Garage Conversion to Permitted ADU — El Cajon

Why this matters in El Cajon

Garage-to-ADU conversions are one of the most cost-effective ways to add a permitted rental unit in San Diego County, but they come with structural surprises that detached new builds don't have. Existing slabs are often undersized for a residential live load. Original wall framing may not be insulated and may not meet current shear-wall requirements. Single 15- or 20-amp circuits cannot support a modern living unit. A conversion that ignores these issues will fail plan check or worse — pass plan check and fail final inspection. Done correctly, conversions can come in 25–40% under the cost of a comparable detached ADU because the existing slab and roof structure are reused.

Materials & Specifications

Specific brands, products, and engineering specs used on this project. We document materials so the homeowner has a complete record for warranty claims and future maintenance.

Foundation

Existing slab reused after engineering review; new underpinning at perimeter where existing footings were undersized

Framing

Interior partition framing, new shear walls per Title 24, replaced garage door opening with framed wall

Insulation

R-15 wall batts, R-30 ceiling batts

HVAC

Single-zone ductless mini-split, 1-ton, 18 SEER

Plumbing

Tied into existing main, new 3/4" copper supply, ABS DWV, on-demand electric water heater

Electrical

60A subpanel from main, all LED, hard-wired smoke + CO detectors

Finishes

LVP flooring, drywall, paint, full tile shower, quartz kitchenette counter