Can roof sandwich panels be used to extend an older building?

Assess supports, connections and material condition before choosing the covering. Timber needs checks for damage and moisture, steel for corrosion and joint condition, and masonry for the bearing of new elements. An old roof’s appearance does not establish its capacity.

Compare archived drawings with the actual building. Later alterations may have changed the arrangement. “It has always held” is not a design basis: an extension can introduce different loads and force directions. Assess both the new section and retained members.

Assume the selected panel has a 100 mm core, 0.5/0.4 mm facings and a mass of 12.4 kg/m². At 100 m², panels alone would weigh about 1,240 kg. This illustrates one variant’s calculation, not every PIR panel or a complete roof. Add all other layers, flashings and equipment.

Include flashings, fasteners, substructure and equipment, plus snow, wind and construction loads. If the old covering remains, its weight stays in the calculation. Low new-material weight is beneficial only when the whole assembly has been checked correctly.

Being able to order a long panel does not mean it can span its full length unsupported. Select the correct thickness, facings and structural arrangement in the load tables. Old purlin spacing may not suit the new covering. Check their condition and connections too; matching panel dimensions are insufficient.

Extensions often require added or rearranged purlins. Check bearing widths and fixing locations. Do not attach new panels to arbitrary retained battens. The design should identify load-bearing members so installers do not have to make structural decisions on the roof.

A junction at a higher wall, step or existing slope needs a precise detail. Water must drain in the intended direction. A broad bead of sealant is not enough. Allow for movement between structural sections too.

A higher building section can change snow distribution and wind effects. These cannot be assessed from extension area alone. Use the actual site conditions. Panel technical details provide a starting point, but an unusual junction to an older building needs adaptation.

An existing roof may have unevenness and deflection. Measure its real geometry, including between supports. Confirm minimum pitch for the chosen panel and joint arrangement. End-lapped panels may require a greater slope than one continuous panel from eaves to upper edge. No single value suits every roof panel.

At low pitches, drainage and freedom from ponding are particularly important. A satisfactory height difference at the ends is not enough if a local depression retains water. If the design requires another flat-roof build-up, select suitable waterproofing and substrate rather than stretching the panel’s application conditions.

If new panels cover retained layers, establish their condition. Damp insulation or a leaking covering should not disappear beneath new work without assessment. Determine drying potential and whether damaged materials need removal.

Changing the build-up affects layer temperatures and condensation potential. A simple analysis does not capture every moisture and air-leakage process. Nominal layer data may be insufficient for an old roof. Inspection and opening-up help prevent false assumptions, including whether retained layers can dry.

Protect the interior from rain during renovation. Agree removal scope, storage and panel handling. Transport and lifting methods must suit actual element sizes and weights. Long panels need organised installation. Minimise the time during which old and new sections lack a watertight connection.

Inspect new supports, fasteners and seals before concealment. Keep photographs of the old-to-new junction. Finally, check drainage and maintenance access. Panels can simplify an extension, but success requires the adjoining elements to be resolved too. They often determine the renovation’s durability.

No. Check the complete arrangement and all loads, including the condition of existing supports.

Only after assessing its condition, moisture, weight and compatibility with the new design.