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Ameristar Home Additions & ADU: The Los Angeles Owner’s Guide
If you’re planning an Ameristar Home Addition or ADU project in Los Angeles, you’re looking at an installed range of $53,100 to $153,400 for a home addition, and $106,200 to $259,600 for a full ADU construction, depending on square footage, site conditions, and finish level. That’s the honest range, and it’s what we quote from at Mason Remodeling Co Los Angeles. Most owners find their way to us when they realize their existing structure isn’t holding up, or when they need to figure out whether to fix, expand, or build new. We’ve been sorting out exactly those decisions for homeowners across Los Angeles County since 2004.
Which Ameristar Projects This Applies To
Ameristar’s product line in this space covers a few distinct builds: attached single-story additions, detached ADUs with utility hookups, and garage-to-living conversions that share structural walls. The compatibility question isn’t about a part number stamped on a box; it’s about matching load-bearing tie-ins, foundation type, and roof line to the existing home. For attached additions, the roof system has to match the original framing or you’ll get water intrusion at the transition. That’s the single most common failure we see in Los Angeles, where heavy rain hits hard and fast after long dry stretches.
For an Ameristar-styled ADU on a slab, the real gotcha is drainage. If the original pad wasn’t poured with proper slope or a French drain, you’ll get moisture wicking up into the flooring within the first two rainy seasons. We spec drainage correction into every ADU estimate we write. And when it comes to materials, we quote specification-grade product lines we trust: KraftMaid for cabinetry, Cambria and Silestone for countertops, because those are the surfaces and storage that have to survive a decade of daily use in a rental or an in-law suite.
Styles & brands we work with
Signs Your Ameristar Home Addition or ADU Is Failing
- Drywall cracks running diagonally from door and window corners. This usually means foundation settling or a roof-load transfer problem where the addition ties into the original house. Cracks wider than 1/16 inch at the joint line are worth a look.
- Doors that stick at the top edge in summer. Los Angeles heat causes expansion, but if a door binds year-round, the header or the floor framing has moved. That’s structural, not seasonal.
- Musty odor that won’t leave, especially after rain. Flat-roof additions common in older Ameristar-style builds in the Valley collect water at scupper drains. One clogged drain, and you’ve got water sitting against the framing for days.
- Floor spring or sag along the addition’s outside wall. This points to joist rot from perimeter water, or an undersized beam spanning the original exterior wall opening. We saw this repeatedly in older neighborhoods like Westchester and Mar Vista.
- Electric circuits tripping when the window AC or washer kicks on. Undersized panels from the original build weren’t designed for an ADU’s load. We re-check load calcs on every job.
See the difference
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After
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After
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AfterReplacement Cost & What’s Included
Here’s how the numbers shake out in Los Angeles. A home addition runs $53,100 to $153,400 installed. An ADU with its own kitchen and bath runs $106,200 to $259,600. What drives the range: site access, foundation work (slab vs. raised), whether we’re tying into existing plumbing or running new sewer, and the finish package you pick. Written line-item pricing is standard on every project we do. No verbal estimate that grows later, no change-order surprises. Every job includes our written guarantee for 365 days from the completion date, and if something fails within that year, we return and make it right at no charge. That’s our 365-Day Done Right Promise, and it’s not a marketing line.
Reference prices for this category in Los Angeles:
| Project | Installed Range |
|---|---|
| Home Addition | $53,100 – $153,400 |
| ADU Construction | $106,200 – $259,600 |
| Garage Conversion | $35,400 – $94,400 |
| Kitchen Remodel | $16,520 – $53,100 |
| Bathroom Remodel | $10,620 – $33,040 |
| Roof Replacement | $9,440 – $23,600 |
DIY or Call Us?
You can check the basics yourself: look for standing water at the foundation line after rain, check for visible roof drain clogs, and note where cracks are and whether they’re growing. That’s useful information for us either way. What you shouldn’t do is start framing, cutting into load-bearing walls, or rewiring. An addition or ADU in Los Angeles means city permits, structural calculations, and inspections. A wrong header size or a missed shear panel can fail quietly for years and then show up as a cracked stucco wall or a sagging roofline. And if you’re working near an existing gas or electric line, that’s not a weekend project. We coordinate permits, pull them properly, and stand behind the build. Call (213) 632-5711 and we’ll give you an honest take on whether your project is a repair or a rebuild.
FAQs
A properly built addition or ADU in Los Angeles should last 50 years or more on the structural side, though finishes like roofing, paint, and flooring will need replacement on shorter cycles. The weak points are drainage details and roof tie-ins, so those get extra attention in our builds.
Yes, in many cases we repair foundation issues, reframe sagging sections, fix drainage, and replace failed roofing without doing a full rebuild. The decision comes down to whether the original structure is sound enough to be worth saving. Call (213) 632-5711 for an exact quote – estimates are free.
A typical home addition takes 3 to 6 months, and a full ADU takes 5 to 9 months, depending on permitting, site access, and finish level. Permit approval with Los Angeles Department of Building and Safety is often the longest single variable. We’ll give you a written timeline before work starts.
Yes. We pull all required permits with the city of Los Angeles, schedule inspections, and don’t call the job done until it passes final. That’s part of the written price, not an add-on.
Know who’s coming, know what it costs, know it’s guaranteed – everything else is just noise.
Mason Remodeling Co Los Angeles is an independent service provider and is not affiliated with Ameristar. We’re a Threshold Group construction company, and every crew member who comes to your door is background-checked, identity-verified, and introduced to you by name and photo before the visit. That’s the Threshold Standard. Call (213) 632-5711 for your free written estimate, and we’ll walk you through exactly what your addition or ADU should cost in Los Angeles.
Written by Isaac Pruett, Owner, Mason Remodeling Co at Mason Remodeling Co Los Angeles, serving Los Angeles and nearby areas.
