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How to select decking timber

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Deck Adam_W.png


A deck can add a wonderful addition to your home for entertaining and relaxing outdoors. But before you strap on your tool belt, consider what type of decking boards to use for your project.


This guide helps you with selecting decking materials that best suit your home.


What conditions will the deck face?


Every deck is installed in different conditions, which can affect what boards to choose. Consider these elements:


  • Wear and tear. What will the level of foot traffic be like? Is the deck at your main entry, is it the primary entertaining area or will it be a way through to the pool or yard? Higher wear areas require durable decking, quality paint and sealant and more frequent maintenance.


  • Environmental. What sort of weather conditions will your deck be exposed to? Is it within the splash-zone of a pool? These sorts of conditions will impact on the useability, durability, lifespan and maintenance required.


  • Care and maintenance levels. How much time are you willing to spend maintaining your deck? Some boards can last a lifetime without being painted, sealed or oiled, while others need yearly treatment. Bear in mind that these maintenance levels aren’t purely down to the boards themselves. The environmental aspects and wear-and-tear come into this too.


  • The look. Do you have specific design needs for the colour and form of the decking material? Different timbers can be stained or oiled a range of colours, but this varies with the natural colour of the timber. Treated Pine, for example, can be stained to mimic almost any natural timber colour.


What size decking boards to choose?


Merbau deck built by Bunnings Workshop member MGusto.Merbau deck built by Bunnings Workshop member MGusto.

When you buy decking boards they are generally priced by the linear metre or as pre-cut lengths. When you are budgeting for your project, you’ll find it easiest to convert any price to linear metre. For price-per-length boards just divide the price by the length. This allows you to compare costs more easily. Make sure you account for the width of the boards in your calculations.


A conventional board width is 90mm, with 140mm being an option with some materials. A 140mm board will have a higher per-linear-metre price, but you won’t need as many boards to complete your deck. For example, a 3m x 3m deck using 90mm boards laid with a 5mm gap between boards would need approximately 32 boards, giving you a total of 96 linear metres required (3000 ÷ 95 = 31.6 then 32 x 3 = 96). If using 140mm boards you would need 21 boards across giving you a total of 63 linear metres needed (3000 ÷ 145 = 20.7 then 21 x 3 = 63).


At first glance the wider boards may seem more expensive, but once you account for the lower overall linear metres, fewer boards mean that laying is at least 25 per cent faster and fewer screws are required.


To start creating the decking materials list for your project, check out this decking calculator.


What are the differences between materials?


You’ll find two main choices when selecting decking boards – timber or composite. Timber options include Treated Pine or hardwoods. Understanding more about these materials will help you to make the right choice for your needs.


Treated Pine


Treated Pine deck by Marty_McFly.Treated Pine deck by Marty_McFly.

Pine is a softwood so it has lower durability and resistance to wear-and-tear than hardwood. Treated Pine is resistant to attack from pests and decay, but it must be oiled or sealed to prevent discolouration and staining and to keep it looking clean and fresh. In a harsh environment (such as beside a pool in full sun) Pine will require resealing at least annually.


Of all the boards, Pine is the most economical option per linear metre and is available in various lengths. This makes it easier to purchase the right amount for your project and to keep wastage to a minimum.

As a softwood, it is much easier to work with than other options – it’s lighter and easier to handle, and it’s easier to cut, drill and nail or screw. Treated Pine joists can easily be nailed down without pre-drilling. For a neat finish, counter-sinking is recommended.

Quality treated Pine decking boards are not CCA (Copper chrome arsenic) treated, making them safer for your family and the environment. Treated Pine has low fire-resistance and should not be used in bushfire-prone areas. Pine is plantation grown so it is considered a renewable material and can be a sustainable option.


Hardwood timber


Spotted Gum deck shared by Workshop member Lappa.Spotted Gum deck shared by Workshop member Lappa.

You’ll find a range of different hardwoods available with varying colours and grain patterns. Hardwoods are denser, heavier and more durable than softwoods.

Hardwood is often chosen for its colour and grain pattern and is clear-oiled or sealed to allow the natural richness to show through. Many can be left unsealed to develop a natural patina with age that will vary with the timber species. If oiled or sealed, the deck will require a reapplication annually in higher traffic or more exposed spots.

Most hardwoods have a natural degree of resistance to insect attack or damage from decay. Talk with a timber specialist if this is an area of concern for you.

Price varies dramatically with each timber species from medium to high per linear metre. Standard sizes are 86 to 90mm wide with 140mm wide boards readily available. You’ll find that some hardwoods are available in a range of pre-cut lengths so it’s easier to buy to suit your needs and minimise wastage.

The hardwood most people will be familiar with is Merbau. This is an imported hardwood that is a dark mahogany colour when new. It is known to leech staining tannins the first few times it receives rain (even if sealed) so it is wise to not use it in areas where it could stain other nearby surfaces. You’ll also find a range of Australian native hardwoods available such as Spotted Gum.

As a dense material, hardwood is heavier to handle and is harder to cut, drill and screw than Pine. It is recommended that hardwood be pre-drilled before nailing down and pre-drilled and counter-sunk before screwing down.


Most hardwood is not treated with any chemical preservatives. Many of the hardwoods have a medium BAL (Bushfire Attack Level) rating and are suitable for more fire-prone areas. Seek specialist advice if a particular level of BAL compliance is needed for your project. Ensure that any hardwood you select has been sustainably certified through its growth and harvesting process. This should be marked on the timber or be readily available information.


Composite decking timber


Composite deck by ProjectPete.Composite deck by ProjectPete.

Composite decking boards are manufactured from a mix of materials such as recycled plastic and reclaimed timber materials. They are available in a range of natural-look colours. The colour is consistent throughout when using quality composite boards – it is not a surface coating or treatment. No painting, sealing or other treatments is required for the life of your deck. Composite boards are also resistant to insects, rot and decay.

When laying composite boards, most builders use a specialised concealed fixture system which makes the boards faster and easier to lay. This also gives a neat screw or nail-free appearance. Boards are most readily available as wide-format such as 137mm. When converted to price per-linear-metre they fall into the medium-to-high range. They are generally only available as full-length boards which can make it difficult to manage wastage and cost.

Composite boards can be sawed and drilled with regular tools, but can be challenging to handle. Each board weighs approximately 22kg and they are extremely flexible. When sawing, it is wise to use three or four saw horses, especially in warmer weather. The material is hard and can be brittle. Care needs to be taken to avoid heavy knocks of ends and edges or chipping may result.

Instead of sawdust, the waste material is primarily a plastic product which must be carefully disposed of to avoid it entering the environment as microplastic waste. It’s recommended that you saw over concrete or a similar hard surface (not the lawn) so this waste can be more easily collected. Use a broom rather than a blower to tidy-up. It is also not yet known if offcuts or boards at end-of-life are reclaimable or biodegradable. More positively for the environment, some composite boards score a big sustainable tick for their use of reclaimed and recycled materials.


In full-sun situations composite boards become very hot (too hot for bare feet). Composite boards expand along their length (not width like timber) so they require expansion gaps at board ends.

Regular composite boards have low fire-resistance, but there are types that have BAL resistance comparable to that of hardwoods. Seek these out if needed for your area.


Need more assistance with choosing the right materials for your project? Please don’t hesitate to ask the ever-helpful Bunnings Workshop community. We’re here to help.


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