MEP Plans in El Cajon, CA

El Cajon project facts we design around

County	San Diego County
Title 24 climate zone	Climate Zone 10, confirmed by ZIP for every project
Electric utility (most addresses)	San Diego Gas & Electric (SDG&E)
Permit review	The City of El Cajon building department
ADU permits issued, 2021–2025	311 (#92 of 450 cities)
ADU approval timeline	Approve or deny within 60 days of a complete application (state law)

ADU building activity in El Cajon

El Cajon issued 311 ADU building permits from 2021 through 2025, the 92nd most among the 450 California cities that reported ADU permits. Permits went from 32 in 2021 to 86 in 2025.

2021	2022	2023	2024	2025
32	50	68	75	86

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

Title 24 in Climate Zone 10

• Windows: U-factor 0.30 or lower and solar heat gain coefficient (SHGC) 0.23 or lower, with total window area up to 20% of floor area (west-facing up to 5%).
• Whole-house fan required (at least 1.5 cfm per square foot of floor area); units of 500 sq ft or less are exempt.
• Cool roof required: steep-sloped roofs need aged solar reflectance 0.2 or higher and thermal emittance 0.75 or higher.
• Solar PV sized by the CEC formula kW = (floor area x 0.627) / 1000 + 1.41; no PV is required if that is under 1.8 kWdc, which for a single ADU works out to about 622 sq ft or smaller.

Climate Zone 10 requirements in full →

HVAC design for El Cajon

The California Energy Commission's design-day data for El Cajon gives the outdoor conditions a Manual J load calculation uses: a summer design temperature of 90°F and a winter design temperature of 29°F.

Summer design (1%)	90°F dry bulb / 69°F wet bulb
Winter design (median of extremes)	29°F
Daily temperature range	30°F
Elevation	525 ft

Both seasons matter here. The heat pump is usually sized for the 90°F cooling condition and then checked to confirm it still covers the heating load at 29°F.

Electrical service from San Diego Gas & Electric (SDG&E)

If the load calculation shows you need a service upgrade, a second meter or a relocated service, San Diego Gas & Electric (SDG&E) handles that through its My Project Center portal, separately from the building permit.

ADU electrical service with San Diego Gas & Electric (SDG&E) →

Plumbing and sewer

The plumbing plan shows the route, slope and cleanouts of the connection to the existing sewer lateral.

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.