Short answer. A bonus room over a garage in Los Angeles runs $350 to $550 per sq ft. A 400 sq ft bonus room runs $140,000 to $220,000. The garage foundation and walls already exist, which saves cost compared to a standalone addition. Structural reinforcement is the largest variable.
2026 pricing by size and finish
| Size and use | Per sq ft | Total cost |
|---|---|---|
| 300 sq ft basic bonus room | $350 to $450 | $105,000 to $135,000 |
| 400 sq ft bonus room | $350 to $500 | $140,000 to $200,000 |
| 500 sq ft suite with full bath | $450 to $600 | $225,000 to $300,000 |
| 600 sq ft bedroom and bath | $450 to $650 | $270,000 to $390,000 |
What is included
- Structural engineer review of existing garage.
- Foundation reinforcement if needed.
- Wall frame reinforcement.
- New floor system over the garage ceiling.
- Stairs (interior or exterior).
- Roof modification or new roof framing.
- Windows and exterior finish to match the home.
- Full HVAC tie-in (or dedicated mini-split).
- Electrical sub-panel if needed.
- Insulation per Title 24.
- Drywall, flooring, paint, and trim.
- Bathroom rough and finish if included.
Bonus room ideas
- Home office or studio (most common).
- Teen or guest bedroom.
- Media or game room.
- Master suite expansion (when accessible from the main house second story).
- Home gym (consider extra floor reinforcement for heavy equipment).
Permitting and zoning
- Height restrictions vary by zoning. Most R1 lots allow 28 to 30 feet to the ridge.
- Front and side setbacks apply to second-story additions.
- Floor area ratio (FAR) limits total habitable sq ft on the lot.
- HPOZ overlays require historic compatibility review.
- Hillside lots have steeper review and grading requirements.
For full second-story comparison, read second story addition cost. For ground-level additions, see home addition cost Los Angeles. For services, see our second story page.
