PIR Insulation Boards

What PIR insulation boards are

PIR insulation boards are rigid panels of polyisocyanurate foam with a thin aluminium foil facing bonded to each side. The closed-cell foam traps a low-conductivity gas, which is why a PIR board insulates far better, thickness for thickness, than mineral wool or expanded polystyrene. The foil facings add rigidity, act as a vapour control layer and give the board a low-emissivity surface that improves performance when it faces an unventilated air gap. PIR insulation boards are used across the whole house: in pitched roofs between and under the rafters, in flat roofs, under screeds and floating floors, inside timber frame and masonry walls, and in extensions, loft conversions and garden rooms.

Every PIR insulation board we sell is a general purpose board. It measures 2400mm x 1200mm, covers 2.88m² and is supplied brand new, factory fresh, straight from the manufacturer. The thermal conductivity is 0.022 W/mK whatever the brand on the foil, so the U-value you calculate for a thickness is the U-value you get on site.

One specification, whichever brand we send

We sell PIR insulation boards by thickness rather than by brand. Order 100mm boards and you will receive 100mm general purpose PIR boards from one of the manufacturers we work with, chosen for your postcode according to local stock. Because every brand is made to the same specification, the result in the building is the same. What changes is the price you pay and how quickly the boards arrive: buying from whichever factory is best stocked near you is how we keep PIR insulation boards at trade prices and lead times short. If your project has been specified by brand name, contact us before you order.

Choosing a thickness

The right thickness depends on the element you are insulating, the U-value you need to reach and the space available. As a guide, thinner PIR insulation boards from 20mm to 40mm are used for thermal breaks, dot-and-dab upgrades behind plasterboard, lining existing walls and topping up under the rafters. The 50mm to 100mm range covers the most common jobs: floors under a screed or chipboard deck, timber frame walls, between-rafter layers and flat roof build-ups. Thicker boards from 110mm to 200mm let you hit current Building Regulations targets in a single layer, for example in a warm flat roof or a new floor where the depth is there to use.

Two thinner boards can also be combined, with joints staggered, which is often the practical answer in a pitched roof where a between-rafter layer and an under-rafter layer are needed together. Our thickness switcher on every product page shows the price of each size, and the bulk buy page lets you add several thicknesses to one order.

How many PIR insulation boards do I need?

Measure the area in square metres and divide by 2.88, the coverage of one 2400mm x 1200mm board, then round up and add around 10% for cuts and waste. A 40m² floor, for example, is 40 ÷ 2.88 = 13.9 boards, so 14 boards plus one or two spare. The calculator on our bulk buy page does this for you and adds the boards straight to your basket.

Fitting PIR insulation boards

PIR insulation boards cut cleanly with a fine-tooth hand saw or an insulation saw. Mark both faces, cut square and fit boards tightly together so there are no gaps, since gaps leave cold bridges that undo the benefit of the insulation. Where boards are fitted between rafters or studs, cut them a fraction oversize so they wedge in place, and foam any small gaps at the edges. Tape every joint with aluminium foil tape to keep the vapour control layer continuous, and leave the required ventilation gap above the boards in a cold pitched roof. Boards should be stored flat, off the ground and under cover until they are used, and the foil facing should not be left exposed to weather.

Brand new boards, trade prices

We only sell brand new PIR insulation boards, never seconds, surplus or reclaimed stock, so every board arrives square, dry and with its foil facings intact. Prices are per board and shown ex VAT, and the price you see on the product page is the price for that thickness whichever brand is delivered. Delivery is by curtain-sided lorry to the kerbside, usually within 3 working days on average when you order before 2:30pm on a working day, and you can choose ASAP or request a date at checkout. Delivery charges are shown on our delivery page, with free delivery on UK mainland orders over £450 + VAT.