Home Additions & ADUs in Brentwood, Los Angeles

Costs vary enormously by type: a single room addition typically runs $25,000 to $75,000 or more, translating to roughly $150 to $400-plus per square foot on this coastal-adjacent stretch of Southern California; a garage conversion to living space or an ADU runs $40,000 to $150,000; and a detached ADU with its own kitchen and bath commonly runs $150,000 to $450,000 or more depending on size and site work. A second-story addition typically falls between $100,000 and $350,000-plus. We give you a fixed written scope after the feasibility review, scoped to your actual lot and the unit you want.

Yes — any project that adds square footage requires a permit through LADBS, since Brentwood is a City of Los Angeles neighborhood, plus structural engineering because new floor area has to carry California's seismic loads through properly sized footings, shear walls and a continuous load path. Additions also trigger Title 24 energy compliance for the new envelope. We prepare and carry the engineering and permit package as part of the job and explain what your project requires at the consultation.

A single-room addition typically runs two to four months of construction, a garage conversion six to twelve weeks, and a detached ADU commonly four to nine months once design and permitting are counted. Second-story additions are larger structural projects that often run four to eight months. Design and LADBS plan-check time is frequently the longest and least predictable part in California, and we set out the full timeline alongside the fixed written scope.

California's 2016 ADU laws — A.B. 2299 and S.B. 1069 — preempt local zoning to allow accessory dwelling units on most residential lots through a streamlined, non-discretionary approval path, so the answer for a typical Brentwood single-family lot is usually yes. The City of Los Angeles went from under 100 ADU permits in 2016 to more than 7,000 in 2022 on the strength of that law. The specifics still depend on your lot's setbacks, size and hillside status, which we confirm during the feasibility review before any design work begins.

Sometimes, and that's exactly what the feasibility review determines. A second-story addition loads the existing foundation and walls below, so an engineer assesses whether they can carry the new weight or need strengthening — a normal part of design, not a red flag. On hillside lots up Mandeville, Sullivan or Kenter Canyon, that assessment also factors in the slope and LADBS grading rules. We establish this early so you know whether a second story is realistic before you invest in full drawings.

Lots up Mandeville, Sullivan and Kenter Canyon fall under LA's hillside and grading regulations, which govern how much earth can move, how a foundation is engineered into the slope, and how drainage is managed once the addition is built. These canyon foothills also sit in a Very High Fire Hazard Severity Zone, so Chapter 7A wildland-urban-interface fire-hardening requirements apply alongside the grading review. We work both into the feasibility review and the engineered drawings before a permit is submitted.

Chapter 7A is California's wildland-urban-interface fire-hardening standard, and it applies to new construction in a Very High Fire Hazard Severity Zone — the designation covering Brentwood's canyon foothills, all of Bel-Air and much of Pacific Palisades. In practice it shapes the addition's exterior materials, venting, roofing and window glazing so the structure resists ember intrusion. The 1961 Bel Air Fire destroyed 484 homes and the 2017 Skirball Fire destroyed six more in this same terrain, which is why the standard exists and why we design to it as a matter of course.

Yes — the City of Los Angeles is fast-tracking Palisades recovery permits, letting a licensed architect or licensed engineer self-certify plans and approving like-for-like rebuilds up to 10% larger than the pre-fire footprint without the standard discretionary review. That 10% allowance is a real opportunity to add a bedroom or expand a primary suite while the property is already being rebuilt. We work within that expedited path for Palisades clients and explain exactly what it allows for your specific lot.

Yes — an ADU is a complete, self-contained living space with its own kitchen, bathroom and entrance, and owners commonly use them as rentals, which is a major reason the state streamlined approvals. Local rules govern the details of how an ADU may be rented and occupied. We flag anything relevant to your specific lot and jurisdiction during the feasibility review so you understand the picture before you build.

Matching an addition to a Cape Cod, Tudor or Spanish Revival original is a core part of the design, so the new work reads as original rather than tacked on. We detail how the addition meets the existing eaves, walls, windows and rooflines, and specify finishes to blend with what's there rather than contrast against it. On a mid-century home, that means keeping the roofline low and the proportions horizontal instead of breaking the original form.

Yes — we design and build additions and ADUs across Bel-Air, Westwood, Pacific Palisades, Santa Monica and the wider Los Angeles Westside. The permitting authority stays the same for the first three — all are City of Los Angeles neighborhoods run through LADBS, with the same hillside, fire-hazard and, in the Palisades, post-fire rebuild rules that shape the work — while Santa Monica additions are permitted separately through that city. Wherever your lot sits, we start with feasibility, and the number to call is (424) 369-0310.