Corrugated roofing is characterized by its repeating pattern of parallel ridges and grooves, which provides structural rigidity and facilitates water runoff. This profile is commonly found in materials like galvanized steel, aluminum, and translucent polycarbonate. The material’s inherent strength-to-weight ratio and relatively low cost make it a popular option for utility buildings, carports, sheds, and patio covers. Its durability and straightforward installation process contribute to its widespread use.
Gathering Materials and Tools
The primary material is the corrugated sheeting itself, which should be selected based on project requirements, such as light transmission or corrosion resistance. Fasteners are specialized self-drilling screws that incorporate a neoprene or EPDM washer. This washer creates a compression seal against the sheet material, preventing water from penetrating the screw hole.
Trim pieces, including gable or rake trim for the sides and a ridge cap for the peak, are necessary to weatherproof the structure and provide a finished appearance. Required tools include a drill or impact driver for securing fasteners, a measuring tape, and a chalk line for establishing straight reference points. For cutting metal sheets, use tin snips or a metal-cutting saw with a specialized blade. Safety gear like gloves and eye protection must be worn to mitigate risks associated with handling sharp metal edges and operating power tools.
Preparing the Roof Structure
The underlying roof structure must be prepared to support the load and ensure correct alignment. Corrugated sheets require horizontal supports, known as purlins or battens, which run perpendicular to the corrugations. Purlin spacing is determined by the sheet material’s thickness and the expected load. Thinner 0.5mm gauge steel sheets typically require spacing no greater than 1.2 meters, while thicker sheets allow for wider spans.
The purlins must be securely fastened to the rafters or trusses to transfer the roof load effectively. Verify that the entire roof frame is square and level, as any misalignment will be magnified during installation. Snap a chalk line across the purlins to establish a precise baseline parallel to the eaves. This line serves as the starting reference point for the first sheet and ensures a straight run across the roof plane.
Laying and Fastening the Sheets
The process of laying the sheets begins at a corner, typically the one opposite the direction of the prevailing wind, which helps prevent wind-driven rain from being forced into the side overlaps. Each sheet must be overlapped with the adjacent one to maintain a weather-tight seal, with a side lap of at least one full corrugation being the standard requirement. For sheets that must be joined end-to-end down the slope, the end lap should be a minimum of 150mm for roofs with a pitch of 10 degrees or greater, increasing to 300mm for shallower pitches to account for slower water runoff.
Fastener Placement
The most important detail in securing the sheets is the placement of the fasteners, which must be driven through the crest, or high point, of the corrugation, rather than the valley. Fastening on the crest elevates the screw head above the primary water channel, significantly reducing the risk of leaks. Conversely, fastening in the valley places the screw directly in the path of water flow, where it can act as a small dam and increase the likelihood of water infiltration.
Fasteners should be driven perpendicular to the sheeting and into the purlins below, using a controlled torque setting to compress the washer without deforming the sheet profile. A common fastening pattern involves securing the sheet at every second or third crest along the purlin, with a denser pattern required at the eaves, ridge, and side laps, especially in areas prone to high winds.
As each subsequent sheet is laid, it must correctly overlap the previous one, and the installer should ensure the sheet’s edge remains aligned with the initial chalk line to maintain a straight course. If a sheet requires cutting to fit around an obstruction or to finish a run, it should be done on the ground using appropriate tools to avoid damaging the protective coating with hot metal filings.
Finishing the Edges and Ridge
Rake or gable trim is installed along the sloped edges of the roof to cover exposed purlin ends and sheet edges, providing a clean, finished line and protecting the substructure. This trim is typically fastened into the purlins and the sheet material.
The ridge cap covers the peak where the two roof planes meet, preventing water entry at the highest point. The cap must be overlapped correctly and secured into the crests of the corrugated sheets on both sides. To enhance weather resistance and prevent pest entry, foam closures or mastic sealant strips are inserted into the open corrugations at the eaves and beneath the ridge cap. These closures conform to the sheet profile, sealing the gaps and completing the weather-tight envelope.