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 call a contractor because they woke up wanting construction. They call because the house stopped fitting the life. Maybe your aging parents moved in. Maybe your adult son can’t afford a place in the LA basin and boomeranged home. Maybe you’ve run the numbers and a detached ADU in the backyard rents for $2,200 a month here because there’s nothing else available. A home addition in San Dimas typically runs $45,000 to $130,000 depending on scope, and an ADU comes in between $90,000 and $220,000. Barrett & Sons Construction has been building both since 1998. Tom Barrett signs every contract and his sons run the crews. Call (877) 610-1318 and we’ll walk your property with you, pull the permit picture together, and hand you a written scope with every allowance on paper before you commit to anything.
Why Barrett & Sons Construction Is San Dimas’s Preferred Home Additions & ADU Company
We’re not a franchise dispatching strangers to your door. Tom Barrett’s name, address, and license number are published on every contract and verifiable before you sign. It’s his face you’ll see at the lumberyard in Glendora on a Saturday morning. The sons are on-site most days, not a rotating cast of subcontractors who couldn’t find San Dimas on a map.
There’s a particular headache in this city that flatland contractors never see coming. Northern San Dimas parcels near the foothills can fall under City jurisdiction or unincorporated LA County, sometimes on the same street. Each has its own plan-check process and its own interpretation of Chapter 7A fire-hardening rules. We’ve shepherded additions and ADUs through both. That dual-jurisdiction experience matters when your permit gets flagged and the clock is running.
Every scope, every allowance, every price change arrives as a written change order before work happens. No surprise invoices at the end. And every job carries our 90-Day Done Right Promise in writing: if it’s not done right, one call brings Tom back to make it right. A live person answers our phone around the clock, not a voicemail box.
Our Home Additions & ADU Services in San Dimas
ADU Design & Permitting
San Dimas has been aggressive about ADU permits in recent years, but the hillside parcels above the 210 corridor throw curveballs flatland projects never see. Cut-and-fill grading, aging retaining walls, and slope-stability reports often land on the plan-check list for the first time after a contractor has already told you “no problem.” We file the geotechnical review before we submit, because re-submittal fees and stopped clocks are a lousy way to learn about your soil. Our Home Additions & ADU team handles the full permit package from survey through signed final inspection.
Garage Conversion ADU
The 1950s to 1980s ranch homes that dominate San Dimas’s flat grid almost all have attached garages built before seismic tie-downs and foundation anchors were standard. Converting one into an ADU means bringing that garage shell up to current code for occupied space, not storage. We open the walls, verify the footing depth, add shear, insulate, and install the utility runs before the drywall goes up. Most garage conversion ADUs in San Dimas land between $30,000 and $80,000 depending on whether we’re adding a bathroom, a small kitchen, or just a studio suite.
New Detached ADU
On larger San Dimas lots, especially those with deeper backyards in the 91773 zip, a detached ADU in the rear yard often pencils out better than reconfiguring the main house. You keep your privacy, the tenant keeps theirs, and the rent is real income. New detached ADU construction here runs $90,000 to $220,000. In the hillside fire zones, that build requires Class A roofing, ember-resistant vents, and ignition-resistant siding. Someone down in Covina can skip those line items. You can’t.
Junior ADU & Interior Conversion
Not every San Dimas household needs a full kitchen in the backyard. A junior ADU, which is typically a converted bedroom or bonus room with its own entrance and a small kitchenette, attaches to the existing house and costs far less than a ground-up build. The tradeoff is shared utilities and a smaller footprint. For families bringing an aging parent home, it’s often the right size. Permits are simpler, and the work usually wraps in weeks, not months.
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 we build a paver patio for an ADU entry or a walkway from the main house to a new detached unit, we install brands you can look up: Techo-Bloc and Cambridge Pavers are two we’ve used for years, with Quikrete products in the base and setting work. No mystery material off a van. If a paver ever fails under our 90-Day Done Right Promise, we’re back out to fix it.
Common Home Additions & ADU Problems We See in San Dimas Homes
- Hillside foundations and cut-and-fill surprises. Homes on the northern foothill parcels were often graded decades ago under looser rules. A room addition triggers a geotechnical review that reveals what the original builder buried. We plan for it in the initial scope, not as a change-order bombshell after excavation starts.
- Chapter 7A fire-hardening compliance. Big chunks of San Dimas sit in the Very High Fire Hazard Severity Zone. Additions touching the existing structure must match current ignition-resistant standards, which means re-siding or re-roofing sections you weren’t planning to touch. Bids that ignore this are fantasy numbers.
- Dual-jurisdiction permits. Some San Dimas streets split between City and unincorporated LA County jurisdiction. Filing in the wrong one stalls the project for weeks. We identify jurisdiction before submittal, every time.
- Aging ranch floor plans that fight expansion. The post-war tract homes here were designed around a linear hallway-and-bedrooms layout. Adding a master suite or a second story means load-path work on original foundations and cutting into slab floors for new plumbing. It’s doable. It’s just not a weekend project.
Pricing for Home Additions & ADU in San Dimas, CA
Real numbers, so you can plan. A standard single-story room addition in San Dimas runs $45,000 to $130,000. A garage conversion ADU lands between $30,000 and $80,000. A new detached ADU with its own kitchen and bathroom starts around $90,000 and can reach $220,000 on hillside lots where grading, retaining walls, and fire-hardening add real cost. Site work is the wildcard here: the foothill topography means some parcels need $15,000 in grading and drainage before a single stud is cut, while a flat-lot project on the grid has almost none. We give you a written line-item quote before work starts, and every change after that arrives as a written change order. No surprises at the final invoice. Call (877) 610-1318 to schedule a free estimate at your property.
We Also Serve Cities Near San Dimas
Our crews work across Charter Oak, La Verne, Pomona, and Glendora, and we bring the same written-scope discipline and 90-Day Done Right Promise to every one of those jobs. If you’re in San Dimas or any of the neighboring foothill communities and you’re thinking about adding space, we’d like to walk the property with you. And while we’re already on-site, plenty of our clients fold in a Kitchen Remodeling in San Dimas or a Bathroom Remodeling in San Dimas as part of the bigger project, since the walls are open anyway.
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
A home addition in San Dimas typically costs $45,000 to $130,000 depending on size, foundation work, and fire-hardening requirements. A garage conversion ADU runs $30,000 to $80,000, and a new detached ADU starts around $90,000 and reaches $220,000 on hillside lots with grading and Chapter 7A compliance costs. Call (877) 610-1318 for an exact quote, estimates are free.
Yes, if your property falls within California’s Very High Fire Hazard Severity Zone, which covers large portions of San Dimas, especially north of the 210. That means Class A roofing, ember-resistant vents, and ignition-resistant exterior assemblies under CBC Chapter 7A. We handle these line items in every applicable scope, and we’ll tell you on the first walk if your parcel falls in the zone.
Yes, and we’ve done it repeatedly. Hillside parcels often require geotechnical review, grading verification, and retaining wall evaluation before the building permit issues. Some northern San Dimas streets fall under unincorporated LA County jurisdiction instead of the City, which changes the plan-check process. We identify the jurisdiction and file the complete package correctly the first time. Call (877) 610-1318 and we’ll check your parcel.
Only if you change the scope, and only in writing. Every change order is a written document you approve before any extra work happens. The original contract carries the original price, and our 90-Day Done Right Promise covers the finished work. If anything isn’t right, Tom Barrett comes back and makes it right, one call.
Yes, and it’s most of what we see. The 1950s to 1980s ranch stock on the flat grid has predictable framing and slab foundations, but the load-path work and plumbing runs need a contractor who’s done it before. We have. We also handle second-story additions where the lot doesn’t allow spreading out. Call (877) 610-1318 and we’ll tell you if your floor plan can support it.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving San Dimas since 1998.