Room Addition Cost in Downey, CA (2026)
A room addition in Downey costs $275–$550 per sq ft, with a typical mid-size room addition running $101k–$203k. Small projects start around $46k; large or high-end work can reach $368k or more.
Costs in Downey run about 8% below the LA County baseline thanks to stable Southeast LA labor pool and predictable permit timelines.
Room Addition Cost by Size in Downey
Totals adjusted for the Downey market (0.92× 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 | $46k | $101k |
| Medium | Suite addition | 300–500 sq ft | $101k | $203k |
| Large | Second story / multi-room | 600+ sq ft | $184k | $368k |
What Affects Room Addition Cost in Downey?
- Foundation type.
- Roofline integration.
- MEP (mechanical/electrical/plumbing) extension.
- Permits.
- Soil condition.
- Downey market premium: local pricing reflects stable Southeast LA labor pool and predictable permit timelines, which shifts totals about 8% 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 Downey
- Get 3 line-itemized bids on the same scope through Keystone Connect — Downey 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 Downey 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 Downey
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