Ventura County · cost guide
Room addition prices in Ventura County: 2026 ranges
A room addition in Ventura County costs $315–$630 per sq ft, with a typical mid-size room addition running $116k–$231k at the county average. Small projects start around $53k; large or high-end work can reach $420k or more.
As of 2026, Ventura County runs about 5% above the LA County baseline due to Coastal Commission review west of the 101, Conejo Valley HOA standards, and wildfire-zone building rules.
Updated
Room Addition Cost by Size — Ventura County Average
County-average ranges (1.05× LA County baseline). Individual cities vary — see the table below.
| Size | Type | Range | Low | High |
|---|---|---|---|---|
| Small | Bump-out / single room | 150–250 sq ft | $53k | $116k |
| Medium | Suite addition | 300–500 sq ft | $116k | $231k |
| Large | Second story / multi-room | 600+ sq ft | $210k | $420k |
Room Addition Cost by City in Ventura County
Every city in Ventura County, sorted alphabetically. Totals reflect each city's local cost multiplier. Cities in color have full project-specific pages.
| City | Small | Medium | Large |
|---|---|---|---|
| Camarillo | $52k–$114k | $114k–$227k | $206k–$412k |
| Fillmore | $45k–$99k | $99k–$198k | $180k–$360k |
| Moorpark | $51k–$112k | $112k–$225k | $204k–$408k |
| Ojai | $55k–$121k | $121k–$242k | $220k–$440k |
| Oxnard | $48k–$105k | $105k–$209k | $190k–$380k |
| Port Hueneme | $47k–$103k | $103k–$205k | $186k–$372k |
| Santa Paula | $45k–$99k | $99k–$198k | $180k–$360k |
| Simi Valley | $50k–$110k | $110k–$220k | $200k–$400k |
| Thousand Oaks | $56k–$123k | $123k–$247k | $224k–$448k |
| Ventura | $51k–$112k | $112k–$225k | $204k–$408k |
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What Affects Room Addition Cost in Ventura County?
- Foundation type.
- Roofline integration.
- MEP (mechanical/electrical/plumbing) extension.
- Permits.
- Soil condition.
- Ventura County market dynamics: Coastal Commission review west of the 101, Conejo Valley HOA standards, and wildfire-zone building rules, which shifts room addition totals about 5% above the LA County baseline.
- City variation within Ventura County: coastal and hillside cities can run 15–30% above the county mid-point, while inland labor markets price 10–20% below.
Room Addition Sub-Type Comparisons
Bedroom Addition vs Master Suite Addition
A standard bedroom addition is the lowest scope; a master suite (bedroom + bath + walk-in closet) roughly doubles the plumbing scope and total.
Second Story Addition vs Sunroom Addition
Second-story additions require foundation reinforcement and full re-roof; sunrooms (prefab or stick-built) skip much of the structural work.
How to Get the Best Price on a Room Addition in Ventura County
- Get line-itemized bids from two or three builders on the same scope; Ventura County room addition pricing commonly varies 10–25% between contractors.
- Compare bids from contractors based in multiple Ventura County cities; inland-based crews servicing coastal jobs often beat coastal-based pricing.
- Bid in shoulder seasons (Jan–Mar or Sep–Oct) when Ventura County 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.
What is a room addition?
A room addition adds conditioned square footage to a house: a bedroom, a primary suite, a family room or a second story. It needs foundation or framing work, a roof tie-in, and extended electrical, plumbing and HVAC.
How to get an accurate price
- 1.Write down the scope: size, any layout changes, the finish level, and who supplies fixtures and materials.
- 2.Get bids from two or three licensed builders who work in Ventura County, all pricing that same room addition scope.
- 3.Line the bids up item by item. Check allowances, permits, exclusions, and whether overhead and profit are shown.
- 4.Before any deposit, check each builder's CSLB license and insurance. As of 2026, California caps a home improvement down payment at $1,000 or 10% of the contract, whichever is less, according to the Contractors State License Board.
Already have a bid? Grade it in two minutes or read how to compare quotes.
Questions about Room Addition in Ventura County
How much does a room addition cost in Ventura County?
A room addition in Ventura County costs $53k–$420k, with a typical mid-size room addition running $116k–$231k at the county average.
Where is room addition cheapest in Ventura County?
Within Ventura County, inland and value-tier cities price room addition jobs 10–25% below the county average, while coastal and luxury-tier cities can run 20–35% above. See the city-by-city table below for exact totals.
Do I need a permit for a room addition in Ventura County?
Yes for most scopes — the city building department (Ventura, Oxnard, Thousand Oaks, etc.) or Ventura County Building & Safety for unincorporated parcels requires permits any time you move plumbing, gas, electrical, or change structure. Like-for-like cosmetic refreshes generally don't.
Keep exploring
Compare room addition costs across Ventura County, or browse other projects and guides.
More Ventura County cost guides
Room Addition by city
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