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 San Dimas
Most San Dimas homeowners don’t realize how much their address changes the price and scope of an addition until they’re three weeks into plan check. The short answer for this market: a Home Addition in San Dimas typically falls between $45,000 and $130,000, while a detached ADU runs higher, usually $90,000 to $220,000 depending on slope, fire-zone requirements, and utility trenching. We’re Barrett & Sons Construction, and we’ve built enough in the 91773 to know exactly where the surprises hide on your particular street. Call Tom’s team at (877) 610-1318 for a number that reflects your lot, not a national average.
San Dimas isn’t a flatland city. The northern parcels climb into the San Gabriel foothills, and that changes everything about how your foundation gets engineered, what your exterior walls have to withstand, and how long permitting actually takes. For San Dimas Roofing projects, those hillside conditions mean materials and methods that flatland contractors often underestimate. We know the difference between a ranch home off San Dimas Avenue and a hillside custom off Foothill Boulevard that needs geotechnical sign-off before the first stake goes in. If you’ve been quoted a price that sounds too clean, it probably skipped over something this city actually requires. That’s the gap we close.
Why Barrett & Sons Construction Is San Dimas’s Preferred Home Additions & ADU Company
Tom Barrett started this company in 1998 and put his name on every truck because he lives with the consequences. His sons run the crews, and they’re on site most days in San Dimas, not phoning in from a franchise office two states away. Every job gets a written change order before any scope change touches the wood, and every permit gets pulled. The permit inspector works for you, not for us, and we like it that way.
Customers in San Dimas keep calling back because we answer the phone like a neighbor, and because the 90-Day Done Right Promise is printed on the contract, not buried in fine print. If something’s not right, one call brings Tom back. We also carry premium brands across every trade we touch, so when you’re deciding between KraftMaid and Cambria for the new kitchen in your addition, you’re choosing from materials you can actually look up.
You won’t get a nationwide call center when you reach out. A live person answers 24/7, and you can verify Tom’s name, address, and license number before you sign anything. That matters when you’ve been burned before by a company that quoted one number on the phone and handed you another at the door.
Our Home Additions & ADU Services in San Dimas
ADU Design & Permitting
Most San Dimas ADU projects stall before a single wall goes up. The reason is specific to this city: parcels in the northern foothills often fall under either the City of San Dimas or unincorporated LA County depending on the street, and the two jurisdictions don’t always interpret Chapter 7A ignition-resistant construction the same way. We identify which plan-check process applies to your parcel before submittal, so you don’t lose six weeks to a rejection you could have avoided on day one. From the initial survey through stamped plans and the final inspection, we handle the ADU Design & Permitting process end to end.
Garage Conversion ADU
Garage conversions are one of the most cost-effective ways to add living space in San Dimas, particularly on the 1950s and 60s ranch lots where the garage sits on slab and the roofline is simple. A typical Garage Conversion ADU in San Dimas runs $30,000 to $80,000, depending on whether you’re adding a bath and how much of the existing electrical panel has capacity. We pull the permits, upgrade the envelope to current code, and run the change orders in writing before anything happens you didn’t approve. That includes any Windows & Doors - San Dimas upgrades needed to meet current energy and safety standards.
New Detached ADU
A New Detached ADU on a San Dimas hillside lot is a different animal than one on a flat parcel. Cut-and-fill grading from the original build may need geotechnical review under current county grading ordinances, and utility trenching uphill toward the main service can add real cost. We quote these honestly, with the site work called out line by line, so you’re not surprised mid-project. Expect $90,000 to $220,000 for a fully permitted detached unit with kitchen, bath, and separate entry.
Junior ADU & Interior Conversion
A Junior ADU or interior conversion inside an existing San Dimas home is often the fastest route to rental income or multigenerational living. We convert underused rooms, basements where they exist, or attached areas into legal dwelling space with their own entrance and efficiency kitchen. Interior conversions typically run $45,000 to $130,000, and we handle the fire separation, occupancy, and egress requirements specific to San Dimas code.
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 San Dimas
When your addition includes hardscape, walkways, or a new driveway approach, the paver choice matters for both drainage and curb appeal. We regularly work with Home Additions & ADU projects that flow into outdoor living spaces, and we stock local volume pricing on Techo-Bloc, Cambridge Pavers, and Quikrete so San Dimas customers aren’t waiting on a truck from Riverside. The same applies indoors: KraftMaid cabinets, Cambria countertops, Andersen windows. Materials you can verify, installed by people who will be at the hardware store on Saturday.
For related interior work on the same property, we also handle Kitchen Remodeling in San Dimas and Bathroom Remodeling in San Dimas as part of a broader addition project. That keeps the scheduling, the permits, and the responsibility under one roof instead of juggling three contractors.
Common Home Additions & ADU Problems We See in San Dimas Homes
- Fire-zone envelope surprises. Because much of San Dimas sits within California’s Very High Fire Hazard Severity Zone, additions and ADUs on those parcels must meet CBC Chapter 7A: Class A roofing, ember-resistant vents, and ignition-resistant exterior walls. Homes a few miles south in Covina or West Covina don’t carry that burden, and an estimate that ignores it will be wrong on day one.
- Dual-jurisdiction permitting stalls. We regularly see San Dimas projects where two neighbors on the same street answer to different plan-check authorities, one under the city and one under unincorporated LA County. If nobody checks before submittal, the project stalls mid-permit. We check first.
- Hillside foundation and drainage issues. The northern foothill parcels in San Dimas, many graded in the 1960s and 70s, often have aging retaining walls and drainage that predates current slope ordinances. An addition on those lots frequently triggers a geotechnical review and drainage upgrade that flatland quotes simply don’t include.
- Post-fire debris flow and washout exposure. Santa Ana wind-driven embers aren’t the only mountain-related risk. After wet winters, alluvial wash events from the San Gabriels hit the steeper residential zones, and we regularly shore up drainage and retaining walls as part of larger addition scopes in San Dimas.
Pricing for Home Additions & ADU in San Dimas, CA
Here’s what you can expect to budget in the 91773 as of this year, based on the projects we’re seeing in San Dimas right now: a Home Addition runs $45,000 to $130,000; a Garage Conversion ADU runs $30,000 to $80,000; a New Detached ADU runs $90,000 to $220,000; and an ADU involving design and permitting as part of a larger addition can fall anywhere within those bands depending on site conditions. Hillside grading, fire-zone assembly upgrades, and utility trenching are the three line items that move San Dimas numbers most. Every scope, every allowance, every price change arrives as a written change order before work happens. No surprises at the end.
We offer a Free Second Opinion on Any Written Estimate and a No Trip Charge Inside the County for your initial visit. A permanent 10% Senior & Veteran discount applies. Call (877) 610-1318 for an exact quote.
We Also Serve Cities Near San Dimas
If you’re outside the 91773 but nearby, we regularly work in Home Additions & ADU in San Dimas and the surrounding communities: Charter Oak, La Verne, Pomona, and Glendora. The same crew, the same written change orders, and the same 90-Day Done Right Promise follow us wherever we go.
Serving San Dimas, CA - Our Local Coverage Area
We’re based in the San Dimas 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 San Dimas
Most San Dimas additions can begin within two to six weeks of your signed contract, depending on whether your parcel needs geotechnical review and which jurisdiction handles your plan check. We start the process with a free estimate and a written timeline. Call (877) 610-1318 to get a schedule for your specific address.
Yes. We work across the full 91773, from the ranch tracts near San Dimas Avenue to the hillside parcels off Foothill Boulevard and the custom-graded lots in the northern foothills. We know which streets fall under city jurisdiction and which fall under the county, and we plan accordingly before we submit anything.
A Home Addition in San Dimas typically runs $45,000 to $130,000, which is generally higher than flatland cities like Pomona or Glendora because of fire-zone assembly requirements, slope grading, and occasionally dual-jurisdiction permitting. You’re paying for the mountain, basically. Call for a free estimate at (877) 610-1318.
Yes, on every eligible job. Permits are not optional in San Dimas, especially in the fire hazard zones where Chapter 7A compliance gets inspected. The permit inspector works for you, not for us, and we’re glad to have him on the job. Every permit, every inspection, every signature is documented.
Every project carries the 90-Day Done Right Promise in writing. If it’s not done right, Tom comes back and makes it right with one call. That applies to additions, ADUs, fire-zone assemblies, and everything else we touch in San Dimas. Call (877) 610-1318 and ask Tom about it directly.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving San Dimas and the surrounding foothill communities.