Composite decking in Victoria and the winter problem

The first generation of composite decks sold in Victoria were a dare. Mix plastic and wood flour, extrude a board that looks like timber from three metres, and tell people they will never oil again. Plenty of those decks are still here. Plenty of them are also chalky, faded, and furred with mould along the grooves because Melbourne winter is not a marketing climate.

Newer capped composites are better. The outer shell resists stains. The colours are less cartoonish. The question for a Melbourne house is no longer “does composite exist?” It is whether the board, the substructure and the way the deck is used can get through July without becoming a skating rink.

What “composite” means on an invoice

The word covers several products. Wood–plastic composite (WPC) is the common one: a core of recycled plastic and timber fibre, sometimes capped with a harder polymer skin. There are also PVC boards with almost no wood in them, and bamboo–plastic mixes that behave like WPC until they do not. Ask for the core, the cap, the warranty in Australia, and whether the warranty still applies if the installer used a different brand of joist or clip.

Capped boards are the ones worth specifying in Victoria. Uncapped WPC drinks tannin, sunscreen and barbecue fat. A cap is not magic — deep scratches still show the core — but it is the difference between a deck you can wash and a deck that permanently records every red-wine night.

Hollow versus solid is the other fork. Hollow boards are lighter and can be kinder on a balcony with a weight limit; they also collect water if the ends are not capped and if the fall is a rumour. Solid boards cost more, span a little better, and forgive a slightly uneven joist. On a ground-level deck in a damp backyard in Preston, solid or a well-drained hollow with sealed ends is the adult choice.

Winter, mould and the gap that does the work

Melbourne’s winter problem is not that composite “rots” like pine. The polymer does not feed fungi the way untreated timber does. The problem is biofilm. Leaves sit in the grooves. The south side never dries. A black film grows on the board and in the gap, and after a July rain the surface has the friction of wet plastic. That is how people fall.

You cannot oil your way out of this. You design out of it. Leave the manufacturer’s gap — usually more than people think, because composite expands along its length in heat. Keep the substructure open. Do not box the deck in with a rendered kickboard that traps still air. Specify a fall, even on composite; water that sheets off dries faster than water that ponds in a hollow.

Cleaning is a hose, a soft broom, and a composite-safe cleaner in spring. High-pressure washers at close range will scar a cap and drive water into end grain of any timber joists below. If the deck sits under deciduous trees, budget for gutter-like discipline: scoop the gaps before the leaves become compost. Our mould-after-winter guide is written for timber but the hygiene is the same.

Heat, fade and the western courtyard

January is the other half of the Victorian complaint. Dark charcoal composite in a west-facing courtyard can be too hot for bare feet. Some brands now publish surface-temperature figures; treat them as comparative, not as a promise, because a brick wall in Yarraville will reflect heat the lab did not model.

Lighter greys and browns run cooler. A covered deck or pergola runs cooler still. If the brief is “no oil, no splinters, kids, western sun”, composite plus shade is a system. Composite alone is a frying pan with a warranty.

Fade has improved. Early boards went a tired khaki. Capped products hold colour longer, especially if you avoid the bargain bin that has sat in a Sunshine wholesale yard through two summers before you bought it. Ask when the batch was extruded. UV starts in the warehouse.

Structure underneath is still timber logic

Composite is a wearing surface. It is not a joist. Most systems want closer joist centres than hardwood — 400 mm or 450 mm is common, sometimes 300 mm for diagonal laying. If you are recovering an old pine frame, measure before you fall in love with a colour. Underspaced joists make a composite deck feel bouncy and then crack at the clips.

Use the brand’s clip. Mixed clip systems are how warranties die. Stainless or the specified coated screw into the joist still matters; a composite board will outlast a dying bugle screw and then rattle. On ground-level frames, keep the same discipline you would for timber: ant caps, clearance to soil, and no garden bed piled against the bearer. Substructure is not optional because the walking surface is plastic.

Balconies add weight and drainage. Some composites are sold as “waterproof” because the board itself does not rot. That is not a waterproofing system. If there is a room below, you still need a membrane, falls and an outlet. See waterproofing over a living space.

Cost against hardwood, and when composite is the right call

A mid-range capped composite deck in Melbourne, supply and install, often lands in the same band as a straightforward spotted-gum deck once you count oiling over ten years. Composite wins if the owners travel, if the house is a holiday place on the Peninsula, or if splinters are a hard no — schools, rentals, older knees.

Composite loses if you want the smell and give of timber, if the site is a furnace without shade, or if the installer has never read the span tables. It also loses when people treat it as invincible and never wash it. Nothing outdoor in Melbourne is invincible.

If you are choosing between species rather than polymers, start with merbau versus spotted gum. If you are choosing composite, choose a capped board with an Australian warranty, a joist plan that matches the board, a fall, and a winter cleaning habit. That is the whole secret. The rest is colour swatches.