How do you check whether a roof has enough fall for sandwich panels?

On a retrofit, survey actual support levels as well as consulting the old drawing. Check each run, particularly by outlets and wall abutments. A satisfactory average fall can conceal a local hollow where water collects. Relate the survey to the expected movement under load.

Put the unit beside every pitch dimension on the drawing. If the design uses degrees and the panel data sheet uses percentages, show the conversion so that successive support heights can be set correctly.

For example, one family of steel-faced PIR roof panels specifies more than 5% for continuous panels without rooflights. With end laps or rooflights it specifies more than 7%. These conditions apply to that particular product family.

In that example, a measured 6% clears the first threshold but falls below the second. Check tolerances and the other system conditions too. Where the requirement says “greater than”, a value exactly on the limit is insufficient. Confirm against current documentation for the offered panel before ordering.

Both the panel and its supporting frame deflect under load. On a low-pitched roof, a small change in shape can alter drainage. Check the relevant design load cases and service conditions for the complete supporting system.

Installation tolerances affect local fall. Use measured differences in support height and have any correction specified by the designer before installation. Do not force panels against misaligned supports to level the frame.

At an end lap, water must flow over the joint. Overlap, core cutback, seals and bearing must follow the system detail. Obtain the permitted overlap length for the selected panel. Also review junctions at walls, rooflights and rooftop equipment.

An obstruction may divert runoff onto adjacent panels or trap debris. Check flashing geometry and cleaning access. Review planned additions before cutting the roof. Even a small opening needs a sealed detail, a load path and protection for exposed edges.

Size gutters, outlets and overflows for the catchment and building geometry. Include any discharge from a higher roof. Inspect the eaves to ensure water can leave every profile trough. A flashing that dams the outlet can defeat an otherwise adequate panel pitch.

Provide planned access for cleaning. Leaves, deposits and snow can restrict drainage. Where parapets enclose the roof, check the emergency drainage detail in the design. Arrange inspections from safe, designated access points.

Before ordering, confirm the panel model, joints, lengths and required pitch against drawings and frame measurements. If the proposed arrangement lies outside the system conditions, revise the geometry or select a suitable roof system. Extra sealant cannot extend the approved use.

At handover check levels, terminations, joints and clear drainage paths. Record measurements and photograph details. Inspect after early rainfall using the planned access. If water stands, investigate the actual geometry and cause.