What appraisers actually look for
Permits and final inspection. This is the biggest single factor, and the one homeowners most often get wrong. An unpermitted garage conversion may look like a beautiful 400-square-foot studio, but if there's no permit on file and no final sign-off, most appraisers won't count the square footage at all. They might add a small lump-sum adjustment for "additional living space," but it's nothing like a permitted unit's contribution. The difference between a permitted ADU and an identical unpermitted one is often $100,000+ in appraised value on the same property.
Whether it's detached or attached. Detached ADUs — separate backyard structures — tend to appraise stronger than attached conversions because they're closer to functioning as fully independent units. A buyer can rent the detached unit, house an aging parent, or use it as a private home office without the unit feeling like part of the main house.
Quality of finishes and systems. A 600-square-foot ADU with its own HVAC, full kitchen, in-unit laundry, and proper sound separation appraises very differently than a converted garage with a hot plate and a window AC unit. Appraisers are looking at whether the unit functions as actual housing.
The variance in actual value-add
Looking at LA-area resale data over the last few years, the value contribution of an ADU at sale typically falls somewhere in this range:
- Unpermitted conversion: 0–10% of property value added (often functionally zero in appraisal)
- Permitted attached conversion: 10–20% of property value added
- Permitted detached ADU, good quality: 20–35% of property value added
The 20–35% number is what gets quoted in headlines. The 0–10% is what catches homeowners who skipped the permitting step. Both are real, depending on what you actually built.
What this means for owners thinking about building one
If you're considering building an ADU primarily as a resale play, the math only works when you treat permits, quality, and detached construction as non-negotiable. The pandemic-era wave of fast garage conversions, often unpermitted, is the cohort most likely to be disappointed at sale.
If you're building one for rental income or family flexibility — and resale value is a bonus — the math is much easier. The income covers itself, and the value-add at sale is upside.
What this means for buyers
Ask for the permit and final inspection on any property listed with an ADU. If the seller can't produce them, that "1,200 sq ft + 400 sq ft ADU" listing might appraise as a 1,200 sq ft house plus some unpermitted bonus space. Lenders treat these very differently, and your offer should reflect that.
ADUs are real value creators in LA — but only the well-built, well-documented ones. The rest are mostly just nicer-looking square footage that doesn't show up on the appraisal.
