Quick Answer: Adding a full second story to a single-story San Jose home costs $350,000-$700,000+ in 2025, depending on the footprint size, structural requirements, and finish level. The high cost reflects: (1) Structural engineering — the existing foundation and first-floor framing must be assessed and potentially upgraded to support the new load; (2) Roof removal and rebuild — the existing roof comes off and a new roof goes on at the second-story level; (3) First-floor disruption — structural posts and beams may need to be added to the first floor to carry the second floor load; (4) Staircase addition — a staircase takes 60-80 sq ft of first-floor space and costs $8,000-$25,000; (5) Mechanical routing — HVAC ducts, electrical, and plumbing must be extended to the second floor. The payoff: a full second story can add 800-1,500+ sq ft and $400,000-$700,000+ in home value in San Jose’s market.
Second Story Addition Cost Breakdown — San Jose 2025
| Cost Category | Cost Range |
|---|---|
| Structural engineering (foundation + framing assessment) | $5,000 – $15,000 |
| Foundation reinforcement (if needed) | $0 – $40,000 |
| First-floor structural work (posts, beams) | $8,000 – $25,000 |
| Second-floor framing (per sq ft) | $40 – $65 / sq ft |
| Roof removal and new roof | $30,000 – $80,000 |
| Exterior finish (siding, stucco match) | $20,000 – $60,000 |
| Staircase | $8,000 – $25,000 |
| Interior finish (drywall, flooring, paint) | $25,000 – $70,000 |
| Bathrooms (2 on second floor) | $60,000 – $140,000 |
| HVAC, electrical, plumbing extension | $25,000 – $60,000 |
| Permit fees (San Jose) | $8,000 – $25,000 |
| Total (800-1,200 sq ft 2nd floor) | $350,000 – $700,000+ |
Quartz Construction designs and builds second story additions throughout San Jose. We coordinate all structural engineering, pull permits, and complete the full project from design to move-in. Learn about room addition services. CSLB #1003436 | Call (650) 749-7436.
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