Decking Tips From the Experts

September 12, 2014
Decking Tips From the Experts

A few months ago we featured a two-part story from our friends at Timber Merchants Association (TMA) regarding selecting the right timber floor for your needs, Choosing Timber Flooring: Part 1 of 2 as well as Choosing Timber Flooring: Part 2 of 2.

Their advice was so spot-on, and we couldn’t believe the level of enquiries we received over the phone from people wanting to hear more!

So – TMA is back!

This time, TMA have looked into that favourite spring topic – decking.

We hope you find this every bit as informative and thanks again to TMA for their invaluable advice and expertise.

Which timbers are available for decks?

Merbau, Jarrah, Spotted Gum, Cypress Pine, Treated Pine, Yellow Stringybark and Blackbutt.

These would be the most common species on the market.

Any others?

Alternative products such as Modwood (wood fibre/plastic composite), Enspire laminated bamboo decking, Lunarwood thermally treated European softwood, and Accoya specially treated European softwood would also be appropriate.

What are the advantages or disadvantages of each type of timber, and how do they vary in cost?

Treated Pine is a softwood and is used more often because it is at the lower end of the cost range; it is preservative treated against fungus growth and termite attack.

Cypress Pine is not that commonly used as a decking timber in Victoria, it doesn’t need to be treated and is naturally resistant to fungus growth and termite attack.

It is mostly used for fence pickets and posts for fences, pergolas etc.

Merbau, Spotted Gum, Blackbutt and Yellow Stringybark are durable hardwood species.

Merbau is imported from Malaysia and the others are Australian grown eucalypt hardwoods.

Generally speaking, Treated Pine and Cypress Pine can be slightly cheaper than the Australian hardwoods.

What criteria should one have for choosing timber for decking?

  1. The first consideration is usually ‘what colour is the client looking for?’

Treated Pine and Cypress are light coloured timbers, Merbau is dark red, Spotted Gum varies from cream to brown to red colourings, Blackbutt and Yellowstringybark are paler coloured hardwoods.

  1. Softwood or hardwood?

Softwoods such as Treated Pine mark easily and may not stand up to heavy foot traffic areas, so the better choice is a hardwood species.

  1. How long the timber will last is another crucial consideration.

Treated pine timber is sold with an expected service life of 25 years and the Class 1 and 2 durable hardwoods should have a service life of 30 year.

However, the eventual service life depends on the level of ongoing maintenance.

For example the type of coating used (water based or oil based), whether a recoating program according to the manufacturer’s guidelines on the can has been followed and the appropriate fixings have been used (normally hot dipped galvanised nails/screws or stainless steel fixings for coastal areas).

  1. What age of timber to go for?

This is not such an important item, assuming that the timber merchant has kept their timber decking stock stored in a suitably protected area, otherwise unrestrained timber decking will warp and twist if allowed to get wet/stored out in the open in the yard, etc.

However, always insist on the timber being as straight as possible, don’t try and use bowed or twisted pieces.

  1. What kind of timber Hazard Grade to look for?

Treated pine is the only hazard treated decking timber on the market and is normally treated to Hazard Level H3 for above ground use.

Treatment is not required for Cypress Pine, Merbau and the other hardwood species timber.

Should one only use timber graded from H3 to H6, as this will be more durable and have a longer lifespan?

If Treated Pine timber is used for in-ground decking stumps, it is normally sold as treated to Hazard Level H5.

This is because water drainage underneath most decks can be inefficient and this level of treatment is recommended and an in-ground service life of up to 70 years may be expected.

Treated Pine timber used for bearers and joists will be preservative treated to H3 hazard level as standard for above ground use and has a normal service life of 25 years.

What Council permits are needed?

Under the Victorian Building Regulations-2006, the following conditions apply:

  1. If the deck is free standing and no more than 10 square metres in area, and no higher above natural ground than 800mm (0.8m), a building permit is not required.

  2. If the deck is free standing and more than 10 square metres in area, irrespective of height above ground, then a building permit would be required.

  3. If the deck is attached to the house and irrespective of the area size and height above natural ground level, a building permit would be required.

How to choose a decking builder?

Sometimes the timber merchant may provide one or two references to the builder/carpenter customers that you can approach for a quote, otherwise check the listings in the local newspaper classifieds and try two or three of these for a quote.

What questions should a decking tradie be asked?

Check out their specific experience, ask for references to previous clients/jobs that you might be able to call and possibly go and inspect the work that has been done, and reaction from the clients.

Are they a registered building practitioner and are they a member of a recognised industry organisation ie: HIA or MBA Vic?

Ask what timber finish they recommend, what timber species they have used in previous projects, what type of fixings they would use, do they comply with recommendations?

What is the alternative to solid timber decking known as composite fibre decking or CFT

There are several CFT (composite fibre technology ) products on the market that comprise a mixture of wood fibre in one form or another and either virgin or recycled plastic in the manufacture.

Some are made in Australia, others are imported from USA and Europe.

One of the more popular brands is Modwood and has apparently performed very well in service; in addition Modwood have recently introduced a bush fire rated decking called Flame Shield that is approved for use as exterior decking in areas designated as BAL-40 rating and requires virtually no maintenance.

Can decking be done as a DIY or is it better to engage a professional?

Generally, small area low level decks can be undertaken by a competent DIY handyman as there are several published guide manuals available showing how to construct a deck, what timber sizes should be used for stumps, bearers, joists, decking etc., fixing guidelines etc.

Structures more than, say, 10 square metres and over 800mm (0.8m) above ground should be constructed by a tradesperson with appropriate experience/reputation and especially where a building permit is required by regulation.

Also, a handrail is usually required for decks above 800mm (0.8m) height above ground.

Steps will be involved at some stage and when that occurs, a tradesman is generally more competent to construct these than the average DIY.

If a council permit is required, a qualified tradesman is mandatory to do the job.

Some industry practice recommendations:

  1. Ensure there is good sub-floor ventilation and proper water drainage is allowed for

  2. Gaps between decking boards should be at least 4.0mm for boards up to 90mm width and at least 6.0mm for decking boards up to 140mm width

  3. Before installing any decking, all the boards should be coated ON BOTH SIDES and cut/trimmed ends, using an oil based coating product (such as CUTEK CD50).

Then, after installation is completed, a second full coating should be applied.

This coating practice will help to stabilise the timber and suppress sap bleeding (such as occurs with Merbau).

  1. A waterproof membrane such as Malthoid strips should be installed over the top of the joists underneath the decking boards, because this is usually the point where the decking timber may rot over time because it never really dries out, in similar fashion to the post and rail joints in a standard timber paling fence.

  2. A decking screw or nail designed for the application (such as ‘Timberdeck’ nails) should be used, always hot dipped galvanised or stainless steel, if close to water either fresh or saltwater, stainless steel should ALWAYS be used.

  3. Use the correct length of fixing, whether nails or screws; if the joist timber is treated pine (the most used timber species) then the nail or screw used to fix the decking boards should be 65mm long for 19mm thick boards and 75mm long for 32mm boards and the size should be at least 10 gauge.

  4. Always predrill a pilot or countersink hole when using decking screws and always predrill when making a decking butt joint over a joist.

This will help to stop the boards splitting and cracking.

Following these straightforward guidelines will ensure a satisfactory result for the best service life from any decking project, whether constructed by a competent DIY or a tradesman.

What about decking around a swimming pool?

Decking areas around a swimming pool should be well maintained with annual coating restoration prior to each summer season, never exceed the recommended board spacing because all hardwoods will shrink a little over time and a gap could develop that a narrow heel will fall into therefore becomes dangerous.

How to maintain your decking to look good and last longer?

Use a good coating product (preferably oil based) according to the manufacturer’s instructions on the can, and apply at the intervals recommended.

Typical brands might be Haymes ‘Dexpress’, CUTEK CD50, Sikkens and Timbercoat.

If you use a clear coating product, be aware that the timber will eventually ‘weather’ to a silver grey colour, even if you apply another coat every year, as the UV inhibitors eventually lose their effectiveness.

The best way to preserve the natural colour of the timber (for example, the reddish colour of Merbau), is by using a pigmented coating that contains a colouring to match the original timber colour should be used ( all oil based coating manufacturers have these).

Timber Merchant Associations Members

The following businesses on RenoExchange are members of the TMA, and you can shop for their timber products by clicking on their logo:

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READ MORE: Choosing Timber Flooring: Part 1 of 2