Whether you’re looking at creating a timber deck in your backyard or you already have a deck that has seen better days, the process of planning and buying timber for decking requires technical knowledge of materials to make the most of your options.
If your decking has aged significantly, it’s important to ensure that your decking is safe. Before you jump to buying new timber to replace your decking, conduct the following safety checks;
- Check that areas aren’t weakening under your feet
- Check for splinters or rusted nails
- Make sure railings and bannisters are all secure
- Check steps and stairs for movement
- Ensure the decking doesn’t sag, bounce or flex more than it should
Timber decking design considerations
If it’s time to buy some new timber decking, it’s worth considering these points when planning your project to design the right deck for your home:
- Designs that incorporate multi-level layouts, custom designs and unusual shapes will be more expensive than simple designs which are more attractive and less costly to build.
- The best-looking decks utilise materials that complement the house and garden.
- Regardless of the design and materials be sure you know the locations of any underground utilities.
Timber varieties for Australia
There are many varieties available, and each timber type has advantages and disadvantages. Pressure treated is common and originates from pine trees; other popular types are Merbau, Spotted Gum, Jarrah, Blackbutt and Batu Timber.
These timbers are hardwearing, weather-resistant, and are the best choice of timber for outdoor bush areas and with barbeques.
Merbau grows in Southeast Asia, Papau New Guinea, the pacific islands, and Australia in Far North Queensland and is a tropical hardwood with a high oil and tannin content. Merbau is a versatile hardwood used in many products ranging from a pale to dark reddish-brown colour.
Jarrah is renowned for being a hardwood that is tough wearing, beautiful, and versatile in nature. Hardwood timber does bleed; Jarrah has a deep red colouring which has the potential to stain surrounding paving and fixtures.
Grown in the Eastern States of Australia, Blackbutt is one of the most common species of timber commercially available in Australia. Blackbutt has an even colour, grain, and texture, ranging from a golden yellow to pale brown colour.
Spotted Gum is Australia’s most harvested native hardwood, making it widely available. Spotted Gum is classed as a dense ground-contact hardwood that will stand up to the elements. It has natural oils and a lower tannin content, so it accepts oil and stain well and doesn’t experience bleed-through.
Hardwood has a relatively higher price and can be divisive as it often can’t be guaranteed to be from an environmentally sustainable source.
Pressure-treated timber is rated according to the protection against fungi and insect attack.
Treated timbers are rated based on level of hazard and are as follows:
| Hazard Level | Exposure | Specific Service Conditions | Biological Hazard | Typical Uses |
| H1 | Inside, above ground | Completely protected from the weather and well ventilated and protected from termites | Lyctid Borer | Framing, flooring, furniture, interior joinery |
| H2 | Inside, above ground | Protected from wetting, Nil leaching | Borers and termites | Framing, flooring, etc., used in dry situations |
| H2F | Inside, above ground | Protected from wetting, Nil leaching | Borers and termites | Framing (envelope treatment) used in dry situations south of the Tropic of Capricorn only |
| H2S | Inside, above ground | Protected from wetting, Nil leaching | Borers and termites | LVL/Plywood (glue-line treatment) used in dry situations south of the Tropic of Capricorn only |
| H3 | Outside, above ground |
Subject to periodic moderate wetting and leaching | Moderate decay, borers and termites | Weatherboard, fascia, pergola posts (above ground), window joinery, framing and decking |
| H3A | Outside, above ground |
Products predominantly in vertical exposed situations and intended to have the supplementary paint coat system that is regularly maintained | Moderate decay, borers and termites | Fascia, bargeboards, exterior cladding, window joinery, door joinery and non-laminated verandah posts |
| H4 | Outside, in-ground contact | Subject to severe wetting and leaching | Severe decay, borers and termites | Fence posts, greenhouses, pergola posts (in-ground) and landscaping timbers |
| H5 | Outside, in-ground contact, contact with or in fresh water | Subject to extreme wetting and leaching and/or where the critical use requires a higher degree of protection | Very severe decay, borers and termites | Retaining walls, piling, house stumps, building poles, cooling tower fill |
| H6 | Marine waters | Subject to prolonged immersion in sea water | Marine wood borers and decay | Boat hulls, marine piles, jetty cross bracing |
When buying treated wood, buy boards that have had time to dry after they’ve been processed. If they are damp, the decking boards are harder to work with and they shrink when they dry, creating gaps between boards and making them bouncier and less well supported.
Aesthetic grading is used for timbers to determine the quality of a surface’s appearance. There are three cosmetic grades:
- Select – has the minimum number of knots, straight grained and uniform in appearance.
- Standard – has a different appearance from piece to piece that gives a distinctive appearance.
- Character – is characterised by knots and sap streaks. Typically used in furniture such as table slab where a natural rustic look is desired.
Deck Maintenance
Timber decking can last many years, but it must be looked after with maintenance considering how it reacts to the weather changes. Maintenance is required for both structural and aesthetic reasons.
Timber decking is an investment, and it is up to the owner to decide how well they look after that investment. Regardless of your choice of decking material, you should always:
- Sweep dry debris off the surface
- Keep debris out of the gaps so that water can escape
- Prevent staining by moving items that are on the decking such as furniture
Timber decking requires oiling or staining to ensure that the wood does not absorb excess moisture when it rains.
Finishing your deck
The finishing is vital to the life of the timber and decking. Finishes generally come in two types such as reactive and coalescing. Your choice will determine the maintenance needed and the final appearance.
Reactive finishes use oils as a base; these products penetrate the timber to achieve the desired coloured or sealed effect. These include oils, oil-based varnishes, oil-based polyurethanes, and oil-based stainers.
Coalescing uses water as a base requiring only one or two coats to penetrate the timber to achieve the desired effect. These products include water-based varnish, enamels, water-based strainers, water-based oils, and water-based polyurethanes.
Water–based finishes have fast drying times and clean-up, while oil-based finishes create a more traditional look with greater durability.
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