How to… Make cavity walls energy-efficient

These days, all New buildings are expected to be energy-efficient – and pressure is growing for this trend to continue. Indeed, the latest Building Regulations' approved document on the conservation of fuel and power in dwellings, which came into effect last year, brought about a further improvement in the minimum standard of thermal insulation.

The benefit of these changes should be a reduction in the consumption of energy required to keep buildings warm – which in turn should lead to lower heating costs for the occupier. And, in using less energy, less carbon will be emitted from power stations, benefiting the environment.

Ins and outs of insulation
Improving thermal wall insulation introduces a number of challenges for designers and installers. They have to resolve the demands of wall stability, resistance to water penetration and integrity of thermal insulation.

Typical modern wall construction in the UK includes a cavity to prevent water penetrating to the inside of the house. Brick or block walls, however, do not have good insulation properties. An insulation layer may be included as part of the wall construction to meet thermal performance levels. "Partial fill insulation" – where a cavity is maintained and the insulation layer is included in the cavity – is a common solution.

Details, details
One option to meet the thermal insulation requirements is to introduce a thicker layer of insulation. There are consequences for the design:

a wider overall wall cavity is needed to ensure a 5 cm wide space is maintained between the insulation and the wall to protect the internal wall from moisture

longer wall ties are required with a wider cavity, to ensure a minimum 5 cm embedment into the brick and block work and link the inner and outer parts of the wall to maintain wall stability

wall ties should be spaced to fully support the insulation panels; this may entail 60 cm horizontal spacing which isn't staggered – this is a more severe requirement for cavity walls without partial fill insulation

wall ties should also be fitted with purpose-designed retaining clips to hold the insulation panels against the inner wall and an "eccentric" drip to shed water within the cavity.

Fix problems before they happen
There are a host of on-site issues that could lead to premature failure or ineffective wall construction, such as:

gaps between adjacent partial fill insulation boards, which compromise the insulation properties of the wall

wall ties tilted to slope back towards the inner wall, which leads moisture to the inner wall and risks internal water stains

partial fill insulation not held tightly against the inner wall, leading moisture to the inner wall and reducing the effectiveness of the insulation.

Building LifePlans is a sister company of Building Performance Group that offers latent defects insurance and risk management services. Feedback from Building LifePlans shows that many failures are a result of not following published guidance codes and standards.

So why not head off trouble at the pass by doing things properly the first time? A building that's energy-efficient today will save energy and money for years to come.

For more information on risk management, contact Jeff Maxted, head of risk management services, on 020 7204 2466 or email: jeff.maxted@buildinglifeplans.com