Wall Insulation
Here at Celotex, we offer a variety of thermal insulation products suitable for wall applications.
U-value Calculator
Start your U-value calculationWall insulation is a material installed within the wall build-up or applied to wall surfaces. The Celotex range of polyisocyanurate (PIR) insulation boards contributes to the reduction of heat transfer between the interior and exterior of the building.
When installed properly, and in conjunction with roof and floor insulation to create a thermally efficient building envelope, wall insulation primarily helps prevent heat loss in winter, while also reducing the rate of heat gain during warmer periods.
Preventing heat transfer in a building could reduce energy demand and energy bills, while also keeping interiors at a more comfortable temperature for building occupants.
As well as the practical benefits, insulating external walls also contributes towards regulatory compliance, specifically the thermal performance requirements of Approved Document L (Conservation of Fuel and Power) and the upcoming Future Homes and Buildings Standards.
When used as thermal wall insulation, Celotex PIR rigid boards can be installed in wall cavities (cavity wall insulation), timber frame walls or solid walls (solid wall insulation).
The different types of wall constructions and wall insulation methods
In the UK, external walls are most commonly constructed from masonry. Depending on how the masonry wall is constructed, different insulation strategies will be required:
| Cavity walls | Most buildings constructed since the 1930s feature cavity walls, which consist of two layers of masonry separated by a gap. The insulation options for masonry cavity walls are partial-fill cavity wall insulation or full-fill cavity wall insulation. |
| Solid walls | Buildings constructed before the 1930s usually have solid walls consisting of a single layer of masonry and no cavity. Insulation can be positioned internally or externally to existing solid walls. Specialist advice should be sought in relation to the correct solution for the solid wall for each individual property. |
Not all walls are masonry; some are built using timber frames or metal frames. For these walls, insulation is usually installed between and with internally or externally to the frame elements.
Celotex wall insulation products
Celotex wall insulation is manufactured from PIR, a rigid foam insulation material. PIR is created through a chemical reaction that produces a closed-cell structure that traps low-conductivity blowing agents. This structure gives PIR boards their low thermal conductivity, which helps to reduce heat loss through external walls while also providing moisture resistance and dimensional stability.
PIR insulation has a typical density of around 30 kg/m³, making it lightweight. This can make it easy to transport, handle and position on site, supporting more consistent installation practices. Celotex Wall products are BBA-certified, and their low thermal conductivity contributes to helping designers, specifiers and installers create wall build-ups capable of meeting the energy efficiency requirements of Approved Document L.
| Thermaclass Cavity Wall 21 | A rigid PIR insulation designed for masonry full-fill or partial-fill cavity wall applications, provides a thermal conductivity of 0.021 W/m·K. |
| Celotex CW4000 | Tailored for partial-fill cavity walls, these boards come in various thicknesses (40mm to 100mm) and provides a thermal conductivity of 0.022 W/m·K. |
| Celotex PL4000 | Brings together both insulation and plasterboard creating a 2-in-1 solution to insulate and dry line walls at the same time, and they provide a thermal conductivity of 0.022 W/m·K. |
| Celotex TB4000 / GA4000 / XR4000 | PIR foam boards with a thermal conductivity of 0.022 W/m·K. They are multi-application boards be used alongside separate plasterboard layers which can be used for drylining and timber frame. |
Why insulate your walls?
Current energy costs1 and regulatory requirements highlight the need for developing energy-efficient buildings. Wall insulation reduces heat loss, helping to minimise the amount of energy required to keep the building warm. This can help to reduce heating bills and enhance occupant comfort.
Thermal wall insulation also helps meet legal requirements for energy efficiency. Approved Document L sets thermal performance standards in England, expressed as U-values. The required U-value applies to the complete wall build-up. Insulation is specified to ensure that, in combination with other building materials, the complete wall achieves the necessary U-values.
Volume 1 of Approved Document L (2021) sets a notional U-value for walls in new-build dwellings or extensions of 0.18 W/m²·K. The limiting value is 0.26 W/m²·K. For refurbishment projects, the improved U-value is 0.55 W/m²·K for cavity wall insulation and .30 W/m²·K for internal or external insulation on other walls.
For buildings other than dwellings, Volume 2 sets a limiting value of 0.26 W/m²·K for walls in new builds. For refurbishment projects, the improved U-value is 0.55 W/m²·K for cavity wall insulation and 0.30 W/m²·K for internal or external insulation on solid walls.
For Wales, Scotland and Northern Ireland, similar requirements exist:
- Wales: Approved Document L (Wales) – Conservation of fuel and power
- Scotland: Section 6 of the Scottish Building Standards – Conservation of Fuel and Power.
- Northern Ireland: Technical Booklet F – Conservation of Fuel and Power.
Celotex provides a range of resources to support designers, specifiers and installers. Try our online U-value calculator to specify suitable roof insulation for your next project.
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1https://commonslibrary.parliament.uk/research-briefings/cbp-9491/
https://www.ons.gov.uk/economy/economicoutputandproductivity/output/articles/theimpactofhigherenergycostsonukbusinesses/2021to2024
https://www.ofgem.gov.uk/information-consumers/energy-advice-households/energy-price-cap-explained
