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 Westmont
Adding square footage or building an ADU on a Westmont property is a different animal than doing the same work in the City of LA. Westmont is unincorporated Los Angeles County, which means every permit, every inspection, and every code ruling goes through LA County Public Works, not LADBS. That single fact trips up a lot of out-of-area contractors. It doesn’t trip us up. A typical Home Additions & ADU project in Westmont runs $45,000 to $130,000, and the price moves based on what we find when we open the walls. Call Barrett & Sons Construction at (877) 610-1318 for a free estimate, and we’ll walk your lot with you before anyone swings a hammer.
Why Barrett & Sons Construction Is Westmont’s Preferred Home Additions & ADU Company
Tom Barrett founded this company in 1998 and has kept it owner-operated ever since. His sons run the crews. When we tell a Westmont homeowner we’ll be there Tuesday, it’s Tom’s truck that shows up, not a dispatcher’s guess. Our reputation in the 90047 is built on the same thing your neighbors care about: we pull permits on every eligible job, we write every price change on paper before the work happens, and we answer our own phone. A live person picks up 24/7, not a voicemail box in another state.
Westmont customers call us after getting burned by companies that quoted one number on the phone and produced a bigger one at the end. That doesn’t happen here. Allowances are written into the contract. Change orders are issued in writing before we touch anything. And every job carries our 90-Day Done Right Promise: if it’s not right, one call brings Tom back. Ask anyone on your street, or look up the license number yourself. We publish Tom’s name, his address, and his license number, because a contractor who won’t stand behind his name isn’t worth hiring.
We know the LA County unincorporated plan check queue, the setback tables specific to R-2 lots, and the inspectors who sign off on Westmont work. That fluency isn’t a marketing line. It’s the difference between a permit clearing in two weeks and a permit stalling for two months while a crew from outside the area figures out which form to file.
Our Home Additions & ADU Services in Westmont
ADU Design & Permitting
Building an ADU in Westmont means navigating LA County Public Works from the first plan check to the final inspection. We handle the drawings, the forms, and the scheduling. If your lot is R-2 and you’ve got an old rear conversion that was never permitted, we’ll fold that into the plan so the new ADU permit doesn’t trigger a surprise compliance review you didn’t see coming. ADU construction in Westmont typically runs $90,000 to $220,000, with the County-specific permitting work included in that figure.
Garage Conversion ADU
Many Westmont homes still have the detached garages they were built with in the late 1940s and early 1950s. Converting one into a legal ADU is often the fastest and most cost-effective way to add rentable square footage, with most jobs landing between $30,000 and $80,000. The catch is that many of these garages were converted once already, without permits. When we pull a permit for the legal version, the County sees the old work, and the whole structure has to be brought to code. We plan for that from the first walkthrough, so the number we quote is the number you pay.
New Detached ADU
If your Westmont lot has the space, a new detached ADU gives you a clean build with no hidden legacy issues. We pour the footings to County depth standards, which matters more here than people expect. Westmont sits on expansive clay soil, the same stuff that causes slab heave through the long dry summers. An ADU that gets built on footings sized for a coastal lot will crack within a year of signing off. We don’t build it that way.
Junior ADU & Interior Conversion
A Junior ADU is a permitted conversion of space already inside your home, usually a spare bedroom with its own entrance and kitchenette. On Westmont bungalows and duplexes, this is often the most practical option when the lot is too small for a detached unit. The permit path still runs through LA County, but the scope is smaller and the price comes in well under a full ADU build. We’ll tell you honestly which route makes sense for your property, even if the cheaper answer is the one we’d rather you pick.
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 Westmont
We’re not a crew that shows up with mystery materials off a van. On Westmont additions and ADUs we regularly install Schluter waterproofing systems in kitchens and baths, Sterling fixtures, and Grohe plumbing. For any roof tie-in work on a second-story addition, we carry GAF materials. These are brands you can look up, and if you’ve already got a preference, we’ll write it into the scope. That’s the whole point: everything on paper before the first nail moves.
Common Home Additions & ADU Problems We See in Westmont Homes
- Unpermitted rear-unit conversions. R-2 lots in Westmont are loaded with garage and rear-unit conversions that were done decades ago without permits. The moment a new ADU permit lands in LA County’s queue, the old work gets pulled into review, and the bring-to-code costs can be significant. We price that in from day one.
- Expansive clay soil heave. The South LA basin has clay soil that shrinks through the rainless summer and swells in winter. Additions built on footings that aren’t sized and drained for that movement develop cracks within a year. We set footings for Westmont’s soil, not for a textbook.
- Undersized framing and outdated wiring. Homes built in the late 1940s and early 1950s often have 2×4 ceiling joists spanning distances they were never meant to carry, plus knob-and-tube wiring still live in the walls. Opening a load-bearing wall for an addition almost always reveals at least one of these, and both have to be brought to code before the County signs off.
- Wrong permit jurisdiction. Out-of-area crews routinely file LADBS forms for Westmont addresses and then wait weeks while the file sits in the wrong queue. LA County has its own forms, its own fee schedule, and its own inspectors. We file to the right jurisdiction the first time.
Pricing for Home Additions & ADU in Westmont, CA
Here’s what Barrett & Sons Construction prices look like for Westmont work. These are the numbers we actually quote, not teaser figures:
| Project Type | Typical Range in Westmont |
|---|---|
| Home Addition | $45,000 - $130,000 |
| ADU Construction | $90,000 - $220,000 |
| Garage Conversion | $30,000 - $80,000 |
What moves the number most is what we find when we open the walls. A 1950s bungalow off South Normandie or Vermont Avenue is going to give us something: undersized joists, old wiring, rotted sill plates. We handle it with an inspection first, allowances written into the contract, and every surprise priced and approved on a written change order before we proceed. You’ll never open an invoice at the end that looks like a different company wrote it. Call (877) 610-1318 for a written line-item estimate on your Westmont addition or ADU.
We Also Serve Cities Near Westmont
If you’re just across the line in Westmont or one of the surrounding communities, we cover that too. Our crews work regularly in View Park-Windsor Hills, West Athens, Inglewood, and Lennox. The permitting jurisdiction changes from city to city, and we handle each one on its own terms.
Serving Westmont, CA - Our Local Coverage Area
We’re based in the Westmont 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 Westmont
We handle it entirely. Your ADU or addition permit goes through LA County Public Works, not LADBS, and we know the County’s forms, setback tables, and inspection scheduling. You won’t file a single document. Call (877) 610-1318 and we’ll walk the permit path for you.
Expect at least two things: undersized framing and outdated electrical. On a 1950s stucco bungalow off South Normandie in the 90047, our crew opened a load-bearing wall to tie in a room addition and found 2×4 ceiling joists spanning too far and knob-and-tube wiring that had never been permitted. We wrote a change order for full joist sistering and a panel upgrade before proceeding, and the County inspector signed off on the rough-in the same week. That’s what we mean by inspection first and everything in writing.
Yes. Westmont has a lot of unpermitted rear-unit and garage conversions on R-2 lots, and California’s ADU amnesty rules allow many of them to be brought into compliance. The catch is that pulling the new permit triggers County review of the existing structure, and the bring-to-code work has to be done before the ADU gets signed off. We’ll tell you honestly what that will cost after a walkthrough. Call (877) 610-1318 for a free estimate.
We write a change order before we touch the work. The change order states exactly what was found, exactly what it costs to fix, and exactly how it changes the schedule. You approve it in writing before our crew proceeds. No surprise invoices at the end, ever. That’s been our rule since Tom Barrett founded the company in 1998.
Yes. We schedule around LA County’s inspection calendar because we know it. Out-of-area crews often build a schedule that assumes City of LA inspection speed and then stall for weeks. We build the County’s actual wait times into the timeline we give you, and we keep the job moving with pre-inspection walkthroughs so the inspector never shows up to an unfinished rough-in. Call (877) 610-1318 and we’ll put your addition on a schedule that reflects how Westmont permits actually work.
Get Your Westmont Home Addition or ADU Started Right
If you live in Westmont and you’re thinking about an addition, a garage conversion, or a new ADU, start with a free estimate from a contractor who knows this jurisdiction. Call Barrett & Sons Construction at (877) 610-1318. We’ll walk your property, talk about what a permit really triggers on your lot, and put every number in writing before anything starts. Tom Barrett answers his own phone.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Westmont since 1998.