Exposure zones and solid wall insulation in Cornwall

30 April 2016 Kingspan Insulation UK
Exposure zones and solid wall insulation in Cornwall

We’ve talked in the past about exposure zones and how they affect cavity wall insulation, but they also apply to solid wall insulation and in this blog post we are looking at properties in Cornwall as examples.

Cornwall has a large percentage of houses with solid external walls, the majority of which are constructed from granite, allowing us to go into specific details to illustrate the issues involved. Most of the points made will also apply to other solid wall constructions.

Cornwall is renowned for its distinctive stone cottages, mostly built using the granite found in the local quarries for hundreds of years. But in order for these properties to be heated efficiently (and therefore as cheaply possible), the correct insulation is needed – an issue which was probably not considered when many of these houses were built.

On its own a typical granite wall with no insulation will have a U-value of 3.1 W/m·K (approximately – depending on thickness) and building regulations for refurbishments suggests that this should be no greater than 0.3 W/m·K. Insulation can be added to this to achieve this – either to the inside or the outside of the wall but before choosing the type of insulation the Exposure Zone has to be taken into consideration.

Exposure zones

The UK is divided up into four different exposure zones, depending on the risk of exposure from wind driven, penetrating rain. The majority of Cornwall is the area of the UK which has a very severe risk of exposure to wind driven rain; exposure zone 4 where there is a risk of approximately 100 or more litres/m2 per spell of wind driven rain. This does affect the choices of insulation. If a building is in a particularly sheltered area, this may be reduced to exposure zone 3, but the majority of buildings will be in Exposure Zone 4. This means that there may be restrictions on the type of insulation that can be used for internal wall insulation but will not affect the choice of external wall insulation. We always recommend contacting our technical department to carry our an exposure risk assessment to examine the risk of damp or rain penetrating the masonry and the suitability of your chosen insulation solution for your project.

External Wall Insulation (EWI)

Adding insulation, such as Kingspan Kooltherm K5, to the outside of a property will easily help achieve the required U-Value. Adding the insulation in this way will enable the granite walls of the building to act as a heat store, retaining the heat and pushing it back into the room. This is particularly useful if the property is heated all day but may mean that the rooms take longer to reach the required temperature. The other benefit is that it does not reduce the internal size of the rooms. Insulating the outside of the walls will not be possible in all circumstances. If the building is listed, or if there are planning restrictions then it may not be possible to change the outside appearance. There may not be sufficient outside space to add in the insulation if the property is adjacent to a pavement or road, or if the property forms part of a terrace then it would look odd adding external insulation to one property and not the entire row.

Internal Wall Insulation (IWI)

Insulating inside the walls will mean that the room heats up quicker, which is a preferable solution if the space is not going to be heated all the time. It will slightly reduce the inside space in the rooms but using a premium performance insulation such as Kingspan’s Kooltherm K118 Insulated Plasterboard will ensure that the space lost will be kept to a minimum. Because Cornwall is in exposure zone 4 we would recommend using an insulated plasterboard which can be mechanically fixed on to metal furrings or timber battens to minimise the risk from damp penetration. Again check with our technical department for suitability.


A mixture of both methods may be possible to provide a hybrid solution. For example it may be possible to use internal insulation on the front of the property where there may be planning restrictions but adding external wall insulation to the sides and rear of the property. If using this approach then you need to make sure that the systems overlap to keep thermal bridges to a minimum.

No matter which method is chosen, adding insulation to a solid wall will help keep the property warm and cosy.

If you need further information please look at our website or contact our Technical Department for specific queries. 

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