Celotex Isover

Insulation for Solid Walls

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For homeowners looking to improve the performance of their solid masonry walled properties - perhaps to achieve compliance with modern building regulations, or perhaps to go beyond that and meet a retrofit standard such as EnerPhit - adding more insulation material to the outer face of the wall is sometimes not possible.

Using an insulated plasterboard product, either adhered to the masonry inner surface or mechanically fixed to timber battens that are themselves fixed to the masonry inner surface, represents a potential option for improving the thermal efficiency of the wall without affecting its external appearance. The lightweight polyisocyanurate (PIR) component of the Celotex PL4000 insulated plasterboard range means they are easy to handle, and their thermal efficiency means overall laminate thicknesses can be kept to a minimum, reducing lost floor space.

As part of a holistic approach to upgrading you will also want to consider building fabric, airtightness and controlled ventilation along with improvements in thermal performance. The composite facing on the insulation board, behind the plasterboard layer, can form part of the air and vapour control layer when the tapered edge plasterboards are taped and jointed.

Alternatively, the solid masonry wall can have timber battens or studwork mechanically fixed to it and the stud zone insulated with a glass mineral wool roll or slab prior to being finished with a suitable air and vapour control layer (AVCL) and plasterboard. In cases where the solid masonry wall is narrower than 200mm the timber studwork may need to be stood-off the solid masonry wall by 50mm rather than being fixed directly to the wall.

In all cases specialist advice should be sought in relation to the correct solution for the solid wall for each individual property, especially in relation to moisture movement and the potential of condensation. Breathable membranes and dynamic hygrothermal calculations may need to be considered.

Key Considerations

When using Celotex or ISOVER products, you need to satisfy yourself that use of the product meets all relevant national Building Regulations and guidance as well as local, national and other applicable standards relevant for your construction or application, including requirements in relation to fire and applicable height restrictions. In addition to the product datasheet, please refer to the following product documents:

Celotex products should not be used in the external walls of buildings over 18 metres in height (England and Wales) or 11 metres in height (Scotland). Recent changes to Building Regulations mean that only non-combustible insulation or insulation of limited combustibility can be used in buildings of that height.

The building detail is for illustrative purposes only. It does not constitute advice and should not be relied upon.


Insulation products
Product Name Thickness Range Sizes Lambda
Celotex TB4000 20-40mm Width 1200mm, Length 2400mm 0.022 W/m.K
Celotex GA4000 50-100mm Width 1200mm, Length 2400mm 0.022 W/m.K
Celotex PL4000 25-65mm (+12.5mm Plasterboard) Width 1200mm, Length 2400mm 0.022 W/m.K
ISOVER Steel Frame Infill Batt 50-100mm Width 600mm, Length 1200mm 0.036 W/m.K
ISOVER Unislab 50-140mm Width 400mm or 600mm, Length 1200mm 0.036 W/m.K