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 Glendora
A home addition in Glendora typically runs $45,000 to $130,000, while a fully permitted detached ADU lands between $90,000 and $220,000 depending on site work, foundation type, and WUI requirements in the hillside zones. We’re Barrett & Sons Construction, and we’ve been building and remodeling in the San Gabriel Valley since 1998. If you live in the 91740 or 91741 ZIP codes, call (877) 610-1318 for a free estimate and we’ll walk through what your specific lot can support before you spend a dollar on plans.
Why Barrett & Sons Construction Is Glendora’s Preferred Home Additions & ADU Company
Glendora isn’t a training ground for us. Tom Barrett and his sons have pulled permits in the foothills above Baseline Road, navigated the geotechnical report requirements on sloped lots near the Colby Fire burn scar, and worked on flatland Ranch homes south of Route 66 that need panel upgrades before any addition gets framed. When a Glendora homeowner calls, the person answering is a live person at our Los Angeles office, and the crew that shows up carries the Barrett name on their trucks and their shirts, not a subcontractor’s logo we rented for the week.
We write every allowance and every change order on paper before work starts. The permit inspector works for you, not for me, which is why we pull permits on every eligible job and get the inspection signed. If your last contractor told you permits were optional, call us and ask to see the difference. Our reviews from Glendora customers point to the same thing: a price that held, a schedule that was honest, and a call answered when something needed attention. The 90-Day Done Right Promise backs every completed job, in writing.
Our Home Additions & ADU Services in Glendora
ADU Design & Permitting
Detached ADUs in Glendora run $90,000 to $220,000, and the permitting path changes dramatically once you cross north of Baseline Road into the 91741 hillside zones. Those lots fall in the Very High Fire Hazard Severity Zone, which means CBC Chapter 7A WUI standards apply: ember-resistant venting, Class A roof assemblies, and ignition-resistant cladding. We handle that from the first site visit, and we’ll tell you before you hire us whether your property will need a soils report for grading approval, a retaining wall for drainage control, or a panel upgrade to carry the new load. No surprises later.
Garage Conversion ADU
Glendora’s flatland neighborhoods are thick with 1950s and 1960s Ranch homes where the attached garage sits right against the house. A garage conversion ADU typically runs $30,000 to $80,000 here, and the older those structures get, the more likely you’re dealing with a slab that needs leveling, wiring that wasn’t built for a kitchen, and a driveway that needs re-sloping for the new entry. We put all of it in writing before the first Saturday of demo.
New Detached ADU
New detached ADUs on Glendora lots need more thought than a builder who only works in flat SGV cities like Covina or West Covina would assume. Alluvial fan soils up against the San Gabriels make foundation design site-specific. We coordinate the geotechnical report, the pier-and-grade-beam or caisson design if your slope demands it, and the drainage plan that keeps heavy winter rain funneling away from the new structure instead of under it.
Junior ADU & Interior Conversion
For homeowners who don’t want to add square footage, a Junior ADU or interior conversion inside the existing footprint can work well in Glendora’s Ranch homes, where long hallways and attached laundry rooms often convert cleanly. This is the entry point where we also talk through whether a Bathroom Remodeling in Glendora project should happen at the same time, since opening walls once saves money even if the ADU itself stays simple. Schluter waterproofing systems come into play frequently in these conversions because of how we tie old slab floors into new wet areas.
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 Glendora
We install materials you can look up yourself. On ADU kitchens and baths we regularly use Schluter for waterproofing and Sterling fixtures for durability in hard-water areas, which includes much of Glendora’s older housing stock. On roofing tied to second story additions, GAF assemblies are what we recommend for the Class A fire rating the hillside inspections require. When Glendora homeowners need parts or replacements, our suppliers in the SGV keep lead times short, and we tell you what’s in stock before you sign the contract.
Common Home Additions & ADU Problems We See in Glendora Homes
- Hillside drainage and debris-flow exposure above Baseline Road: properties in 91741 sit on alluvial fan deposits below the Colby Fire burn scar, and we regularly see retaining walls that were never engineered and downspouts that empty against the foundation. Any addition up there without a drainage plan is a leak and erosion problem waiting for the next wet winter.
- Aging flatland panels and plumbing: Glendora’s Ranch-era stock from the 1950s through 1970s often still runs on 60-amp services and cast iron waste lines. Framing a new bedroom is simple; feeding it power and tying it into a 70-year-old sewer line is where we see the real cost.
- WUI code surprises north of Foothill Boulevard: contractors who only build in flat SGV cities lose weeks and thousands when Glendora’s building department requires ember-resistant venting and ignition-resistant siding. We quote that from the start because we’ve pulled those permits here already.
- Slab-on-grade foundation complications: many Ranch homes in 91740 sit on slabs that were never meant to carry a second story or a heavy addition. When we’re planning a room addition or a second story, we check the slab thickness and existing footings before we promise anything.
Pricing for Home Additions & ADU in Glendora, CA
Here’s the honest range for our Glendora work. A conventional home addition runs $45,000 to $130,000 depending on whether it’s a single room bump-out or a full second story. A new detached ADU runs $90,000 to $220,000, with the higher end landing on hillside lots in 91741 where geotechnical reports, caissons, retaining walls, and WUI materials all stack onto the cost. A garage conversion runs $30,000 to $80,000 depending on what the old slab and wiring need. The price we quote is the price we build to unless you change the scope, and any change order comes to you in writing before the work happens. Call (877) 610-1318 for a free, line-itemed estimate.
We Also Serve Cities Near Glendora
While this page covers Glendora’s 91740 and 91741 ZIP codes, our Home Additions & ADU team works across the surrounding foothill and flatland communities. Homeowners in San Dimas, Azusa, Citrus, and Charter Oak see the same crews, the same written change orders, and the same verification process. If you’re reading this from a neighboring city, call the same number and ask for a free second opinion on any written estimate you’ve received.
Serving Glendora, CA - Our Local Coverage Area
We’re based in the Glendora 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 Glendora
Home additions in Glendora run $45,000 to $130,000, garage conversions run $30,000 to $80,000, and new detached ADUs run $90,000 to $220,000. Hillside lots in 91741 above Baseline Road land at the higher end because geotechnical reports, WUI materials, and drainage engineering are mandatory, not optional. Call (877) 610-1318 and we’ll put exact numbers against your specific lot before you commit.
The only thing that changes the price is a change you ask for, and every one of those arrives as a written change order before work proceeds. We don’t hand you a surprise invoice at the end because something “came up” in the wall. Tom Barrett has run the company that way since 1998, and the 90-Day Done Right Promise backs the finished product. Call (877) 610-1318 if you want to see what that looks like on paper.
Yes, on every eligible job, including Hillside Review Board items north of Baseline Road where Glendora’s building department requires geotechnical reports before grading or foundation approval. The inspector works for you, not for us, and we want that inspection signed. If you’ve had a contractor tell you permits are optional, call (877) 610-1318 and we’ll show you the difference in writing.
A garage conversion typically runs 3 to 5 months, a room addition 4 to 7 months, and a new detached ADU 6 to 10 months once permits are issued. Hillside jobs in 91741 add time for the geotechnical and grading approvals that the flatland cities don’t require. We set an honest schedule before the first nail moves and keep it on paper. Call (877) 610-1318 if you want a start-to-finish timeline for your specific project.
Every completed job is covered by the written 90-Day Done Right Promise, and we’ll make it right if something isn’t. One call to (877) 610-1318 brings Tom Barrett back to your street. We also carry the manufacturer warranties on materials like GAF roofing, Schluter waterproofing, and Sterling fixtures, and we tell you what’s covered before you buy.
If you’re planning a home addition or ADU in Glendora, start with a free estimate and a straight conversation about what your lot actually requires. Call (877) 610-1318 and ask for Tom or one of his sons. We’ll walk the property with you, put the numbers on paper, and leave you with a plan you can verify.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Glendora since 1998.