Fixing a thermal insulation layer to the exterior of a building is an extremely potent method of generally up-grading the wall’s thermal performance and the building’s habitability. Almost invariably internal condensation problems are alleviated. As a result of the increased thermal stability, comfort levels together with the external appearance are both markedly improved. Whole estates of sub-standard dwellings can undergo a remarkable face-lift with all its consequent social and political benefits. Finally, the whole building obtains an additional structural protection which may significantly increase its expected life and value.
For external wall insulation to be successful a number of physical criteria have to be satisfied if the main object of heat retention is to be effective.
Insulation materials lose their heat retaining properties if they become moist. Resistance to rainwater penetration and reduction of the risk of interstitial condensation are also important physical criteria. In order to satisfy the former condition the surface should be waterproof and crack free, since cracks of above 0.5mm will admit some moisture.
Weatherproofing should not be achieved with a vapour impermeable layer since the building must still continue to breathe in the traditional manner. Although water is unlikely to penetrate the insulation from inside the building, water vapour may do so. This is a potentially unwelcome phenomenon as it is difficult to alter the position of the dew point in an externally insulated wall. This invariably occurs at the interfaces of differing materials.
By definition insulation is usually a fairly soft material and generally speaking the more open it is the better its insulation properties. A good quality insulation needs a tough skin to protect it against the usual casual impacts and even malicious damage or vandalism. This requires that both the reinforcing layer and fixing systems be robust and sufficiently strong to deter damage and carry the weight of the protective skin.
To appeal to the maximum number of Clients, Designers and Specifiers, any system offered should be capable of accepting a wide variety of finishes. That is not as easy as it seems since putting (say) roughcast render on the top surface of insulation material is not the same as applying it onto the surface of ordinary brick, block or masonry.
Insulation immediately behind rendered finishes causes surface temperatures and other stresses to build up inside the whole system and to a much greater extent than if it were able to make use of the heat sink available in any other masonry substrate. The ability of masonry walls to retain heat also provides frost protection to the uninsulated external finish. Where external insulation is applied, this heat sink protection is significantly reduced and the final finish has to be of sufficient quality and strength to withstand the rigours of thermal shock and water penetration.
All of these properties implies that certification and testing is an essential requirement to any system preferably through the British Board of Agrement or similar.
Additional advantages and considerations in the use of external wall insulation includes the following :-
“Incidental” reduction in transmitted sound into the building.
Possible availability of financial Government and Local Authority grants via energy providers
Carbon Dioxide emission reduction.
Reduced use of fossil fuels.
Low taxes (VAT) on energy.
Improved Thermal Performance Certification.