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 â sized to Hardie's HZ5/HZ10 install specs and IRC §R703.10.2.
Walls to clad
One row per wall. Mark a gable triangle on top of any wall that has one.
Windows and doors
Counted across all walls. Deducted from net wall area for board calc.
HardiePlank product
All HardiePlank lap profiles are 12 ft long à 5/16 in thick
Why does an 8¼Ⳡplank only cover 7� See the exposure diagram
HZ5 covers north / freeze-thaw climates; HZ10 covers south / high-humidity / coastal. Installing the wrong zone product voids the 30-year warranty.
Install configuration
Stud spacing affects fastener count; complexity drives waste factor
Materials to include
Toggle off anything you're sourcing separately
4/4 (¾") is the casing / band / inside-corner default. 5/4 (1") gives outside corners and fascia greater visual weight and rigidity.
Prefer to skip the math? Get free quotes from local pros
How HardiePlank coverage actually works
Four things trip homeowners up on a HardiePlank take-off: a plank covers less than its width (the 1¼″ minimum overlap), the exposure is tuned so courses land even at the eave, you size the order by net area (not the whole wall), and the layers behind the siding go on in a set order. The diagrams below walk through each one and how it feeds the estimate above.
The exposure-and-overlap cross-section is why HardiePlank coverage is not a simple width calculation. The HardiePlank installation spec requires a 1¼″ minimum overlap at every course, so the calculator counts courses by dividing wall height by the exposed reveal, not the plank face width. A wider plank therefore does not cover proportionally more wall — most of the extra width disappears under the course above.
The even-coursing elevation shows why the calculator eases the reveal instead of running planks at maximum exposure. It solves for the whole number of equal courses that fills the wall, so the top course lands full height at the eave rather than as a thin, hard-to-nail sliver. Expect the course count to come out one higher than a maximum-exposure estimate — that extra course is the coursing being evened out, and it is what keeps the reveal lines straight across the elevation.
The wall-area diagram sets the sequence the calculator uses: subtract window and door openings from the gross wall first, then add a 10–15% waste factor. That waste is not padding — each opening breaks courses, so planks run past it as cut pieces and the factor covers those offcuts. Working from the gross wall instead would overbuy planks across the openings and still underbuy the cut waste around them.
The wall-assembly cross-section is why the take-off includes a starter strip, sealant, and fasteners, not just planks. The starter strip cants the first course to the same pitch the rest sit at, so skipping it throws off every reveal above it; the sealant closes butt joints and openings on fiber cement as the Hardie spec requires. The calculator sizes the starter strip and base flashing to the wall base run, which is why they scale with width rather than total area.
Calculation Formulas
Sum every wall rectangle, add the gable triangle on any gable wall, then subtract every opening. All HardiePlank lap profiles are 12 ft long × 5/16 in thick (JH HardiePlank IB, p. 4).
Example:
40 × 9 + 30 × 9 + ½ × 30 × 6 = 720 SF gross. Subtract 8 windows × 12 SF + 2 doors × 20 SF = 624 SF net.
Hardie publishes pieces-per-square for every profile in the Coverage Chart. For 6¼" × 5" exposure: 5.00 SF per 12-ft board, 20 boards per Square. Waste tier is the only judgment call.
Example:
624 SF ÷ 5.00 SF/board × 1.10 (standard 10%) = 138 boards (raw 125 + 13 waste).
Industry consensus across Siding Authority, BuildWithDave, and ContractorTalk. Hardie publishes no waste factor — the Coverage Chart explicitly excludes it. Slightly conservative tiers reflect HardiePlank dye-lot and 12-ft pallet ordering reality.
Example:
6 openings, simple 1-story gable → 8%. 10 openings, two stories → 10%. Dormers + bay windows → 15%.
A 1¼" wide × ¼" thick starter strip sets the first course angle. Most installers rip starter from a HardiePlank cut to 1¼" — permitted by Hardie and ESR-2290 §4.2.4.
Example:
140 LF bottom perimeter − 2 × 36"/12 = 134 LF → ⌈134 ÷ 12⌉ × 1.10 = 13 starter pieces.
HardieTrim is the system Hardie uses in place of vinyl-style J-channel. 4/4 (¾") covers casing, band, frieze, and inside corners. 5/4 (1") gives outside corners and fascia more visual weight (JH HardieTrim IB, p. 1).
Example:
4 outside corners × 9 ft × 2 boards = 72 LF of 5/4. 8 windows × (2 × 48 + 36)/12 = 88 LF of 4/4 casing.
Hardie-recommended butt-joint detail: 6" wide piece overlapping course below by 1". Joints must land off-stud (ESR-2290 §4.2.4) — centrally between studs, no closer than 4" from the stud edge, staggered on subsequent courses.
Example:
40-ft wall, 9 ft high, 5" exposure: ⌈40/12⌉ − 1 = 3 joints/course × ⌈108/5⌉ = 22 courses = 66 pieces.
Per JH HardiePlank IB p. 2, blind-nail with 0.09" siding nail 3/8" from top edge, one fastener at every stud plus plank ends. 24" o.c. = 7 nails per plank; 16" o.c. = 10 nails per plank. 10% drop/loss allowance.
Example:
138 boards × 10 nails @ 16" o.c. × 1.10 = 1,518 nails.
Hardie publishes no tube-coverage rate. Industry caulk-table convention: 24 LF per 10.1 oz tube at a ¼" round bead. Do NOT caulk butt joints on ColorPlus — caulk and ColorPlus weather differently; use Hardie joint flashing instead.
Example:
320 LF of trim joints + opening surrounds ÷ 24 × 1.10 = 15 tubes.
"A kick-out flashing shall be installed to divert the water away from where the eave of a sloped roof intersects a vertical sidewall. The kick-out flashing on the roof shall be a minimum of 2-1/2 inches long." Min 0.019" / No. 26 galvanized metal.
Example:
1 detached garage attached to house = 1 kickout per side roof termination, typically 2 per garage.
HardieWrap product brochure: 9 ft × 150 ft roll = 1,350 SF. Use 10% overlap allowance for 6" horizontal + 6" vertical laps. HZ5 product is 25-perm (cold-wet); HZ10 is 15-perm (hot-humid).
Example:
720 SF gross × 1.10 = 792 SF ÷ 1,350 = 1 roll covers small house. 3,000 SF → 3 rolls.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| Plank length (all profiles) | 12 ft (144 in) | Every HardiePlank lap profile ships 12 ft long. Source: JH HardiePlank HZ5/HZ10 IB, p. 4 Coverage Chart. |
| Plank thickness | 5/16 in (≈0.312 in) | All HardiePlank lap profiles are 5/16" thick per ESR-2290 Table 1. |
| Minimum overlap | 1¼ in | Less than this voids the warranty and the IRC §R703.10.2 prescriptive path. Source: JH HZ5 HardiePlank IB, p. 3 fig. 15; IRC 2021 §R703.10.2. |
| Maximum stud spacing | 24 in o.c. (wood or 20–16 ga steel) | Or direct to ≥ 7/16" OSB sheathing without framing. 16" o.c. yields ~30–40% higher allowable wind speeds in ESR-2290 Tables 3–26 — recommended for exposure C/D coastal. |
| Clearance to grade | 6 in min, grade sloping ≥ 6" over first 10 ft | Per JH HZ5/HZ10 HardiePlank IB, p. 1, fig. 8. Below 6" risks splash-back and is a common warranty-denial path. |
| Clearance to paved surfaces | HZ5 = 2 in / HZ10 = 1 in | Differentiated by climate per ESR-2290 §4.2.4. HZ5 needs more clearance for snow / freeze cycle. |
| Blind nail position | 3/8 in from top edge of plank | Concealed by the course above. If no factory nail line is present, fasten 3/4" – 1" from top. Source: JH HZ5 HardiePlank IB, p. 1 fig. 2. |
| Pieces per Square (6¼" × 5" exposure) | 20 boards per 100 SF | Hardie published coverage. Other profiles: 5¼" = 25/Sq; 7¼" = 17/Sq; 8¼" = 14/Sq; 9¼" = 13/Sq; 12" = 10/Sq. |
| Warranty period | 30 years (Plank/Panel/Shingle/Soffit), 15 years HardieTrim, 15 years ColorPlus, 10 years HardieWrap | All non-prorated and transferable once from the original purchaser. HZ10 product warranty void in AK, UT, ID, CO, WY, MT and portions of WA, OR, CA, NV, AZ, NM. |
| Acceptable nail types (wood framing) | Galvanized, hot-dipped galvanized (preferred), or stainless | Stainless required near ocean / large water bodies / very humid coastal HZ10. Aluminum fasteners, staples, and clipped-head nails are prohibited. |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
James Hardie HardiePlank® Lap Siding Installation Instructions(JH HS11119 (HZ5 Dec 2019 / HZ10 May 2016))
View StandardThe manufacturer's primary install spec — the document HardiePlank's warranty references. Covers fastener tables, clearances, butt-joint detailing, kickout flashing, painting, and HardieZone product matching. Two regional variants: HZ5 for north / freeze-thaw and HZ10 for south / high-humidity / coastal.
Key Requirements:
- •Minimum 1¼ in overlap on every course
- •Maximum 24 in o.c. stud spacing (16 in o.c. for higher allowable wind speeds)
- •Blind nail 3/8 in from top edge with 0.09" × 0.221" HD × 2" siding nail
- •Off-stud butt joints, no closer than 4 in from stud edge, staggered on consecutive courses
- •6 in min clearance to grade; 2 in (HZ5) or 1 in (HZ10) min to paved surfaces
- •Paint factory-primed product within 180 days; unprimed within 90 days
ICC-ES Evaluation Report ESR-2290 — HardiePlank, HardieShingle, Artisan(ESR-2290 (Reissued March 2022, Revised May 2023))
View StandardICC-ES recognition report establishing HardiePlank's compliance with the 2021 and 2024 IRC §R703.10 and Table R703.3, and with the IBC. Tables 3–26 cross-index fastener / framing / sheathing / spacing to maximum allowable basic wind speeds (ASCE 7 mph). Required by some jurisdictions for high-wind permitting.
Key Requirements:
- •ASTM C1186 Type A, minimum Grade II compliance
- •ASTM E84 Class A: flame-spread 0, smoke-developed 5
- •ASTM E136 — noncombustible classification
- •Wind-load tables assume I = 1.0, Kzt = 1, Kd = 0.85, GCpi = ±0.18, GCp = −1.4
- •Off-stud butt joints, 1 in min from plank ends, 4 in min from stud edge
- •Verify table row for your specific fastener × framing × sheathing × spacing × exposure
IRC 2021 / 2024 §R703.10 — Fiber-Cement Siding(2021/2024 IRC §R703.10 and §R703.10.2)
View StandardCode basis for fiber-cement lap siding in one- and two-family dwellings. Requires ASTM C1186 Type A min Grade II or ISO 8336 Cat A Class 2; mandates 1¼ in min lap; requires installation per manufacturer's instructions OR Table R703.3(1) prescriptive nailing schedule.
Key Requirements:
- •ASTM C1186 Type A minimum Grade II OR ISO 8336 Category A min Class 2
- •Maximum 12 in width for lap siding
- •1¼ in minimum overlap
- •Manufacturer install instructions OR Table R703.3(1)
- •Fastener heads exposed or concealed per Table R703.3(1) or approved instructions
IRC 2021 §R903.2.1 — Kickout Flashing(2021 IRC §R903.2.1)
View StandardVerified text: "A kick-out flashing shall be installed to divert the water away from where the eave of a sloped roof intersects a vertical sidewall. The kick-out flashing on the roof shall be a minimum of 2-1/2 inches long." Metal flashing must be ≥ 0.019 in (No. 26 galvanized).
Key Requirements:
- •Kickout flashing at every roof-to-wall eave intersection
- •Minimum 2½ in long
- •Min 0.019 in (No. 26 galvanized) metal
- •Continuous step flashing along the roof-wall step (separate detail, also required)
- •Diverter shape — water must clear the wall plane, not run along it
IRC 2021 / 2024 §R703.2 — Water-Resistive Barrier(2021/2024 IRC §R703.2)
View StandardMandates one or more layers of water-resistive barrier behind exterior wall coverings. HardieWrap is recognized in ICC-ES ESR-2658; ASTM E2178 air-barrier and ASTM E96 vapor-permeance properties are documented in the product brochure. HZ5 product is 25-perm (cold-wet); HZ10 product is 15-perm (hot-humid).
Key Requirements:
- •One or more layers of WRB behind all exterior wall coverings
- •Recognized products: HardieWrap (ESR-2658), Tyvek (various ESRs), Typar, Grade D paper
- •Lap 6 in vertical / 6 in horizontal minimum
- •Integrate with window/door flashing per manufacturer instructions
- •Vapor permeance and air-barrier ratings vary by product — match to HardieZone
ASTM C920 — Elastomeric Joint Sealants(ASTM C920 NS Class 25+ (or ASTM C834 latex))
View StandardStandard specification for elastomeric joint sealants. HardiePlank install instructions accept either ASTM C920 NS Class 25+ OR ASTM C834 latex. NS (non-sag) is required for vertical joints; Class 25+ means ±25% joint movement capability.
Key Requirements:
- •NS (non-sag) classification for vertical joints
- •Class 25 minimum movement capability
- •Use at plank-to-trim junctions, not at ColorPlus butt joints
- •Verify sealant manufacturer install-temperature SDS (typical 40–90 °F)
- •Maintain ¼ in min joint to horizontal flashing — do NOT caulk this gap
California Building Code Chapter 7A — WUI Ignition Resistance(CBC §707A (Wildland-Urban Interface))
View StandardHardiePlank is classified noncombustible per ASTM E136 (ESR-2290 §3.0) and Class A (FSI 0, SDI 5) per ASTM E84. Accepted as a noncombustible exterior wall covering meeting CBC 7A ignition-resistance requirements. Required in California Fire Hazard Severity Zones (FHSZ) and increasingly adopted by other Western states.
Key Requirements:
- •Noncombustible (ASTM E136) classification — HardiePlank qualifies
- •OR Heavy-timber per CBC §602.4 (not applicable to lap siding)
- •OR ignition-resistant material per ASTM E84 ≤ 25 / 450 (Class A)
- •Flashing details at roof-wall junctions per §707A.4
- •Soffit ventilation per §707A.6 — pair with HardieSoffit vented or non-vented
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
HZ5 vs HZ10 — Climate-Engineered Product
Two formulations matched to climate stress, with warranty consequences
Hardie engineers HZ5 for freeze-thaw resistance and improved cold-climate water management; HZ10 for high-humidity, high-heat, and coastal exposure. The differences are formulation-level and install-detail-level. Warranty geography is enforced — installing HZ10 product in an HZ5 area (or vice versa) voids the 30-year warranty.
Regional Examples:
Wind Speed and Stud Spacing
ESR-2290 wind tables cross-index fastener × framing × spacing to max allowable mph
HardiePlank's wind-load capacity isn't a single number — it's a 24-table matrix in ESR-2290 (Tables 3–26). Each table gives the maximum basic wind speed for a specific combination of fastener type, framing material, stud spacing, and product width. 16 in o.c. spacing typically yields 30–40% higher allowable wind than 24 in o.c. for the same assembly.
Regional Examples:
Painting and Finish — ColorPlus vs Primed
Three product tracks: ColorPlus baked-on, factory-primed, unprimed
Hardie sells HardiePlank in three finish tracks. ColorPlus® Technology arrives baked-on in a Hardie-selected palette with a 15-year limited finish warranty. PrimePlus arrives factory-primed and must be field-painted within 180 days. Unprimed must be painted within 90 days. All field-paint must be 100% acrylic topcoat — no stain, oil/alkyd, or powder coating, ever.
Regional Examples:
Foam Sheathing and Continuous Insulation
IECC 2021 zones 4+ continuous insulation drives detail changes
IECC 2021 / 2024 requires continuous insulation (CI) above some R-value threshold in climate zones 4 and colder. Foam sheathing under HardiePlank requires Hardie's USTB 19 Technical Bulletin (Installation over Non-Nailable Substrates). The key constraint: avoid over-driving fasteners — foam compresses and dimples the siding.
Regional Examples:
Rainscreen vs Direct-Applied
Hardie does not mandate rainscreen for HardiePlank, but local code may
James Hardie does not require a rainscreen behind HardiePlank lap siding. HardiePanel vertical siding is the only Hardie product where they recommend a rainscreen as a best practice (JH HardiePanel HZ5 IB, p. 1). However, IRC §R703.1.1 requires a means for drainage, and some jurisdictions now require a min 3/16 in drainage space — verify locally.
Regional Examples:
Pre-1978 Homes — Lead-Safe Removal of Existing Siding
EPA RRP rule applies when removing painted siding ahead of HardiePlank
HardiePlank itself is lead-free. But removing existing painted siding in pre-1978 homes triggers the EPA Renovation, Repair and Painting (RRP) rule when disturbed area exceeds 20 sq ft outside. This affects the demolition / disposal phase, not the new install.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
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Want to Learn More?
HardiePlank installation rules from James Hardie HS11119 + ESR-2290: HZ5/HZ10 differences, fastening, butt joints, HardieTrim, kickout flashing, warranty.
Read the HardiePlank Installation Guide
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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). The exposure and overlap diagram shows how overlap sets coverage.
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. The wall assembly diagram shows the flashed, staggered joints.
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).