Can sandwich roof panels be installed on a low-pitch roof?

PIR insulation can be used in flat roof build-ups with a suitable waterproofing layer. That suitability does not establish a minimum pitch for a metal-faced roof panel. Select the complete build-up and drainage arrangement first. Then establish the geometry, materials and joint details for that particular roof.

For one sandwich roof panel system, the stated minimum is 5% for panels running continuously down the slope with no end laps or rooflights. Where end laps or rooflights are present, that system specifies at least 7%. These figures apply to the particular system and conditions described.

Other panel systems may specify different limits. Check the manual for the actual panel you intend to install, including the conditions for the planned openings and joints. The roof geometry, slope length and drainage arrangement may require a steeper pitch than the product minimum.

Percentage fall is the height difference divided by the horizontal distance, multiplied by 100. A fall of 5% is a drop of 5 cm over 1 m horizontally, equivalent to about 2.86°. A fall of 7% is about 4.00°. Include the unit on drawings and measurement records.

Over a horizontal distance of 6 m, a 5% fall gives a height difference of 30 cm and a 7% fall gives 42 cm. These geometric calculations exclude deflection and junction details. A panel measured along the slope is slightly longer than the horizontal run. Determine its order length separately.

Water needs a continuous path to the outlet. Even if the levels at the top and bottom are correct, a hollow can form between supports. The structural assessment must account for deflection, and the installation crew should check the plane of the supports. This matters particularly on existing roofs where support levels vary.

Check flashings, rooflights and service penetrations for obstructions to drainage. A raised transverse detail or a poorly finished edge can hold water back. More sealant cannot correct the drainage geometry. At low pitches, detailing and workmanship matter as much as the panel specification.

If the slope requires more than one panel length, design each end lap with the bearing, cutback and seal specified for that system. Fix its position before ordering. Shortening panels for transport can introduce a new lap and change the minimum pitch and the work needed on the supporting structure.

Size and position gutters, outlets and other drainage components to suit the roof. Allow access for cleaning, particularly where leaves collect. Direct the discharge away from adjacent walls. On an existing building, also check the condition and capacity of any downpipes you plan to retain.

If the available height cannot provide the required pitch, the design needs to change. Options may include altering the structure or selecting a build-up with a separate waterproofing layer and designed falls. Compare load capacity, available height at adjoining walls, design loads and how the building will be used.

A thicker core or extra sealing tape cannot be assumed to compensate for insufficient fall. At handover, check the levels, details and drainage, and retain the panel system documentation. Adding a rooflight or equipment later changes the design conditions and calls for a fresh assessment.