James Hardie New Detached ADU Nationwide

James Hardie New Detached ADU: The West Hollywood Owner’s Guide

James Hardie siding and trim systems for new detached ADUs in West Hollywood typically run $28,000-$52,000 installed for a complete envelope on a 400-750 sq ft unit, depending on whether you’re specifying HardiePlank lap siding, HardiePanel vertical siding, or HardieShingle for a Craftsman match. We stock James Hardie ColorPlus factory-finished boards and matching trim in West Hollywood, and most detached ADU envelope repairs or full reclads can be scoped within 48 hours. If you’re seeing cracked boards, color fade streaking, or moisture intrusion at the butt joints, the issue is usually failed caulk, improper clearance above grade, or the original install missing the required 2-inch minimum gap between siding and soil that West Hollywood’s hillside lots make tricky.

Call (213) 329-7167

Which James Hardie Models This Applies To

James Hardie makes no single “ADU kit,” so matching the right system means reading the existing stamp or job record. HardiePlank lap siding comes in 5/16-inch and 7/16-inch thicknesses, with the thicker LP SmartSide-competitive line showing up on ADUs spec’d after 2019. HardiePanel, the 4×8 and 4×10 vertical sheets, appears on modernist detached units along West Hollywood’s northern hillside streets where horizontal lines would fight the slope. HardieTrim boards run 3/4-inch or 1-inch nominal, and the 4/4 (1-inch) version is what you’ll need if your ADU was designed with flush window returns rather than recessed.

Here’s the compatibility gotcha we see twice a month in West Hollywood: ColorPlus prefinished siding from different production lots can vary slightly, and James Hardie’s touch-up pens are formulated for specific ColorPlus codes, not generic matching. If your detached ADU needs partial replacement after a termite repair or plumbing chase opening, we source from the same production run when possible, or we reclad the entire elevation to eliminate the line. OEM James Hardie carries a 30-year limited product warranty and 15-year finish warranty on ColorPlus; aftermarket fiber-cement boards exist but void the system warranty and rarely carry the same ASTM E136 noncombustible rating that West Hollywood’s hillside fire zones require.

Signs Your James Hardie New Detached ADU Is Failing

• Cracking or spalling at the board ends. Fiber-cement absorbs moisture at cut edges if not factory-sealed or field-primed with James Hardie’s specified primer. In West Hollywood, morning marine layer followed by afternoon heat cycles accelerates this. The fix is replacement with proper end-sealing, not caulk over the crack.
• Color fade or chalking unevenly across elevations. ColorPlus finish failure before year 10 usually means the original install happened in direct summer sun without the required 48-hour curing window, or the boards were stored flat and got wet before install. South- and west-facing walls on detached ADUs above Sunset Boulevard show this first.
• Soft or discolored sheathing behind the siding. This is the expensive one. Hardie siding is not waterproof; it’s a rainscreen that depends on proper flashing and a drainage plane. If your ADU was built without a drainable housewrap or the Z-flashing above windows was omitted, water hits the OSB and the siding looks fine until it doesn’t.
• Boards pulling away from studs at fasteners. James Hardie specifies ring-shank nails or screws set flush, not countersunk. Over-driving breaks the face and creates a moisture funnel. We see this on ADUs where a general carpenter, not a siding specialist, handled the install.
• Ground contact or less than 6-inch clearance above finished grade. West Hollywood’s tight lots sometimes push ADUs close to retaining walls or slope fills. Hardie requires 6 inches minimum to soil, 2 inches minimum to hardscape. Less than that, and you’ll get wicking failure at the bottom course within three to five years.

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Replacement Cost & What’s Included

For West Hollywood detached ADUs, partial envelope repair (one to two elevations, localized rot repair, new housewrap and Hardie reinstall) typically runs $14,000-$24,000. Full reclad of a 500 sq ft detached unit, including tear-off, sheathing inspection and replacement as needed, drainable housewrap, new HardiePlank or HardiePanel with ColorPlus finish, trim, and paint touch-up, lands at $28,000-$52,000. The wide range depends on scaffolding requirements for two-story ADUs, hillside access for material staging, and how much sheathing needs replacement once we open the wall.

Every quote is itemized: siding line-item by square, trim by linear foot, sheathing by sheet if exposed, and labor separated from material. Under Haven Standard Clause 1, that written price is locked before any work starts. We pull the permit, coordinate West Hollywood Building & Safety inspection, and the 365-Day Done Right Promise covers both workmanship and material defect. The document is the promise. Everything else is a conversation.

DIY or Call Us?

What you can safely check: walk the perimeter with a screwdriver and probe any soft spots near the bottom course, look for missing or cracked caulk at penetrations, and verify your downspouts aren’t dumping directly onto the siding. Take photos of any stamp markings on the back of a loose board if you find one.

Where DIY goes wrong: fiber-cement generates silica dust when cut. Dry-cutting without a HEPA vacuum and respirator is a genuine health hazard, and West Hollywood’s tight lots mean your neighbor’s windows are close. More critically, the structural and waterproofing layers behind the siding are where the real money lives. Pulling boards to “see what’s back there” without knowing how to flash the opening before nightfall can turn a $3,000 repair into a $14,000 reclad. We’re not being dramatic. We’ve documented the photo record on both outcomes.

Call (213) 329-7167 and we’ll scope it, price it in writing, and schedule around your tenant’s schedule if the ADU is occupied.

FAQs