Celotex Insulation Board

If you looked up "PIR insulation board" in the Oxford English Dictionary it may well list Celotex as a synonym. The board - and its manufacturer - have become so entrenched in the lexicon of domestic homeowners and tradespeople alike, that it has achieved an almost "hoover" level of association with its core product.

Celotex Insulation Boards are a premium-grade, multi-purpose, BBA-certified thermal solution designed for use in a huge range of domestic and commercial applications. Celotex PIR insulation board offers excellent thermal performance thanks to its tough polyisocyanurate (PIR) core and low emissivity foil facings.

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What is Celotex Insulation?

Celotex have taken the "If you're going to do something, do it right" approach to thermal insulation, and are recognised as the market leader in a crowded space of wannabes that includes other excellent brands such as EcoTherm, Kingspan and Recticel.

The primary purpose of Celotex insulation - and that of most insulation, for that matter - is to retain heat within the building structure without compromising building regulations or internal floor or wall space. To this aim, Celotex have worked throughout the years to develop a product that maximises thermal efficiency while remaining as thin as possible.

PIR (an abbreviation for an otherwise unpronounceable piece of scientific jargon) insulation board comprises a rigid, tacky foam that is sandwiched between two layers of low emissivity foil facings. These facings add to the thermal resistance of the boards and help in overcoming thermal bridging (more on that later).

Celotex keeps tree huggers at bay by using a blowing agent that has zero ozone depletion potential (zero ODP) and low global warming impact, making the boards as ecologically gentle as they are thermally efficient.

The boards achieve a thermal conductivity (the yardstick by which all insulating products are measured) of 0.022 W/mK, making them one of the most thermally efficient insulation products on the market.

General Purpose Celotex Insulation Boards

Celotex's most popular product is its range of general purpose or "general application" boards, which vary in thickness from 20mm (good luck finding this anywhere other than at Materials Market) to 150mm.

These boards are so-called because they have a variety of uses, including pitched roofs, flat roofs, ceilings, floor systems and masonry walls. Whilst the product composition is identical regardless of thickness, different applications require different thicknesses. To make it easier to navigate, Celotex break down their general purpose boards into three distinct groups:

TB4000 - The "TB" stands for "Thermal Bridging"; a negative escaping of heat from the building structure through a highly conductive material. The TB4000 range contains the thinnest Celotex insulation boards (20mm, 25mm, 30mm & 40mm), and the name alludes to their effectiveness at preventing thermal (or cold) bridging.

GA4000 - The "GA" stands for "General Application"; relating to the fact that Celotex boards can be used in numerous applications, including roofs, floors, ceilings and walls. The GA4000 range contains mid-range thicknesses (50mm, 60mm, 70mm, 75mm, 80mm, 90mm and the famous 100mm).

XR4000 - The "XR" stands for "Extra Resistance"; and emphasises the fact that a thicker board will give you a better thermal U Value when measured on overall buildup. Rather confusingly, when it comes to thermal resistance (the inverse of thermal conductivity), a higher value is better. The XR range contains the thickest boards (110mm, 120mm, 130mm, 140mm & 150mm).

Celotex CW4000 Cavity Wall Insulation Boards

Buildings lose over a third of their heat through walls; a pertinent fact in these times of rising bills and increasing environmental sensibility. A cavity wall - which separates the "inner leaf" blockwork from the "outer leaf" brickwork - can be a major culprit of heat escapism if it is not properly insulated.

Celotex CW4000 - where the "CW" stands for "Cavity Wall" - is specifically designed to address this problem. Whilst its composition is no different to that of the general application boards in the Celotex range, it is sized differently at 1200mm x 450mm, which allows it to fit easily between standard wall tie spacings.

This partial filling of the wall cavity captures heat and prevents it from escaping, helping to meet current building regulations and carbon reduction programmes.

Frequently Asked Celotex Insulation Board Questions

What Are the Benefits of Celotex Insulation Boards?

With nearly a century of experience creating thermal solutions, Celotex is firmly established as the go-to choice for PIR insulation boards. Like other typical PIR products, Celotex greatly reduces thermal bridging and increases heat retention. In addition to its low thermal conductivity of 0.022 W/mK, it also offers a variety of other benefits, such as:

What is Celotex's Fire Classification?

Celotex PIR Insulation Boards are tested to BS EN 13501-1 with a classification of E. Simply put, this means they are combustible and will contribute to the spread of fire. Because of this, the boards must not be used in the external facades of buildings over 18m in height in England and Wales or over 11m in height in Scotland.

When using Celotex - or any other type of insulation - it's important to ensure your installation meets all relevant national Building Regulations and guidance and local, national and other applicable standards relevant to your construction or application.

Is Celotex Waterproof?

Celotex PIR is a closed-cell, moisture-resistant insulation board, meaning it does not hold water or retain water. Whilst this attribute helps it to prevent water ingress - especially in the wall cavity where this can be a persistent problem - it does not mean that the board is suitable for external use. Celotex insulation boards should only be installed inside the building structure, and not on an external facade or inverted roof.

How to Install Celotex Boards?

There are lots of different methods for installing Celotex insulation, and much depends on the application in question.

For instance, when installing Celotex under floor screed, the boards can be loose laid, whereas installation between rafters requires the boards to be cut to size and friction fitted.

There is no "one-size-fits-all" answer on how to install Celotex insulation boards, but luckily we've created a helpful guide that explains the correct installation process for all relevant applications.

How to Cut Celotex Boards?

Inflated egos and Stanley knifes don't make a good combination, and many a finger has been lost by an overconfident DIYer thinking "that looks easy", before proceeding to cut the boards without due process or consideration.

First off, you should only undertake this task if you have industry-standard equipment. Before getting your tape measure out, you should don the appropriate protective clothing. This includes overalls, safety glasses and gloves.

Mark your intended cuts with a tape measure and pencil first, and make sure you have a dedicated construction space with more than enough room to manoeuvre.

Whilst Stanley knifes can be used to cut boards that are less than 50mm thick, a jigsaw or handsaw should be used for thicker boards.

A pro tip if using a handsaw is to place a length of timber - ideally 4x2, which (conveniently) you can buy on Materials Market - on the board along your cutting line. This will give you a flat edge to hold the saw in place and ensure that you don't deviate from the cutting line.