Module 14 · Lesson 4
Does an ADU Increase Property Value?
ADUs typically add substantial value — often near or above their cost in strong markets. How appraisers see them and what happens to your property taxes.
The quiet half of ADU economics: whatever the rent does, what did the asset do? Short answer: in strong California markets, a permitted ADU typically adds value near — often above — its construction cost. Longer answer, with the mechanics:
How appraisers actually value your ADU — two approaches: the sales comparison approach finds comps: recent nearby sales with ADUs versus without (increasingly available as ADUs proliferate — every conversion on your block is future evidence for your appraisal). The income approach capitalizes the rent: your documented $2,300/month is an income stream a valuer (and an investor-buyer) can price. Homes with legal income units increasingly sell to a wider buyer pool — families wanting the multigenerational setup (Module 1.4's buyers) plus house-hackers pricing the offset — and wider demand is what holds value up.
The word carrying all the weight: permitted. Appraisers count documented, legal square footage; lenders lend against it; buyers' inspectors verify it. The unpermitted unit from 13.1 appraises at somewhere between zero and negative (a flagged liability). The certificate from 12.12, the stamped plans, the forever-file — that folder is the value. This entire course has been, among other things, an appraisal-defense manual.
Property taxes — the fear, defused: California reassessment on new construction adds only the ADU's assessed value — your house keeps its Prop 13 base. A $300K build adds very roughly $3,000–$3,750/year (~1.0–1.25% of added assessed value, varying by county and district). Against $21K+ of net rent, it's a real cost, not a reason to hesitate — and 14.2's waterfall should include it. (Notice the asymmetry working for you: taxed on cost-ish basis, valued at market.)
When value-add disappoints — honest cases: over-improved for the neighborhood (a $400K showpiece behind a $500K house strains comps — Module 4.7's discipline was also a resale lesson), markets where lot-size norms make backyard density unusual, and yard-consumed properties where the main house's appeal suffered (4.7 again). The remedy was always the same: build the right-sized, well-designed unit for your street — which the whole course has been teaching.
Key takeaways
- Permitted ADUs typically add value near or above cost in strong markets — via comps and capitalized income.
- "Permitted" is the load-bearing word: the certificate and document file are the value's proof.
- Taxes rise only on the ADU's added assessment (~1.0–1.25% of it yearly); the house keeps its Prop 13 base.
- Value disappoints mainly through over-improvement — right-sizing was always also a resale strategy.