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What does the composite decking calculator do?
It turns your deck size into boards, packs, joists and clips for a composite board. Pick a verified product and the calculator fills in the board’s published width and length, plus its maximum joist centres where the maker states them. Otherwise, type your own board size. If your boards come in packs, enter the number per pack and it rounds up to whole packs.
What gap should I enter?
The gap your clip system creates. EnviroBuild’s clips make a 3 mm or 6 mm gap, and Millboard’s guide specifies 4 mm between board sides with 1 mm at butt ends and 10 mm to any solid surface. Composite Prime sets 10 mm to fixed objects. If you’re unsure, leave the default and check the maker’s guide.
What joist spacing should I enter?
The maximum your board maker allows, which varies: Millboard 400 mm for residential use and 300 mm for commercial, Composite Prime 300 mm, Eva-Last Apex 300 mm, Eva-Last Infinity 400 mm. EnviroBuild gives 300 mm as the standard maximum for composite. At 45 degrees Millboard says 300 mm. The calculator uses the figure you enter and doesn’t check it.
How do fixings add up?
Millboard needs two fixings at each joist crossing and three at board ends, and its Durafix screws are a warranty requirement. The calculator counts two screws per crossing, which suits a screw-fixed board, and one clip per crossing for clip systems. Treat both as estimates and round up. For clip counts, packs of 100 are common: NeoTimber sells starter clips and 3 mm and 6 mm clips in 100s.
Where do prices come from?
From you. The panel has no built-in prices. Pick a verified board with a recent dated price and it fills the board price in with the date, so you can see how old it is; those prices are in the price tables. Typical totals are in the decking cost calculator guide. For waste, EnviroBuild suggests 5 to 10 percent, and 15 or more for diagonal layouts.
Questions
How do I work out a composite decking cost?
Choose a board or type its size, enter your deck size, then open the price panel and add what you have been quoted for boards, joists, clips and any labour. The result is a total with a cost per m², or a partial total if a required price is missing.
How many clips do I need?
The calculator estimates one clip per board at each joist, so rows times joists. Real counts depend on the clip system and on starter clips: EnviroBuild says one box of 100 starter fasteners covers about 25 m² and sells clips in 3 mm and 6 mm gaps, and Composite Prime uses one clip and screw on every joist.
Sources
- Millboard Installation and User Guide (hosted by Cladco)
- HD Deck Pro Fitting Guide and Composite Prime Care & Maintenance Guidelines (Taylor Maxwell, 2022)
- Hidden Fastener System - EnviroBuild
- Composite decking fixings - NeoTimber
- Composite Decking Board Guide - EnviroBuild
- Eva-Last Apex Grooved Composite Deck Board 140mm (manufacturer)
- Eva-Last Infinity I-Series (IS 113) Composite Groove Deck Board (manufacturer)