MEP Plans in Castro Valley, CA

Castro Valley project facts we design around

County	Alameda County (unincorporated)
Title 24 climate zone	Climate Zone 3, confirmed by ZIP for every project
Electric utility (most addresses)	Pacific Gas and Electric (PG&E)
Permits issued by	Alameda County Public Works Agency – Building Inspection Division
ADU permits issued, 2021–2025	263
ADU approval timeline	Approve or deny within 60 days of a complete application (state law)

ADU building activity in Castro Valley

Alameda County issued 263 ADU building permits from 2021 through 2025 for addresses in Castro Valley, based on the county's reports to the state. Permits went from 2 in 2021 to 89 in 2025.

2021	2022	2023	2024	2025
2	34	80	58	89

Source: California Department of Housing and Community Development, Annual Progress Report data (ADU building permits by year).

Title 24 in Climate Zone 3

• Windows: U-factor 0.27 or lower (no SHGC limit in this zone), with total window area up to 20% of floor area.
• Solar PV sized by the CEC formula kW = (floor area x 0.628) / 1000 + 1.12; no PV is required if that is under 1.8 kWdc, which for a single ADU works out to about 1,083 sq ft or smaller.

Climate Zone 3 requirements in full →

HVAC design for Castro Valley

The California Energy Commission's design-day data for Castro Valley gives the outdoor conditions a Manual J load calculation uses: a summer design temperature of 85°F and a winter design temperature of 24°F.

Summer design (1%)	85°F dry bulb / 67°F wet bulb
Winter design (median of extremes)	24°F
Daily temperature range	25°F
Elevation	177 ft

Both seasons matter here. The heat pump is usually sized for the 85°F cooling condition and then checked to confirm it still covers the heating load at 24°F.

Electrical service from Pacific Gas and Electric (PG&E)

If the load calculation shows you need a service upgrade, a second meter or a relocated service, Pacific Gas and Electric (PG&E) handles that through its Your Projects portal, separately from the building permit.

ADU electrical service with Pacific Gas and Electric (PG&E) →

Plumbing and sewer

The plumbing plan shows the route, slope and cleanouts of the connection to the existing sewer lateral or septic system. Some Bay Area cities also have private sewer lateral inspection rules, so ask whether your project triggers one.

Pricing is flat statewide: ADU plans from $995, full ADU MEP package from $2,295, Title 24 add-on $240. See what's in a complete ADU MEP set.