When is an insulated sandwich roof panel the right choice?

A typical roof panel has two steel facings bonded to a core. In a PIR panel this is rigid insulating foam. The outer face has pronounced trapezoidal ribs; the inner face can be flat or lightly lined. The bonded layers act together, unlike separate sheeting and insulation.

A PIR insulation board with thin aluminium facings needs a supporting deck and other roof layers. A sandwich panel transfers specified loads to its supports, but does not replace primary beams, purlins or the building frame.

Deep external ribs help the panel carry loads and drain water. The side joint is designed for a roof slope. Wall panels use different profiles and joints. Matching core thicknesses do not make the two types interchangeable.

Distinguish the thickness at the rib valley from the overall depth over the crest; a pair of dimensions may refer to these two measures. Screw length depends on the fixing position and section depth. Specify the side lap and eaves cutback for the laying direction. A change of colour or thickness will not reverse a handed detail.

Start with the required U-value of the complete roof. Lower core conductivity can reduce the thickness needed for a given insulation performance, but does not describe the whole assembly. Include joints, fasteners and indoor conditions: an unheated store and a heated workshop have different needs.

Do not assume that ten centimetres will suffice. Published U-values for the same thickness can vary with the product and calculation method. In a cold store or humid room, joint tightness is just as critical. A thicker core will not close a gap at the wall junction.

Minimum pitch is system-specific. Some instructions allow about 5% for continuous panels, with a steeper pitch at end laps; other products need more. Use the figure for the specified system, not one from a similar panel. A slope of 5% is not an angle of 5 degrees.

Use the load tables and structural design to set purlin spacing. Snow, wind, self-weight, permitted deflection, facing thickness, number of spans and bearing widths all matter. Check any photovoltaic installation separately. A roof designed for snow cannot automatically carry any proposed array.

Reaction to fire describes a particular panel under stated conditions. Fire resistance of the roof is a separate requirement; a complete assembly’s classification cannot be assigned to the PIR core alone. Where REI performance is required, check the classification document, including its support and fixing conditions.

Steel facings restrict vapour movement, but the joints still need care. Maintain continuity at internal seals, flashings and service penetrations. Water can enter through a damaged fixing or poorly formed lap. A factory-fitted gasket does not replace the remaining installation details.

Coordinate rooflights, fans and other openings with the supports. Their positions can affect panel capacity and pitch requirements. Do not cut an opening at an arbitrary location in a finished panel. Larger penetrations may need additional support and their own flashings.

Roof-mounted equipment needs a designed load path. A thin facing is not a base for an arbitrary heavy unit. Plan access and servicing before the panels go on so that maintenance staff do not have to cross areas unsuitable for foot traffic.

Panels suit simple slopes where a quick enclosure and a finished internal face are priorities. Long panels reduce end laps. Check delivery access, storage space and lifting equipment; unloading damage can wipe out any purchase saving.

Compare complete installed costs including flashings, fixings, seals, delivery and labour. State the cutback side, lengths and both facings in the order. The main gain comes from several roof functions working together as specified, not just from driving screws quickly.