Material benefits

Mineral wool has long been the most popular choice amongst housebuilders, but there are other options which are as efficient in terms of both installation method and thermal performance. Bill Rumble, director of BillSave UK, which has been insulating homes for over 40 years, explains.

We all want to live in a warm, comfortable home, and certainly for those who have just invested their hard earned cash in a pristine new build property, they want to be able to put their feet up and enjoy all the creature comforts it has to offer. To make this possible, housebuilders need to ensure insulation has been installed to the required specification, within budget and build timelines.

Insulation is a requirement of building regulations and so it should be, given that a properly insulated home can cut CO2 emissions by up to 1,100g per year, not to mention reducing energy bills for the homeowner by up to £275 per year for a four bedroom detached home. The retrofit market for cavity wall insulation has nose dived somewhat in recent years but for new homes, energy efficiency is top of the agenda and with increasing authority. However, builders should be aware that a new, larger energy efficiency programme for existing homes has the potential to divert contractor capacity away from the new homes market when it launched in less than a year.

Mineral wool is by a long way the material of choice for cavity wall insulation. It has been for years. To briefly explain what it is and how it works, it’s made of mechanically granulated spun glass or rock wool, which has been treated with a binder or water repellent during the manufacturing process. It’s installed by trained technicians who ‘inject’ the material into the cavity via small holes strategically drilled in the outer leaf of the building. It’s quick to install, doesn’t hold up the build programme, is effective and covered by a 25 year guarantee through CIGA (Cavity Insulation Guarantee Agency) providing the work has been done by a registered installer.

In terms of performance, a U-value of around 0.27W/mK can be achieved depending on the properties of the product specified and the width of the cavity. It’s tried, tested, very cost effective and widely used so you might ask why you should bother considering anything else? Well, there is the school of thought that you shouldn’t bother mending anything that isn’t broken, but it materials are available and understand if they might be more suitable for your developments.

Expanded polystyrene (EPS) bead is a well known alternative to mineral wool and has many material benefits. It is less commonly used but is considered a premium option having a U-value of 0.23W/mK when filling a 100mm cavity. Installation can happen at any point after both leaves of the cavity wall have been built, right up to the roofline – meaning no stopping and starting in the construction process. On builds where slab insulation is used, as much as 12 per cent extra time can be wasted.

The beads themselves are about the size of a small pea and are combined with an adhesive when injected into the cavity to form a solid, breathable mass. The way this structure is formed means the gaps which occur naturally between the beads allow any water which makes its way through the outer wall of property, to drain away freely – so retaining thermal efficiency.

Over the years, the home insulation industry has seen a fair number of accusations that cavity wall insulation causes damp in new homes. It doesn’t. Water cannot travel across insulation and therefore insulation cannot cause damp in homes, despite what some ‘experts’ might say.

EPS beads also provide excellent coverage in the cavity. They flow easily to fill the space effectively, getting neatly into all the crevices around doors and windows where cold spots can occur – a criticism levelled at some other forms of insulation. Then, when the adhesive bond is formed, a consistent barrier for temperature regulation seamlessly wraps the entire house.

Looking at the bigger picture, both materials are viable options – as indeed is insulated board which some builders choose to use. Board is as thermally efficient as bead but its installation can slow down the construction process and it has site storage requirements too. Installation for bead and mineral wool can be carried out in all weathers, but for industry guarantees to be valid, work must be done by registered installers. It’s worth mentioning as well that all materials used for home insulation must comply with BBA (British Board of Agrément) requirements.

We’re starting to see a rise in the number of housebuilders increasing insulation levels and as consumers become more clued up generally on energy costs, their expectations are increasingly high when looking to buy a new build home. By considering the different materials available you can provide education to your customers, telling them what material has been used and the thermal performance/energy savings they may be able to enjoy.

What products will be available in five or 10 years’ time? Well the energy efficiency industry is growing and new technologies are being developed all the time. While it’s likely insulation for our homes will still be a requirement for many years to come, there are other applications creeping on to the market now which could dramatically improve the thermal performance of buildings – and perhaps change the practices we’ve relied on for decades.