Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across Kentfield
Home additions and ADU construction in Kentfield typically runs $45,000 to $130,000 for an addition and $90,000 to $220,000 for a detached ADU, with permits running through Marin County rather than a city building department. That county path adds review layers most flatland Marin jobs never face, especially when your parcel sits near the hill edge where WUI fire-resistant construction rules kick in. If you’re planning a room addition above Sir Francis Drake Boulevard or a detached ADU near Kent Woodlands, call Barrett & Sons Construction at (877) 610-1318. We know what the county inspectors will flag before you’ve bought a single sheet of plywood.
Why Barrett & Sons Construction Is Kentfield’s Preferred Home Additions & ADU Company
Tom Barrett founded this company in 1998, and his sons run the crews you’ll see on your Kentfield job. That’s the difference. You’re not getting a rotating cast of subcontractors from three counties away. You’re getting the same family that’s been answering its own phone for over 29 years, and Tom publishes his name, address, and license number so you can look it up before you sign anything.
Our Home Additions & ADU team has worked the uphill streets of Kentfield long enough to know what the marine air does to framing, what the county wants on a drainage plan, and why a foundation opened in November needs temporary waterproofing that would look like overkill in Novato. A live person answers our phone 24/7, not a call center. When you call with a question about your permit or your allowance, you get a human being who knows your project.
Every Kentfield job we take gets the same treatment: pull the permit, pass the inspection, and put every allowance and every scope change in writing before work moves. The 90-Day Done Right Promise is written into the contract. If something’s not right, one call brings Tom back. That’s not a slogan. That’s how we’ve stayed busy in Marin for nearly three decades.
Our Home Additions & ADU Services in Kentfield
ADU Design & Permitting
A detached ADU on a Kentfield hillside lot isn’t a stock plan you pull off a shelf. Marin County’s WUI fire rules, slope stability requirements, and stormwater drainage standards all land on your permit set before the first inspection. We handle the design, the engineering coordination, and the county submittals inch by inch. A typical ADU construction in Kentfield runs $90,000 to $220,000, and the design and permitting phase is where surprises either get found early or turn into five-figure change orders later.
New Detached ADU
Building a new detached ADU in the Kent Woodlands or along the College of Marin edge means Class A roofing, ember-resistant vents, and fire-rated exterior cladding if your parcel falls under the WUI overlay. That’s an added material cost and an added inspection step that a flatland Marin contractor might not even mention until the county flags it. We price it in from the start. Your contract reflects the real spec, not a hope that the inspector won’t look up.
Garage Conversion ADU
Garage conversions in Kentfield run $30,000 to $80,000 and are often the fastest path to a rental unit on a sloped lot where new excavation would trigger slope stability review. The catch is that many of these garages were built in the 1950s and 1960s with post-and-pier foundations that have settled under decades of 50 to 60 inch rainfall. We open the walls, check the framing, re-level what’s moved, and only then start the conversion. You don’t want a finished ADU sitting on a foundation that’s still creeping downhill.
Junior ADU & Interior Conversion
A Junior ADU carved out of existing square footage in your Kentfield home avoids some of the detached-unit requirements, but you can’t skip the fire-resistant siding upgrades just because the unit is interior. Marin County applies WUI review based on the parcel, not the specific room. We’ll tell you what applies to your street before you spend a dollar on drawings. Then we’ll pull the permit, pass the inspection, and hand you the signed paperwork.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in Kentfield
We carry premium materials across the trades we touch on Kentfield jobs. Schluter systems in wet-area waterproofing for ADU baths, Sterling fixtures where the spec calls for dependable plumbing, and we’ve installed enough GAF roofing to know how it handles the kind of rain the Marin hills throw at a roof deck. When your project spec calls for a brand you can look up, we stock and source it through local suppliers so you’re not waiting on a mystery shipment from three states over.
Common Home Additions & ADU Problems We See in Kentfield Homes
- Settled post-and-pier foundations on hillside streets. Kentfield’s mid-century homes above Sir Francis Drake Boulevard were built on stepped foundations that move with each wet season. We regularly find uneven settlement before framing ever starts.
- Undersized stormwater drainage causing sill plate rot. The orographic lift effect dumps 50 to 60 inches of rain on these hills each year. When that water doesn’t get carried away, it wicks into framing and rots the bones before you see it on the drywall.
- WUI compliance gaps on hill-edge parcels. Fire-rated cladding and ember-resistant vents aren’t optional near the Kent Woodlands edge. We’ve seen homeowners fail their first fire inspection for unrated vents and have to tear out brand-new cladding.
- Verbal allowances that become five-figure surprises. Custom millwork sounds simple until a designer specs rift-sawn white oak and the allowance is for paint-grade maple. We put every allowance in writing with a signed change order before the material order goes in.
Pricing for Home Additions & ADU in Kentfield, CA
Here’s what our Kentfield customers actually pay, based on the scope and the parcel:
| Project Type | Kentfield Price Range |
|---|---|
| Home Addition | $45,000 - $130,000 |
| ADU Construction | $90,000 - $220,000 |
| Garage Conversion ADU | $30,000 - $80,000 |
What moves you toward the top of those ranges is the Kentfield-specific stuff: WUI fire-resistant materials, slope stability engineering, drainage plans that satisfy Marin County, and the long-lead architectural finishes you actually want. The schedule on this tier is set by lead times on custom millwork and specialty glass, not by how fast a crew can frame. We fix the price in writing before we order a single long-lead item. Call (877) 610-1318 for a free estimate broken out line by line.
We Also Serve Cities Near Kentfield
Our crews serve Home Additions & ADU in Kentfield and the surrounding Marin communities, including Larkspur, San Anselmo, Corte Madera, and Fairfax. If you’re outside Kentfield proper but still in the county, call (877) 610-1318 and we’ll tell you honestly whether we can get to your street and when.
Serving Kentfield, CA - Our Local Coverage Area
We’re based in the Kentfield 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 - Home Additions & ADU in Kentfield
Your detached ADU will need fire-rated exterior cladding, ember-resistant vents, and Class A roofing if your parcel falls under the Wildland-Urban Interface overlay, which adds inspection steps and material costs a flatland Marin job doesn’t face. We price those requirements into the contract from the start so you don’t fail a fire inspection and eat the rework. Call (877) 610-1318 to have us check your specific parcel before you commit to drawings.
Kentfield’s position at the base of the Marin hills creates orographic lift that produces 50 to 60 inches of rain per year, roughly triple what San Francisco gets, and that water moves downhill through your property. Marin County requires drainage engineering that accounts for slope, soil saturation, and runoff so your new foundation doesn’t become a dam. We include that plan in our permit package. Call (877) 610-1318 for a free estimate on your addition.
Every allowance goes on paper with a signed change order before the material order is placed, so a designer spec from rift-sawn white oak instead of paint-grade maple becomes a written line item you approve, not a surprise invoice at the end. Tom’s rule is simple: an allowance that isn’t on paper is a surprise waiting for a date. Call (877) 610-1318 and we’ll show you exactly how the numbers break down.
Expect the Kent Woodlands second-story addition to run longer than a flatland job because the county’s WUI review, slope stability sign-offs, and drainage plan all add review days before you even get to framing. Then the long-lead items, custom millwork and architectural glass, set the rest of the calendar. We’ve done enough of these to give you a real schedule, not a sales pitch. Call (877) 610-1318 to talk about your street and your lot.
No. Marin County applies WUI fire-resistant construction requirements based on the parcel location, not on whether the unit is attached or detached, so a garage conversion on a hill-edge lot still needs the fire-rated cladding and ember-resistant vents. We’ll tell you exactly what applies to your address before you spend money on plans. Call (877) 610-1318 for a free estimate.
Why Drainage and WUI Rules Define Every Kentfield Project
Kentfield sits at the base of the Marin hills where marine air stalls and releases, making it one of the wettest spots in the entire Bay Area. Roughly 50 to 60 inches of rain falls here annually, compared to San Francisco’s 20 inches. That one fact shapes nearly every home addition and ADU project in this town. Your foundation sits on soil that gets saturated every winter. Your drainage system, if it’s original to a 1950s or 1960s house, was probably undersized for what the hills actually deliver.
On a Kent Woodlands room addition above Sir Francis Drake Boulevard, we opened the subfloor and found post-and-pier framing that had settled unevenly after decades of that rainfall, with undersized drainage letting moisture wick into the sill plates. Our crew re-leveled the structure, sistered the damaged joists, and installed a French drain that now carries hillside runoff around the new foundation before we framed the addition. That’s not a story we pulled from a training manual. That’s what we find on Kentfield hillside lots with regularity.
And because Kentfield is unincorporated, every permit runs through Marin County’s building department, not a city counter. That adds review layers, including WUI fire-resistant construction requirements for any project near the hill-edge parcels. The combination of heavy rain, sloped lots, and county fire standards means your Kentfield addition or ADU needs a contractor who knows the inspector’s checklist before the framing crew shows up. That’s what we bring.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Kentfield and surrounding Marin communities since 1998.