Polycarbonate roofing sheets are the standard choice for pergolas, lean-to roofs, side entrances, carports and greenhouse glazing across Ireland — combining high light transmission with far greater impact resistance than glass. But "polycarbonate roofing sheet" isn't one product: the right thickness, wall structure and colour depend entirely on what you're covering, how far apart your rafters are, and how much insulation you need. This guide breaks down the full specification range so you can choose with confidence before you order.

What Are Multiwall Polycarbonate Roofing Sheets?

This guide covers multiwall polycarbonate — the sheet type built for roofing. If you're looking for flat, solid polycarbonate for glazing, signage or protective screens instead, see our full solid polycarbonate sheets range.

Multiwall polycarbonate sheets are built from two or more flat layers of polycarbonate joined by internal ribs, creating a series of air channels running the length of the sheet. Those air channels are what give multiwall its main advantage over solid polycarbonate for roofing: built-in insulation, at a lower weight and cost per square metre. Solid polycarbonate still has its place on a roof — typically small skylight inserts or areas needing maximum optical clarity — but for the roof itself, multiwall is the standard specification.

We stock multiwall polycarbonate in four thicknesses: 6mm, 10mm, 16mm and 25mm. There's no 4mm or 8mm option in our range — each of the four stocked thicknesses is engineered with a different internal wall structure (twinwall, triplewall, or multi-wall) to match its intended span and insulation performance.

Thickness Guide: 6mm, 10mm, 16mm & 25mm

The single most important spec when ordering a polycarbonate roof is maximum rafter spacing — how far apart your supporting bars can be before the sheet needs additional support. Get this wrong and the roof will sag or flex between fixings.

Not sure how many sheets you need for your dimensions? Use our roof calculator to get an instant material list and quote for pergola, lean-to and apex configurations.

Light Transmission & Colour Options

Colour isn't just about looks — it directly controls how much light and heat comes through the roof. Clear lets the most light through; bronze cuts the most glare and solar gain.

Clear suits greenhouses and anywhere maximum daylight matters. Opal diffuses light evenly and hides roof debris and condensation better — a popular middle ground for pergolas and patios. Bronze is best where glare and overheating are the bigger concern, such as south-facing lean-to roofs.

Strength & Impact Resistance

Thermal Performance & U-Values

The air channels inside multiwall sheets act as insulation, and thicker sheets with more internal walls trap more air — giving a lower (better) U-value.

The lower the U-value, the better the insulation. If your roof covers a space you'll use year-round — a garden room or an area near the house you want to keep warmer — stepping up from 10mm to 16mm makes a noticeable difference to heat retention.

Fire Rating & Service Temperature

Which Thickness for Which Roof?

Once you've settled on a thickness, our step-by-step multiwall polycarbonate installation guide walks through fitting glazing bars, sealing edges and preventing condensation. If you're planning a pergola specifically, our polycarbonate pergola roof guide covers lean-to, freestanding and apex designs in more detail. You'll also need to know how to cut sheets to size — see our cutting guide.

Accessories You'll Need

A polycarbonate roof needs more than just sheets — the accessories are what keep it weathertight and looking neat long-term:

Frequently Asked Questions