Prefab vs stick-built
Prefab vs stick-built ADU: the price gap closes after site work.
Prefab ADUs are advertised at lower per-square-foot prices and faster delivery timelines. Both are real — but only on the unit itself. Once site preparation, foundation, utility connections, and finish completion get added, the all-in cost typically lands close to a stick-built ADU. The honest comparison is total project cost, not the price tag on the factory module.
Option
Prefab / modular ADU
Built in a factory, delivered to site
Typical cost
Unit $80K–$300K; all-in $200K–$450K (LADU + BuildX 2026)
Option
Stick-built ADU
Built on site from the foundation up
Typical cost
$200K–$400K+ all-in CA (DQB 2026)
Side-by-side comparison
| Attribute | Prefab / modular ADU | Stick-built ADU |
|---|---|---|
| Unit price (per sq ft) | $150–$300/sf (LADU 2026) | $250–$400+/sf (CA, DQB 2026) |
| All-in price after site costs | $200K–$450K typical — site prep + foundation + utilities + permits + finishes pull cost up by $130K–$250K above advertised unit price (BuildX 2026) | $200K–$400K+ in California — site costs already included in the bid |
| Timeline | 2–6 months order-to-final (LADU 2026); parallel factory build + site work | 6–10 months construction; 10–18 months total project |
| Customization | Configurable models; layout and most finishes from a menu | Full custom — designed to your lot, your aesthetic, your lifestyle |
| Site work flexibility | Limited — needs flat, accessible delivery path, crane staging, often street permits | Works on sloped, narrow, and tight-access lots that prefab can't reach |
| Quality control | Factory production = repeatable processes, tight tolerances, fewer change orders | Variable — depends entirely on the builder's QA and your supervision |
| Payment structure | Usually requires full unit payment before placement (BuildX 2026) | Pay in draws tied to construction milestones — better cash protection |
Pick Prefab / modular ADU when
- Your lot is flat, accessible, and crane-friendly.
- You want a defined timeline more than full design flexibility.
- You can fund the lump-sum unit payment without straining cash flow.
- Existing utilities, septic, and electrical panel can support a new dwelling without major upgrades.
Pick Stick-built ADU when
- Your lot has slope, narrow access, hillside conditions, or major utility upgrades needed.
- You want full design control — heritage trees, specific privacy considerations, an exact layout that matches your main home.
- You'd prefer to pay in stages as construction progresses.
- You're in a market where local builders quote competitively against prefab.
Want to run the math on your project?
Open the cost calculator with your inputs, or get matched with builders who can scope your specific lot.
FAQ
- How much cheaper is prefab than stick-built?
- 10–20% cheaper on the per-square-foot price of the unit itself (LADU 2026). All-in (including site work, foundation, utilities, finishes, and permits) the numbers usually converge. BuildX (2026) documents real cases where a $150K advertised prefab unit became a $350K–$450K all-in project — identical to a same-size stick-built ADU.
- Is prefab faster than stick-built?
- Usually yes for the construction phase. Factory build runs in parallel with on-site foundation and utility work, so the overall calendar compresses by several months. LADU (2026) reports 2–6 months order-to-final for LA prefab projects versus 6–10 months construction for stick-built.
- What questions should I ask any prefab quote?
- Confirm in writing: unit spec and finishes; foundation cost; delivery and crane plan with route survey; utility connection allowances; permit handling; interior finish completion (or shell-only); payment terms. If any answer is vague, treat the quote as incomplete — that's how the gap between advertised and real price opens up.
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