Timber Decking Fundamentals

Decking Installation Guidelines & Maintenance

Over recent times we have come to recognise products that have a history of post-installation problems and decking certainly falls into that category.

However, rather than just state the guidelines we thought we would explain what we believe are the timber decking fundamentals and why they are so important to achieve a sound, problem-free deck.

Wood is Hygroscopic:

It will absorb/ lose moisture depending on the climatic or environmental effect the deck is exposed to. Obviously, this will vary on the time of year; it will likely absorb moisture in winter and lose it in summer.

Decking Board Gaps:

Appreciating natural timber movement, we recommend gap spacing between boards so they will not come together in winter. Allow about 4 millimeters for boards up to 90mm and about 6 millimeters for boards about 140mm. Leaving wider spacings could result in a gap, too big in summer, however, a good suggestion if the decking is low to the ground.

Ventilation:

Ventilation is often one of the most misunderstood fundamentals. The main goal is to create an environment where the underside of the decking boards experiences similar conditions to the top, ensuring board stability. To achieve this, there needs to be sub-deck air entry points and corresponding air exit points on the opposite side.

If this is not possible, particularly around swimming pools, or decks less than 400 millimeters from ground level, other consideration should be taken into account. These can include increasing the decking spacings, ensuring good drainage to avoid pooling of moisture or a plastic membrane over the sub-deck area to prevent wet soil. Use durable and stable decking species in a narrow width such as Merbau. In addition, a possible suggestion could be mechanical ventilation.

Drainage:

Another timber decking fundamental that is often overlooked for a deck to perform as envisaged is drainage. If moisture is allowed to remain in the sub-deck area, the decking boards are likely, perhaps even with reasonable ventilation, to pick up moisture resulting in unwanted board movement such as expansion and cupping.

Exceptional Climatic Conditions:

Whether it is rainfall or heat, we would recommend a reduced board width, or a timber modified product where board movement is greatly reduced.

Decking Board Width & Thickness:

This decision should not only be solely based on a desired wish of a client or homeowner, it should be suitable for the site conditions of the job. Keep in mind the wider a decking board is, the more it will move, particularly if conditions like ventilation are not ideal.

Timber Decking Coatings:

We recommend a preparatory oil-based coating be applied in the factory prior to installation and another topcoat manually applied after installation. This will penetrate the wood and keep any possible expansion/ shrinkage to more stable levels. Ongoing seasonal re-coating will provide extended protection.

End Coatings:

Board deterioration is most likely to occur on the board ends. This is because wood fibers are like a series of straws that are either sucking in moisture in winter or losing moisture in summer. The swabbing of board ends is to protect these straw ends and in doing so reduce the board’s unwanted movement. This is a manual application during the installation operation, whereby the installer thoroughly swabs the trimmed ends. This can also help minimise tannin bleed in species like Merbau and Blackbutt.

Sub-Deck Protection:

For treated pine joists, we recommend using a proprietary joist protector between the joist and the decking boards. This helps maintain a relatively consistent moisture content in the joists. Without a joist protector, the moisture content in the treated pine joists can become too high, causing the decking fixings to loosen easily.

Fixings:

All fixings should have an appropriate coating such as hot dipped galvanised, Chemshield or stainless steel. However, if close to a swimming pool or the ocean, stainless steel is recommended. We don’t recommend electroplated fixings because the coating can break down.

Note: The minimum length for a screw/ nail, should be 65mm if fixing into treated pine and 50mm if fixing into a durable hardwood. Dense durable hardwoods may have to be pre-drilled.

Joists should be at centres no further than 450mm for 19mm hardwood decking or 22mm thick treated pine decking.  Obviously thicker hardwoods can facilitate a wider joist span.

Iron Staining:

The cutting and grinding of metal products should be avoided around the deck. It can cause black staining that may not show up until the deck is finished and the homeowners have moved in.

Suggested guidelines are available with every decking purchase with Bowens. For more information, contact Jeff Harvey on 0412550740.