A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateFast, Reliable ADU Builders Across Kensington
If you own a home on one of Kensington’s steep, tree-covered lots, you already know the county rules here are different from Berkeley or El Cerrito. Every accessory dwelling unit in Kensington is permitted through Contra Costa County, not a city planning desk. That single fact changes how your project gets scoped, priced, and built. Our ADU Builders team works in Kensington every month, so we plan for the things outsiders miss: septic and well setbacks, wildfire-zone material requirements, and access roads that punish a full-size concrete truck. You don’t have to figure out the county’s hillside development rules on your own. Call (707) 760-0502, tell us about your lot, and we’ll give you a written price and a plan that actually fits Kensington.
Why Lodgewick ADU San Francisco Is Kensington’s Preferred ADU Builders Company
Kensington homeowners tend to ask sharp questions. Many of them have dealt with contractors who bid low, then discovered the lot had a problem the contractor never mentioned. Our reputation here comes from doing the opposite: we investigate the lot before we quote. Russ Delmar, who leads our team, insists on walking every Kensington site before a number goes in writing. That means checking the county assessor’s parcel, locating the septic field and well, measuring the slope, and confirming the truck access. When we hand you a written price, it’s based on what’s actually in the ground and on the hillside, not a stock plan from a catalog.
The Kingswell Guarantee is in writing on every project. Written price before work starts. Defined arrival window. Clean job site every day. A guarantee on the build itself, with a free return visit if the work fails within 365 days. That’s the 365-Day Done Right Promise, and it applies to every ADU we frame in Kensington.
Our ADU Builders crews know the difference between a flat lot in Hayward and a hillside parcel off Purdue Avenue. We schedule smaller trucks, we stage materials where the road allows, and we don’t crack driveway aprons learning lessons on your property. We’re also the people who answer the phone when you call. A live person, 24 hours a day. Not a chatbot, not a voicemail tree.
ADU Construction in Kensington
ADU construction in Kensington means building an accessory dwelling unit on a lot that’s usually sloped, often fire-prone, and always under Contra Costa County’s jurisdiction. That’s a different animal from building in an incorporated city with a planning counter and standard setbacks. A typical ADU construction project in Kensington runs $250,000 to $420,000 for a one-bedroom unit, depending on slope, foundation work, utility connections, and fire-hardening requirements. When a homeowner needs it, it’s usually because the house works but the lot is underused, or because aging parents or grown kids need a place of their own without leaving the property.
County Permits and Septic Logic
Before we draw anything, we verify the septic system location, the well, and the county’s required setbacks from both. On an acreage lot, that often shrinks the buildable area dramatically. We do this before design, so your foundation doesn’t get moved after permits are drawn.
Foundation and Drainage Planning
Sloped lots need reviewed grading plans. We plan drainage so runoff moves away from the foundation and the septic field, not into them. If winter rains are going to saturate the hillside, we want the water going where we choose, not where gravity chooses.
Detached ADU in Kensington
A detached ADU in Kensington is a separate small house on your existing lot, which is what most acreage owners here want when they have the room. It gives the most privacy for both households and avoids the structural tie-in complexity of attaching to a mid-century home’s foundation. A detached ADU in Kensington typically runs $280,000 to $480,000 depending on size, site access, utility trenching, and the slope. When a homeowner needs it, it’s usually because the main house is 1,600 square feet built in 1962, and there’s simply nowhere to add on without losing the yard.
Siting on the Lot
Where the unit goes is the first conversation. We walk the acreage, stake the buildable envelope, and account for the well, leach lines, tree drip lines, and the county’s hillside setbacks. The right site isn’t always where the view is best; it’s where the ground will hold the structure and the county will sign off.
Fire-Resistant Envelope
Kensington sits in a high wildfire-risk zone. That means the county requires fire-hardened materials on the exterior. We specify fiber-cement siding, Class A roofing, and ember-resistant venting so the unit passes inspection and actually protects itself. This also affects cost, and we put that in the written price up front.
Trusted Brands We Service in Kensington
We work hands-on with the prefab and materials systems that make sense on Kensington’s sloped, fire-prone lots. For a hillside project with tight access, a Plant Prefab panelized build can reduce the number of trucks on your road and the time your site is exposed. We’ve used James Hardie fiber-cement siding on Kensington units for its fire resistance and how it holds up through wet winters and dry summers. For a flatter lot with better access, a Tuff Shed based studio can keep the budget reasonable. We match the brand to your lot and your budget, and we stock the common materials needed to frame and finish these systems without waiting on long lead times.
Common ADU Builders Problems We See in Kensington Homes
- Septic and well setbacks ignored until after design. A contractor draws a plan for where the ADU looks best, then finds out the county won’t approve it because it’s too close to the leach field. We verify setbacks before the first drawing, so the foundation doesn’t move mid-project.
- No drainage plan for the wet winter. An ADU gets framed on a hillside without erosion control. The first big rain saturates the slope, the new foundation shifts, and the hillside starts moving downhill. We include grading and drainage in every Kensington quote, and we show it to you in writing.
- Full-size trucks on roads that can’t take them. A concrete truck gets ordered for a steep, narrow Kensington street. It blocks the road for hours and cracks the driveway apron trying to turn around. We plan smaller trucks or a pump line, and we plan the turnaround before the truck ever rolls.
- Foundation mismatch with a mid-century house. Many Kensington homes sit on original 1950s and 1960s foundations. Tying a new structure to one without an engineering review risks differential settling. We look before we build, and we tell you if a foundation upgrade is necessary and what it costs.
Pricing for ADU Builders in Kensington, CA
Here’s what we see in Kensington right now: a simple studio ADU runs $180,000 to $280,000. A one-bedroom detached ADU with a small kitchen and bath runs $280,000 to $420,000. A two-bedroom unit, or anything on a steep lot with significant foundation and retaining work, runs $380,000 to $520,000 and can go higher if the access is severe or the septic system needs relocation. What moves the number: slope and soil, distance from the house for utility trenching, fire-hardening requirements, and whether the county requires engineered retaining walls. We give you a written line-item price before work starts, so you can see exactly where the money goes. Call (707) 760-0502 for a free estimate on your Kensington lot.
We Also Serve Cities Near Kensington
While this page focuses on Kensington, our crews regularly work across the nearby communities of San Francisco, Oakland, Hayward, and Richmond. If your property is just over the line in one of those cities, the permitting will be different, but the way we scope, price, and build stays the same: written price first, county or city rules handled, and a guarantee in writing.
Serving Kensington, CA - Our Local Coverage Area
We’re based in the Kensington 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 ADU Builders in Kensington
Kensington is unincorporated, so every ADU is permitted through Contra Costa County, not the City of Berkeley. That means county hillside development rules, county septic and well setback requirements, and county wildfire-zone material standards all apply. A contractor who assumes Berkeley’s rules apply will draw a plan that doesn’t get approved. We work with the county’s process from day one. Call (707) 760-0502 and we’ll tell you what applies to your parcel.
They often determine the entire buildable area. Contra Costa County requires minimum distances from the ADU foundation to the well, the septic tank, and the leach lines. On a typical Kensington acreage lot, that can rule out the most obvious spot for the unit. We survey the acreage, stake the actual envelope, and design within it before you spend a dollar on permits. That’s the only way to avoid moving the foundation after the plans are drawn.
Kensington sits in a high wildfire-risk zone, so the county requires ignition-resistant exterior materials. That typically means fiber-cement siding like James Hardie, Class A rated roofing, and ember-resistant venting. Some slopes also trigger requirements for defensible space and vegetation management. We specify materials that pass county inspection and actually hold up to ember exposure. We’ll show you the material list and the cost in the written quote.
Sometimes not, and that’s exactly why we plan access before we quote. On steep, narrow roads like the ones off Purdue Avenue, a full-size concrete truck can block the street or crack the driveway apron. We often use smaller trucks, a pump line, or a different foundation method altogether. The access plan goes into the written price, so you know how we’ll get the work done before we start. Call (707) 760-0502 and tell us about your road; we’ll tell you what’s realistic.
You may need to upgrade the ADU’s own foundation system if the soil or slope requires it, and you’ll almost certainly need a drainage and erosion-control plan for the whole site. Kensington’s wet winters make hillside foundation movement a real risk if water isn’t managed. If we’re attaching to the existing home, we’ll also check the original foundation before we tie in. We’ll put any required upgrades in the written estimate, so there’s no surprise after we start digging.
Ready to talk about your lot? Call (707) 760-0502. We’ll walk the site, explain what Contra Costa County will require, and put a written price in your hands. Free estimate, no pressure, and a live person answers the phone.
Written by Russ Delmar, Owner at Lodgewick ADU San Francisco, serving Kensington with written-price, guaranteed ADU construction.
