Most masonry-built houses have an inner and outer skin wall tied together with a cavity void between the layers. Ventilated wall cavities were introduced to enable moisture from driving rain to escape before passing through the inner skin and into the home. It is also important to allow the inner skin wall to breathe and let moisture from within the home, escape accordingly. Certain types of cavity wall insulation such as injected polyurethane, can prevent moisture from passing through the inner skin wall which is why additional ventilation may be required.
Fundamentally, cavity wall insulation should be high on your agenda when looking to make your home more energy efficient. When the appropriate types of insulation are used, there should be no concerns for damp and mould to form within the home. Historically, during the 1990’s and 2000’s mineral wool was blown into cavity voids to provide thermal insulation; however, this type of insulation tends to shrink, slip and degrade within the wall cavity to create cold spots where damp can thrive. We come across many homes where mineral wool insulation has failed over time and requires extraction from the cavity.
As the quality of insulation materials has developed over time, there are two recommended modern methods to insulate a cavity wall. EPS Resin Bonded Beads are a cost-effective way to fill the cavity void by blowing them into place through drill holes in the external wall. The resin bonding of the beads helps to hold them together into a seamless, monolithic insulation layer whilst the coating on each individual bead enables driving rain and moisture to flow down through the material and escape at Damp Proof Course level. EPS Resin Bonded Beads are now one of the most popular materials used to insulate cavity walls and are expected to last for 25 Years and beyond.
The most thermally efficient insulation material per inch, is Polyurethane Closed Cell Injection Foam. This is a liquid version of PIR Insulation like Celotex and it’s injected as a viscous liquid into the cavity before rising gradually like a loaf of bread to seamlessly fill the entire void. Offering good structural performance and a barrier against driving rain and even flood water, Closed Cell Injection foam is a robust system that will last the life of the walls. As a premium insulation system, Closed Cell Injection Foam is around 35% more expensive than EPS Resin Bonded Beads but it’s worth considering a high-performance material for insulating cavity walls given that it’s a retrofit installation that you should only expect to have to do once during the life of the property.
In conclusion, cavity wall insulation will help to save between 15-35% on your heating costs when installed correctly. This depends on the type of insulation used and whether other areas of your property are already insulated. Heat will always try to escape your home through the path of least resistance, therefore, if you have adequate loft insulation but nothing in the walls, you might expect to lose more heat in this in area. To help improve your EPC level, reduce energy costs, and live sustainably, cavity wall insulation should be a primary investment into your home.