Polycarbonate or Colorbond Roof for a Steel Pergola?

Pick Colorbond steel if you want real shade and a cooler space underneath, and polycarbonate if you want daylight to reach the house. In bushfire prone parts of the Hills and the Barossa, steel is the safer sheet. Plenty of people use both: steel sheets for most of the roof, with a few polycarbonate sheets where the light matters. Either way, the steel frame underneath decides how long the pergola lasts.

We build custom steel pergolas, attached or freestanding. One of ours, in Tanunda, has steel posts and beams with purlins and cross-bracing under a corrugated roof. Here is how the two roof sheets compare.

Side by side

Light and heat

This is the real decision. A pergola off a living area that faces north or west can make the room behind it dark if it is roofed in steel. Polycarbonate fixes that. Manufacturers make it in clear, opal (frosted) and tinted versions; Palram, for example, says its Suntuf sheets offer up to 90% light transmission and long-term weather and UV resistance.

The trade-off is heat. Light coming through brings some warmth with it. Colorbond steel blocks it, and BlueScope says its Thermatech solar reflectance technology is designed to reflect more of the sun's heat on hot days. Lighter colours stay cooler. For an outdoor area used in an Adelaide summer, that matters.

Hail, rain and upkeep

Both sheets handle normal weather. Check what the polycarbonate product is warranted against: Palram, for one, warrants Suntuf against yellowing, loss of light transmission and hail damage. Clear sheets show every leaf and dust layer from below, so plan on cleaning them, especially under gum trees. Rain is audible on either. Steel needs little more than a hose down.

Bushfire prone areas

Much of the Adelaide Hills and parts of the Barossa and Murraylands are bushfire prone. Polycarbonate is a plastic. The CFS advice on preparing your home notes that metal roofing offers more protection, provided it is firmly secured and sealed, and that plastic fittings melt. A pergola attached to the house is part of what embers and radiant heat reach first, so in those areas we would steer you to steel, with any polycarbonate kept to a few sheets away from the house wall.

How the frame changes

The steel frame is designed around the roof sheet you pick. Each product has its own maximum purlin spacing and minimum roof pitch in the manufacturer's span tables, so purlins are laid out to suit the sheet, not the other way round. Polycarbonate moves more with temperature than steel, so manufacturers specify their own fixings and pre-drilled holes. Steel sheeting goes on with standard roofing screws. Tell us which sheet you want at quote stage, so the frame is right from the start.

Approval

A pergola with no solid roof can be exempt from approval in SA. Once it has roof sheeting, steel or polycarbonate, plan on needing development approval. Our guide to council approval for carports, verandahs and pergolas explains the rules and what to lodge.

A common job: the long, narrow pergola

One recent enquiry was for a freestanding 7 x 2 m pergola at the back of a unit, with a polycarbonate roof. Long and narrow is a good shape for a courtyard. Freestanding means it stands on its own posts with its own bracing rather than leaning on the house. Behind a unit, check with the strata or community corporation before you lodge, because the ground may be common property.