Ameristar Home Additions & ADU Nationwide | Barrett & Sons Construction

Ameristar Home Additions & ADU: The Los Angeles Owner’s Guide

Ameristar home additions and ADUs in Los Angeles typically run $53,100 to $153,400 fully permitted and built, depending on square footage, foundation work, and whether you’re adding up or out. We install Ameristar-specified framing, windows, doors, and roofing packages on these projects, and we keep the common materials in stock so a job doesn’t stall waiting on a backordered window or a wrong-size header. Most owners find this page because something specific failed: a roofline junction is leaking, an old addition is pulling away from the main house, or an unpermitted ADU done by a previous owner now needs structural correction before the city will sign off. If that sounds like your situation, you’re in the right place.

Call (877) 610-1318

Which Ameristar Models This Applies To

We work on the full range of Ameristar home additions and ADU structures common across Los Angeles County: attached room additions, detached backyard ADUs, garage conversions, and second-story additions. The Ameristar difference matters most at the structural and envelope level. These buildings are typically framed with engineered lumber packages that have specific load ratings, and the window and door rough openings are sized to Ameristar’s standard dimensions. Before you order anything, check the permit drawings or the original plans. The rough opening size is the number that matters. If you don’t have plans, we measure on site before anything gets ordered. For fasteners and flashing, we use Ameristar-specified or equivalent-rated materials, never whatever is cheapest off the shelf. We’re an independent contractor, not affiliated with Ameristar, so we can tell you honestly when an aftermarket equivalent does the job and when you’re better off staying with the OEM spec.

Signs Your Ameristar Home Additions & ADU Is Failing

• Drywall cracks at the junction where the addition meets the main house. This is the classic sign of differential settlement. The addition’s foundation moves at a slightly different rate than the original slab, and the crack follows the seam. It’s normal in the first year, but cracks wider than a quarter inch after that need a structural look.
• Doors and windows suddenly stick or won’t latch. When a corner of the addition settles, the rough openings go slightly trapezoidal, and the door or window binds. In Los Angeles’s clay-heavy soil, this happens after heavy rain years followed by dry spells.
• Water staining at the roofline tie-in or the wall-to-roof junction. The flashing detail where an addition roof meets the original house is the number one leak point we see. Ameristar’s roof transition requires step flashing and counter-flashing done in a specific order; shortcuts here fail within five years.
• A soft spot in the floor near the exterior wall. This usually means a rim joist or sill plate has been wicking moisture from a missing termite shield or a kickout flashing that was never installed. Los Angeles termite pressure makes this worse than in drier inland climates.
• The ADU feels like it’s “breathing” during high winds. A properly sheathed and shear-paneled addition shouldn’t flex noticeably. If you can feel movement, the shear transfer at the floor and roof diaphragms is incomplete, which is an LA seismic code issue more than a comfort issue.

Replacement Cost & What’s Included

Home addition work in Los Angeles falls mostly in the $53,100 to $153,400 range, and ADU construction runs $106,200 to $259,600. What drives the spread comes down to three things: whether you’re building on a slab or need pier drilling, how much of the existing structure has to be corrected before new work can tie in, and the finish level inside. Our estimates break out the structural and envelope work line by line, so you can see exactly what you’re paying for. We pull permits on every eligible job, and the inspector’s sign-off is part of the scope. Every price change arrives as a written change order before work proceeds. That’s not a courtesy; it’s how we’ve done it since 1998, and it protects both of us.

DIY or Call Us?

If you’re dealing with a failed section of an Ameristar addition or ADU, there’s a real structural component to this work, and seismic safety in Los Angeles isn’t a place for guesswork. You can safely do the detective work: look for the crack patterns, check doors for binding, note where water stains show up after rain. That gives us a head start when you call. But moving load-bearing walls, correcting settlement, replacing shear panels, or re-flashing a roof tie-in is trained professional work. Done wrong, it’s a safety risk for everyone in the building, and the city will catch it on resale. If you’d like our eyes on it, call (877) 610-1318 and we’ll schedule a look. No trip charge inside the county.

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