Room Addition Cost in Fontana, CA (2026)
A room addition in Fontana costs $250–$500 per sq ft, with a typical mid-size room addition running $92k–$183k. Small projects start around $42k; large or high-end work can reach $332k or more.
Costs in Fontana run about 17% below the LA County baseline thanks to Inland Empire labor rates and newer suburban housing.
Room Addition Cost by Size in Fontana
Totals adjusted for the Fontana market (0.83× LA County baseline). Ranges include labor, materials, permits, and contractor overhead.
| Size | Type | Range | Low | High |
|---|---|---|---|---|
| Small | Bump-out / single room | 150–250 sq ft | $42k | $92k |
| Medium | Suite addition | 300–500 sq ft | $92k | $183k |
| Large | Second story / multi-room | 600+ sq ft | $166k | $332k |
What Affects Room Addition Cost in Fontana?
- Foundation type.
- Roofline integration.
- MEP (mechanical/electrical/plumbing) extension.
- Permits.
- Soil condition.
- Fontana market premium: local pricing reflects Inland Empire labor rates and newer suburban housing, which shifts totals about 17% below the LA County baseline.
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Get MatchedRoom Addition Sub-Type Comparisons
Bedroom Addition vs Master Suite Addition
A standard bedroom addition runs $50k–$110k; a master suite (bedroom + bath + walk-in closet) doubles the plumbing scope and lands at $110k–$220k.
Second Story Addition vs Sunroom Addition
Second-story additions require foundation reinforcement and full re-roof at $200k–$400k; sunrooms (prefab or stick-built) skip much of the structural work at $30k–$90k.
How to Get the Best Price on a Room Addition in Fontana
- Get 3 line-itemized bids on the same scope through Keystone Connect — Fontana room addition pricing varies 10–25% between contractors.
- Lock major materials and finishes before signing; mid-project change orders are the #1 cost driver on room addition jobs.
- Bid in shoulder seasons (Jan–Mar or Sep–Oct) when Fontana contractor schedules are open and rush premiums disappear.
- Verify CSLB license, insurance, and bond before paying any deposit. California caps deposits at $1,000 or 10% of contract, whichever is less.
Frequently Asked Questions — Room Addition in Fontana
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