Decking Calculator
Calculate decking boards, joists, posts, and costs for South African outdoor decks. Covers SA pine, Balau, Meranti, composite WPC, and Ipe with supply and installation estimates.
Quick Calculator Get a fast estimate
m
m
mm
mm
mm
Deck area
20 m²
Decking boards needed
46 boards × 5m
Joists required
14
Board material cost
R 3 960
Joist cost
R 2 520
Installation (labour)
R 5 600
Total estimated cost
R 12 080
Cost per m²
R 604/m²
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How to Use the Decking Calculator
Enter deck dimensions, select your preferred timber species, and set the board width and gap. The calculator gives board count, joist quantities, and a full cost breakdown with 2024 South African pricing.
The Extended Calculator adds subframe quantities (joists, bearers, posts) and fastener estimates. The Professional Calculator covers structural joist sizing, balustrade quantities, and a maintenance cost schedule.
Need more detail?
Extended Calculator More options, charts, and scenario comparison
m
m
mm
mm
Board quantities
46 boards
Deck area
20 m²
Board pitch
96 mm centre-to-centre
Total linear metres
230 m
Board cost
R 3 960
Decking Board Formula
Board count = ceil(deck width ÷ (board width + gap)) × 1.1
Pitch = board width + gap (mm)
Linear metres = board count × board length
Joist count = ceil(deck length ÷ joist spacing) + 1
SA Timber Decking Comparison
| Species | Cost/m² | Durability class | Maintenance |
|---|---|---|---|
| SA pine (CCA H3) | R180–R250 | Class 3–4 (treated) | Annual oil |
| Meranti | R380–R500 | Class 2 | 18-month oil |
| Balau | R600–R800 | Class 1 | 2-year oil |
| Composite WPC | R450–R600 | N/A (synthetic) | Annual wash |
| Ipe (Brazilian) | R850–R1,100 | Class 1 | 2-year oil |
Need full precision?
Professional Calculator Complete parameters, sensitivity analysis, and detailed breakdown
kPa
m
Joist sizing
50 mm depth
Design load (UDL)
1 kN/m
Max bending moment
0,2813 kN·m
Section modulus needed
18 750 cm³
SA NHBRC live load
2.0 kPa (decks <1m), 1.5 kPa (ground)
Note
Consult structural engineer for decks >1m high
Frequently Asked Questions
Boards = ceil(width ÷ pitch) × 1.1. For 4m deck with 90mm boards at 6mm gap: pitch = 96mm, ceil(4000÷96) = 42, × 1.1 = 47 boards. Each board runs the full deck length. Order slightly more for diagonal lay patterns (+15%).
Budget: CCA-treated SA pine (H3 for above-ground, H4 for in-ground). Mid-range: Meranti. Premium: Balau or Ipe. Composite: low maintenance but cannot be sanded. Balau is the most popular premium choice in Gauteng and coastal areas.
5–8mm for most timbers. Pine expands significantly — use 8mm in humid areas. Composite boards: check manufacturer spec (usually 5mm). Gaps allow drainage, prevent warping, and improve non-slip performance.
Decks >1m high or attached to main structure typically need municipal approval. Under SANS 10400-A, structures over 12m² or altering the existing building need plans. Contact your local municipality. Non-compliant structures can cause insurance claim refusals.
Pine: every 12–18 months. Balau/hardwood: every 18–24 months. Test: sprinkle water — if it soaks in, oil is needed. Clean with Oxalic acid first, sand lightly, then apply 2 coats penetrating oil (Woodoc, Prestik, Osmo). Avoid varnish on outdoor decks.