Decking Installation

Before undertaking any construction work you must consult with your local authority to check that any construction requirements are met and to determine if a Building Concent is required. A qualified tradesman should be consulted where expert services may be required. 

Click here, to find the Decking Installation Manual download.


  • Joint Spacing: Joists should be at maximum 450mm between centres but can be extended (up to 600mm) by using larger cross sections (100 x 32mm, 140 x 40mm, etc), an engineer should be consulted for specifications.


  • Defects: Some boards may contain defects that will require docking out.
  • Length Sorting: Sort the timber lengths to optimise usage.
  • Coating: Although not very common in New Zealand, coating your deck will extend its life. We recommend a minimum of one coat of a suitable exterior timber decking coating or oil is applied to all four sides plus cut ends of the decking prior to installation.


  • 90 x 19mm Decking: Fix the decking to every supporting joist with two 65mm 8g Stainless Steel Annular Grooved Decking Screws.
  • 140 x 19mm and 24/25mm Thick Decking: Fix the decking to every supporting joist with two 65mm 10g. Stainless steel ecking screws (Accoya 316 grade). Fixing 32mm thick decking requires minimum 75mm screws.


  • Pilot Holes: Predrill pilot holes slightly smaller than the screw gauge before fixing. 
  • Location: Fixings should be located 12.5 mm in from the edge of the board for 19mm Decking or 15mm in from the edge of the board for 24/25mm Decking.
  • Stagger Fixings: Staggering the fastenings across the joists will help reduce the risk of splitting.
  • Expansion Gaps: An expansion gap is required between the boards to allow for movement and drainage of surface water.  The gap required depends on the species and profile size. Consult table below for correct spacing.


  • Placement: Joins must be placed over a joist.
  • Method: Decking should be cut square and butted together. Planning an angled 2-3mm chamfer off the end of each board will mask any unevenness in height. 
  • Fixing Location: Fixings should be 20mm in from the butted join and angled toward the centre of the joist to maximise holding performance.


  • Cleaning: Annually cleaning your deck will help prolong its life, a light detergent that contains an anti-fungal against is best. Find here our Cleaning and Maintenance Guide.
  • Recoating: Any coating or oil applied may require another coat to maintain desired look or colour. 
  • Winter: Removing any items that will trap water underneath them (furniture, pot plants, etc for the duration of winter will extend the life of your deck and reduce the risk of mould, fungi or gunge on the surface.

Fastener Types

Fastener Types
Nails We do not recommend using nails for hardwood decking profiles.

Screws These are suitable for decking boards up to a maximum size of 140x19mm, anything larger may require bolts.

Hidden fasteners These are relatively new to the marketplace and different brands work slightly different to each other but all are essentially fixed to the joists and attach to the side of the decking board.  The end result is a very modern clean-looking deck because no nail or screw heads are visible on the surface.

Expansion Gaps

Expansion Gaps are essential for many reasons, but primarily to provide ventilation and drainage and to allow for the timbers natural tendency to shrink and swell. This will be dependent on the amount of moisture in the immediate environment. Three factors need to be considered in determining the gap between boards:

  • Moisture Content: Decking can be supplied in a range of moisture contents, from near green to kiln dried. A kiln dried product will swell, whereas a green or air dried board will shrink, in either case, please see below for recommended expansion gaps. 
  • Species: Kwila is a very stable species which does not shrink and swell in comparison to other species such as Jarrah, Saligna, Massa, Greenheart etc.
  • Size (width of the board): Wider boards will shrink/swell more than narrower boards so generally require a larger expansion gap.

Recommended Expansion Gaps for Hardwood Decking

This table gives recommended expansion gaps for Timber Decking:

  90-120mm Wide 130-140mm Wide
Species Green / Shipping Dry Air Dried / Kiln Dried Green / Shipping Dry Air Dried / Kiln Dried
N/A 3-4mm N/A 4-6mm
Blackbutt 3mm 4mm Not recommended 6-8mm
Jarrah Not recommended 5mm Not recommended Not recommended
Kwila 3mm 4mm Not recommended 6-8mm
Saligna Not recommended 5mm Not recommended Not recommended
Vitex 3mm 4mm Not recommended 6-8mm

For more information download our hardwood decking brochure, visit our downloads page.