The Best Decking Timber for Coastal Newcastle and Lake Macquarie

Salt air, relentless UV and humidity make our coastline hard on timber. Species selection matters far more here than it does an hour inland.

Durability classes

Australian timbers are rated 1 to 4 for natural durability above ground:

• Class 1: more than 40 years. Ironbark, grey gum, tallowwood.
• Class 2: 15 to 40 years. Spotted gum, blackbutt, jarrah, merbau.
• Class 3: 7 to 15 years. Some eucalypts, western red cedar.
• Class 4: less than 7 years. Not suitable for decking.

For coastal exposure, stay in class 1 or 2. Class 3 will not give you the life you are paying for.

The species worth considering

Spotted gum. Our most common recommendation. Class 2, hard-wearing, excellent colour variation, widely available and reasonably priced. Handles UV well.

Blackbutt. Class 2, paler and more uniform than spotted gum. Slightly less hard but very stable and takes oil beautifully. Also has good bushfire performance, which matters on some blocks.

Ironbark. Class 1, extremely hard and dense, and it will outlast everything else. Heavy to work with, harder to fix and dearer. If you want maximum life, this is it.

Merbau. Class 2, imported, stable and consistent. The drawback is significant tannin leaching for the first six to twelve months, which will stain paving, render and anything below. Also worth checking sourcing credentials.

Treated pine. Not naturally durable but chemically treated. H3 minimum for above ground decking. Fine when painted and maintained, and it is the budget option.

What kills coastal decks

Fixings, more often than timber. Galvanised screws within a few hundred metres of surf will corrode. The corrosion then attacks the surrounding timber and the board fails around a sound fastener.

Use grade 316 stainless steel near the ocean. Grade 304 is acceptable further back. Hot dip galvanised is adequate well inland only.

This is not an area to save $200.

Trapped moisture. Poor ventilation underneath, boards butted too tight, or debris packed in the gaps. Timber that cannot dry does not last.

Ground contact. Any structural timber near or in soil needs H4 or H5 treatment, or a class 1 durability species, or preferably a galvanised post shoe keeping it off the ground entirely.

Detailing that extends life

• Gap boards 3 to 5mm so water and debris fall through
• Ventilate the subfloor space, do not enclose it solidly
• Keep the frame at least 150mm above ground
• Seal cut ends, which are where moisture enters most readily
• Use post stirrups rather than setting posts in concrete
• Flash the ledger connection to the house properly

Oiling near the coast

Expect to oil every 12 months rather than 24. UV and salt strip coatings faster. Use a decking oil with UV inhibitors and reapply before the timber goes grey rather than after.

When to just use composite

If the deck is exposed, north or west facing, within sight of the water, and you do not want to be oiling it every spring, composite is the sensible answer. It is not cheating.

We build in all of these across Newcastle, Lake Macquarie, Belmont, Nelson Bay and the coastal villages, and we will specify fixings appropriate to how close you are to the water.