| Type | Cost | Advantage | Notes |
|---|---|---|---|
| Garage conversion | $50K-$150K | Cheapest option | Uses existing structure |
| Detached new build | $150K-$300K+ | Most flexibility | Highest cost and value |
| Prefab/modular | $80K-$200K | Faster build | Growing in popularity |
| Addition | $100K-$250K | Attached to house | Good for in-law suites |
Compare ADU builders in your area Negotiating is always worth trying — most service providers have some flexibility in pricing, especially for larger projects or repeat customers. Professional associations and licensing boards maintain directories of vetted providers — check these resources before hiring. Ask about package deals and bundled pricing — many providers offer 10-15% discounts when you combine multiple services.
The cost of adu depends on several interconnected factors that can shift the final number significantly in either direction. Material quality is typically the largest variable — the gap between standard and premium options can double or triple the total project cost. Labor rates vary by region, with major metros running 30–50% higher than rural areas for identical work.
Project scope is the other major cost driver. What seems like a simple project can escalate quickly once walls are opened or existing conditions are revealed. This is why experienced contractors build contingency into their estimates, and why homeowners should too. The most common budget-breaker is changing the scope mid-project, which resets timelines and pricing.