Home Additions & ADU in Whittier - One Fixed Price, Permits Handled

Fast, Reliable Home Additions & ADU Across Whittier

Home additions and ADU construction in Whittier typically run $45,000-$130,000 for a standard addition, while a detached ADU falls between $90,000 and $220,000 depending on size, site conditions, and finish level. Those numbers reflect what we actually see on the hillside lots of Friendly Hills and the flat tracts of East Whittier, not a national average. If you’re weighing whether to add square footage to a 1920s bungalow near Uptown or build a rental unit in your backyard off Mar Vista Street, we can walk you through the real numbers before you spend a dime. Call (877) 610-1318 and Tom or one of his sons will give you a straight answer.

Call (877) 610-1318

Why Barrett & Sons Construction Is Whittier’s Preferred Home Additions & ADU Company

We’ve been building in Los Angeles County since 1998, and the Whittier projects stick with us for a reason: the houses here have character, and they also have quirks. Tom Barrett started this company with his name on the truck and his sons on the crew, and that’s still how it works. No franchise dispatcher sending strangers to your door. When you call, a live person answers, 24 hours a day, seven days a week.

What our Whittier customers tell us they value most is the paper trail. Every change order arrives in writing before any work happens. Every permit gets pulled and every inspection gets signed. If the scope shifts, you see the new number before the crew touches a hammer. That’s the difference between a quote and a promise. The 90-Day Done Right Promise puts it in writing: if something isn’t right, one call brings Tom back to make it right.

We also know Whittier’s building terrain the way only a local crew does. The fault line running through the city changes how we anchor additions and ADUs. The hillside lots in Friendly Hills sit on expansive clay that moves. The older raised foundations near Uptown need bolting and bracing before you add a second story on top. A contractor who doesn’t know that will give you a pretty render and a structural headache. We start with the ground under the house.

Our Home Additions & ADU Services in Whittier

ADU Design & Permitting

Whittier homeowners building an ADU are usually doing it for one of three reasons: rental income, aging parents, or adult kids who can’t afford to move out. All three deserve a design that respects the existing house and the neighborhood. We handle the plans, the structural calculations, the city submittal, and the permit process from start to finish. Whittier’s planning department has its own rhythms, and after years of working here, we know what gets approved the first time and what gets sent back with a comment letter.

Garage Conversion ADU

If your detached garage is more storage than car, a garage conversion in Whittier typically lands between $30,000 and $80,000 - and we also handle Windows & Doors - Whittier when the project calls for it. The biggest variable we see is the foundation. Older garages in the 90601 and 90603 ZIP codes were often poured as a thin slab with no footing, which means we’re pouring new footings and sometimes reinforcing the existing slab before framing interior walls. We also address the seismic question directly: a garage that was never tied to the foundation needs anchor bolts before it becomes living space, especially given the Whittier Fault running through the middle of the city.

New Detached ADU

A new detached ADU in Whittier runs $90,000 to $220,000, and the spread comes down to site work. On flat lots in East Whittier, we’re usually looking at standard excavation, utility trenching, and a straightforward foundation. On hillside lots in Friendly Hills or Whittier Hills, we’re dealing with cut-and-fill soil, retaining walls, and drainage that has to be engineered, not guessed at. Either way, we pull the permits, schedule the inspections, and build it like it’s going to be inspected by someone who’s seen a lot of shortcuts. Because it will be.

Junior ADU & Interior Conversion

A junior ADU converts existing space, usually a spare bedroom or a converted den, into a self-contained living unit with its own entrance, kitchenette, and bathroom. In Whittier, these projects often run lower than a full addition because the framing is already there. The cost we see most often is $45,000-$130,000 depending on how much plumbing and electrical work the conversion requires. If you have a 1950s tract home near Michigan Park with original galvanized pipes, the plumbing side of a JADU matters more than the floor plan. We’ll tell you which it is before you sign anything.

Every one of these scopes is part of our broader Home Additions & ADU work, and we treat each one as its own job with its own permit file and its own paper trail. If you’re also thinking about updating adjacent spaces while we’re on the property, we handle Kitchen Remodeling in Whittier and Bathroom Remodeling in Whittier, which often makes sense to sequence together when walls are open and the crew is already on site.

Trusted Brands We Service in Whittier

We install materials you can look up. For kitchens and baths that means Schluter waterproofing systems and Grohe fixtures. For our Roofing in Whittier on a new addition or attached ADU, GAF shingles are our standard spec. We don’t show up with mystery brands off a van and hope you won’t ask. If a material is going into your Whittier home, we’ll tell you the manufacturer and the model line before we order it. That’s true on every job, from a Junior ADU in 90601 to a full second-story addition near La Habra Heights.

Common Home Additions & ADU Problems We See in Whittier Homes

• Seismic gaps between old and new construction. The Whittier Fault runs directly through the city, and the 1987 Whittier Narrows earthquake exposed how badly older homes were connected to their foundations. When we tie an addition onto a pre-WWII Craftsman bungalow near Uptown, we’re almost always bolting the existing sill plate and bracing cripple walls first, because adding square footage to an unbolted house just gives the earthquake more house to move.
• Expansive clay movement on hillside lots. Friendly Hills and Whittier Hills are full of 1960s and 70s cut-and-fill lots where the original drainage was never adequate. We see cracked slabs, bowed stem walls, and retaining walls that are failing quietly. Any ADU or addition on one of those streets starts with a foundation and drainage assessment, because pouring new concrete onto moving ground is just spending money twice.
• Knob-and-tube wiring hiding in the walls. Whittier’s older core neighborhoods near Uptown still hold a surprising amount of original knob-and-tube electrical. It’s ungrounded, it doesn’t meet current code for living space, and adding an ADU or second story means the existing panel and branch circuits usually have to be upgraded at the same time. We flag this in the estimate, not after the walls are open.
• Storm runoff funneled into the wrong place. Whittier sits at the inland edge of the Puente Hills, and when Santa Ana wind events hit, they’re stronger and more sustained than what coastal LA feels. Between the wind and the way the hillside funnels storm water, drainage problems show up on almost every hillside addition we build. French drains and slope stabilization are recurring line items, not afterthoughts.

Pricing for Home Additions & ADU in Whittier, CA

We Also Serve Cities Near Whittier

Our crews work throughout the Whittier area, including Whittier neighborhoods like Friendly Hills, Uptown, and East Whittier, and we’re on the road to South Whittier, West Whittier-Los Nietos, East La Mirada, and Santa Fe Springs on a regular basis. If you’re just outside the city line, chances are we’re already working down the street from you.

FAQs - Home Additions & ADU in Whittier