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Owens Corning Home Additions & ADU: The Miami Owner’s Guide
If you’re planning a home addition or ADU in Miami using Owens Corning materials, the complete installed price typically runs $53,100–$153,400 depending on square footage, foundation work, and finish level. Most homeowners call us because their existing addition or ADU structure shows signs of water damage, failing insulation, or compromised sheathing — the layers Owens Corning materials are meant to protect. We stock and install Owens Corning-compatible sheathing, insulation, and weather barrier systems, and we can usually diagnose what failed within a single visit.
Penhallow Remodeling Miami is an independent general contractor, not affiliated with Owens Corning. That independence matters: we’re free to tell you exactly which Owens Corning product makes sense for your addition, and which aftermarket option does the same job for less.
Key Takeaways
- Home additions and ADUs in Miami run $53,100–$153,400 installed, with ADU construction alone at $106,200–$259,600 for detached units.
- Owens Corning’s insulation and weather barrier failures in South Florida are almost always about humidity, not impact — moisture gets behind the barrier and sits there.
- We pull permits, pass inspections, and write the number down before a single wall goes up.
- The 365-Day Done Right Promise covers every addition and ADU we build. If it fails inside a year, we return and fix it at no charge.
Which Owens Corning Models This Applies To
Your addition or ADU isn’t tied to a single Owens Corning “model” the way a furnace is. What matters is the product line in your walls and roof. In Miami, we most often work with Owens Corning FOAMULAR® extruded polystyrene (XPS) rigid insulation, Thermafiber® mineral wool, and Owens Corning sheathing panels — each with its own R-value and moisture behavior. The FOAMULAR® 250 series, for example, carries an R-value of 5 per inch and is rated for direct ground contact in certain below-slab applications, which is why it shows up on so many Miami ADU foundations. But here’s the compatibility gotcha: FOAMULAR® XPS does not breathe. When it’s installed on the exterior of a wall without a proper drainage plane (the gap that lets water escape), Miami’s humidity condenses behind it and rots the sheathing. That’s the single most common failure we see in additions built by the lowest bid — not a bad Owens Corning product, but a missed detail in how it was applied.
On the roof, Owens Corning Duration® shingles are engineered for high-wind zones, with SureNail® technology that gives a wider nailing area — genuinely useful in Miami’s hurricane season. But shingles sit on top of Owens Corning Deck Defense® or RhinoRoof® synthetic underlayments, and those underlayments are what actually keep a roof watertight between shingles. If you’re checking what’s on your home, look for the product stamp on the edge of a sheathing panel or the printed face of insulation batts. We match OEM when it’s structural (sheathing, underlayment) and use quality aftermarket only where it makes honest sense — insulation batting, for instance, where performance is equal and the cost drops meaningfully.
Styles & brands we work with
Signs Your Owens Corning Home Additions & ADU Is Failing
- Musty, humid smell that doesn’t go away. Trapped moisture behind foam board or under a failed weather barrier saturates wood framing and drywall. Once it’s smelled constantly, the structural sheathing has likely already started to soften.
- Discoloration or staining on interior walls near the floor or ceiling corners. This usually means water is wicked in through a failed seam in the housewrap or underlayment — not a leak you can see from the outside. Corners fail first because that’s where the barrier gets folded and stapled.
- Visible swelling, warping, or delamination of exterior sheathing. Owens Corning oriented strand board (OSB) sheathing is rated for moisture exposure during build, but not for daily South Florida humidity against a bad drainage plane. Bulging edges mean the panel has absorbed water and lost structural integrity.
- Batt insulation that’s sagging or darkened at the bottom. Owens Corning PINK® fiberglass batt insulation loses R-value when compacted or damp. Dark staining at the lower edge is condensation travel — the wall assembly isn’t drying, and the insulation is now part of the problem instead of the solution.
- Rising interior temperatures in the addition despite running AC. Foam insulation that was compressed, gapped, or wet stops doing its job. In Miami, that utility bill climbs fast, and it’s often the first thing homeowners notice before any visible water damage appears.
See the difference
Before
After
Before
After
Before
AfterReplacement Cost & What’s Included
In Miami, a full home addition runs $53,100–$153,400, and a detached ADU runs $106,200–$259,600. These numbers include permits, foundation, framing, Owens Corning sheathing and insulation, drywall, roofing, electrical, plumbing, and finish trim. What moves the price is square footage first — then foundation type (a slab-on-grade on sandy Miami soil costs very different money than block on a stem wall), then finish level. Kitchen-grade finishes in a 400-square-foot ADU can add $18,000–$55,000 on their own if you’re building out a full kitchen, per our standard kitchen remodel ranges.
We don’t hand out a low verbal number to get a signature and then amend it after demo. The written number we give you before work starts is the number on your invoice — unless you change the scope, and then we’ll hand you a written change order before anything else gets ordered. Every addition and ADU we build includes our 365-Day Done Right Promise in writing, and a live person answers our phone 24/7 if something comes up after the dust settles.
DIY or Call Us?
What you can safely check yourself: visible gaps in insulation in an open attic or crawl space, cracked or missing roof shingles after a storm, and water staining you can point at from a ladder’s base. What you shouldn’t do: peel back Owens Corning weather barrier or sheathing to “see how bad it is.” Once you expose the building envelope in Miami’s humidity, you start a clock you can’t stop — and if you open a structural wall without shoring it properly, you can create a failure that didn’t exist before. I’ve seen a homeowner remove one corner of sheathing to investigate a stain and end up with a sagging roof line inside a month because the load path was compromised.
Trevor Nash grew up in Los Angeles and learned the trade at Los Angeles Trade-Technical College, then spent three decades swinging a hammer and running crews on everything from compact bath refreshes to full structural overhauls. He’s been working throughout Miami for years, including plenty of Coconut Grove projects where older homes have a story hiding behind every wall. Call (850) 988-7559 and we’ll come out, look at what failed, and give you a number first — then pick up the tools.
FAQs
A properly detailed Owens Corning building envelope — meaning foam board, sheathing, housewrap, and underlayment installed with correct drainage — should last 30 to 50 years in South Florida before any of those layers need real attention. What fails early, usually inside 5 to 8 years, is the installation detail: missing drainage gaps, improper flashing, or tape seams that peel in humidity. The material doesn’t wear out; the weak points were born on install day. Call (850) 988-7559 if you want us to inspect your existing walls before you spend money fixing the symptom.
Yes, in specific cases. Dry, uncompressed Owens Corning PINK® fiberglass batts can be re-seated and supplemented where gaps exist. But if the batts are damp, darkened, or compacted, they lose structure and R-value permanently — there’s no drying them out and putting them back. Same rule for sheathing: a panel with minor edge swelling can sometimes be reinforced in place, but delamination or rot means replacement. We’ll tell you which one you have before any money changes hands. Call (850) 988-7559 to get a straight answer on your specific wall.
For a single wall section or a partial roof plane, we typically complete the replacement in 2 to 5 working days once materials are delivered. A full exterior re-sheath of a detached ADU runs 1 to 2 weeks depending on access and Miami’s afternoon rain patterns. The longest variable is permit review in your municipality — Miami-Dade and Coral Gables move at different speeds, and we submit both sets the same week we start.
We stock common Owens Corning FOAMULAR® rigid foam in 1-inch and 2-inch thicknesses, PINK® batt insulation in R-13 and R-19, and roll stock of Owens Corning synthetic underlayment on our trucks. For full addition and ADU builds, we order directly from our supply house in project quantities, which usually arrives in 3 to 5 business days in Miami. We also work with KraftMaid, Cambria, and Silestone on the finish side when your addition includes a kitchen or bath, so materials come from suppliers we’ve relied on for years.
Written by Trevor Nash, Owner, Penhallow Remodeling Miami at Penhallow Remodeling Miami, serving Miami and nearby areas.
