San Francisco · Cost matrix
Tiny Home Cost Matrix: DIY THOW vs Turn-Key vs Foundation ADU
Buyers under-estimate soft costs. This matrix compares three common paths — DIY tiny home on wheels, turn-key THOW, and permanent-foundation ADU — and surfaces hidden line items that dominate Bay Area budgets: crane rentals, utility trenching, municipal permits, delivery, and contingency.
Last reviewed 2026-08-20
Authored by the doihave.space Regulations Expert. Pre-written cited briefing — not generative AI legal advice. Role: Regulations briefing agent.
Build paths compared
DIY THOW
Owner-built or shell build on a trailer chassis. Lowest sticker price; highest schedule and compliance risk.
Turn-key THOW
Factory or builder-finished wheeled unit. Higher unit cost; still needs a lawful placement path in SF.
Foundation ADU
Permanent accessory dwelling on an approved foundation — the primary SF residential path under State ADU Law.
Line-item cost matrixCrane, trenching, permits, and path-specific totals
| Line item | DIY THOW | Turn-key THOW | Foundation ADU |
|---|---|---|---|
| Base unit / shellFinish level, size, and labor market drive the spread. ADU figures are SF-typical soft+hard ranges, not bids. | $25,000–$80,000 | $80,000–$200,000+ | $150,000–$450,000+ |
| Trailer / chassis | $5,000–$15,000 | Often included | N/A |
| Foundation / pier / padPermanent residential ADUs need an approved foundation system; wheeled pads are not a substitute for that path. | $0–$8,000 (if temporary pad) | $0–$12,000 (if temporary pad) | $15,000–$60,000+ |
| Delivery / tow / escort | $500–$3,000 | $1,500–$8,000+ | $2,000–$15,000 (modular delivery) |
| Crane / lift (tight SF lots)Narrow lots, overhead wires, and rear-yard access often force a crane day even for “small” units. | $1,500–$6,000+ | $1,500–$8,000+ | $2,500–$12,000+ |
| Utility trenching (water / sewer / electric)Distance to laterals, rocky soils, and street opening fees push the upper end. Budget $1,000–$5,000+ before surprises. | $1,000–$5,000+ | $1,000–$5,000+ | $1,000–$5,000+ |
| Municipal permit & plan-check feesSF Planning / DBI fees vary by valuation and scope. Confirm current fee schedules — this tool does not scrape live fee APIs. | $500–$5,000+ (path-dependent) | $500–$5,000+ (path-dependent) | $5,000–$25,000+ |
| Contingency (recommended) | 15–25% of hard costs | 10–20% of hard costs | 10–20% of hard costs |