Project Spotlight: Merbau Pool Deck with Extreme Joist Frame — Killarney Heights

Location: Killarney Heights, 2087 NSW
Year: 2025
Materials: Merbau decking boards, extreme joist subframe

Why This Deck Needed Replacing

The owners of this Killarney Heights property had a pool deck that was only 8 years old — but already failing. The old deck had been built with a standard treated pine subframe sitting very close to ground level. That combination is a recipe for premature failure.

Pine joists at ground level in a pool environment trap moisture. With constant evaporation from the pool, splash water, and minimal airflow beneath the deck, the pine frames had rotted from the underside — invisible until the deck started feeling soft underfoot.

When we lifted the old boards, the frame was almost entirely compromised. This was a full replacement, not a repair.

Specifying Extreme Joist

The challenge with this site is that the pool area is quite flat and low, leaving minimal clearance between the frame and the ground. Standard timber joists at this height will rot again within 5–10 years regardless of species, because airflow can't do its job.

Our solution was Extreme Joist — a composite structural member that:

• Is impervious to moisture — won't rot, warp, or swell
• Is termite proof — no food source for insects
• Maintains structural integrity in perpetual ground-level conditions
• Is certified for use as a joist in structural deck applications under Australian Standards

It costs more than pine or even hardwood. But for this application — low clearance, pool environment, high moisture — it's the only specification that makes long-term sense.

Merbau Decking

For the deck boards, we specified Merbau — a popular hardwood for pool surrounds because:

• It's naturally oily, which makes it resistant to moisture absorption
• It doesn't splinter easily, important around bare feet at a pool
• It's Durability Class 1 for in-ground contact
• The rich red-brown tones look beautiful against pool coping and landscaping

We laid 90mm Merbau boards with a small gap to allow drainage and airflow through to the subframe.

A Long-Term Investment

The owners asked a fair question: why spend more on the subframe when you can't see it?

Our answer: because the subframe is the whole deck. The boards on top last as long as the structure underneath. Invest in the frame, and the whole deck lasts 20 years. Skimp on it, and you're back in 8 years — same problem, same cost.

This is the approach we take on every build. What's hidden matters as much as what's visible.

Killarney Heights & North Shore

Killarney Heights sits on Sydney's North Shore, surrounded by bushland and near the Lane Cove National Park. We work extensively throughout this area and understand the specific conditions — high humidity, variable soil, and proximity to heavy tree cover that keeps areas damp.

If you're in Killarney Heights, Forestville, Frenchs Forest, Davidson, or surrounding areas, we'd love to help with your project.

Call us on 0468 093 569 or get a free quote.

MJ Leckie Carpentry — Licensed Carpenters, Lic 353438C