Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
Before
After
Before
After
Before
AfterFast, Reliable Home Additions & ADU Across Westminster
Most room additions and ADU projects in Westminster sit somewhere between $45,000 and $130,000, and the single biggest mistake we see is a homeowner signing with a contractor who hasn’t built in this city before. Westminster’s housing stock is overwhelmingly single-story ranch homes on concrete slabs from the 1950s through the mid-1970s, which means foundation work, drainage planning, and title issues around ADUs take more local care than a generic Orange County crew will give them. Our Home Additions & ADU team works the full grid of Westminster from the 92683, 92684, and 92685 zip codes every week. Call (877) 610-1318 and we’ll come look at your lot, your set backs, and your existing slab before anyone quotes you a number.
Why Barrett & Sons Construction Is Westminster’s Preferred Home Additions & ADU Company
Tom Barrett founded this company in 1998 and his sons run the crews, which is a fact we state plainly because in Westminster you’ll meet a lot of contractors who are harder to find after the work starts than before it. We publish Tom’s name, address, and license number. Look it up before you sign anything, and then ask any customer on your street whether we returned the call when something came up at month three. The 90-Day Done Right Promise goes on every contract. It is not buried in fine print; it says Tom comes back and makes it right with one call.
Westminster jobs get scheduled by crews who know the city’s parking constraints, the permit desk at City Hall on All American Way, and the pressure the marine layer puts on exterior finish schedules. We answer the phone live, 24/7, and background-checked crew members wear our name on their shirts. That matters when you’re letting people into your home for weeks on an addition.
Our Home Additions & ADU Services in Westminster
ADU Design & Permitting
Westminster sits close enough to the coast that ADU plans need careful attention to the city’s specific lot size rules, rear yard setbacks, and parking replacement requirements. We draw ADUs that fit your lot, not a catalog plan, and we sit with you through the City of Westminster planning and building reviews until permits are signed. Most ADU permit sets in Westminster move faster when the drawings match the existing home’s roofline and slab conditions on the first submission, and that is exactly where our local Westminster Roofing and drafting experience pays off.
Garage Conversion ADU
Most Westminster garage conversions start with a detached two-car garage built in the 1960s or early 1970s. The slab is frequently thin by current code, the electrical panel is often zinsco or federal pacific, and the garage sits exactly at the property line. We scope the conversion honestly: new slab reinforcement where needed, panel upgrade, insulation, and proper sewer tie-in. A typical garage conversion in Westminster runs $30,000 to $80,000 depending on how much of the original framing you want to keep.
New Detached ADU
On the wider lots in Westminster’s residential grid, a detached ADU is often the better play if you’re thinking about renting the space or giving an adult child room to breathe. Concrete slab work here requires careful compaction testing; Westminster’s flat alluvial soils can settle unevenly if the base isn’t prepared right. We scope full foundation systems, utility runs from the street or main house, and a structure that matches your home’s mid-century lines rather than a box that looks shipped from a catalog, with Windows & Doors - Westminster selections that fit the original style. ADU construction in Westminster generally lands between $90,000 and $220,000.
Junior ADU & Interior Conversion
A junior ADU is the fastest way to create a legal, private living space inside the envelope of your existing home, and it is a strong option on the narrower lots east of Beach Boulevard where a detached unit has no room to go. We convert a spare bedroom, a den, or an overbuilt laundry room into a JADU with its own entrance, small kitchen, and independent climate. Because these projects stay inside the home’s existing footprint, permits move quicker and the cost typically stays at the lower end of the $45,000 to $130,000 range for room-scale additions.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in Westminster
Hardscape and outdoor living tie-ins for ADU projects in Westminster often call for pavers that can take the city’s marine moisture without shifting, and we install Techo-Bloc and Cambridge Pavers for exactly that reason. For concrete driveway approaches and slab walkways around new ADU entrances, we use Oldcastle and Quikrete products that our Westminster crews know how to place and finish in the persistent morning marine layer that rolls in off the Santa Ana River coastal plain. Naming the brand matters when you’re comparing bids; you can look up any of these materials yourself.
Common Home Additions & ADU Problems We See in Westminster Homes
- Thin original slabs. Many Westminster ranch homes were poured in the 1950s and 1960s to residential codes that did not anticipate a fully plumbed ADU addition. Before we tie new walls into that slab, we core-test and reinforce it; skipping this step leaves you with a cracked floor and a cracked relationship with your contractor.
- Original low-slope roofs complicating second-story work. A Westminster home with a low-slope roof from the tract era is not a simple platform for a second-story addition. Roof framing, drainage planes, and parapet flashings all need rework, and a contractor who has not done it in this specific housing stock will underbid it.
- Drainage and soil compaction on flat alluvial land. Westminster is flat. That is the whole problem: water pools, soils settle unevenly, and any ground-up slab pour without compaction testing and drainage design is a crack waiting for its first rainy season.
- Multigenerational household reconfigurations. More Westminster families are adding space for aging parents or adult children than nearly any city around us. This changes sound insulation, private entrance, and kitchen separation requirements, and it is why our ADU designs in Westminster lean toward true separation rather than one shared wall of noise.
Pricing for Home Additions & ADU in Westminster, CA
Expect a room addition or full ADU in Westminster to run between $45,000 and $130,000 depending on whether you’re converting an existing garage, adding a ground-floor suite, or building a detached unit from scratch. Detached ADUs typically land higher, in the $90,000 to $220,000 range, because they include a full foundation, separate utility runs, and their own roof. A garage conversion typically runs $30,000 to $80,000. Every allowance, every change, and every price movement arrives as a written change order before work proceeds. We do not bid a number on the phone and surprise you later. Call (877) 610-1318 for a written line-item estimate on your Westminster property – free, no trip charge inside the county.
We Also Serve Cities Near Westminster
We work regularly in Westminster and also run crews into Midway City, Garden Grove, Stanton, and Huntington Beach. If your project sits right on the border of one of those cities, call us and we’ll tell you straight which permit jurisdiction governs your address. You will also find our Kitchen Remodeling in Westminster and Bathroom Remodeling in Westminster teams working the same neighborhoods, and a Home Additions & ADU project often starts with one of those rooms.
Serving Westminster, CA - Our Local Coverage Area
We’re based in the Westminster 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 Westminster
Our scheduling is coordinated from our Los Angeles office and we serve Westminster locally, so a site visit can usually be arranged around your schedule within the week, not the month. We have no trip charge inside the county. Call (877) 610-1318 to set a day and time; a live person answers the phone around the clock.
Yes. On every eligible job in Westminster we pull the permits and sit with the inspector through each sign-off. The permit inspector works for you, not for us; we want every inspection passed in the open, and if a scope item or change comes up, it becomes a written change order before anything gets touched.
Only if the scope changes, and only in writing before that change begins. We don’t do surprise invoices at the end of a Westminster job. Every allowance is on paper, every change order is on paper, and the 90-Day Done Right Promise means if something is not right after we finish, Tom comes back and makes it right.
Yes. We cover all of Westminster including the 92683, 92684, and 92685 zip codes, from neighborhoods east of Beach Boulevard to the residential streets west of Hoover Street. If you are not sure your project is in our Westminster service area, call (877) 610-1318 and give us your cross streets.
Westminster sits in the same coastal Plain cost band as Fountain Valley, but we typically see more slab reinforcement and drainage work here because Westminster’s original tract housing carries thinner slabs and flatter lots. That tends to push Westminster ADU and addition pricing toward the middle of the $45,000 to $130,000 range rather than the bottom. For an exact quote on your lot, call (877) 610-1318 and we’ll come look at the slab before we talk numbers.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Westminster, CA since 1998.