MEP Plans in Solano County, CA

Solano County project facts we design around

County seat	Fairfield
Population	455,101 (Census 2024 estimate)
Incorporated cities	7
Unincorporated residents	About 18,351 (4% of the county)
Permits in unincorporated areas	Solano County Department of Resource Management – Building & Safety Services
Title 24 climate zones	CZ 12 (about 84% of residents), CZ 3 (about 16% 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 Solano County

Climate Zone 12: Central Valley-style climate — hot summers, cool winters (about 84% of residents)

This is a two-sided load: long stretches above 100°F in summer and cold, foggy winter mornings. The heat pump is usually sized for cooling, then checked to make sure it still carries the heating load at the local winter design temperature. High summer peaks also mean the AC is often the single biggest electrical load, which is what pushes many ADUs into a panel or service upgrade.

• Heat pump sized for cooling and verified for winter heating
• Panel / subpanel sizing that accounts for a large cooling load
• Title 24 envelope and HVAC assumptions that hold up in a demanding zone

Climate Zone 3: mild Bay Area climate (about 16% 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 Solano 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 Solano 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.

Solano County cities

Place	Climate zone	Electric utility
Benicia	CZ 12	Pacific Gas and Electric (PG&E)
Dixon	CZ 12	Pacific Gas and Electric (PG&E)
Fairfield	CZ 12	Pacific Gas and Electric (PG&E)
Suisun City	CZ 12	Pacific Gas and Electric (PG&E)
Vacaville	CZ 12	Pacific Gas and Electric (PG&E)
Vallejo	CZ 3, 12	Pacific Gas and Electric (PG&E)

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

Solano County ADU MEP questions

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

In unincorporated areas, home to about 18,351 residents (4% of the county), ADU and residential permits go through Solano County Department of Resource Management – Building & Safety Services. Inside the county's 7 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 Solano County?

Solano County spans 2 Title 24 climate zones: CZ 12 (about 84% of residents), CZ 3 (about 16% 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 Solano County?

It depends on the address. In the Solano 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 Solano 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 Solano 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.