Celotex GA4 PIR Insulation Board

Celotex is one of the first names UK trades reach for when a job calls for rigid polyisocyanurate (PIR), and GA4000 is its general-purpose board: a single product that covers roofs, walls and floors. PIR earns its place by reaching a target U-value in less thickness than most other insulation types, and the GA4000 range runs from 50mm to 100mm, so you match the depth to the job rather than over-specifying.

Every board in the range shares the same rigid PIR core with a low-emissivity aluminium foil facing on both sides. The declared lambda is fixed at 0.022 W/mK across the range, so thermal resistance climbs with thickness, from 2.25 m²K/W at 50mm up to 4.50 m²K/W at 100mm. Boards measure 2.4m x 1.2m, giving 2.88m² of cover each, with straight edges that butt together cleanly.

Insulation UK stocks the GA4000 range in seven thicknesses, from 50mm to 100mm. Whether you are insulating a pitched roof, building up a floor or lining a wall, this is the part of the Celotex range worth understanding before you order.

The Celotex GA4000 range at a glance

All thicknesses are the same 2.4m x 1.2m board with the same 0.022 W/mK lambda. Board size and coverage stay constant across the range, while thermal resistance climbs steadily as thickness increases. The R-values below are taken from the current Celotex GA4000 datasheet.

Why Celotex GA4000 stands out

The value here is not just the lambda figure, though at 0.022 W/mK it is among the best you will find in a general-purpose board. What sets GA4000 apart is that one product covers the three elements most projects need insulating: roofs, walls and floors. You are not switching product types as you move around a build, you are changing the thickness to suit each element.

The board is faced both sides with a low-emissivity aluminium foil, which lifts thermal performance further when it faces a sealed cavity air space. One face carries a printed logo and the other is plain, and the plain face should be turned towards the cavity for best performance. A compressive strength of CS(10\Y)140 kPa means the board takes the loads involved in floor build-ups, and at around 4 kg per square metre it is light to handle and quick to cut with a sharp knife or fine-toothed saw.

For trade buyers, that translates into one familiar product across multiple jobs. For self-builders and serious DIYers, it means a board that is straightforward to handle, cut and fit without specialist kit.

Thermal performance and building regulations

Every thickness in the range carries a declared thermal conductivity of 0.022 W/mK. The R-values step up clearly with depth, from 2.25 m²K/W at 50mm to 4.50 m²K/W at 100mm, so the thicker the board, the more thermal resistance it adds to the build-up.

Because PIR conducts heat so slowly, it reaches a given U-value in noticeably less thickness than mineral wool or polystyrene, which is why it is the go-to where space is tight. The exact thickness you need depends on the element you are insulating and the U-value target set by your specification or building control under Part L. The low-emissivity foil facing adds a further gain where it sits against a sealed cavity air space.

It is worth being straight about one thing. A board's R-value is not the whole story: the U-value of the finished element depends on the full build-up, the other materials in it and how cleanly it is installed. Use the R-value to compare thicknesses, and confirm the target U-value for your specific element before you order.

Installation and site practicality

GA4000 is light and rigid, and it cuts cleanly with a sharp knife or fine-toothed saw. Boards should be butted tightly, with gaps and joints sealed, including at service penetrations, to keep the insulation layer continuous. Where the board faces a cavity, fit it with the plain, unprinted foil face towards the cavity to get the rated thermal performance.

If you would rather skip the offcuts and the dust, the bespoke cutting service can supply boards cut to your sizes. Store the boards flat, raised off the ground, kept dry and protected from prolonged sunlight before they go in.

Fire safety and sustainability

GA4000 carries a reaction-to-fire classification of Euroclass F to BS EN 13501-1. Like all PIR, it is a combustible product, so it must be installed behind a suitable lining such as plasterboard in line with the relevant Building Regulations. There is also a height restriction worth noting early: GA4000 should not be used in the external walls of buildings over 11 metres in height. That is a specification point to settle before you order rather than a fault.

On the environmental side, the board is manufactured with a blowing agent that has zero ozone depletion potential and low global warming potential, and is free of CFCs and HCFCs. It achieves a BRE Green Guide rating of A (certificate ENP413), which can support a BREEAM assessment, and it is CE marked to BS EN 13165.

Which thickness should you choose?

The right depth comes down to the element you are insulating, the U-value you need to hit and how much room you have in the build-up. The GA4000 range spans 50mm to 100mm, so within it the thinner boards suit tighter build-ups and the thicker boards earn their place where lower U-values are the priority. If you are unsure, the Insulation UK team can help you size it.

How GA4000 fits in the wider Celotex range

Celotex splits its PIR boards into ranges by thickness, which makes it easier to land on the right board for the space you have. GA4000 is the general-applications range covering 50mm to 100mm, the depths most commonly used in walls, floors and pitched roofs.

Below it sits TB4000, a thinner range from 20mm to 40mm for tight spaces and multi-layer build-ups where thermal bridging is the concern. Above it sits XR4000, from 110mm to 150mm, for situations where space is not the limiting factor and a higher thermal resistance is wanted from a single board. All three share the same PIR core and 0.022 W/mK lambda, so if your target depth falls outside 50mm to 100mm, the sister range is the place to look.

Quality and specification confidence

GA4000 is backed by the documentation specifiers and building control look for. It holds BBA Agrément Certificate 17/5405, covering pitched roof, dry lining and floor insulation, with a separate certificate (16/5352) covering timber frame dwellings. It is CE marked to product standard BS EN 13165, and manufactured under ISO 9001:2015 quality management and ISO 14001:2015 environmental management. A current datasheet and Declaration of Performance are available for the range.

That breadth of paperwork matters because insulation is not a category where vague confidence is enough. It makes the board straightforward to put in front of an architect, energy assessor or building control officer. Always check the latest Celotex datasheet, Declaration of Performance and BBA certificate for the exact application before specification.

Any drawbacks?

The main thing to keep in mind is the fire classification. GA4000 is a combustible product with a Euroclass F rating, so it always needs a suitable lining over it to meet Building Regulations, and it should not be used in the external walls of buildings over 11 metres in height. Those are standard considerations for PIR rather than faults, but they are points to settle before you order.

A couple of practical notes too. The foil facing is printed on one side only, so the board has to go in with the plain face to the cavity to perform as rated, which is easy to get wrong in a hurry. And while PIR is moisture resistant, it is not waterproof, so boards should be kept dry on site and are not the choice for below-ground or permanently wet conditions.

Our expert verdict

Celotex GA4000 is one of the most dependable choices in the general-purpose PIR category because it gets the fundamentals right. The fixed 0.022 W/mK conductivity gives strong thermal performance in a slim board, the foil facing lifts performance against a cavity, and the 50mm to 100mm range covers the depths most walls, floors and roofs call for.

The real strength is how cleanly it slots into a project. For most walls and floors the mid-range thicknesses do the job, while roofs and lower U-value targets are covered up to 100mm at 4.50 m²K/W. Match the depth to your element and your target U-value, check the datasheet figure for that thickness, and GA4000 does the job without fuss.

For any roof, wall or floor project where thermal performance and a clean install both matter, the Celotex GA4000 range belongs on your shortlist.