Which PIR board size should you choose: 120 × 60 cm or 120 × 240 cm?

These dimensions apply to the board in the example. For the product you intend to order, check whether the quoted price is per board, pack or square metre. Board thickness also affects how many pieces fit in a pack. Two packs that look the same can cover different areas.

In a flat undergoing renovation, a stairwell, a sharp turn in a corridor or a doorway may determine what size you can use. A 2.4 m board might fit the room yet be impossible to carry up the stairs without damaging it. Before delivery, check the turns with a light batten of the same length and measure the clearance available for the board’s width.

Smaller boards are easier to carry and turn, though they introduce more joints. A large board takes fewer handling operations on an open roof slope, but a gust of wind can catch it as it is carried. Plan the handling and installation around the conditions on site so the work can be carried out safely.

Mark windows, recesses, slopes and service penetrations on the plan. Lay out the boards according to the system instructions. See whether an offcut can start the next row with the required support and the right edge profile. Some small pieces will have no suitable place in the layout.

For a simple 22 m² area, the calculation gives eight large boards if each covers approximately 2.83 m². Using that rounded figure gives 22.64 m² before cutting. The actual number can rise if openings produce offcuts you cannot reuse. A blanket 5% allowance may be too little for one layout and unnecessarily generous for another.

Follow any instructions about laying direction and which face goes uppermost or outwards. An offcut can have the right area but the wrong orientation for a particular gap. Assign larger offcuts to specific positions while you draw the layout.

Cutting a board to length removes the factory-machined profile from that edge. The resulting butt joint needs its own treatment. Follow the system detail for the gap and for continuity of the sealing layer. A workable cutting plan leaves edges that can be joined and sealed correctly.

For a multi-layer installation, set out the joints in advance in accordance with the instructions. Staggering them is usually required. On a mechanically fixed roof, board size and edge positions must also suit the specified fixing pattern.

A smaller format may reduce waste in a tight interior while requiring more time to seal the joints. Large boards can reduce the number of joints on a plain roof slope, though getting them to the roof may take more work. Include materials, labour, sealing and transport when comparing the installed cost per square metre.

Check the sizes offered for the facing and board type you need. Façade boards, floor insulation and PIR bonded to plasterboard can come in different dimensions. Choose the suitable product first, then compare the formats available in that range.

Place packs on a stable base and protect them from water and damage. Provide adequate weather protection in addition to the transport packaging. On a roof, the structure’s load capacity and the sequence of work limit how much material can be stored. Consider the weight of all the packs together, even when a single board feels light.

Open packs in the order in which each area will be insulated and protected. Keep damp boards out of areas about to be covered with waterproofing. If you order well in advance, check the permitted storage period and conditions so the boards retain their properties until installation.