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External Wall Insulation

External wall insulation is a highly advanced insulation system that is applied to a house’s outside walls.Thesystem comprises of a layer of insulation, a layer of insulating render implanted with reinforcing mesh, followed by a final coat of render finished to the desired decorative effect.

External wall insulation is a particularly effective method of insulation for homes constructed from solid walls, referred to by some as ‘hard to treat’, because quite simply they have no cavity which can be filled with insulation. External wall insulation is applied to the outer face of a property’s walls improving the thermal efficiency of the walls significantly as well as giving the property a new and/or improved look.

Uninsulated solid walls lose even more heat than cavity walls, at a rate of around 45 per cent, meaning that for every £100 spent on heating an uninsulated solid wall property, something like £45 is escaping into the outside environment.

Insulating the walls of a solid wall property is one of the most effective home improvements that can be made, particularly with ever-increasing heating bills. The insulation will reduce your heating bills and make your home warm and cosy, as well as a host of other benefits.

External wall insulation is a relatively new product to the UK market (although is well-established in mainland Europe), in comparison to cavity wall insulation, but means there is now an insulation system for solid wall properties, meaning they can banish their ‘hard to treat’ label and benefit from reduced heating bills too.

Installing external wall insulation requires an advanced set of skills and expertise and Domestic and General were one of the first insulation installers to begin offering this product to their customers in 2009. Our expert crews now install external wall insulation at around two properties every week.

External wall insulation is also suitable for homes constructed from cavity walls, concrete, stone or steel and timber framed homes.

Want to know more about our External Wall Insulation? Download PDF here

Features and Benefits

The key benefits of external wall insulation are:

  • Reduces heat loss by up to 45 %
  • Could save you £45 for every £100 currently spent on your heating bill
  • Provides a high level of thermal efficiency making your home warm and cosy
  • Minimum disruption for the householder
  • No reduction of interior living spaces
  • Can help with condensation problem and black mould growth
  • Improves appearance of the building
  • Complements the existing building and colours
  • Has long term durability
  • Virtually maintenance free
  • BBA (British Board of Agrément) approved

The key features of external wall insulation are:

  • Available in over 300 colours
  • Choice of textured finishes
  • Crack resistant
  • Water repellent
  • Ten year guarantee
  • BBA (British Board of Agrément) approved

Product information

Manufacturers of external wall insulation systems require installers to be approved before they can install their products, because of the complex installation process which must be carried out by experience, skilled professionals. Domestic and General are approved to fit the following systems:

  • Permarock
  • Powerwall
  • Weber
  • Wall-Reform I/II

As part of the free home survey, Domestic and General will specify the best product for your particular property

Technical information

Heat will always flow from a warm area to a cold one, and in winter, when it is even colder outside, the heat will escape from your home into the surrounding air even quicker.

External wall insulation can significantly slow down the rate at which heat escapes, keeping as much of it inside your home as possible.

External wall insulation works by adding layers of material that only allow heat to pass through it very slowly. This reduces what is known as the ‘U value’ of the walls – the rate at which heat can flow through them. The lower the U value, the more slowly heat is lost – and the less money you will need to spend on fuel bill to keep your home warm.


Achievable U value (w/m²K)

9″ solid wall with 70mm external wall insulation


9″ solid wall with 60mm external wall insulation


Maximum U value of new build walls permitted


11” insulated brick block cavity


0.75 inch plywood


9″ uninsulated solid wall (typically built before the 1930s)


0.5 inch of hardboard


Single pane of glass



By installing 70mm of external wall insulation on your solid walls, you will feel an immediate effect as the U value reduces from around 2.1 to around 0.24.

Installing 60mm of external wall insulation means your solid walls can achieve a U value equivalent to that of new build walls built under today’s strict regulations regarding insulation. Installing a further 10mm means the U value of your solid walls can be even better than a new, modern home.

External wall insulation testimonial

“Last winter, being the coldest on record for some time, was a real test for the external wall insulation we had installed last summer. Of course it came through with flying colours. We’ve been kept nicely warm, with the central heating on its lowest setting. We haven’t had the bill yet for this period, but were expecting it to be much reduced. We’re snug and smug!”

Stu Allerton, Evesham, Worcestershire