Quick Answer
A 1,500 sq ft house with 8′ walls needs roughly 175–200 linear feet of HardiePlank per wall side. Use the calculator above for exact board counts, trim lengths, and complete materials lists.
What Is Siding Exposure (Reveal)?
Exposure — also called "reveal" — is the portion of each lap siding board that remains visible after the board above overlaps it. If a board is 8.25″ wide and overlaps 1.25″, the exposure is 7″.
Exposure directly controls how many courses (horizontal rows) appear on a wall and how much material you need. A smaller exposure means more courses, more boards, and higher material cost. A larger exposure means fewer courses but risks exceeding the manufacturer's maximum — which voids the warranty.
Exposure vs. Board Width
Even Coursing: The Critical Calculation Most Guides Skip
The biggest mistake DIYers make is installing lap siding at maximum exposure without adjusting for the wall height. The result: the top course is a narrow sliver that looks amateurish and requires difficult cuts.
Even coursing slightly reduces the exposure so that all courses are equal height and the final course lands cleanly at the soffit or eave line. The formula:
Even Coursing Formula
Without this adjustment, course 16 would be only 3″ tall (108 − 15 × 7 = 3″) — an ugly result requiring complicated cuts against the soffit.
Lap Siding Material Types: Specs & Coverage
Each material has different board dimensions, maximum exposures, and overlap requirements set by both the manufacturer and IRC R703. Using the wrong exposure voids warranties and may fail inspection.
| Material | Board Width | Min Overlap | Max Exposure | Weight (per sq) |
|---|---|---|---|---|
| HardiePlank® (fiber cement) | 8.25″ | 1-1/4″ | 7″ | ~325 lbs |
| LP SmartSide® (eng. wood) | 8″ / 12″ | 1″ | 7″ / 10.5″ | ~225 lbs |
| Wood Bevel Siding | 6″ / 8″ / 10″ | 1″ | 5″ / 7″ / 9″ | ~180–260 lbs |
| Vinyl Siding (double 4″) | 8″ panel | — | 4″ per row | ~60 lbs |
| Vinyl Siding (Dutch lap 5″) | 5″ | — | 4.5″ | ~65 lbs |
Sources: James Hardie Installation Guide, LP SmartSide Installation Guide, IRC R703.11. Vinyl siding has no structural overlap spec — manufacturer exposure varies by style.
How to Calculate Linear Feet of Siding Needed
Once you have your adjusted exposure, calculating linear feet is straightforward. The key is to work from net wall area — total wall area minus windows and doors — not gross area.
Worked Example: 1,500 sq ft Ranch House
Trim & Accessories: What You're Forgetting to Order
Siding boards are only part of the materials list. A complete installation requires trim, starter strips, fasteners, flashing, and caulk — all of which must be ordered before work begins.
Corner Boards
- •Outside corners: 2 boards per corner (full wall height)
- •Inside corners: 1 board per corner (full wall height)
- •Fiber cement corners: 1×4 or 1×6 PVC or fiber cement board
- •Vinyl: use pre-formed corner posts, measured in linear feet
- •Measure from top of foundation to soffit — add 2–3″ for trimming
Starter Strip & J-Channel
- •Starter strip: total perimeter of structure at first course
- •Sets exposure height for bottom course — required for warranty
- •J-channel: around all windows, doors, and at soffit
- •= (2 × width + 2 × height) per opening × 1.10
- •Vinyl: use manufacturer-matched J-channel only
Drip Cap & Flashing
- •Drip cap over every window (horizontal top edge)
- •= total window width + 2″ per window for overlap
- •Fiber cement: aluminum or galvanized drip cap only
- •IRC R703.4 requires flashing at all wall penetrations
- •Count diverter flashing at roofline intersections
Fasteners & Caulk
- •Nails: corrosion-resistant (galvanized or stainless) per IRC R703.11
- •HardiePlank: 1-3/4″ siding nails, 16″ o.c. — no staples allowed
- •LP SmartSide: 1-1/2″ nails or approved staples
- •Caulk: 1 tube per ~25 linear feet of vertical butt joints (fiber cement)
- •Vinyl: NO caulk — must expand/contract; leave gaps at channel
Waste Factors by Project Complexity
Lap siding waste comes from end cuts at corners, angled cuts at gables, and course-height offsets around windows. Gables are particularly wasteful because each board is cut at a different angle.
| Project Complexity | Waste Factor | Description |
|---|---|---|
| Simple — rectangular walls | 10% | 4 walls, few windows, no gables, experienced installer |
| Moderate | 12–15% | Multiple windows/doors, some architectural features |
| Complex — gables included | 15–18% | Gable ends, bay windows, dormers, many corners |
| Very complex | 18–22% | Multiple gables, curved walls, first-time DIY install |
| DIY allowance (add to above) | +3–5% | Additional buffer for learning curve on first installation |
Gable ends are the biggest waste driver. Each board in a gable requires an angled cut — waste is highest at the peak where boards are very short. Budget 20%+ for homes with multiple gables.
HardiePlank® vs LP SmartSide®: Which Do You Need?
These are the two dominant premium lap siding products, and they're usually quoted in overlapping price bands, so the decision is rarely about price. James Hardie (fiber cement) wins on fire, rot and pest immunity, warranty strength, and lifespan. LP SmartSide (engineered wood) wins on hail impact, cold-weather flex, and a lighter, faster install. Your climate and how long you'll own the home decide it.
| Factor | James Hardie (fiber cement) | LP SmartSide (engineered wood) |
|---|---|---|
| Composition | Portland cement, sand, cellulose (inorganic) | Wood strands + resin, wax, zinc borate |
| Fire | Noncombustible (ASTM E136), Class A flame spread | Combustible; Class A flame spread only |
| Hail / impact | Harder, but can crack or chip | Flexes; best impact resistance |
| Lifespan | 30–50 yrs | 20–30 yrs |
| Repaint cycle | 10–15 yrs (ColorPlus finish warranted 15) | 8–12 yrs |
| Warranty | 30-yr non-prorated + 15-yr ColorPlus finish | “5/50”: 5 yrs full, then prorated to year 50 |
| Weight | ~2.3–2.5 lb/sq ft; two-person job | ~1.3 lb/sq ft |
| Cutting | Shears or dust-collecting saw; silica dust (OSHA 29 CFR 1926.1153) | Ordinary wood tools; seal every cut edge |
| Best climate | Wildfire (WUI), heat, coastal, high wind | Hail, cold and freeze-thaw |
| Resale (2025 Cost vs. Value) | 113.7% recouped (fiber cement) | Not separately tracked |
Warranty: read past the headline number
What matters is the non-prorated period, how long you get full replacement value. James Hardie's substrate warranty is 30 years, non-prorated and transferable. LP's “5/50” gives five years at 100%, then prorates about 2.22% per year from year 6, so roughly 45% of the value remains at year 30. LP's headline number is bigger; Hardie's coverage is stronger. Terms per the manufacturers' warranty documents; read the current PDF for your product line.
Fire vs. hail: the two rows that usually decide it
Wildfire zones favor Hardie outright. Fiber cement is noncombustible per ASTM E136, documented in ICC-ES ESR-2290 with California Chapter 7A ignition-resistant listings. LP carries a Class A flame-spread rating too, but flame spread isn't noncombustibility, and LP assemblies often need a gypsum layer behind them to earn a WUI listing.
Hail country favors LP. Its wood-strand core flexes and absorbs impact, and its limited warranty covers hail up to 1.75 inches when properly installed. Fiber cement is harder but more brittle. LP's published side-by-side hail test is manufacturer-sponsored, so treat the exact figures as LP's claim; the direction matches how the materials behave.
Choose HardiePlank® if…
- ✓ You're in a wildfire (WUI) zone
- ✓ You want the longest life and rot/pest immunity
- ✓ You plan to stay, or resale value matters
- ✓ You want a non-prorated warranty
- ✓ Your climate is hot, humid, coastal, or high-wind
- △ Pro install: heavy, brittle, silica dust when cut
- △ Min 6″ clearance from grade per James Hardie
Choose LP SmartSide® if…
- ✓ You're in hail country
- ✓ Your winters bring hard freeze-thaw cycles
- ✓ You want a lighter, faster, year-round install (16-ft boards, fewer seams)
- ✓ You want a slightly lower upfront price
- △ Keep 6″ from grade and 1″ from rooflines
- △ Prime/seal every field cut before installation
- △ Prorated warranty after year 5
Pricing the job? Installed ranges for Hardie, LP SmartSide, and vinyl are on the siding cost guide. Sizing Hardie specifically? The HardiePlank Calculator handles HardieZone matching and Hardie trim and flashing. Weighing vinyl too? See vinyl vs fiber cement siding.
6 Lap Siding Installation Mistakes That Void Warranties
Regional Considerations: Material Selection by Climate
- ✓ Non-combustible
- ✓ Salt-air resistant
- ✓ Pest-proof
- ✓ No expansion from humidity
- ✓ Flexible substrate handles thermal cycling
- ✓ Primed cuts resist moisture absorption
- ✓ ICC ESR report coverage
- ✓ Noncombustible (ASTM E136)
- ✓ Required by many WUI ordinances
- ✓ ICC 7A compliant
- ✓ Ember-resistant
