Rooflights in corrugated fibre-cement roofs: matching profiles and keeping out rain

Consider different times of day and seasonal changes in use. A symmetrical strip on a roof drawing may light an unused aisle while a workbench stays in shadow. Use the layout inside the building to decide where the light should enter.

Compare the corrugation pitch, height and edge geometry on technical drawings. Differences often first show up where the sheets overlap. Specify a rooflight approved for the particular fibre-cement profile and check the current versions of both products. Never force the sheets together to close a gap. A substitution requires checking the whole joint, including its edges, even when the overall sheet widths match.

Establish the permitted support spacing for the rooflight from its own mechanical data. Coordinate the support layout for both materials and check the end and side laps. The rooflight may need a different support or an additional detail depending on its position and the snow and wind loads. Geometric fit alone tells you little about its load capacity at that span.

Follow the instructions for each material when selecting hole sizes, seals and clamping pressure. The rooflight may expand differently from fibre cement, so the adjoining sheet must allow the movement specified for the joint. Check how the seal remains effective during movement. Extra screws can restrain the sheet or damage the connection. Order the correct fixing kits and label them on site so they are used on the intended material.

In a heated hall, assess heat loss, condensation and continuity of the roof layers where the material changes. Obtain fire performance data for the precise rooflight, thickness and application and include it when checking the whole roof. The fibre-cement sheet’s classification applies to that product. When comparing thermal figures, distinguish the U-value of the element from the thermal conductivity of its material.

Dirt and changing light can make rooflights difficult to see. Treat them as fragile surfaces. Provide suitable walkways and fall protection across the fibre-cement roof as well. Mark rooflights in the building records and brief teams installing equipment later. Plan access to nearby plant in advance. Keep the zones visible and provide places to set down equipment without loading the sheets.

At handover, check profile fit, supports, fixings and laps against the agreed system. Record the rooflight model so a replacement can be identified years later. Check approved cleaning methods for each surface. During inspections look for debris obstructing drainage, movement at joints and damage. If water enters, investigate support and movement before applying sealant. A surface patch can leave the underlying fault in place.

Choose the rooflight for the use of the space and the exact roofing system. Confirm profile geometry, supports, fixings, performance data and safe maintenance access before ordering.