Extending an industrial building with corrugated roofing. How to join old and new

Identify the roofing material before planning removal. Then assess the condition of the sheets separately, including cracks, holes, corners and joints. Confirmation that a sheet is asbestos-free does not establish that it can stay in place or be reused in the altered layout. Mark the different construction phases on a roof plan. This helps explain whether a change in appearance reflects age, a repair or a different product.

The new volume changes local wind and snow loading and may divert runoff onto the existing slope. Assess the old covering in its future surroundings. Before directing extra water onto it, check drainage capacity and the junction detail. Give the designer the heights of both parts and the line of their junction. Even a modest increase in roof height can create a location that needs a specific detail. Adding roof area changes the behaviour of the original building as well as the new part.

A similar corrugation height does not ensure a weathertight lap. Compare the pitch of the corrugations, edge geometry, sheet thickness and effective cover width. Sheets from different systems may not sit together at the overlap. Do not force them into shape by tightening the fixings. If the original product is unavailable, decide before ordering whether to extend the replacement area or design a separate transition. Use technical drawings and measurements taken during a safe survey. An oblique photograph cannot give reliable profile dimensions.

The extension and original frame may differ in support layout, stiffness and deflection. Design the junction for their expected movement. Fibre-cement sheets need suitable support and fixings and must not be used to lock two structures together without assessment. Identify the members that transfer forces and the pieces that simply weatherproof the junction. Explain any movement joint on the installation drawings. An installer filling what looks like an unfinished gap may otherwise prevent the intended movement.

Opening the dividing wall changes airflow. New heating or production processes can change indoor humidity. A previously dry roof may therefore experience condensation after the extension. Review the layers and ventilation of both roofs, especially where an insulated section meets an uninsulated one. Rainproof flashing outside does not in itself prevent thermal bridging or stop warm, moist indoor air from reaching a cold area under the roof.

Before opening the roof, plan interior protection, the sequence of work and suitable weather conditions. Have all materials needed to close the junction on hand. Handle asbestos-free sheets without putting loads on adjacent sheets, and provide work routes off the covering. Cordon off the operating areas below and coordinate machinery movements. Assign responsibility for temporary weather protection at the end of each shift. An unfinished junction can expose a much larger part of the building than the immediate work area.

Keep the product data for the new sheets and document the junction and changes to the assumptions for the old roof. Mark sheets from different phases on the plan and record approved details, fasteners and service access. At handover, check drainage, continuity of required layers and access for inspection. Observe the junction from a safe place after the first heavy rainfall. The records will help distinguish a fault in the new detail from an existing roof problem revealed by the change in geometry or use.

Survey the existing roof and assess the future conditions before extending the building. Confirm the compatibility of profiles, structures and layers before ordering materials or opening the roof over an operating hall.