Cavity wall insulation would seem to make a lot of sense. Uninsulated homes are lose approximately a third of all their heat through the walls. What makes this worse is that heat will naturally always flow from a warm area to a cold area – so it will travel from the inside to the outside of a home.
This isn’t much use to a homeowner who wants a nice, warm house! Even worse than that, of course, is the fact that this issue is even more of a problem during the colder months of the year – when you want a warm house the most. This is because, the colder it is outside, the quicker the heat will travel outside. So, on the face it cavity wall insulation is a no-brainer, especially as government grants have been available in recent years to cover the cost.
But, there is a snag, cavity wall insulation can cause damp! Cases are relatively rare, but cavity wall insulation damp problems can end up costing a lot more than the savings made on annual energy bills from having the insulation in the first place.
Some houses are more at risk than others
We often hear that damp is more common in older properties, which is generally true. A similar issue is true with cavity wall insulation too, in that most properties built since the 1990s, because of building regulations, will have wall insulation included. Generally, older homes are less likely to have been built with wall insulation included. However, with cavity wall insulation damp problems, the issue is less about the age of a property and more about where the house is in the country.
For weather monitoring purposes, the UK is categorised into 4 ‘exposure zones’. These categories assesses the areas of the UK that are most exposed to wind and rain. The four stages are:
- Very Severe.
Areas of the UK to the west, including Northern Ireland, Wales, the West Country, Cumbria and Western Scotland (with the exception of a few anomalies) tend to be categorised as 3. Severe and 4. Very Severe.
Properties located in these areas of the UK, and especially ones that are in an unsheltered position (with no protection from trees or other houses) are those that are most susceptible to cavity wall insulation damp problems.
The problem with cavity walls
Of course, this doesn’t mean that every house in western areas of the UK that lies in an unsheltered position will suffer from damp problems as a result of having cavity wall insulation. Cases are rare, and when it does occur it is often a combination of factors, such as cracks to brickwork or rendering that contributes to the damp damage.
But the essential problem is this. Cavity walls exist as a barrier against penetrating damp. It is the cavity – the gap in the wall – that allows moisture to evaporate before it comes into contact with the inner wall. But, if that cavity is filled with insulating material this means that it is no longer a cavity wall. Instead, it is a filled wall and the barrier against damp has gone. Indeed, one of the most common causes of penetrating damp is when cavities become blocked with debris or bits of broken bricks and mortar. Once the debris is cleared, the cavity can do its job once more. With insulation, the cavity is deliberately filled, but the result is the same.
The irony is that the first cavity masonry walls were built in properties on the western coasts of the UK and Ireland, as early as the nineteenth century, to provide extra protection and to prevent heavy rains from penetrating to the inner walls. But the practice gradually spread more widely across all regions of the UK.
Despite all this, cavity wall insulation damp problems are not particularly widespread. However, the potential problems that can arise should be a timely reminder to anyone considering having cavity wall insulation installed in their home. Professional advice should be sought and special care and consideration should be taken if the property lies in a ‘severe’ or ‘very severe’ risk area. The potential costs of treating damage caused by penetrating damp will quickly cancel out the energy savings of having cavity wall insulation in your home.