Sandwich panel roofs on steel buildings: designing the complete roof

Roof loads pass through the panels to the purlins or other supports shown on the drawings and then into the main frame. The number and spacing of supports must suit the specified roof panel. Check its load resistance and deflection. Excessive deflection can compromise weathertightness and drainage. Wall panels require explicit approval for any proposed roofing use.

There is no single minimum pitch for every sandwich panel roof. Consult the system details for the slope length, joint arrangement and any rooflights or penetrations. A continuous panel run can have different pitch requirements from a roof with end laps.

Check the geometry the roof will actually have after installation and under load. At shallow pitches, construction tolerances and deflections take on particular importance. Lowering the pitch on site to suit a door or façade changes the design of the roof and its supporting steelwork and requires assessment.

A panel running from ridge to eaves eliminates an end lap on that run and can simplify the weather seal. Long panels also need adequate delivery access, lifting equipment and room to manoeuvre. Check these conditions before ordering for a site with a narrow entrance.

Where two panels meet along the slope, use the system’s end-lap detail. It sets out the overlap, support, seals and fixings. Arrange the joint so rain runs over it without entering beneath the outer facing. Agree delivery lengths and joint positions before panels reach the site.

Snow applies a downward load, whereas wind suction can lift the cladding off the purlins. Fixing requirements may differ between the middle of the roof and the edge zones. Select the panel, washer and screw together, taking the support material and its thickness into account.

Follow the specified compression for the sealing washer. Overtightening can distort the facing, while too little compression can let water in. Check the support alignment before installation. Pulling panels down hard against misaligned purlins can distort the roof.

Rooflights, smoke vents and service penetrations interrupt the cladding and need suitable flashings and supports. Establish how equipment loads at each opening reach the frame. The design may require trimmer members around the opening or a separate support for the equipment.

Size gutters and outlets for the area and shape of the roof draining to each one. Route the discharge clear of the plinth and foundations. At handover, check that the outlets are clear and remove drilling swarf, sheet offcuts and installation debris.

A taller extension can change snow drifting on the existing roof and alter where water runs. Check both roofs before fixing the extension height. Review the new loads, gutter positions and junction details, even when the new panels match the old ones. Provide access to inspect the junction later and agree which contractor is responsible for each part of it. This avoids relocating outlets or reinforcing a finished roof during installation.

The system documentation and project design determine whether and how people may walk on the roof. A sandwich panel has limits on concentrated loads. Where equipment needs regular servicing, specify suitable access routes and fall protection. The same applies to a building supplied as a modular kit.

Inspect flashings, seals, fixings and drainage periodically on storage, production and agricultural buildings. Before adding photovoltaic modules, check the extra loads and the points where they enter the frame. Use the structural assessment to establish whether the roof has sufficient spare capacity.