Selecting the appropriate thickness for PIR (polyisocyanurate) insulation hinges on various elements, such as your project’s specific needs, adherence to UK building regulations and the intended thermal efficiency.

PIR insulation boards are available in a range of thicknesses from 20mm to 150mm. Generally, a thicker board equates to better insulation properties. For example, in loft conversions or for roofing insulation, more substantial boards are typically recommended to attain optimal thermal efficiency. Conversely, in scenarios like internal wall insulation where space is at a premium, a slimmer board might be more apt.

The key is to strike a balance between achieving effective insulation and maintaining spatial efficiency. For precise advice suited to your particular requirements, it’s wise to consult a building professional or refer to the most current UK building standards. The objective is to enhance energy efficiency whilst meeting spatial and structural considerations.