James Hardie Junior ADU Conversion: The Dallas Owner’s Guide
If you’re reading this, the siding on your junior ADU has likely cracked, warped, or started pulling away from the frame, and you need to know what a replacement actually costs in Dallas before you call anyone. We stock James Hardie-compatible siding, trim, and the specialty flashing used on junior ADU conversions, and a typical siding replacement on a 400 – 600 square foot junior ADU in Dallas runs $6,800 – $11,400 installed, depending on how much of the underlying water barrier needs to be rebuilt. Most Dallas owners discover the failure after a heavy spring storm, when they notice paint bubbling near the bottom edge or a diagonal crack running from a window corner that wasn’t there last fall.
Before we get into specifics: Fielding ADU Dallas is an independent builder, not a James Hardie dealer or affiliate. That matters because we have no incentive to push a replacement when a repair makes more sense. Reed Calloway and our crew have been running ADU projects in Dallas long enough to know that James Hardie products fail differently here than they do in, say, Houston or Austin. The clay soil shifts, the summer heat bakes the caulk joints, and the February freezes do the rest.
Key takeaways:
- Junior ADU siding replacement in Dallas typically costs $6,800 – $11,400 installed.
- Most failures start at the bottom edge or at window and door penetrations, not in the middle of the wall.
- We put the price in writing before the first nail goes in.
- Every job carries the Garrison Standard: a written one-year guarantee on workmanship.
Which James Hardie Models This Applies To
Junior ADU conversions in Dallas almost always use one of three James Hardie product lines: HardiePlank lap siding (the 5/16-inch thick, 8.25-inch exposure boards), HardiePanel vertical siding (4×8 or 4×10 sheets), or HardieTrim boards around windows, doors, and corners. The compatibility gotcha most owners miss is that these three lines use different fastening schedules and different flashing details, and mixing them incorrectly is how a “minor” siding repair turns into a full wall rebuild.
To identify exactly what you have, look for the product code printed on the back of a removed piece, or measure the thickness. HardiePlank lap siding is 5/16 inch thick, while HardiePanel is 7/16 inch. The trim boards run 3/4 inch thick. If your junior ADU was built before 2015, check for the older 5/16-inch HardiePlank with the square butt edge; the current stock uses a beaded or smooth lap profile that doesn’t always match the older runs without a slight reveal adjustment. We stock both profiles in our Dallas yard, along with ColorPlus pre-finished trim in the colors most common to ADU builds here: Cobble Stone, Monterey Taupe, and Arctic White.
On the OEM versus aftermarket question: for James Hardie siding and trim, we use James Hardie product. There are aftermarket fiber-cement boards that claim compatibility, but the expansion rates and fastener-holding characteristics differ enough that we won’t put them on a Hardie job. The risk isn’t theoretical here; we’ve seen aftermarket boards cup within two Dallas summers. For flashing and housewrap, we use quality aftermarket equivalents, because the Hardie-branded flashing is overpriced for what it is.
Signs Your James Hardie Junior ADU Conversion Is Failing
- Paint bubbling or peeling along the bottom 12 inches. This is almost always a wicking problem, where the siding is sitting too close to grade or the drip edge was never installed. Water climbs the back of the board and pushes the paint off from behind. In Dallas, where we get sudden heavy downpours followed by 100-degree heat, this failure mode is more common than anywhere else we’ve worked.
- Diagonal cracks running from window or door corners. Fiber cement doesn’t flex. If the framing behind it settles, the board cracks. Dallas clay soil expands and contracts through the year, and junior ADUs on slab foundations are especially vulnerable because the slab moves as a unit. A single crack at a corner means the wall racked at some point.
- Gaps opening at butt joints between boards. James Hardie siding is installed with a 1/8-inch gap at each joint, filled with caulk that’s rated for movement. When you see the caulk pulling away from one side of the joint or the gap widening beyond 1/4 inch, the boards have moved independently. That’s usually a fastener failure, not a caulk failure.
- Soft spots you can press in with your thumb, usually near the bottom plate. This is the one that scares us, because by the time the siding feels soft, the water has been working on the OSB or plywood sheathing behind it for months. A siding replacement is straightforward. Replacing rotted sheathing and rim joist is a different job entirely, and the price changes accordingly.
- Mold or staining in a repeating pattern that matches the stud spacing. When you see vertical ghost lines on the siding every 16 or 24 inches, the wall cavity isn’t breathing, and condensation is collecting on the studs and wicking outward through the siding. This is common on junior ADUs where the original builder skipped the rainscreen gap, and it means the whole wall assembly needs reworking, not just the siding.
Replacement Cost & What’s Included
A junior ADU siding replacement in Dallas runs $6,800 to $11,400 installed before permit fees. The range depends on how much of the existing water barrier and sheathing is still sound, whether we’re doing a full tear-off or a partial replacement, and which Hardie profile your ADU uses. Here’s the breakdown:
- Siding tear-off and disposal: $900 – $1,500, depending on dumpster access and whether the old siding tests positive for asbestos (rare on juniors built after 1990, but always checked before we start).
- Housewrap and flashing replacement: $1,200 – $2,100 for a junior ADU footprint. This is the part homeowners never budget for, and it’s the part that determines whether the new siding lasts 5 years or 25.
- HardiePlank or HardiePanel installation: $3,400 – $6,200, including all fasteners, joint flashing, and trim around windows and doors.
- Paint or ColorPlus finish matching: $800 – $1,600 if you’re painting field boards to match the rest of the property. ColorPlus pre-finished boards cost more upfront but skip this line item.
The Garrison Standard sits behind all of it. That means a written price before any work starts, a written one-year guarantee on workmanship, and if something fails inside that year, we come back at no charge and correct it. No change orders, no “we found rot so now it’s more” phone call. The price you approve on day one is the number on the final invoice.
DIY or Call Us?
Fiber cement siding is not high-tension, and it won’t electrocute you, but it will cut you, and the dust from cutting it contains silica, which isn’t something you want in your lungs. If you’re just checking the extent of the damage, go ahead and run a flat pry bar along the bottom edge and see if the boards feel solid or give way. That tells you what to expect on the phone.
Where DIY goes wrong on James Hardie siding in Dallas is the flashing and the weather barrier. The boards themselves are only one part of the wall assembly. If you replace the siding without addressing the flashing detail at the bottom, the windows, and the roof-to-wall intersection, you’ve bought yourself two or three years before the same failure comes back. We’ve fixed more than one DIY siding job where the boards looked fine and the wall behind them was rotting. Replace a single board, sure, if you know what’s behind it. A whole side of a junior ADU? That’s a two-day job for a crew that’s done hundreds of them, and a week for a homeowner who hasn’t. If you’d rather not guess, call (903) 342-8977 and we’ll put eyes on it, free.
FAQs
James Hardie siding itself carries a 30-year limited product warranty, and the boards can last that long in Dallas if the installation details are right. The weak points are the caulk joints, which need re-sealing every 5 – 7 years here, and the bottom edge, which fails early if the sill flashing was skipped. We see original Hardie siding on Dallas ADUs from the early 2000s that’s still structurally sound, and we see 8-year-old siding that’s rotted at the bottom because the original builder set it 2 inches into the soil. Installation quality decides lifespan more than the product does. Call (903) 342-8977 if you want us to look at your specific installation.
Yes, individual boards can be swapped out if the failure is localized and the sheathing behind them is still solid. We do partial replacements all the time on junior ADUs where one wall takes the brunt of the western sun or one corner catches all the roof runoff. If the failure wraps around a corner or climbs above a window, you’re usually looking at a bigger tear-off. The honest answer depends on what’s behind the boards, and we’ll tell you that after a free inspection rather than sell you a full replacement you don’t need.
A typical 400 – 600 square foot junior ADU siding replacement takes 2 – 3 working days from tear-off to final paint, assuming the sheathing is sound. Add a day if we find rot behind the boards and need to rebuild sections of the wall. Permit timing in Dallas varies by season; plan for a week or two between the estimate and the first day of work during the spring rush.
We stock the three James Hardie profiles most common on Dallas junior ADUs, plus the standard trim widths and the paint colors we see most often, so most jobs start without waiting on a supplier. If your ADU uses a specialty color or a discontinued profile, we order it directly from James Hardie’s Dallas distribution, and that usually adds 3 – 5 business days to the schedule. We also carry compatible flashing, housewrap, and fasteners on the truck, and we’re familiar with James Hardie-specific transitions on Abodu, Cover, and Dvele prefab structures if that’s what your junior ADU started as.
Written by Reed Calloway, Owner, Fielding ADU Dallas at Fielding ADU Dallas, serving Dallas and nearby areas.
