ADU Builder · Brentwood
Detached ADUs, guest houses, and private suites for Brentwood’s estate lots. We pull the permits through LADBS and build to the standard the main house sets.
ADU Builder in Brentwood
Most Brentwood lots have room to spare. That extra Westside land can become a detached ADU, a guest house for visiting family, a private suite for parents or staff, or the office you can finally close a door on. And at Brentwood’s land values, permitted square footage is one of the smartest things you can add.
Athenian Builders Group is a licensed California general contractor (CSLB #1045030) that designs and builds ADUs across Brentwood. One accountable team. A fixed price in writing, a firm timeline, and a 2-year workmanship warranty. See our full ADU construction services.
Permits
Brentwood is part of the City of Los Angeles, so ADU permits go through LADBS. We draw the plans, handle the submittal, and walk every inspection through to final approval.
Transparent Pricing
Real 2026 Los Angeles-area ranges by type. Where you land depends on size, site conditions, and finishes. After a free on-site visit, we give you a fixed, itemized price.
| ADU Type | Typical Size | Typical Cost (2026) |
|---|---|---|
| Garage Conversion | 300–500 sq ft | $100k – $180k |
| Junior ADU (JADU) | up to 500 sq ft | $90k – $160k |
| Attached ADU | 400–800 sq ft | $180k – $320k |
| Detached New-Build | 500–1,200 sq ft | $250k – $450k |
Typical ranges for 2026, not quotes. Financing is available for qualified homeowners. See remodel financing options. Considering a smaller in-home unit? See our Junior ADU page.
Estimated project cost
Why Athenian
Plenty of “ADU builders” are really design shops or brokers who sub the construction out. We’re not. We design it, pull the permits, and build it with our own crews. That gets you one point of contact, a fixed itemized price before we start, a firm timeline in writing, and a written 2-year workmanship warranty on everything we build in Brentwood.
Questions
Yes. We design and build detached ADUs and guest houses across Brentwood, finished to the same standard as a high-end main residence.
Brentwood is within the City of Los Angeles, so LADBS issues the permits. We manage the full process for you.
Type and size drive it. A garage conversion typically runs $100k–$180k. A detached new-build lands between $250k–$450k. Either way, you get a fixed, itemized price after a free on-site walkthrough.
Most of our ADUs finish in 3 to 5 months once permits are in hand, depending on type, size, and city review times. You get a firm timeline in writing before construction starts.
Start with a free on-site feasibility visit. You’ll get a fixed, itemized price for your Brentwood ADU, so you know exactly what it costs before we break ground. Call (310) 857-2520.
Takes about a minute. We reply the same business day and set up a free on-site visit.
