Cavity Wall Insulation (CWI), Coastal Homes, Defects Investigations
Everyone should know by now, the outer leaf of any masonry cavity wall construction is not watertight!
Water will inevitably penetrate the outer leaf of cavity walls in sheltered and moderate exposure regions during prolonged periods of wind driven rain, and also in relatively short periods in severe and very severe exposure regions including coastal areas.
Complete filling of a wall cavity with standard insulation can increase the risk of rain water penetration into the inner leaf of the wall: the type of cavity wall insulation measure chosen and the exposure of the site should therefore be carefully assessed.
Homes in much of Scotland, Wales and South West England down to Cornwall are affected by more severe weather conditions (see Fig 1. Wind Driven Rain Exposure Map) than the rest of Britain and are at greater risk of rain water penetration. This exposure map is important when considering what type of cavity wall insulation measure to use.
Fig 1. Wind Driven Rain Exposure Map
When selecting a cavity wall insulation measure for coastal locations it is imperative that the requirements of the relevant independent third party UKAS accredited product certification
(for example, British Board of Agreement (BBA) are strictly adhered to. Standards of workmanship and site supervision are critical as there will be no residual cavity to prevent rain penetration to the inner leaf.
An assessment of the wind-driven rain exposure risk is critical and should be regarded as a necessary and worthwhile first step in selecting the appropriate cavity wall insulation measure for use in coastal conditions.
Extreme care is required when considering any retrofit full fill cavity wall insulation measure in coastal locations as the wrong choice can create major problems of wind driven rain penetration.
Fig 1 – Wall Tie Corrosion
Fig 2 – Cracking and bulging of brickwork
Coastal (salt laden driving rain) environmental conditions may cause premature corrosion of the wall ties and will be exacerbated by damp, wet or saturated cavity wall insulation and may lead to cracking and bulging of the outer leaf of brickwork and consequent catastrophic brickwork detachment and wall collapse.
When determining the potential risk, the most exposed part should be given particular attention as this may affect the choice of appropriate cavity wall insulation measure for the whole of the building.
A good knowledge of local construction methods, detailing and terrain is essential and may prove areas on the map marked as moderate or sheltered in Fig 1 are in fact subject to severe conditions and the chosen cavity wall insulation measure should reflect a protective approach.
The following factors affect the wind driven rain resistance of the outer leaf of the cavity wall:
mortar joint profile and finish
architectural features and local practice
presence of applied external surface finishes
quality of workmanship to be achieved on site
It should be noted that for fully filled cavities where local conditions accentuate wind effects such as coastal locations, the exposure rating must be increased by one.
If you have had cavity wall insulation (CWI) carried out on your home which has caused cracking or bulging of the outer leaf of brickwork, or internal damp, black mould, etc., and you require the assistance of a chartered building engineer please click here to contact us