 estimate)
Incorporated cities	11
Unincorporated residents	About 66,905 (26% of the county)
Permits in unincorporated areas	Marin County Community Development Agency – Building and Safety Division
Title 24 climate zones	CZ 2 (about 72% of residents), CZ 3 (about 28% 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 Marin County

Climate Zone 2: North Coast inland climate — warm dry summers, cool winters (about 72% of residents)

Summers are warm and dry while winters are cool and wet, so the heat pump has to cover both seasons well. Many projects here are rebuilds or additions on older lots, so confirming the existing service, panel and sewer before design avoids redesign later.

• Heat pump sized for both heating and cooling seasons
• Existing service and panel capacity confirmed before layout
• Ventilation and moisture control for wet winters

Climate Zone 3: mild Bay Area climate (about 28% of residents)

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 Marin 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 Marin 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.

Marin County cities and communities

Place	Climate zone	Electric utility
Belvedere	CZ 3	Pacific Gas and Electric (PG&E)
Bolinas (unincorporated)	CZ 3	Pacific Gas and Electric (PG&E)
Corte Madera	CZ 3	Pacific Gas and Electric (PG&E)
Fairfax	CZ 2	Pacific Gas and Electric (PG&E)
Kentfield (unincorporated)	CZ 2	Pacific Gas and Electric (PG&E)
Larkspur	CZ 2	Pacific Gas and Electric (PG&E)
Mill Valley	CZ 3	Pacific Gas and Electric (PG&E)
Novato	CZ 2	Pacific Gas and Electric (PG&E)
Ross	CZ 2	Pacific Gas and Electric (PG&E)
San Anselmo	CZ 2	Pacific Gas and Electric (PG&E)
San Rafael	CZ 2	Pacific Gas and Electric (PG&E)
Sausalito	CZ 3	Pacific Gas and Electric (PG&E)
Stinson Beach (unincorporated)	CZ 3	Pacific Gas and Electric (PG&E)
Tiburon	CZ 3	Pacific Gas and Electric (PG&E)

Shown for most addresses in each city. We also serve every unincorporated community in the county.

Marin County ADU MEP questions

Who issues building permits for an ADU in unincorporated Marin County?

In unincorporated areas, home to about 66,905 residents (26% of the county), ADU and residential permits go through Marin County Community Development Agency – Building and Safety Division. Inside the county's 11 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 Marin County?

Marin County spans 2 Title 24 climate zones: CZ 2 (about 72% of residents), CZ 3 (about 28% 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 Marin County?

It depends on the address. In the Marin 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 Marin 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 Marin 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.