--- title: "Room Addition Cost in Thousand Oaks (2026)" description: "Room addition in Thousand Oaks, CA: $335–$670 per sq ft in 2026. A mid-size job runs $123k–$247k. Free bids from vetted builders." url: https://keystoneconnect.us/cities/thousand-oaks/room-addition updated: 2026-10-27 --- Thousand Oaks, CA · Conejo Valley & East County # Room addition prices in Thousand Oaks, CA: 2026 ranges A room addition in Thousand Oaks costs $335–$670 per sq ft, with a typical mid-size room addition running $123k–$247k. Small projects start around **$56k**; large or high-end work can reach **$448k** or more. As of 2026, costs in Thousand Oaks run about 12% above the LA County baseline due to HOA standards, hillside lots, and wildfire-zone rules. Updated October 2026 Get matchedCost by size Cost per sq ft $335–$670 per sq ft ## Room Addition Cost by Size in Thousand Oaks Totals adjusted for the Thousand Oaks market (1.12× LA County baseline). Ranges include labor, materials, permits, and contractor overhead. Room Addition cost by size in Thousand Oaks, CA | Size | Type | Range | Low | High | | --- | --- | --- | --- | --- | | Small | Bump-out / single room | 150–250 sq ft | $56k | $123k | | Medium | Suite addition | 300–500 sq ft | $123k | $247k | | Large | Second story / multi-room | 600+ sq ft | $224k | $448k | ## What Affects Room Addition Cost in Thousand Oaks? - Foundation type. - Roofline integration. - MEP (mechanical/electrical/plumbing) extension. - Permits. - Soil condition. - Thousand Oaks market premium: local pricing reflects HOA standards, hillside lots, and wildfire-zone rules, which shifts totals about 12% above the LA County baseline. ## Get exact room addition bids in Thousand Oaks Two or three licensed builders who work in Thousand Oaks, pricing the same scope. Tell us about your project[or call (818) 482-8365](tel:+18184828365) ## Room 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 Thousand Oaks 1. Get line-itemized bids from two or three builders on the same scope; Thousand Oaks room addition pricing commonly varies 10–25% between contractors. 2. Lock major materials and finishes before signing; mid-project change orders are the #1 cost driver on room addition jobs. 3. Bid in shoulder seasons (Jan–Mar or Sep–Oct) when Thousand Oaks contractor schedules are open and rush premiums disappear. 4. 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. 1.Write down the scope: size, any layout changes, the finish level, and who supplies fixtures and materials. 2. 2.Get bids from two or three licensed builders who work in Thousand Oaks, all pricing that same room addition scope. 3. 3.Line the bids up item by item. Check allowances, permits, exclusions, and whether overhead and profit are shown. 4. 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](https://keystoneconnect.us/grade-my-bid) or read [how to compare quotes](https://keystoneconnect.us/pillars/how-to-read-compare-contractor-quotes). ## Questions about Room Addition in Thousand Oaks ### How much does a room addition cost in Thousand Oaks, CA? + A room addition in Thousand Oaks costs $56k–$448k, with a typical mid-size room addition running $123k–$247k. Per-unit pricing falls in the $335–$670 per sq ft range. ### Do I need a permit for a room addition in Thousand Oaks? + Yes for most scopes — the city building department requires permits any time you move plumbing, gas, electrical, or alter structure. Like-for-like cosmetic refreshes generally don't. ### How long does a room addition take in Thousand Oaks? + Plan for 4–14 weeks of construction in Thousand Oaks depending on size and complexity, plus 2–8 weeks for design, permits, and material lead times. ## Official sources - [Look up a contractor's license on the CSLB website](https://www.cslb.ca.gov/OnlineServices/CheckLicenseII/CheckLicense.aspx) - [California home improvement contract requirements (Business and Professions Code §7159)](https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=BPC§ionNum=7159) Need more answers? Visit our [contractor FAQ hub](https://keystoneconnect.us/faq). ## Get Matched with Licensed Thousand Oaks Contractors Tell us about your room addition and we'll line up two or three licensed builders who work in the area. Ventura County overview [See Room Addition costs across all Ventura County cities →](https://keystoneconnect.us/cost/ventura-county/room-addition) ## Related Thousand Oaks Projects [All projects← Back to Thousand Oaks](https://keystoneconnect.us/cities/thousand-oaks)[Thousand OaksKitchen Remodel Cost →](https://keystoneconnect.us/cities/thousand-oaks/kitchen-remodel)[Thousand OaksBathroom Remodel Cost →](https://keystoneconnect.us/cities/thousand-oaks/bathroom-remodel)[Thousand OaksADU Construction Cost →](https://keystoneconnect.us/cities/thousand-oaks/adu) ## Room Addition in Nearby Cities [Camarillo, CARoom Addition Cost in Camarillo →](https://keystoneconnect.us/cities/camarillo/room-addition)[Ventura, CARoom Addition Cost in Ventura →](https://keystoneconnect.us/cities/ventura/room-addition)[Simi Valley, CARoom Addition Cost in Simi Valley →](https://keystoneconnect.us/cities/simi-valley/room-addition)