How do you choose roof panel thickness without overspecifying it?

Consider planned changes of use. If heating will become more intensive, include that operating scenario in the comparison. Estimate the feasibility and cost of a later upgrade to decide whether extra thickness now is justified.

In one example range of steel-faced PIR roof panels, the 120, 150 and 180 mm versions have Uc values of 0.19, 0.15 and 0.12 W/(m²K) respectively. The figures apply to those configurations. Another panel of the same thickness can have different values and conditions of use.

For a design target of 0.15 W/(m²K) over the roof field, the first panel falls short. The other two warrant further comparison, including any required corrections and junction details. Check openings, connections and remaining design requirements before selecting a panel.

Use the load table for the actual facing thickness, core, supports and number of spans. Include snow, wind and relevant additional loads. Check both resistance and deflection, with particular attention to corners and edge zones.

Include any extra purlins needed for a thinner panel in the cost. A thicker panel may reduce alterations if calculations show that the existing spacing is suitable. Check fasteners and the capacity of the fixing substrate separately.

Check the permitted pitch for the panel and joints. Extra thickness cannot remedy poor drainage or insufficient fall. Keep the ridge, eaves and wall junctions insulated and sealed. In heated buildings, local cold surfaces may encourage condensation.

Fire documentation must cover the installed assembly, including supports and joints. Check the field of application before using a classification for another thickness. In humid rooms also check the seals and internal coating. The chosen assembly must satisfy all requirements together.

Cost the panels, supports, fixings, flashings, seals, transport and installation. Estimate differences in heating costs for the same climate and operating schedule. An intermittently heated building will give a different result from a hall heated around the clock. State those assumptions with any savings figure.

Specify loads and fixing arrangements for planned plant or photovoltaic panels. Extra thickness gives no blanket allowance for equipment. The load may need to go directly to the frame. Record the assumptions before ordering to avoid redesign after installation.

Record thickness, facings, coating, lengths and joint layout in the selection schedule. Include loading conditions, thermal performance and handover documents. Set out restrictions on future openings and equipment so the installer knows exactly what to order.

Check the affected properties whenever a substitute is proposed. Different steel facings can change capacity even at equal thickness. A different joint can affect weathertightness. At delivery, inspect labels and condition against the accepted configuration.