Case Study: The 400 SF Garage Conversion

1. The property. A 6,000 SF lot in the San Fernando Valley: 1950s three-bedroom house up front, detached two-car garage at the rear corner, sitting 18 inches from the rear property line.

2. The goal. Rental income with the smallest possible budget. The owners, a couple in their 40s, wanted mortgage relief — not a construction adventure.

3. The constraints. The garage's location was actually its superpower — that 18-inch setback could never be replicated with new construction (lesson 2.2's conversion exception). The real constraints: a 1950s floating slab of unknown quality, a 100-amp main panel (7.3's classic), and the owners' hard budget ceiling.

4. Options considered. (a) Convert the garage as-is — cheapest if the slab cooperated. (b) Demolish and build a new 600 SF unit — bigger, but new-construction setbacks would pull it off the property line and the budget was nearly triple. (c) Do nothing and keep storing bikes. The pre-design structural assessment (11.3's cheap de-risking move — $450 here) found perimeter footings present but shallow — partial retrofit, not full replacement. That single finding made option (a) viable, and they took it.

5. The final design. A 400 SF open studio following 4.8's pattern: kitchen along the shared plumbing wall, bathroom stacked in the corner, sleeping alcove behind a partial wall, vaulted ceiling (the old garage's bones allowed it — 4.3's best-friend move), and two new egress-sized windows facing the yard, none facing the neighbors (8.5).

6. City issues. One planning-desk hiccup: an initial comment requesting a 4-foot rear setback — for a structure that had stood at 18 inches since 1954. A polite citation of the existing-structure conversion rules (10.7, rung 1) resolved it in a single phone call.

7. Permitting. Complete set submitted; one correction round, 14 items, mostly info requests (window specs, insulation values, panel load calc). Response in 8 days. Permit in 11 weeks total.

8. Construction. 14 weeks. The retrofit footings went in first (sectioned pours — 12.3's conversion variant). One genuine surprise: termite damage in two wall sections found at demolition — $4,200 change order, paid from a contingency that had been set at 18% on the structural engineer's advice (6.9 vindicated). The panel got a 200-amp upgrade; the unit went all-electric (7.6).

9. The final result. A bright, vaulted studio with a full kitchen, laundry closet, and private patio where the driveway apron used to end. Rented in 9 days.

10. Cost range. $118,000–$128,000 all-in including soft costs, the panel upgrade, and the termite surprise — the middle of 6.3's licensed-GC band.

11. Timeline. Assessment to keys: about 8 months (5 weeks design, 11 weeks permit, 14 weeks construction, plus gaps).

12. Lessons learned. The $450 structural assessment was the highest-leverage dollar in the project — it turned the scariest unknown into a scoped line item. The 18-inch setback the owners considered a defect was the single most valuable feature of the property. And an 18% contingency on a 70-year-old building isn't pessimism; it's arithmetic.