A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateFast, Reliable Home Addition Contractor Across Kentfield
Home additions in Kentfield run $180,000 – $420,000 for most projects, with detached ADUs and second-story work at the higher end of that range. That’s the honest number before anyone picks up a hammer. We’re Sutton ADU San Francisco, and we’ve been building additions and ADUs in Marin County since 2006. Kentfield is different from the flat lots you find in Larkspur or Corte Madera. The hillsides, the flood zone, the protected oaks, the 1950s and 1960s construction that hides surprises behind every wall. We know that. Call (831) 272-7212 for a free estimate, and we’ll send you a written price before any work begins.
Why Sutton ADU San Francisco Is Kentfield’s Preferred Home Addition Contractor Company
Kentfield homeowners don’t have time for vague promises. They want a contractor who understands what a permit triggers when you open walls on a 1962 hillside build. Our crews work these properties regularly. We know that a bedroom addition off Sir Francis Drake Boulevard might mean drilled piers and a retaining wall. We know that a garage conversion near Corte Madera Creek needs flood-zone elevation and backflow valves. That local knowledge keeps your inspection on schedule.
Every technician we send to your Kentfield property is background-checked, identity-verified, and photo-badged under the Threshold Standard. Before the visit, we send their name and photo to your phone. They arrive in a marked uniform and show a photo ID at the door. Miles Hartwell, who leads our team, built this system because homeowners deserve to know exactly who is walking onto their property. Founded in 2006, we’ve been part of the Threshold Group family the whole time, operating under standards that are written, not spoken.
Bathroom Addition Contractor in Kentfield
A bathroom addition contractor in Kentfield typically takes on projects that run $45,000 – $95,000, depending on whether you’re adding to an existing footprint or extending the structure. Kentfield’s older homes, many built in the 1950s through 1970s, often have one bathroom for three or four bedrooms. Adding a second or third bath means opening walls, and opening walls in this housing stock often reveals outdated wiring, corroded galvanized pipes, or rotted mudsills that the original builder never addressed.
What We Check Before Pricing
We inspect the existing foundation, joist spacing, and supply lines before we write your estimate. On a recent Kentfield job, a hallway bath addition uncovered knob-and-tube wiring behind a 1963 addition. That upgrade went into the contract as a written allowance, not a surprise invoice. You approve it in writing before we proceed.
Wet Wall Planning
Kentfield’s wet winters mean bathroom additions need proper ventilation and waterproofing at every seam. We size exhaust fans to the room’s cubic footage and use moisture-resistant drywall throughout the wet zone. The 365-Day Done Right Promise covers any workmanship defect for a full calendar year from completion.
Bedroom Addition Contractor in Kentfield
A bedroom addition contractor in Kentfield handles projects that typically run $90,000 – $180,000 for a ground-floor addition, with second-story bedrooms pushing higher because of structural reinforcement and stairwell integration. Kentfield’s estate-style lots give you room to build out, but the hillside terrain often means retaining work and geotechnical review before the foundation goes in. That’s the reality of building here, and it’s why flat-lot pricing from a contractor in San Anselmo or Novato won’t hold up on your Kentfield property.
Foundation Requirements on Sloped Lots
Many Kentfield lots slope enough that a bedroom addition needs drilled piers or a retaining wall before framing starts. We don’t guess at these numbers. We bring in a licensed geotechnical engineer, get the report, and write the actual cost into your contract. No change orders appear from the shadows later. You see the number, approve it in writing, and then we move.
Second-Story Work Over Existing Rooms
Adding a second-story bedroom over a 1960s single-story Kentfield home means the existing walls and footings have to carry new load. We typically find 2×4 rafters that are undersized for the added dormer weight. We write those seismic and structural upgrades into the allowance line of the contract. You’re never guessing what the next invoice says.
Trusted Brands We Service in Kentfield
We work with James Hardie exterior systems on most Kentfield additions because they hold up to wet winters and offer the fire-resistant cladding that matters in the wildland-urban interface. For detached ADUs, we have experience with Abodu and Cover prefab models, both of which can work well on Kentfield lots if the site access and slope conditions check out. We also handle Tuff Shed conversions for homeowners who want a simpler, faster garage-to-living-space build. We keep local material knowledge current for Kentfield so you’re not waiting on parts from out of state.
Common Home Addition Contractor Problems We See in Kentfield Homes
- Hidden knob-and-tube wiring: Kentfield’s 1950s – 1970s homes frequently still have active knob-and-tube in attic and wall cavities. Once a permit is pulled, the county requires it be decommissioned. A fixed-price quote that doesn’t include this allowance will bill you for it later, often at a markup.
- Rotted mudsills at the foundation line: Wet winters near Corte Madera Creek and on shaded hillsides mean sill plates rot. We open the wall, show you the damage, and price the replacement in writing before any further work happens.
- Ross Valley flood zone requirements: Additions in the flood zone need elevated foundations, flood vents, and often backflow valves. Ignore these and you fail inspection. We factor them into the estimate from day one.
- Hillside geotech surprises: Steep Kentfield lots sometimes need retaining walls and drilled piers that add $30,000 – $70,000 before framing even starts. We bring the geotech report before we write your final number, not after.
Pricing for Home Addition Contractor in Kentfield, CA
Here’s the straight answer. Ground-floor additions in Kentfield run $90,000 – $180,000. Second-story additions typically run $180,000 – $420,000 depending on structural upgrades and site conditions. Detached ADUs on Kentfield lots usually run $180,000 – $320,000 before site work, with hillside retaining and geotech adding to that base. A bathroom addition inside existing walls runs $45,000 – $95,000. The factors that move your number: slope, flood zone status, protected tree proximity, and the condition of your 1960s framing and electrical. Call (831) 272-7212 and we’ll give you a written, itemized price before any work begins. The estimate is free.
We Also Serve Cities Near Kentfield
Our crews work throughout central Marin. We’re scheduling free estimates in Kentfield this week, and we also serve San Anselmo, Fairfax, Novato, and San Pablo. If you’re in one of those areas and considering a home addition, the same written-price standard applies. As a Home Addition Contractor serving the Ross Valley, we bring the same Threshold Verified crew standards to every job, every town.
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 About Home Addition Contractor in Kentfield
Opening walls in Kentfield homes from that era commonly triggers electrical upgrades to decommission knob-and-tube wiring, seismic anchoring of existing framing, and sometimes plumbing replacement of galvanized pipes with copper or PEX. Each of these upgrades becomes a permit condition once the wall cavity is exposed, so they cannot be deferred. We write these into your contract as allowances, with the actual price shown and approved before we do the work.
If your Kentfield property sits in the Ross Valley flood zone, your addition must meet FEMA and county requirements for elevated foundations, flood-resistant materials below the base flood elevation, and often backflow valves on sewer lines. These requirements add cost and engineering time, but ignoring them guarantees a failed inspection. We identify flood zone status early in our estimate process. Call (831) 272-7212 for a free estimate that includes these factors from the start.
Protected oak trees in Kentfield are governed by county tree ordinances that restrict foundation placement, roof height, and even construction access routes. A live oak near your planned addition may require a certified arborist report, root protection zones, and a design that works around the tree rather than removing it. These constraints add design and permitting time. We’ve built around mature oaks on multiple Kentfield lots and will explain exactly where the extra cost sits in your written estimate.
A Kentfield addition contract should include a written scope of work, a written allowance line for hidden-condition discoveries like knob-and-tube wiring or rotted mudsills, and a clear process for approving any cost above the allowance. If a contractor hands you a fixed-price contract that doesn’t mention allowances for what’s behind the walls, they either don’t know Kentfield’s housing stock or they plan to bill you later. Our contracts include allowances, and any change is priced and approved in writing before we proceed. Call (831) 272-7212 and we’ll walk you through a sample contract.
Yes, in most cases you can add a second-story bedroom over an existing garage in Kentfield, but the garage’s footings and walls must be evaluated for the added load. Older Kentfield garages, particularly those built in the 1950s and 1960s, often have slab-on-grade foundations and 2×4 walls that cannot carry a second story without reinforcement. We assess the existing structure, then write the required seismic and structural work into your contract allowance before any framing begins. This is a common project for us on Kentfield’s estate-sized lots.
Call (831) 272-7212 to schedule your free estimate. You’ll get a written price before any work starts, and you’ll know exactly who is coming to your door.
Written by Miles Hartwell, Owner at Sutton ADU San Francisco, serving Kentfield since 2006.
