A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateFast, Reliable Room Addition Contractor Across Brentwood
A permitted room addition in Brentwood typically runs $180 to $340 per square foot for the build itself, before permit fees and design work. On a 400-square-foot addition, that pencils out to roughly $72,000 to $136,000. Those numbers are honest starting points for this market, not teaser rates. Call (361) 315-4177 and we’ll put a written price in your hands before any work starts.
We know Brentwood’s streets because we work them. Our crews are out here week after week on room additions, in-law suites, and ADU projects from Balfour Road down to the newer subdivisions off Lone Tree Way. The Room Addition Contractor team at Fielding ADU Builders handles everything from plan check submittals through final inspection, so you don’t end up with an unpermitted addition that can’t be appraised as living space. Dispatch and scheduling run from the brand’s San Francisco Bay Area office; the crew on your Brentwood site is local, background-checked, and in uniform.
Why Fielding ADU Builders Is Brentwood’s Preferred Room Addition Contractor Company
We operate by a written code, and it was not written for a marketing brochure. The Garrison Code is five plain rules: show up in the window, price in writing, build by the book, leave it clean, and stand behind it for a year. The one-year guarantee is the Garrison Standard, and it’s on paper, not verbal. If the work fails within 365 days, we return and correct the defect at no charge.
Reed Calloway runs Fielding ADU Builders, and every project here carries the same expectations the Garrison Partners organization has held since 2006. You’ll get a written price before a single nail is driven. You’ll get a crew that’s been background-checked and shows up in uniform. And when you call, a live person answers, 24 hours a day, 7 days a week. No voicemail, no callback queue. If you’re calling at noon or midnight, someone picks up.
We’ve built to the Garrison Standard across Brentwood’s housing stock, from the 1990s single-story tracts near Brentwood Hills to the newer two-story homes further east. That matters because a room addition on a 1990s rancher is a different job than one on a 2015 build. The roof pitches differ, the framing conventions differ, and the HVAC tie-in differs. We’ve seen them all here.
Home Addition Plans in Brentwood
Home Addition Plans in Brentwood start with the lot, not the sketch. Most existing Brentwood homes sit on standard suburban parcels where the maximum addition size is capped by lot-coverage limits and rear and side setbacks. A neighbor’s approved 500-square-foot family room addition does not mean your parcel will pencil out for the same footprint. Your setback and lot-coverage numbers come from the City of Brentwood’s Building Division, and they are specific to your parcel. That’s the first thing we check before drawing a line.
Plan fees for a room addition in Brentwood typically run $2,500 to $5,000 depending on the complexity of the structural design and whether you’re tying into existing systems or adding new ones. That covers the architectural drawings, structural calculations, Title 24 energy compliance, and the city’s plan-check submittal. It does not include the city’s permit fees, which are separate and assessed by the city at intake.
What the plan set needs to include
The City of Brentwood has its own plan-check queue, separate from Contra Costa County. Your plan set needs structural calcs, Title 24 energy documentation, and a site plan showing the addition against your parcel’s setback lines. Missing any of these triggers a correction cycle, and each correction adds days to a city queue that already moves on its own calendar.
Realistic timeline from plan to permit
Plan preparation takes two to four weeks. City plan check in Brentwood currently runs three to six weeks, depending on the queue and how clean the submittal is. Once you have the permit in hand, a 400-square-foot addition typically takes 10 to 14 weeks from foundation to final inspection. We coordinate the inspections with the city directly so the job does not stall waiting on a phone call.
In Law Suite Builders in Brentwood
In Law Suite Builders in Brentwood work primarily with homeowners who want a permitted secondary living space attached to the existing home, whether for aging parents, adult children, or rent-paying tenants. An in-law suite built as a room addition in Brentwood typically runs $220 to $360 per square foot, with a kitchenette or wet bar pushing the higher end of that range. The number goes in writing before work starts.
In Brentwood, an in-law suite built as an attached room addition must meet the same lot-coverage and setback rules as any other addition, plus whatever additional requirements the city applies to accessory living space. That means the suite needs its own entrance or a clear path to one, and the plumbing for a bathroom or kitchenette must be approved on the plan set before permit issuance. We’ve built these on homes across Brentwood, including several off Lone Tree Way where the existing floor plan gave us a clean tie-in at the rear wall.
Appraisal and permit reality
A permitted in-law suite appraises as living square footage. An unpermitted conversion does not, and can actually complicate a sale when buyers ask to see the permit record. We pull the permit, pass the inspections, and leave you with documentation the next appraiser will accept.
Kitchenette and wet bar scope
A kitchenette with a sink and a small refrigerator adds $12,000 to $25,000 to the project depending on whether you’re running new plumbing or tying into an existing drain line. We price that line item separately in the written quote so you can see exactly what the amenity costs and decide with the real number in front of you.
Trusted Brands We Service in Brentwood
We work across the build methods Brentwood homeowners are already researching. On conventional room additions, we regularly use James Hardie siding to match or complement existing stucco and hardie-board exteriors common in the city’s newer subdivisions. For prefab and modular builds, we’re fluent with Abodu, Cover, and Dvele platforms, which matters when a Brentwood homeowner wants factory-built quality with a faster on-site timeline. We carry the consumables and finishing materials our Brentwood jobs need locally, and when a specific James Hardie color or trim profile is required, we have the supplier relationships to get it quickly without a run to Sacramento.
Common Room Addition Contractor Problems We See in Brentwood Homes
- Lot coverage kills the dream before design starts. Many Brentwood parcels have lot-coverage caps that limit a detached ADU and a room addition combined. If you’re planning both, we scope them together from day one so the city’s math does not force a redesign later.
- Roof tie-ins on 1990s ranchers leak when done wrong. Brentwood’s older single-story homes have shallow roof pitches, and a poorly flashed tie-in is the first place water finds its way in during winter rains. We match pitch and shingle color and flash the junction properly.
- Homeowners underestimate the HVAC load change. Brentwood summers hit triple digits, and adding 400 square feet of conditioned space without upsizing the HVAC results in a room that never cools. We size the system for the new square footage, not the old one.
- Skipping foundation inspections catches up later. Brentwood’s Building Division inspects footings, foundation forms, and the slab pour. If those inspections don’t happen on the city’s schedule, the addition cannot be permitted as livable square footage, and that is a five-figure mistake.
Pricing for Room Addition Contractor in Brentwood, CA
A standard 400-square-foot room addition in Brentwood runs $72,000 to $136,000 for construction, which includes foundation, framing, roofing, electrical, HVAC tie-in, drywall, paint, and interior finishes. Larger additions with a bathroom run $220 to $360 per square foot. A basic bedroom addition with no plumbing starts around $180 per square foot. City permit fees are separate and typically run $3,000 to $7,000 depending on the valuation of the work.
The written price we hand you before work starts includes every line item. If the city requires a structural upgrade we could not have known about, we identify it during plan check and reprice before you commit, not after the wall is open. That is how the Garrison Standard works. Call (361) 315-4177 for a free estimate on your Brentwood addition.
We Also Serve Cities Near Brentwood
Fielding ADU Builders handles room additions across the East Bay and beyond. If you’re in Brentwood proper or nearby in Ojai, Oak View, Ventura, or Santa Paula, we can scope your project and put a written price in your hands. The same written-price-first policy and one-year guarantee apply wherever the job is.
Serving Brentwood, CA - Our Local Coverage Area
We’re based in the Brentwood area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs About Room Addition Contractor in Brentwood
Yes. Any room addition that adds conditioned square footage to your Brentwood home requires a building permit from the City of Brentwood’s Building Division, along with structural calculations, Title 24 energy documentation, and passing inspections at the foundation, framing, and final stages. A room addition built without a permit cannot be appraised as living square footage and can create problems when you sell. Call (361) 315-4177 and we’ll handle the entire permit process, from plan set to final inspection.
Brentwood’s rear and side setback rules, combined with each parcel’s lot-coverage limit, cap how large a room addition can be regardless of what you’re willing to spend. A neighbor’s large addition may have been built on a larger lot or under a different coverage calculation. We check your parcel’s specific numbers with the city before design starts, so you don’t pay for plans that can’t be permitted. The first step is a free site assessment; call (361) 315-4177.
Yes. An attached in-law suite with its own entrance, a bathroom, and optionally a kitchenette is a common room addition type in Brentwood, typically running $220 to $360 per square foot. The suite must be included in the permitted plan set, and plumbing for the bathroom or kitchenette must be approved by the city as part of the permit. For an exact quote on your floor plan, call (361) 315-4177.
Plan preparation takes two to four weeks, Brentwood’s plan-check queue typically runs three to six weeks, and construction on a 400-square-foot addition runs 10 to 14 weeks. That puts a realistic full timeline at four to six months from first conversation to final inspection. We coordinate the city inspections directly and keep the job moving on Brentwood’s calendar. If you’re planning for a specific date, call (361) 315-4177 and we’ll map out the schedule.
The honest answer: nothing changes the price once it’s in writing unless you change the scope, or the city requires a structural modification during plan check that could not have been known upfront. We identify plan-check corrections before work begins and reprice before you commit. Field change orders are not how we operate. The written price you approve on day one is the number on the final invoice, plain as that. For a written quote, call (361) 315-4177.
Written by Reed Calloway, Owner at Fielding ADU Builders, serving Brentwood and the surrounding Bay Area communities.
