Before comparing two PIR quotes, establish what the insulation layer needs to achieve. One board may be thinner and another cheaper per square metre, but neither figure tells you whether both meet the design requirement. Put the figures for the two actual products side by side: thickness, declared thermal resistance, facing and coverage per pack. A worked example below shows how to spot a unit error and why a cheaper pack need not mean a cheaper insulated surface.

A supplier cannot deliver the specified board and offers another of the same thickness. Record precisely what would change: just the manufacturer, the facing, the board format or the way the layer is installed. Without that detail, one party may expect an equivalent material while another has priced a cheaper assembly with different accessories. Here is a practical way to compare the two proposals and record a decision before delivery. It is especially useful when the client buys the material and a separate contractor installs it.

When comparing PIR boards, it is easy to place numbers side by side that describe different things. Lambda is a material's thermal conductivity, R accounts for layer thickness, and U describes heat transmission through a defined building-element assembly. None of these values is itself a percentage saving on heating. This guide organises the symbols and units and works through an explicitly hypothetical calculation. Its inputs are not assigned to a particular product. The purpose is to read quotations and documentation correctly: identify what each number describes, where it comes from and what a designer needs before selecting insulation thickness for a roof, wall or floor.

An internal ceiling can separate a heated or climate-controlled room from the roof void. In a cattle shed or warehouse, its appearance is only one consideration. Choose insulation, facings, supports and wall junctions to suit the space. PIR boards help keep the build-up thin. For a durable ceiling, plan how to control moisture, clean the lining and reach services above it. This is an internal ceiling, distinct from decorative soffit cladding beneath the eaves outside. In a farm building, the ceiling can form the room’s thermal boundary. The design must define the height and use of the void above: moving that boundary changes the room volume, ventilation and service routes.

A loft fit-out starts well before the first plasterboard goes up. Inspect the roof, plan the insulation and establish how the layers will be made airtight. Framing, lining and jointing follow. PIR boards can reduce the insulation thickness needed, but form only part of the lining system. The materials must work together around windows, walls and services. Check the roof covering, flashings, window junctions and timbers before concealing them. Repair leaks and timber damage first. When converting a loft, establish the load capacity of the floor and the applicable approval requirements. Partitions, flooring and furnishings add loads. Adequate headroom alone does not make a loft suitable for habitation.