HardiePlank Calculator
How many HardiePlank boards do you need? This free HardiePlank lap siding calculator gives DIYers and contractors an instant material list pulled directly from James Hardie's published install specs — boards by profile width (5¼" / 6¼" / 7¼" / 8¼" / 9¼" / 12"), HardieTrim takeoff in both 4/4 and 5/4 thicknesses, kickout and butt-joint flashing pieces, fasteners by stud spacing, sealant tubes, HardieWrap rolls, and ColorPlus touch-up kits.
HardiePlank ships in two regional formulations — HZ5 for northern freeze-thaw climates and HZ10 for southern high-humidity and coastal exposure. Installing the wrong zone product voids the 30-year warranty. The differences also show up in install details: 2" min clearance to paved surfaces on HZ5 vs 1" on HZ10, 25-perm HardieWrap on HZ5 vs 15-perm on HZ10, and block-penetration sleeving recommended in HZ10. The calculator handles both.
Built on James Hardie HardiePlank Installation Instructions HS11119 (HZ5 Dec 2019 / HZ10 May 2016), ICC-ES ESR-2290 (Reissued May 2023), IRC 2021/2024 §R703.10.2 fiber-cement lap siding, IRC §R903.2.1 kickout flashing, and ASTM C920 sealant specifications. Free, no signup.
New to HardiePlank? Read our HardiePlank Installation Guide (HZ5 vs HZ10, nailing patterns, butt-joint detail). Not installing HardiePlank? See our generic lap siding calculator (LP SmartSide, wood bevel, vinyl).
HardiePlank Lap Siding Calculator
HardiePlank boards, HardieTrim, kickout & butt-joint flashing, fasteners, sealant, and HardieWrap — sized to Hardie's HZ5/HZ10 install specs and IRC §R703.10.2.
Walls to clad
Windows and doors
HardiePlank product
HZ5 covers north / freeze-thaw climates; HZ10 covers south / high-humidity / coastal. Installing the wrong zone product voids the 30-year warranty.
Install configuration
Materials to include
4/4 (¾") is the casing / band / inside-corner default. 5/4 (1") gives outside corners and fascia greater visual weight and rigidity.
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Related Code Guides
Building code, climate zone, and standards references that change defaults for this calculator.
Climate Zone 1: R-Value Requirements (2021 IECC)
Climate Zone 1 R-value minimums for ceilings, walls, floors, and slabs in Florida Keys, Hawaii, and southern Texas under the 2021 IECC.
Climate Zone 2: R-Value Requirements (2021 IECC)
Hot-humid Climate Zone 2 R-value minimums for most of Florida, the Gulf Coast, and southern Arizona under the 2021 IECC.
Climate Zone 5: R-Value Requirements (2021 IECC)
Cool Climate Zone 5 R-value minimums for Pennsylvania, New York, Michigan, Illinois, Iowa, and the Pacific Northwest interior under the 2021 IECC.
Climate Zone 6: R-Value Requirements (2021 IECC)
Cold Climate Zone 6 R-value minimums for Minnesota, Wisconsin, Maine, Vermont, Montana, and North Dakota under the 2021 IECC.
Climate Zone 7: R-Value Requirements (2021 IECC)
Very-cold Climate Zone 7 R-value minimums for northern Minnesota, North Dakota, and high-altitude pockets of Alaska under the 2021 IECC.
Florida HVHZ Roofing Requirements
Florida HVHZ wind-zone roofing rules: shingle ratings, fastener schedules, NOA approval, and underlayment per FBC 8th Edition (2023) and Miami-Dade County.
Texas Windstorm Roofing Requirements
Texas Department of Insurance Seacoast windstorm rules: shingle ratings, fastening, WPI-8 inspection, and Tier I/II requirements for the Texas coast.
How to Use This Calculator
- Add a row for every wall: length, height, and whether it has a gable triangle on top. Mark outside and inside corners on each wall that borders one — the calculator divides by 2 since corners are shared.
- Enter total windows and doors across all walls (average width and height for the calc) — the calculator deducts opening area from gross wall SF and adds 3-sided HardieTrim casing per opening.
- Pick HardiePlank profile by board width and exposure: 5¼"×4", 6¼"×5", 7¼"×6", 7½"×6¼", 8"×6¾", 8¼"×7", 9¼"×8", 9½"×8¼", or 12"×10¾". Default is 6¼"×5" — the national best-seller.
- Pick HardieZone — HZ5 (north / freeze-thaw, IECC zones 5–7) or HZ10 (south / high-humidity / coastal, IECC zones 1–4). Verify your installation address is in the correct zone — wrong-zone install voids warranty.
- Pick stud spacing (16" preferred for higher wind tolerance, 24" max permitted) and complexity tier (Simple 8% / Standard 10% / Complex 15% waste).
- Pick weather-resistive barrier (HardieWrap, generic housewrap, or skip if already installed) and HardieTrim thickness for outside corners (5/4 for greater visual weight, 4/4 for budget).
- Toggle the accessory categories on or off: HardieTrim takeoff, fasteners, sealant, butt-joint flashing, kickout flashing. Click Calculate — see boards, trim pieces, flashing counts, fasteners, sealant tubes, and HardieWrap rolls.
How the HardieZone Math Works
Both HZ5 and HZ10 HardiePlank Installation Instructions share the same fastener inventory and spacing rules — the climate-zone differentiation is enforced through warranty geography, paved-surface clearance (HZ5 = 2" min, HZ10 = 1" min per ESR-2290 §4.2.4), HardieWrap perm-rating pairing (25-perm for HZ5, 15-perm for HZ10), and "block penetration recommended in HZ10" detailing. The HZ10 warranty is explicitly void in AK, UT, ID, CO, WY, MT and portions of WA, OR, CA, NV, AZ, NM. The calculator surfaces those differences in the installation notes so you can verify against your install address before ordering.
Frequently Asked Questions
How many HardiePlank boards in a Square (100 sq ft)?
James Hardie publishes this directly on the HardiePlank Coverage Chart (HS11119, p. 4). Per 100 sq ft: 5¼" plank at 4" exposure = 25 boards; 6¼" at 5" = 20 boards; 7¼" at 6" = 17 boards; 7½" at 6¼" = 16 boards; 8" at 6¾" = 15 boards; 8¼" at 7" = 14 boards; 9¼" at 8" = 13 boards; 9½" at 8¼" = 13 boards; 12" at 10¾" = 10 boards. These are Hardie's rounded ordering figures (the math is 100 ÷ (12 × exposure/12) and Hardie rounds up). Add an 8–15% waste factor depending on job complexity.
What's the difference between HZ5 and HZ10 HardiePlank?
Hardie engineers two product formulations targeting different climates. HZ5 (IECC zones 5–7, northern) is formulated for freeze-thaw resistance and improved cold-climate water management. HZ10 (IECC zones 1–4, southern) is formulated for high-humidity, high-heat, and coastal exposure. Install-detail differences include paved-surface clearance (HZ5 = 2" min, HZ10 = 1" min per ESR-2290 §4.2.4), HardieWrap perm-rating pairing (25-perm HZ5 vs 15-perm HZ10), and a 'block penetration recommended in HZ10' detail. Critically, the HZ10 warranty is void in AK, UT, ID, CO, WY, MT and portions of WA, OR, CA, NV, AZ, NM — installing HZ10 product in those areas voids the 30-year warranty entirely.
What's the minimum HardiePlank overlap and why does it matter?
1¼ inches minimum, per JH HardiePlank HZ5 Installation Instructions p. 3 fig. 15 and IRC 2021/2024 §R703.10.2. Anything less voids the James Hardie 30-year limited warranty AND violates the IRC prescriptive code path. The calculator enforces this by using Hardie's published exposure for each profile (which already accounts for the 1¼" lap).
Can I face-nail or do I have to blind-nail HardiePlank?
Blind nailing is preferred (one fastener at every stud, 3/8" from the top edge of the plank, concealed by the next course up). Face nailing is permitted but restricted: planks must be ≤ 9¼" wide AND fasteners spaced ≤ 12" o.c. when face-nailing to OSB (JH HZ10 HardiePlank IB, p. 2). Face nailing is typically used only where required by code for high-wind regions. For most installations — including coastal hurricane zones with 16" o.c. studs — blind nailing per ESR-2290 wind tables is sufficient and looks cleaner.
What sealant works with HardiePlank?
ASTM C920 NS Class 25+ (elastomeric, non-sag, ±25% movement) OR ASTM C834 latex (JH HZ5 HardiePlank IB, p. 3). Apply at plank ends butting trim (with a ¼" min gap), at field-cut edges, and at window/door surrounds per the opening manufacturer's instructions. Do NOT caulk butt joints on ColorPlus product — caulk and ColorPlus weather differently. Use Hardie's joint flashing detail instead (6" wide piece behind the joint, overlapping the course below by 1").
Do I need HardieWrap, or can I use Tyvek?
Either works — IRC §R703.2 requires one or more layers of water-resistive barrier behind exterior wall coverings, and HardieWrap is recognized in ICC-ES ESR-2658 but not mandated by Hardie. Most installers use HardieWrap because it's color-matched to the Hardie warranty package and stocked alongside HardiePlank. Functionally, Tyvek HomeWrap, Typar, and Grade D building paper all meet the code. Note that HardieWrap comes in two perm ratings: 25-perm for HZ5 (cold-wet) and 15-perm for HZ10 (hot-humid) — match to your HardieZone for product-system consistency.
Where should HardiePlank butt joints land?
Off-stud, per ESR-2290 §4.2.4: 'Vertical joints must be made off-stud. Joints may be located centrally between studs but no closer than 4 inches from the edge of a stud. Nails must not be placed within 1 inch of the end of the planks. Vertical joints must be staggered on subsequent courses.' Hardie also recommends a 6" wide butt-joint flashing piece behind every joint, overlapping the course below by 1". The calculator counts those flashing pieces by wall length and exposure automatically.
Is HardiePlank approved for California Chapter 7A (WUI) and Florida HVHZ?
Yes for California 7A — HardiePlank is classified noncombustible per ASTM E136 (ESR-2290 §3.0) and meets CBC 7A ignition-resistance requirements as a noncombustible exterior wall covering. For Florida HVHZ (Miami-Dade and Broward), HardiePlank requires a Notice of Acceptance (NOA) review for the specific wall assembly — Hardie maintains HVHZ-approved assemblies; verify the current NOA with the local building department before specifying. Texas TDI Windstorm certification works similarly — Hardie maintains TDI-approved assemblies for both HZ5 and HZ10 (most coastal Texas is HZ10).