Wall Insulation

External Wall Insulation

External wall insulation is without doubt the new 'buzz word' when it comes to the most effective energy saving measures for our homes and businesses, yet despite many people assuming it's a new process, it has actually been successfully used in the UK for almost 30 years.

Many local authorities, housing associations and private landlords have realised the positive environmental influence external wall insulation has to offer, especially when faced with the necessary renovations that many social housing developments require to bring them in line with thermal levels that are enforced by Building.

Changes in Government legislation such as Part L of the Building Regulations, The Code for Sustainable Homes and more recently the introduction of Governmental Initiatives such as CERT, CESP and the Green Deal have significantly increased the demand for truly efficient insulation systems which demand more innovative solutions for both new build and refurbishment of residential, commercial and public buildings.

It also prevents fibres being released into the air when being worked on during maintenance or changes to the fabric of the building.

Internal Wall Insulation

Internal wall insulation is ideal for period properties which are typically solid walled and very 'hard to heat'. The insulation is applied to the internal side of the wall which means that the external appearance is undisturbed. Internal wall insulation is one of the most effective ways of improving a building's Energy Performance Certificate (EPC) rating, reducing overall heat loss and making big savings on fuel bills.

Thermal comfort

An internal wall insulation system enables comfortable room temperatures to be achieved more quickly than with an external wall insulation system. Heating time periods can be reduced, particularly in intermittently heated buildings such as dwellings.

Air leakage

Existing buildings can suffer from excessive air leakage which, if not treated, can lead to high energy costs, occupant discomfort from draughts and external noise, as well as a reduction in indoor air quality. To ensure that upgrading of external walls is as effective as possible, it is very important to prevent air leakage through the structure or at least keep it to an absolute minimum. Air leakage can be between the interior and exterior, as well as between different elements of the building envelope. Air leakage through the masonry wall occurs through cracks and gaps where there is poor adhesion between the mortar and the masonry units, or diffusion through the masonry units themselves. Where the plaster has been removed and air leakage through the wall is thought to be excessive, it should be tackled before the internal insulation system is installed by applying a parge coat to the inner surface of the existing wall.


Interstitial condensation occurs when warm, moist air from inside a building penetrates into the fabric of a structure and meets a cold surface, where it cools, reducing its ability to carry water vapour and increasing the risk of condensation forming within the construction. Interstitial condensation does not occur within external walls that have been upgraded by the installation of internal wall insulation. This is due to the presence of a vapour control layer (vcl) on the warm side of the insulation which can take the form of foil backed plasterboard or a separate vcl such as a sheet of polyethylene. Surface condensation will not occur as the internal face of the insulation system is kept warm and above the dewpoint temperature by the presence of the thermal insulation behind it.

Thermal bridging

Thermal bridging can occur when the continuity of the insulation layer is broken, especially when a material with lower thermal resistance, such as timber and metal components are the bridging materials. Junctions between internal and external walls require treatment as do window and door jambs, sills and heads. Masonry separating walls can present the most significant thermal bridges and if left untreated can be the cause of additional heat loss and also increase the risk of surface condensation and mould forming. The effect on the separating wall can be reduced by returning the internal wall insulation up the separating wall (back into the room) by approximately 400mm, which is usually sufficient to minimise the effect of the thermal bridge.

Dampness in walls

The most common causes of dampness in solid masonry external walls are, penetrating damp (often caused by deterioration of the existing mortar, blocked gutters or faulty rainwater goods), rising damp and condensation, particularly surface condensation. Dampness can have a negative effect on the physical properties of the materials used to construct the wall. Best practice is to cure any damp problems before installing an internal insulation system to protect the building fabric from long term damage. For instance, missing or damaged render should be reinstated, faulty or missing flashings should be repaired or replaced and areas suffering from mortar deterioration should be repointed with a suitable mortar mix.