Aerated concrete and PIR board can form an effectively insulated wall if the right system is chosen. Under render, a board intended for that application is required. A low λ alone is not enough. The masonry must be identified, the finish system checked and the whole building element calculated. Project requirements must be determined separately. PIR boards have different facings. The foil variant is not automatically a substrate for mortar and render. In façade systems, a suitably prepared glass fleece is used, among other things. Its surface and the way it is bonded to the core are properties of the specific product.

Choosing the PIR thickness starts with the conditions of use. Temperature, heating duration and humidity matter. Next, the specific panel's parameter and the joints are checked. More millimetres usually restrict heat flow, but do not fix a leaky joint. A good choice also covers load-bearing capacity, coatings and fire requirements. Determine the target temperature and how long it is maintained. A small service point operating daily differs from a storage room heated occasionally. Frequent door opening and ventilation also matter. The panel requirements must be linked to the whole building's balance.

The board format affects the number of joints, the way it is handled and the amount of waste. Smaller elements can be more convenient in a tight interior. Larger ones allow a large area to be covered with fewer pieces. However, a distinction must be made between the nominal dimension and the effective coverage. A rebate on the edge can reduce the area that the board actually covers. One family of foil-faced PIR boards includes formats 600 × 1200 and 1200 × 2400 mm. Nominally these correspond to 0.72 and 2.88 m². The large board therefore has four times the rectangular area. This does not mean that every PIR is available in both sizes and all thicknesses.