Build a timber deck

Mitre 10 MEGA
Thursday, December 1, 2011
Build a timber deck
Build a timber deck


  • Timber piles 125 x 125 H5 treated Radiata
  • Concrete, Easicrete, or cement and builder's mix
  • Bearer: 100 x 100 H3.2 M/G No.1
  • Stringer: 150 x 50 H3.2 M/G No.1
  • Joists: 150 x 50 H3.2 M/G No.1 (@ 450mm centre to centre for 100 x 40 decking; @ 400mm centre to centre for 100 x 25 decking)
  • Decking: 100 x 40 or 100 x 25 Griptread
  • Nails: Galvanised 100mm and "U" shaped nails.
  • Galvanised strap
  • Nails: Flathead 30mm
  • Bolts: M12 diameter galvanised or stainless steel


  • Hammer
  • Sledge Hammer
  • Stringline
  • Spirit level/stringline spirit level
  • Tape measure, square and pencil
  • Spade
  • Chisel
  • Circular saw or handsaw
  • Electric drill and drill bits
  • Adjustable wrench

A deck is a rewarding extension to any home. If you are a competent handy person with basic carpentry skills, a few tools, patience and enthusiasm, you can achieve a very satisfying result building your own deck. Here is a step by step guide on how to build a timber deck.

The example deck is 3.6 metres wide by 3.6 metres long and 0.75 metres high above the ground. It is attached to the existing house along one side.

Your deck may differ from this because it may be larger or higher off the ground. Although the construction technique is similar, consideration needs to be given to bracing and handrails in such cases.

Tips to Get Started

•Prepare a sketch plan outline of your deck with dimensions, indicating boundaries and existing site features.

•The design should complement the house, it needs to be functional and have aesthetic appeal. Preferably locate the deck on the warm, sunny side of the house or facing the view.

•Decks should be clear of any sub soil drains and services (eg. electricity, gas, water or sewer lines.)

•Decks should have safety features such as hand rails (required for decks that are 1m or more above ground), non-slip surfaces and adequate bracing.

•Check ground conditions and contour.

•Approach the local authority or council to ascertain whether Resource and/or Building Consent is required before construction starts.

•Check for any possible infringements near boundaries. For example, decks less than 1m above ground and 10m square may not need to go through consent procedures.

•Determine the deck's size and shape to accommodate people and furniture. For instance, a deck that is 1.8m wide is the absolute minimum width to accommodate a standard table and four chairs.

•Always remember to measure twice and cut once.

Important Bracing Requirements for Decks:
Any deck that projects more than 2 metres from a building requires bracing. New Zealand Standard 3604 (1999) sets out the requirements, while geographical location also has an impact on the requirements for bracing. If the deck you are planning projects more than 2 metres from the building then it is recommended that additional expert advice be sought from your Local Authority or an appropriately qualified technical expert.

Illustration 1 - Deck Profile Set Out

Step 1: Setting Out the Deck

Select a datum point - generally the existing floor level. Set the finished deck level below this datum point. (To prevent rain entry.) In some situations, the New Zealand Building Code requires a step down to an open, framed permeable deck. (Your local Authority or Council will be able to advise you.)

Determine a working height to set the profile boards. In this How to Guide, the deck profile boards are set at the top of the bearers and ledger (see Illustration 1 above).

Identify the length of the deck along the wall of the house. From position A, string a level line through to position B (see Illustration 1)

At points A and B, drive a nail or cup hook. From each point (A and B), run a string line at right angles. The string line should be the length of the deck plus 600mm (working clearance) for profile locations.

Erect profile boards at the determined height.

Set string lines for correct level and deck size (see Illustration 1).

Check everything is square by using the 3, 4, 5 triangle method and equal length diagonals (see Illustration 2). Do not damage string lines and check positions are consistently correct and taut.

Illustration 2 - Square Check and 3, 4, 5 Triangle Rule

Mark postitions on existing house wall of solid framing for ledger bolt locations. Set ledger wall plate the length of A to B. Cut packers and shape to fit weatherboard or cladding angle if necessary (see Illustration 3). Lay bituminous damp proof coarse behind ledger packers. Fix ledger on packers to solid framing with 2 x M12 bolts at a maximum spacing of 1.2m centre to centre (see Illustration 3).

Illustration 3 - Fitting Packers

The New Zealand Building Code requires a minimum separation of 12mm between the wall cladding and a timber slat deck so that water will not become trapped. This separation can be provided by 12mm x 150mm long H3.2 packers at bolt fixings. Alternatively the junction between the decking and the stringer can be protected by the installation of a weatherproof flashing.

Step 2: Spacing Pile Foundations

Run a string line between pegs or from profiles at the desired depth, width and length of deck. See Illustration 7.

Locate corner piles and set out pile positions along string line and mark on the ground (see Illustration 1).

Dig holes with post hole borer or spade to a depth of 450mm (see Illustration 4).

Clean out holes of any loose material.

Place piles in holes on a concrete pad 100mm thick. Check vertical with spirit level and face alignment to within 1mm of string line (see Illustration 4).

Note: Constantly check alignment is square.

Tack temporary braces to pile and ground pegs for final position (see Illustration 4.)

Fill holes with concrete, take care to ensure the post is vertical. The concrete may be bagged, pre-mised, dry concrete or a 6:1 ratio of builders mix and cement, mixed with water to a stiff mix.

Compact the concrete into the hole around piles with a stick to remove air pockets. Leave the concrete to set around piles for at least 24 hours.

Illustration 4.

Illustration 5.

Illustration 6.

Step 3: Positioning of Bearers

The two methods shown in this brochure for fixing bearers to piles are:

1 - The 100 x 100 H3.2 treated Radiata bearers are to be checked onto the top of the piles and drilled for a M12 diameter galvanised or stainless steel bolt.

2 - The 100 x 100 H3.2 Radiata bearer on top of the shaped head pile are to be connected to pile with 2 galvanised "U" shaped nails each side. These may be substituted for a galvanised strap and 30mm flathead nails (see Illustration 5 and 6).

Illustration 7 - Deck Foundation Piles

Step 4: Fix Decking Joists

Joists used in this brochure's example are 150 x 50 Radiata H3.2 spaced 450mm apart, centre to centre. Cut joists to length and square. Leave a gap where they meet the house to allow for moisture to drain away. Skew nail bottom of joist to bearers on each side (see Illustration 3).

Step 5: Lay Decking

When laying decking boards, start from the furthest outer edge of the deck and work inwards.

Create a 15mm setback from board edge to fascia plate. Check spacing as you go to ensure boards are square and running true to line. (Tip: Curved boards may be straightened using a suitable pry bar.)

Butt boards hard up to each other to allow for shrinkage.

The last board against the house may have to be scribed to fit and reduced in width.



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