Siding Calculations
Siding Waste Factor Explained
Published June 16, 2026
If you order siding based purely on your net wall area, you’ll almost certainly run short. That’s because installation always produces some amount of unusable material — and a waste factor accounts for that upfront so you order enough the first time.
Where siding waste comes from
- Cuts at corners and openings. Every window, door, and corner requires a cut piece, and the offcut is often too small to reuse elsewhere.
- Angled cuts at gables. Diagonal cuts along a roofline waste more material than straight cuts.
- Pattern and color matching. Natural materials like wood and cedar need extra material to match grain and color across a wall.
- Handling and installation damage. A percentage of pieces are damaged during transport, staging, or installation.
- Complex rooflines. Dormers, bay windows, and multiple roof pitches multiply the number of cuts needed.
Typical waste percentages
| Project complexity | Typical waste |
|---|---|
| Simple rectangular home, few corners | 5–10% |
| Typical home with several corners and gables | 10–15% |
| Complex roofline, dormers, or natural materials | 15–20%+ |
These are starting points, not guarantees — always round up to the nearest full box, carton, or board when you actually place an order.
How waste factor changes your total
Waste is applied to your net area (after subtracting openings), not your gross area. The formula is:
For a home with 1,580 sq ft of net area:
- At 10% waste: 1,580 × 1.10 = 1,738 sq ft
- At 15% waste: 1,580 × 1.15 = 1,817 sq ft
- At 20% waste: 1,580 × 1.20 = 1,896 sq ft
That’s a difference of over 150 sq ft between the low and high end — enough to matter when you’re placing a material order.
Choosing the right number for your project
Start with 10% for a straightforward rectangular home. Increase it if your home has more than four corners, any gables or dormers, or if you’re using a natural material like wood or cedar that requires pattern matching. When in doubt, round up slightly — most suppliers accept returns of unopened material, but a mid-project shortage can mean delays or a mismatched dye lot on a rush reorder.
Calculate your own waste allowance
Use the Siding Waste Calculator to see exactly how much extra material a given waste percentage adds to your project, or the full Siding Calculator to include waste in a complete take-off. If you already know your material, the vinyl, fiber cement, wood, cedar and metal calculators each start from a sensible waste default for that material.