Internal wall insulation – why insulate on the inside?

The winter snow offers a rare opportunity to see effects of poorly insulating homes. Take any row of homes and look for the ones with no snow on the roof. All that wasted heat is money down the drain (or through the roof in this case). Sadly, this only works for roofs and doesn’t help to reveal one of the other major causes of heat loss – uninsulated walls.

According to the latest Government statistics, around two thirds of cavity-walled dwellings are now insulated. However, just 8% of the UK’s 8.5 million solid walled homes have any wall insulation. Many of these homes were constructed at a time when energy efficiency wasn’t a consideration. This makes them inefficient and costly to heat.

This extra cost is bad news for any homeowner but it’s made worse by the fact that around 45% of all fuel-poor households live in solid walled or hard-to-treat dwellings. With a University College London study estimating that 9,000 people died in England and Wales last winter due to cold homes, improving the thermal performance of these properties is a real life and death matter.

On a much wider scale, the UK is committed to reducing its carbon emissions 80% on 1990 levels by 2050. Many of the solid wall properties will still be standing by then so improving their energy performance is crucial. What are the options for insulating a solid wall?

External Wall Insulation (EWI)

As you might have guessed, in EWI applications the insulation is fitted on the outside of the existing external walls (typically as part of a cladding or render system). EWI applications are a relatively straightforward means of insulating a solid walled property. There are, however, some scenarios where it may not be possible or desirable to use this approach.  The most common reason for this is when the property is located within a conservation area.

There are thousands of conservation areas across Britain, each with its own planning restrictions. These restrictions, contained within article 4 directions from the local planning authority, usually prevent significant changes to the exterior of properties.

Homeowners living outside of conservation zones may also simply wish to keep the original aesthetic of their homes. In these cases, the alternative is to fit insulation on the internal face of the external walls.

Internal Wall Insulation (IWI)

IWI applications are usually accomplished by stripping back walls and fitting rigid insulation boards. In addition to avoiding external changes to a property, IWI applications can also make homes more responsive to heating. This is because the heat is retained directly within the room, rather than being stored in the walls (which gives longer heat retention but also takes longer to heat up). As such, it can provide a more effective solution for heating individual rooms. This may be helpful for people living in fuel poverty, who can only afford to heat the room they are occupying.

Obviously, IWI applications will have an impact on living space within the property. This makes the lambda value of the insulation a key consideration. Insulation boards with a lower lambda value can achieve the required thermal performance with reduced product thickness – maximising internal space (you can read more about lambda values in Linzi Hobbs’ blog).

In the next blog in this series we’ll take a detailed look at how lambda values can affect construction thicknesses within IWI applications.

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