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 Corte Madera
Adding square footage to a Corte Madera home almost always means one of two site conditions: saturated bay mud on the flat east side, or steep WUI-regulated hillside terrain rising toward Corte Madera Ridge. Both change the engineering, the permit path, and the honest price. We’re Barrett & Sons Construction, owner-operated since 1998, and our Home Additions & ADU crews work Corte Madera every week. Call (877) 610-1318 and Tom or one of his sons will walk you through what your specific lot actually requires before you commit to a number.
Why Barrett & Sons Construction Is Corte Madera’s Preferred Home Additions & ADU Company
We’re not a franchise dispatching strangers to Corte Madera. Tom Barrett’s name, address, and license number are published, and his sons run the crews. That matters in a town where a ground-up ADU on a hillside parcel will be inspected by Marin County under fire and slope ordinances that don’t bend, and where a flat-lot addition near the bay can stall for weeks if the dewatering plan wasn’t scoped from day one. Our written change order policy means every allowance adjustment arrives on paper before any scope change hits the job. The 90-Day Done Right Promise is on every contract. If something’s not right, one call brings Tom back.
We’ve pulled permits through both the Town of Corte Madera and Marin County depending on the parcel, and we know which agency has jurisdiction when. That’s the kind of local knowledge that keeps an Home Additions & ADU in Corte Madera project moving instead of stalling at the counter. No-hassle upfront pricing, free estimates, and a live person answers the phone 24/7.
Our Home Additions & ADU Services in Corte Madera
ADU Design & Permitting
An ADU in Corte Madera starts with the lot question: are you on bay fill, or are you on the ridge? Bay-side parcels in 94925 require geotechnical review for settlement and liquefaction, plus drainage plans that address a water table that sits two to three feet below grade even in dry season. Hillside parcels in 94976 trigger Marin County WUI fire review, slope-stability calcs, and erosion-control documentation. We handle both paths and keep the permit file moving through the right agency from day one.
New Detached ADU
A detached ADU on a Corte Madera bay-fill lot is a foundation project first and a framing project second. We anticipate active dewatering during excavation, specify pier-and-grade-beam or post-tensioned slab designs where geotech calls for it, and write the dewatering line item into the scope before you sign anything. On hillside lots, expect caissons or piers, engineered shear walls, and Class A roofing with ember-resistant vents. Budgets for a new detached ADU in Corte Madera typically run $90,000 to $220,000, with the site work often outrunning the framing cost on the flat side of town.
Garage Conversion ADU
Corte Madera’s 1950s and 1960s ranch homes often came with attached or detached garages on slab-on-grade foundations, and many of those slabs have cracked as the underlying bay mud consolidated over decades. When we convert a garage to an ADU, the first question is whether the existing slab can be structurally reused or needs to be cut out and replaced. We answer that with a site visit and, when warranted, a geotech review. Garage conversions in Corte Madera run $30,000 to $80,000 depending on foundation condition and whether the existing structure needs seismic upgrade under current code.
Junior ADU & Interior Conversion
A JADU carved from an existing bedroom or bonus room is the least expensive path to rental income on a Corte Madera property, and it usually avoids the foundation issues entirely. The typical scope includes a kitchenette, separate entrance, and egress compliance. What surprises people is the electrical panel load calculation: older Corte Madera homes with 100-amp panels often need an upgrade to 200 amps to pass inspection for a permitted JADU. We scope that in writing before the first wall opens.
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 Corte Madera
We put our name on materials you can look up. For hardscape and site prep around Corte Madera additions, we use Techo-Bloc and Cambridge Pavers for retaining walls, patio areas, and permeable surfaces that help with the drainage requirements the county enforces on hillside lots. For concrete and footing work on bay-fill parcels, we spec Quikrete products suited to high-moisture exposure. If you’re planning an ADU with a paver courtyard or a driveway extension to reach a new detached unit, we’ll write the brand and the allowance into the contract.
Common Home Additions & ADU Problems We See in Corte Madera Homes
- Groundwater surprises on bay-fill lots. On the eastern flat side of Corte Madera, standing water appears in footing trenches even in August. Contractors who don’t scope dewatering stop work mid-excavation and hit you with a change order. We price it up front.
- Cracked slabs on 1950s-1970s ranches. Differential settlement under older bay-side homes means a new addition tied directly to an existing slab will crack at the connection if the foundation isn’t engineered independently. We have seen this firsthand and won’t fake a tie-in that won’t hold.
- WUI fire-code failures on hillside ADUs. Marin County inspects ember-resistant vents, tempered glazing, and shear wall assemblies on hillside parcels. A scope that skips these will stall at inspection and cost more in retrofit than it would have cost to build right the first time.
- King tide and storm surge drainage on low-lying parcels. Finished-floor elevation is a code-reviewed item near the bay. We set ADU and addition floor heights with an eye toward Marin County’s FEMA Flood Insurance Rate Map, and we design site drainage to move water away from the structure.
Pricing for Home Additions & ADU in Corte Madera, CA
Honest numbers for Corte Madera are not the same as nearby Marin towns. A full home addition on a flat bay-side lot runs $45,000 to $130,000, with foundation and dewatering costs on the low end eating into what you’d expect to be framing budget. A detached ADU runs $90,000 to $220,000. A garage conversion sits at $30,000 to $80,000. Hillside second-story additions skew higher because of shear walls, caisson foundations, and fire-rated assemblies. We write every allowance on paper and every change as a written change order before work proceeds. Call (877) 610-1318 for a free estimate on your specific parcel.
| Project Type | Corte Madera Price Range |
|---|---|
| Home Addition | $45,000 - $130,000 |
| ADU Construction | $90,000 - $220,000 |
| Garage Conversion | $30,000 - $80,000 |
We also honor a permanent 10% Senior & Veteran discount, offer a free second opinion on any written estimate, and never charge a trip fee inside the county. A live person answers the phone 24/7.
We Also Serve Cities Near Corte Madera
Beyond Corte Madera, our crews work Larkspur, Mill Valley, Tamalpais Valley, and Tamalpais-Homestead Valley. Each has its own site conditions, but the rule is the same: scope it in writing, permit it properly, and stand behind it when it’s done. If you’re just outside town, call and ask.
Serving Corte Madera, CA - Our Local Coverage Area
We’re based in the Corte Madera 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 Corte Madera
The high water table adds a dewatering line item to nearly every excavation on a flat bay-side lot, typically adding several thousand dollars and extra days to the foundation phase. We scope it in the written quote before you sign. Call (877) 610-1318 and we’ll walk your specific lot with that cost already in hand.
Yes, in most cases hillside additions and ADUs fall under Marin County jurisdiction for fire, slope, and geotechnical review, even when the address is in Corte Madera. We pull the right permits through the right agency the first time. Estimates are free; call (877) 610-1318 to find out which path your parcel takes.
Rough-in covers below-grade work: excavation, dewatering, formwork, steel, and concrete before framing begins. On Corte Madera’s bay-fill side, that’s where the real cost and risk sit, so we show it as its own line item instead of burying it in a lump sum.
Sometimes the slab can be structurally reused with an overlay and new perimeter footing, but if differential settlement is active, cutting it out and repouring is the only honest fix. We’ll tell you which one applies after we see it, and the number will be in writing. Call (877) 610-1318 for a free garage conversion estimate in Corte Madera.
Yes. Marin County’s WUI code for hillside parcels requires Class A roof assemblies, ember-resistant vents, and often tempered or dual-pane glazing on the addition. We spec those materials into the scope from the start so inspection doesn’t surprise you later.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Corte Madera since 1998.