Deck planning guide · 5 min read
Deck-board gaps and waste allowance
Choose realistic spacing and waste inputs for wood or composite decking without under-ordering the job.
Gap for the material you are installing
Board spacing affects drainage, ventilation, debris, appearance, and the total number of courses. Wood movement depends on species and moisture condition; composite and PVC products use manufacturer-specific spacing rules that can change with temperature and butt-joint conditions.
Use the decking manufacturer's current installation instructions when they exist. A generic calculator input does not override product-specific requirements.
Choose waste deliberately
Waste is not a universal number. Build a rough cut plan when the order is expensive, the material is special-order, or colour batches may not match later.
- Simple rectangular layout with suitable full-length stock: start near 5%.
- Butt joints, borders, sorting, or moderate complexity: consider 8–10%.
- Diagonal patterns, many short cuts, or complex geometry: 12–15% or a project-specific cut plan may be safer.
- Add known damaged or unusable boards separately instead of hiding every uncertainty in one percentage.
Dry-layout the final courses
Small differences in actual board width and gap accumulate across the deck. Before committing to the first courses, divide the measured width by the planned module and see what remains. Slightly adjusting gaps within the permitted range can produce balanced edge boards.