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 Half Moon Bay
Adding square footage to a coastal home in Half Moon Bay is a different animal than building inland. The salt air, the Coastal Commission, the older housing stock, the fog that hangs over everything from Pilarcitos Creek to Frenchmans Creek. A typical home addition in Half Moon Bay runs $45,000-$130,000, while a detached ADU starts around $90,000. If you’re reading this because you need more room and you’re not sure where to start, call our Home Additions & ADU team at (877) 610-1318. We’ve built additions and ADUs in this town, and we know what the inspectors here look for.
Why Barrett & Sons Construction Is Half Moon Bay’s Preferred Home Additions & ADU Company
Tom Barrett started this company in 1998, and he still answers his own phone. His sons run the crews. When you hire us for a room addition or ADU in Half Moon Bay, the person you talk to on Monday is the same person who walks your job site on Wednesday. That matters in a town where word travels fast and neighbors talk.
We’ve pulled permits and passed coastal inspections in Half Moon Bay on projects from downtown near Main Street to the hills above Higgins Canyon Road. Our customers in the 94019 zip code keep bringing us back, and they refer us to their neighbors. The reason is boring, and that’s the point: we write down the scope, we write down every allowance, we pull every permit, and we don’t show up at the end with a bill that looks nothing like the estimate. You can look up Tom Barrett’s name and license number before you sign anything. We want you to.
We live in the Bay Area and we schedule work in Half Moon Bay every week. When you call, a live person picks up, day or night. Not a call center.
Our Home Additions & ADU Services in Half Moon Bay
ADU Design & Permitting
An ADU in Half Moon Bay sits inside the California Coastal Commission’s coastal zone, which means the design phase has to account for more than just floor plans. Setbacks, visual review, environmental constraints. We handle the design work and the permit package so you’re not sitting on the phone with the Coastal Commission’s San Francisco District office trying to figure out what “exempt” actually means. We handle it so you don’t have to.
Garage Conversion ADU
Garage conversion is typically the most affordable path to an ADU in Half Moon Bay, running $30,000-$80,000 depending on how much plumbing and electrical work the existing shell needs. Many of the mid-century ranch homes along Highway 92 corridors have attached garages that convert cleanly. The catch in Half Moon Bay is that even a garage conversion can trigger Coastal Development Permit review if it changes exterior square footage, so we scope that early.
New Detached ADU
A new detached ADU in Half Moon Bay runs $90,000-$220,000, and the Coastal Commission review is the long pole in the schedule. Not because the commission is unreasonable, but because the process has strict visual and environmental requirements that an inland contractor never has to think about. We’ve been through it enough times to know what gets approved the first time and what gets kicked back.
Junior ADU & Interior Conversion
A junior ADU, or an interior conversion of existing space, is often the fastest way to add a rental unit or an in-law suite without touching the exterior footprint. In Half Moon Bay, this can sidestep some coastal review triggers, but not always. We read the Coastal Act categories carefully before we scope anything, because the last thing you want is a project frozen mid-construction while a review clock runs.
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 Half Moon Bay
We install products from brands that have to stand up to this climate. Salt air chews through cheap fasteners and flashing in a couple of years, so we lean on materials built for the coast. You’ll see Cambridge Pavers and Techo-Bloc on hardscape and patio work, and Quikrete products in our site prep and foundation mixes. We keep our supply chain tight for Half Moon Bay customers so material lead times don’t stall your schedule longer than the permitting process already does.
Common Home Additions & ADU Problems We See in Half Moon Bay Homes
- Rot in sill plates and sheathing. The older fishing and farming cottages in the Old Town core, along with the 1950s-70s ranch homes, have spent decades in damp, salt-laden air. Once we open a wall for an addition, we routinely find rot that was invisible from outside. We budget for it and we show you what we found before we fix it, with a written change order.
- Coastal permit surprises. A project that looks like a simple interior remodel can trigger full Coastal Development Permit review if it touches a nonconforming structure or alters exterior square footage. We’ve seen out-of-area contractors get blindsided by this and leave a homeowner with a half-finished project waiting on the Coastal Commission’s clock.
- Fog drip moisture problems. The cypress and eucalyptus belt along the hills keeps rooflines and foundation perimeters wet even in summer. Any addition or ADU in this climate needs vapor barriers and stainless or hot-dipped fasteners, not the standard hardware that works fine in Burlingame.
- Foundation perimeter corrosion. The persistent marine layer means exposed structural hardware corrodes fast. If you’re adding onto an older home in Half Moon Bay, we inspect the existing foundation hardware as part of the scope, because a new addition anchored to failing hardware is a future lawsuit, not a home improvement.
Pricing for Home Additions & ADU in Half Moon Bay, CA
Here are the numbers for this market. A room addition in Half Moon Bay runs $45,000-$130,000. A new detached ADU runs $90,000-$220,000. A garage conversion ADU runs $30,000-$80,000. A junior ADU or interior conversion can come in lower, but it depends on what’s already inside the footprint. What moves the price: the Coastal Development Permit process, the age and condition of the existing structure, whether we’re cutting into a hillside or building on a flat lot near Miramar, and how much of the old framing has to be replaced once we open it up. Every allowance goes in writing before we start, and every change comes as a written change order. Call (877) 610-1318 for a free estimate, and we’ll give you a line-item scope you can actually compare.
We Also Serve Cities Near Half Moon Bay
Half Moon Bay is home base for this page, but our Half Moon Bay crews also work in El Granada, Hillsborough, Burlingame, and Millbrae. If you live over the hill and you’re planning an addition or ADU, we know the different permit realities in each of those towns and we’ll tell you straight what to expect. We also handle Kitchen Remodeling in Half Moon Bay and Bathroom Remodeling in Half Moon Bay for homeowners who want to stay coastal and not lose the light or the view.
Serving Half Moon Bay, CA - Our Local Coverage Area
We’re based in the Half Moon Bay 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 Half Moon Bay
A home addition in Half Moon Bay typically runs $45,000-$130,000, depending on the size of the addition, the condition of the existing structure, and whether the Coastal Development Permit process adds review time and scope constraints. Call (877) 610-1318 for an exact quote, and we’ll put the full line-item scope in writing before you decide anything.
Yes. Nearly every construction project in Half Moon Bay’s developed area sits inside the California Coastal Commission’s coastal zone, so we handle the Coastal Development Permit alongside the standard city permits. We don’t tell you permits are optional, because the permit inspector works for you, not for us. Call (877) 610-1318 and we’ll walk you through which permits your specific project needs.
The Coastal Development Permit review is the variable. A straightforward garage conversion can move in a few months, while a new detached ADU with full coastal review can take the better part of a year from design to certificate of occupancy. We give you a schedule in writing and we tell you early if the Coastal Commission’s clock is running longer than expected. Call (877) 610-1318 for a realistic timeline for your specific lot.
Only if something changes, and only in writing first. If we open a wall and find rot in the sill plate or sheathing, you get a written change order before we touch it. We don’t do surprise invoices. An allowance that isn’t on paper is a surprise waiting for a date, so we put every allowance on paper before the first nail moves. Call (877) 610-1318 if you want to talk through how that works on your project.
Yes. Every job we complete carries the 90-Day Done Right Promise, written on the contract. If it’s not done right, one call brings Tom Barrett back to make it right. We also offer a Free Second Opinion on any written estimate, so if you have a competing bid, bring it in. Call (877) 610-1318 to schedule your free estimate today.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Half Moon Bay and the surrounding coast.