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James Hardie Home Additions & ADU: The Fort Worth Owner’s Guide
Adding square footage with James Hardie siding and trim in Fort Worth typically runs $45,000 – $130,000 for a full addition, depending on size, foundation work, and whether we’re tying into existing Hardie lap or panel siding. We install HardiePlank, HardiePanel, and HardieTrim to match existing exteriors, and we carry the flashing, sealant, and trim stock needed to make the new work disappear into the old. Most Fort Worth homeowners call us after a smaller addition or ADU attempt goes sideways: mismatched siding profiles, gaps at the roofline, or Hardie that’s cupping and cracking because the substrate wasn’t prepped right in the first place.
The common thread is usually the same. Somebody cut corners on the water-resistive barrier behind the Hardie, or they installed siding too tight to the roofline and now moisture is getting behind the boards. Curtis Lane has pulled enough failed siding off Fort Worth additions to know what’s lurking back there before we even open the wall.
Which James Hardie Models This Applies To
We work with the full James Hardie exterior line: HardiePlank lap siding in 4″, 5.25″, 6.25″, 7.25″, and 8.25″ exposures; HardiePanel vertical siding in 4×8, 4×9, and 4×10 sheets; HardieTrim boards in smooth and woodgrain textures; and HardieSoffit for eaves. The catch most homeowners hit: Hardie lap siding is sold by exposure, not by board width. If your existing siding is a 5.25″ exposure and someone orders a “5-inch siding” without checking, the reveal lines won’t match and the whole addition will look like an afterthought.
OEM James Hardie product is our default for additions and ADUs, and it’s what we recommend. The board is factory-primed and carries Hardie’s 30-year nonprorated substrate warranty when installed to spec. Aftermarket fiber cement exists, but mixing brands on an exterior wall creates differences in expansion rate, thickness tolerance, and paint absorption that you’ll see within two Texas summers. If your existing Hardie is more than 15 years old, we’ll also need to match the current ColorPlus finish or plan for full paint on the new and old sections so the addition doesn’t read as a patch.
Styles & brands we work with
Signs Your James Hardie Home Additions & ADU Is Failing
- Cupping or wavy Hardie planks on the addition. Almost always means the siding was nailed too tight or the substrate behind it is swelling. Hardie needs a 1/8″ gap at butt joints and flashing at every horizontal transition. When water gets behind, the board swells at the edges and the face looks wavy from the street.
- Paint peeling in vertical stripes on lap siding. This is moisture wicking through the bottom edge of each plank. The kickout flashing at the roofline or the clearance above grade is wrong, and the bottom edge of the board is sitting in water. Repainting fixes the look for a season. It doesn’t fix the water.
- Cracks at inside corners where the addition meets the original house. Fort Worth clay soil moves, and additions settle differently than the original foundation. Hardie at that transition needs a properly flashed expansion joint. If it’s hard-jointed, the board cracks and the crack invites water behind both sections.
- Gaps opening between trim boards and siding. James Hardie products expand and contract with temperature and humidity. In Fort Worth’s 100-degree summers and sudden temperature drops, trim that was butted tight will separate. The fix is re-flashing, not caulk. Caulk fails in two seasons.
- Soft spots in the soffit or underside of the eaves. Fort Worth’s storm season drives water sideways. If the soffit wasn’t vented and flashed correctly when the addition was built, moisture sits on the underside and the HardieSoffit degrades from the back. You’ll feel the give before you see the stain.
See the difference
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AfterReplacement Cost & What’s Included
For Fort Worth additions and ADUs, the honest numbers break down like this:
- Full home addition with James Hardie exterior: $45,000 – $130,000. This is foundation to roofline: framing, rough-in, Hardie siding and trim, windows, doors, and finish work. The spread is driven by square footage, foundation type (pier and beam costs more than slab-on-grade in most Fort Worth neighborhoods), and whether we’re matching existing Hardie or residing the whole elevation.
- ADU construction with Hardie exterior: $90,000 – $220,000. Detached ADUs carry their own foundation, utility runs, and separate mechanical systems, which is why they price above a bump-out addition.
- Siding replacement or re-cladding on an existing addition: generally $7,000 – $18,000 depending on square footage of wall, tear-off of failed material, and any substrate repair underneath.
Every quote includes parts, labor, disposal of the failed material, flashing, sealant, and the substrate corrections that keep the new Hardie from failing the same way. We put every line item in writing before work starts under The Garrison Standard. No numbers move at the door. And when we finish, you get the 365-Day Done Right Promise in your hand: if the work fails inside a year, we come back and correct it at no charge.
DIY or Call Us?
What you can safely do: inspect your addition’s exterior for visible cracking, cupping, gaps at the roofline, and paint failure. You can take photos, measure lap exposures, and check whether the bottom edge of the siding has the required 6″ clearance above grade. That inspection tells you what failed. It doesn’t tell you what’s behind it.
Where DIY goes wrong on James Hardie additions is the substrate and flashing work. Fiber cement is unforgiving if the wall behind it isn’t flat, dry, and properly flashed. Cut a Hardie board wrong and you’ve destroyed a $40 plank. Install it wrong and you’ve hidden a water problem behind new siding that’s going to rot your framing for five years before it shows. This is work where the cost of the fix exceeds the cost of doing it right the first time. Call Bradford Remodeling Co Fort Worth at (682) 204-4897. We’ll give you a written scope and a firm price before a single tool comes out.
FAQs
Installed correctly with proper flashing and the required clearances, James Hardie siding and trim last 30 – 50 years in Fort Worth’s climate. The substrate warranty from Hardie runs 30 years nonprorated. What shortens that lifespan here isn’t the product. It’s Fort Worth’s clay soil shifting the framing, storm-driven moisture, and installs where someone skipped the flashing details. We see failed Hardie that’s eight years old and Hardie that’s 35 years old and fine. The difference is always what’s behind it. Call (682) 204-4897 if you want us to inspect what you have before you spend on replacement.
Yes, in many cases. A section of cupped siding on one wall can be pulled, the substrate corrected, and new Hardie installed without touching the rest of the exterior. The honest caveat is matching. If your existing Hardie has years of Texas sun on the factory finish, new boards won’t match exactly, which usually means painting the entire elevation after repair. We’ll tell you which walls are salvageable and which need full replacement before you commit. Estimates are free.
A bump-out addition with Hardie siding, trim, and soffit typically runs 8 – 16 weeks from permit pull to final walkthrough. A detached ADU runs 4 – 9 months depending on utility work, foundation, and the mechanical systems inside. The Hardie portion of the scope is one of the fastest phases once the framing and substrate are ready. We’ll put the schedule in your written scope, and we’ll show you the permit log so you know the inspections are passing.
We keep standard HardiePlank lap siding, HardiePanel, HardieTrim, and HardieSoffit in the most common Fort Worth profiles and exposures in our inventory, and we order project-specific pieces directly through our James Hardie supplier. That means we don’t start a job hoping the right profile shows up. It’s ordered, checked against your existing exposure, and staged on site before we set the first plank. Call (682) 204-4897 and we’ll confirm we can match what’s on your house today.
Straight scope, firm price, no surprises at final walkthrough.
Written by Curtis Lane, Owner, Bradford Remodeling Co Fort Worth at Bradford Remodeling Co Fort Worth, serving Fort Worth and nearby areas.
