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Owens Corning Home Additions & ADU: The Los Angeles Owner’s Guide
Owens Corning home additions and ADU construction in Los Angeles typically run $53,100 to $153,400 for a full project, and most homeowners discover an underperforming existing space during the first heat wave or rainy season. You’re likely here because a room you added or converted isn’t holding temperature, has moisture intrusion at the roofline, or the insulation packed around a failed wall assembly isn’t doing what the Owens Corning spec sheet promised. We inspect, diagnose, and rebuild these spaces with Owens Corning-compatible materials, and a written price lands in your hand before any work starts.
Mason Remodeling is an independent service provider and is not affiliated with Owens Corning. But we’ve torn open enough failed additions across Los Angeles to know exactly where the weak points live.
Which Owens Corning Models This Applies To
This page covers the full Owens Corning building-envelope product range used in home additions and ADUs: PINK Next Gen fiberglass insulation, FOAMULAR XPS rigid foam board, Duration Series shingles over addition roof decks, and the Owens Corning air-sealing system specified in their addition and accessory-dwelling-unit product bundles. The compatibility gotcha most Los Angeles homeowners miss is this: FOAMULAR comes in compressive strengths from 15 PSI to 100 PSI, and using the 15 PSI board under a floor slab or below-grade wall in an ADU foundation will eventually deform under load. The 25 PSI and higher board is what you need against soil pressure, and it must be paired with the correct vapor-retarder facing for our climate zone.
To identify what’s in your existing addition, look for the printing on the insulation batt or rigid board face. For roofing, the Duration Series shingle has a distinctive SureNail fabric strip visible at the nail line. When matching replacement materials, OEM Owens Corning stock is always our first recommendation on active warranty projects, but on out-of-warranty work a quality aftermarket equivalent can save 15 to 25 percent with zero performance difference when spec-matched correctly.
Styles & brands we work with
Signs Your Owens Corning Home Addition or ADU Is Failing
- Temperature swings between the addition and the original house. The insulation batts were likely compressed during install, or gaps were left around electrical boxes. Owens Corning fiberglass loses R-value fast when it’s crammed into a space smaller than its loft rating.
- Damp drywall or a musty smell at the floor line. Missing or incorrectly lapped rigid foam behind the siding is letting moisture wick into the wall cavity. In Los Angeles marine-layer zones like Playa del Rey or San Pedro, this shows up fast.
- Visible daylight through the roofline transition. The junction where an addition roof ties into the original house is a chronic failure point. Improper flashing job, and the Owens Corning shingles will do their job while the gap behind them rots the framing.
- Cracking at the addition’s foundation seam. The original house settles differently than new construction. If the slab wasn’t isolated correctly, you’ll see hairline cracks within the first two seasons, and they’ll widen.
- Higher energy bills in summer. Los Angeles DWP rates, especially in the San Fernando Valley, punish a poorly insulated addition. If your AC runs constantly from June through October, the ceiling insulation is failing or was under-spec’d.
See the difference
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After
Before
After
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AfterReplacement Cost & What’s Included
A home addition in Los Angeles runs $53,100 to $153,400 depending on square footage, foundation work, and the condition of the existing structure you’re tying into. ADU construction lands higher, at $106,200 to $259,600, because it includes separate utility runs, a full kitchen or kitchenette, and independent access requirements under California ADU law. Here’s the line-item reality in this market:
- Full home addition: $53,100 – $153,400
- ADU construction (from slab): $106,200 – $259,600
- Garage conversion to living space: $35,400 – $94,400
- Room addition roof replacement (Owens Corning Duration shingles): $9,440 – $23,600
Every quote includes a written line-item breakdown: demolition, framing, insulation, drywall, electrical rough and finish, roofing, paint. No allowances that balloon later. No verbal estimate that morphs into a final bill. The price we write is the price you pay, and if something goes wrong in the first 365 days, we return and make it right at no cost. That’s the 365-Day Done Right Promise, and it’s written into every contract.
DIY or Call Us?
You can safely check a few things yourself: look for daylight at the roofline, press on drywall to feel for softness or moisture, and check whether the addition feels ten degrees off from the rest of the house at midday. What you shouldn’t do is cut into a wall assembly to inspect insulation, because you don’t know what’s behind the drywall: live electrical, plumbing runs, or in older Los Angeles additions, asbestos-containing materials. And you definitely shouldn’t get on a roof with a pitch steeper than 4:12 without fall protection. Roof falls are the most common serious injury we hear about from homeowners who tried to save a buck. Call (803) 680-2547 and we’ll send someone who knows exactly what to look for.
FAQs
Properly installed Owens Corning fiberglass insulation should hold its rated R-value for 20 to 30 years in Los Angeles conditions, assuming no moisture intrusion or pest activity. The roof system above it typically lasts 15 to 25 years on an addition, depending on sun exposure and whether the original roofer got the flashing detail right at the transition seam. Call (803) 680-2547 if your addition is over ten years old and you’re noticing temperature or moisture issues.
Most failing additions can be repaired without a full tear-down. We regularly open one wall or roof section, replace the compromised insulation and any rotted framing, and close it back up. The exception is foundation failure, which sometimes means partial demolition. The only way to know is an inspection, and ours comes with a written diagnosis at no charge.
A permit-ready single-room addition typically takes 3 to 5 months from first inspection to final walkthrough in Los Angeles, with city plan-check and inspection scheduling driving part of that timeline. An ADU runs 5 to 9 months because of separate utility work and the additional plan-check review. We give you a written schedule up front and update it honestly if something shifts.
We stock Owens Corning PINK Next Gen batts, FOAMULAR rigid board in 25 and 40 PSI, and Duration Series shingles at our Los Angeles yard, along with materials from KraftMaid, Cambria, and Silestone for the interior finish work. That means fewer supplier delays mid-project, and when a replacement piece is needed, it doesn’t stall your job for a week while a distributor ships it in.
Know who’s coming, know what it costs, know it’s backed up – everything else is just noise. Call Mason Remodeling at (803) 680-2547 for a free estimate on your Owens Corning addition or ADU project in Los Angeles. Isaac Pruett grew up in the San Fernando Valley and has spent two decades rebuilding homes across this city, and his standard hasn’t changed: a written price before work starts, a photo ID badge at the door, and a 365-Day Done Right Promise in writing.
Written by Isaac Pruett, Owner, Mason Remodeling at Mason Remodeling, serving Los Angeles and nearby areas.
