How to choose a roof panel thickness for heating and future rooftop equipment

Collect structural data too, including span lengths, the number and arrangement of spans and the supports. Check snow, wind and equipment loads as well as access for maintenance. Assess thermal performance and structural capacity in parallel. Satisfying either requirement still leaves the other to be checked.

The table gives illustrative U-values for one range of steel-faced PIR roof panels with a core thermal conductivity of 0.021 W/(m·K). Use these figures for an initial comparison within this range. Another PIR panel of the same nominal thickness can have a different declared U-value.

Check the limit for the roof element, the corrections to be applied and the effect of thermal bridges. A quoted U-value just at the limit still requires assessment of the complete roof build-up. Confirm also whether the stated thickness is the core depth in the flat section or the overall depth including the outer profile.

Use a load table specific to the core thickness, metal facings and panel type. Each entry assumes particular supports and design criteria. To select a span, the designer checks load combinations, fixings and permissible deflections, including the effect of deflection on drainage. The longest span in the table is not necessarily suitable for this roof.

On an existing building, inspect the supports themselves. A thicker panel may be stiffer, but it cannot restore a corroded purlin or correct insufficient bearing. Snow can drift beside a higher adjoining wall. Assess the local loading from the actual roof geometry in addition to the loading on unobstructed areas.

Equipment adds load and transmits forces at specific attachment points. A rooftop photovoltaic array transmits wind forces through its mounting system as well as adding weight. Increasing core thickness alone cannot establish suitability. Check the panel, fasteners and the entire supporting structure underneath.

Plan supports and flashings for fans, air handling units and service penetrations. Account for vibration, maintenance access and weathertightness. If the equipment will be selected later, specify the permissible loads and where they may be applied. An unspecified allowance for future equipment gives an installer too little information.

Increasing core thickness changes the levels at wall junctions, eaves and ridge. Longer fasteners, different flashings or revised penetration details may be needed. Check that the components work together. A late switch in thickness calls for revised drawings as well as an updated order.

Check the fire classification and environmental suitability of the selected version. A classification may cover only certain thicknesses and support arrangements. The internal coating must withstand the conditions in the building. For intensive washdown or agricultural use, assess the complete envelope and its joints alongside the panel U-value.

Compare options that pass all the required checks. Include delivery, installation, supports and junction details in the cost. A thicker panel may allow a different structural layout if calculations confirm it. Do not assume the change allows alternate supports to be omitted or fewer fixings to be used.

Assess the energy effect of a lower U-value in the context of the whole building. Extra roof insulation has a different impact in an airtight hall than in a building where vehicle doors are often open. Weigh comfort, costs and intended use together. Keep the design assumptions on record so future equipment can be checked against them.