Cavity Wall Insulation History
Cavity walls were first introduced on the wind driven rain exposed West and Southwestern coastal areas of the UK in the latter part of the nineteenth century, to prevent wind driven rainfall from penetrating through the solid masonry walls of homes. The traditional cavity wall is built with two skins of brickwork, an inner and an outer leaf separated by a void or air gap (the cavity). These two skins are usually tied together with metal wall ties or brick ties at specific intervals to provide stability to the wall structure. The latter brick or stone ties can allow penetrating dampness and cold bridging across the cavity that can be further exacerbated by retro fitting insulation.
Cavity walls gradually gained popularity and became the preferred method of construction for external load bearing walls across the whole of the UK, because not only did they prevent wind driven rainfall from reaching the internal leaf of the wall, it was also realised that the air gap (cavity) provided a degree of thermal insulation and stopped heat loss through the wall by conduction. In addition the cavity provided ventilation around joist ends and to the subfloor which reduced the build up of dampness from condensation.
Since the 1970’s this insulation quality was further enhanced by the use of lightweight aerated blocks, rather than brick to build the inner leaf of the cavity wall, The primary reason for building cavity walls has always been to keep penetrating wind driven rain, out, a principle that seems to have almost been forgotten in our modern world. To our detriment! You will hear older builders and construction professionals state that ‘that cavity is there for a reason’.
Cavity Wall Insulation Standards
In the 1980’s the UK Building Regulations introduced requirements for new houses to be built with increasing levels of insulation materials within the cavity. Since this time, consecutive governments have encouraged home owners to insulate their homes to save energy and its effect upon our environment.
Building Regulations insist upon cavity wall insulation systems in new build properties. These systems include a clear cavity in addition to the insulation to allow any wind driven rainfall that permeates through the outer leaf to trickle down the internal face of the outer leaf of the cavity wall and this residual cavity prevents the moisture from wetting the insulation and the inner leaf of the cavity.
Successive government initiatives have encouraged the owners of older properties that have cavity walls, to fit cavity wall insulation and there have been grant and incentives made available to the homeowners under various schemes.
Retrofit cavity wall insulation is full fill and is in direct contact with the wet outer leaf of the cavity wall and this is where serious problems can start to occur.
Despite the constant insistence by manufacturers/system designers, the BBA and installers that cavity wall insulation cannot allow rainwater to cross the cavity, the Building Research Establishment has found that it can.
Their findings have been published in BRE Good Building Guide 44: part 2: “Insulating masonry cavity walls – principal risks and guidance”
This states, “There can be an increased risk of rain penetration if a cavity is fully filled with insulation, ie moisture is able to transfer from the outer to the inner leaves resulting in areas of dampness on internal finishes.
Rainwater, under certain driving rain conditions, can penetrate the outer leaf of masonry leading to wetting of the cavity insulation and subsequently cause damage to internal finishes.
Problems with Cavity Wall Insulation
Even though there can be benefits to having cavity wall insulation, everyday increasing numbers of people are discovering that issues with damp, condensation and damage to their homes is caused by cavity wall insulation.
Damp, condensation and damage is most commonly caused by the incorrect installation of cavity wall insulation or having cavity wall insulation installed in a property when it’s simply not suitable for the property.