Matching thickness is not enough when substituting PIR on a flat roof. If the membrane will be bonded, the installer needs to know which surface it will adhere to. Even boards sold under similar names can have different facings. Start with a drawing: label both sides of the board, the layers touching them and how each joint is made. You can then check the instructions for that combination and identify gaps in the quote. This is particularly useful for a partial roof repair where the new build-up meets existing waterproofing.

Before insulating a plinth, look at the junction between the wall and the driveway. Mark the paving level, the direction of rainwater runoff and any places where water lingers against the wall. A section showing these features helps establish where the insulation will sit, what it will touch and how its exposed edge will be protected. Even a short stretch beside a garage door can need a different finish from the adjoining wall facing the garden.

PIR boards are often considered where an existing threshold, window, eaves detail or room height restricts insulation space. Available board thickness alone should not decide the choice. Finishes, fixings and the designed junction arrangements must also fit in the same area. This guide helps prepare dimensional information before discussing materials. It shows how to identify limiting points, separate the total build-up from the space for insulation and record questions needing a designer's assessment. It does not recommend compressing boards or omitting necessary layers to fit a target dimension. A sound selection begins with a section through the complete construction.

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.