Home Additions & ADU in Agoura Hills - One Fixed Price, Permits Handled

Fast, Reliable Home Additions & ADU Across Agoura Hills

Home additions and ADU construction in Agoura Hills typically run $45,000-$130,000 for a room addition and $90,000-$220,000 for a new detached ADU, with garage conversions landing between $30,000-$80,000. Those numbers come with a caveat nobody tells you until you’re standing in the plan-check line at the LA County building office: Agoura Hills sits in a Very High Fire Hazard Severity Zone. That means Chapter 7A fire-hardening standards shape nearly every exterior wall, vent, and window choice on your project. Barrett & Sons Construction has been working through those requirements for our Roofing in Agoura Hills and other projects since 1998. Tom Barrett grew up running crews through the Santa Monica Mountains foothills, and his sons are on-site most days. Call (877) 610-1318 and we’ll walk your property before you spend a dime.

Call (877) 610-1318

Why Barrett & Sons Construction Is Agoura Hills’s Preferred Home Additions & ADU Company

Tom Barrett publishes his name, his address, and his license number. Look them up before you sign anything. That’s not a marketing line; it’s how we’ve done business in Agoura Hills for over 29 years. When a homeowner on Driver Avenue or up in Morrison Ranch calls about a hillside addition, they get Tom or one of his sons on the phone, not an out-of-state call center.

Our Agoura Hills customers keep coming back because of the 90-Day Done Right Promise written into every contract. If something isn’t done right, one call brings Tom back. No arguing, no fine print. We’ve rebuilt enough Woolsey Fire-damaged homes in the 91301 and 91376 zip codes to know what LA County plan reviewers will flag before we submit, which saves you weeks.

Dispatch and scheduling are coordinated from our Los Angeles office, but crews serving Agoura Hills live in and near the community. We are not a franchise sending strangers to your door. Background-checked, uniformed crew members carry the Barrett & Sons name, and price changes arrive as written change orders before any work moves forward.

Our Home Additions & ADU Services in Agoura Hills

ADU Design & Permitting

Getting an ADU permitted in Agoura Hills isn’t a formality. Hillside lots with expansive clay soils routinely trigger mandatory geotechnical reports, even for a modest detached unit. We handle the full design and permitting path: drafting, soils coordination, Chapter 7A compliance for ember-resistant vents and ignition-resistant cladding, and plan-check submittal to LA County. The permit inspector works for you, not for me. That’s why we like him there.

Garage Conversion ADU

Converting an existing garage is the most cost-effective ADU route in Agoura Hills, typically $30,000-$80,000 depending on whether the slab needs structural reinforcement or the existing roofline can stay. Many 1970s-era homes near Chumash Park and the Agoura Hills Recreation Center have attached garages that convert cleanly. Older canyon-edge builds sometimes need lateral bracing upgrades before drywall goes up.

New Detached ADU

For homeowners with room on their lot, a new detached ADU runs $90,000-$220,000 in Agoura Hills. The spread comes down to foundation type, utility trenching distance, and fire-hardening material upgrades. On canyon lots near Liberty Canyon or the Las Virgenes Valley floor, caisson footings are common where natural grades exceed what a standard slab can handle. We build to current code, not the code that was fine in 1985.

Junior ADU & Interior Conversion

A junior ADU carved from an existing bedroom or bonus space with a kitchenette and separate entrance often falls at the lower end of the $45,000-$130,000 range. This works well in the ranch-style homes off Kanan Road where floor plans have spare square footage that can become a legal second unit without foundation work. Interior conversions still need California Building Code sign-off on egress windows, fire separation, and ventilation, and we pull every permit.

As part of our Home Additions & ADU work, we coordinate the full permit path. If your Agoura Hills project overlaps with interior work, we also handle Kitchen Remodeling in Agoura Hills and Bathroom Remodeling in Agoura Hills under the same crew and same written-change-order rules. One contract, one crew, one name on the truck.

Trusted Brands We Service in Agoura Hills

We install windows and doors in Agoura Hills meant for wildfire country. Simonton and PGT windows are common choices on Agoura Hills additions because they meet multi-pane glazing and impact requirements Chapter 7A demands in high hazard zones. When homeowners along Thousand Oaks Boulevard or near Old Agoura want a coastal-style casement with real storm performance, we usually quote Ply Gem or PGT lines. We keep parts and sample stock accessible to our Agoura Hills customers, so ordering windows for a second-story addition doesn’t add weeks to the timeline. Every allowance for brands, finishes, and upgrade packages goes in writing before you sign.

Common Home Additions & ADU Problems We See in Agoura Hills Homes

• Wind-tunnel roofing and envelope issues. Agoura Hills sits between the Santa Monica Mountains and the Simi Hills. Santa Ana winds get amplified through that gap, and roof-to-wall connections on additions need uplift consideration that flat-valley projects skip. We fasten and frame for wind loads that regularly exceed what San Fernando Valley builds require.
• Chapter 7A plan-check failures. Contractors unfamiliar with VHFHSZ rules submit plans with standard attic vents and vinyl soffits. LA County rejects them. Every Agoura Hills addition we design already includes ember-resistant vents, ignition-resistant cladding options, and Class A roofing.
• Expansive clay soil surprises. The Las Virgenes Valley portion of Agoura Hills runs on clay that swells when wet. A simple room addition can trigger a soils report and deepened footings. If the contractor doesn’t tell you this before you sign, the price jump arrives later as an ugly surprise.
• Post-Woolsey two-tier housing stock. Some Agoura Hills homes are brand new fire-resistant construction. Others are 1980s originals that never got retrofitted. When we add onto an older home, we often recommend bringing the existing envelope up to current fire code. The allowance that isn’t on paper is a surprise waiting for a date, so we scope it before we bid.

Pricing for Home Additions & ADU in Agoura Hills, CA

We Also Serve Cities Near Agoura Hills

Barrett & Sons Construction serves all of Agoura Hills, including the 91301 and 91376 zip codes, plus nearby Agoura, Westlake Village, Oak Park, and Thousand Oaks. If you live near the Ventura County line or just over the hill, the same crew and the same written-contract rules apply. We’re local enough to know your street and close enough to show up when we say we will.

FAQs - Home Additions & ADU in Agoura Hills