External Wall Insulation
The Suitability Of EWI

External Wall Insulation is an extremely versatile way of making a building significantly more energy efficient and can be used on most construction types … but not all!

External Wall Insulation And Residential Refurbishment

EWI is one of the most effective solutions when it comes to the thermal upgrade of existing homes. Typically, these older properties will have a low EPC rating and were built with minimal focus of insulation and will typically fall into one of three categories of construction.

1: Solid Wall Construction

Solid wall construction was the preferred method of construction from throughout the 1800s and up until around 1920. As the name suggests, such houses were built to a minimum single brick thickness with no insulation.

You may often hear EWI referred to as solid wall insulation because it is an obvious solution to thermally improve such properties. With there being no form of cavity, insulation can only be retrofitted internally or externally. Internally installing insulation means a major upheaval and a loss of living space whereas insulating externally can be much more effective, be less intrusive with an added benefit of improving the appearance too.

The easiest way to tell if a property is built this way is to examine the brick pattern (if it’s not been coated or rendered over). If all the bricks are laid lengthways there’s likely to be a cavity. But if some are laid lengthways and some end to end this usually means solid wall.

Check the Landmark register to see If the property has an Energy Performance Certificate (EPC). If it does the construction type should be within this document.

2: Cavity Wall Construction

The traditional cavity wall construction that we associate with building today was first introduced into the UK after the first world war. The concept involves two independent walls built with a space between them and fastened together with wall ties.

Initially the cavities were narrow and the reasoning behind such a build was to reduce the passage of moisture through the walls in an effort to reduce damp and condensation rather than to incorporate insulation.

If you have cavity walls, in theory EWI could be put on top of it, but this would be unusual. In most cases cavity wall insulation is considered sufficient and you shouldn’t have any need to add a different type of insulation on top.

It therefore stands to reason that many properties built in this way may not need external wall insulation because the insulation can be injected into the existing cavity. That’s not the same in every case though – narrow cavities may be deemed as unsuitable to be insulated due to the risk of damp ingress and hence classed as “hard to treat” and requiring a more specialist upgrade.

3: Non-Traditional Construction

The building scene changed after the second world war to combat a significant housing shortage, a need to build quickly and an opportunity to utilise a workforce previously focussed on the war efforts.

New and quick ways of building houses evolved which we know as non-traditional construction and fall into one of four categories:

1: Timber frame construction – single storey timber frame panels which were typically externally clad with brickwork, tile hanging or render.

2: Metal frame construction – A load bearing frame of metal columns, joists and roof trusses and externally clad with brickwork, imitation brick or render.

3: Pre-cast concrete construction (PRC) – Load bearing concrete columns and external concrete cladding infill panels (often textured or decorated), all of which were cast off site before being fixed into place on site.

4: In-situ concrete construction – Steel reinforcements were added between form-work before a liquid concrete (often dense, or a clinker no-fines type) was poured in to create the framework on site. Single skin or cavity – depending on the external finish.

Park Homes

There is a fourth type of residential property which is not officially classified as a building but, instead, is described as a mobile home – that is the Park Home.

Whilst the Park Home makes up only a small proportion of UK dwellings they are an increasingly popular form of permanent living. Because of the nature of these properties, they can often benefit significantly from retrofitting with external wall insulation and there are a number of suitable EWI systems on the market specifically designed with Park Homes in mind.

EWI And Non-Residential Refurbishment

Depending on the construction there’s no reason why EWI can’t be used to thermally upgrade non-residential and commercial buildings.

It’s been widely used a wide variety of buildings in particular schools, colleges, universities, hospitals along with commercial office buildings etc.

Before Any EWI Refurbishment Specification

External wall insulation is extremely versatile and can be used on most types of substrates and construction. That said, it’s important to note that, whilst EWI may be generically suitable for a substrate it’s not right in every case. Therefore, it’s vital that each project is assessed by an INCA member EWI system manufacturer prior to specification. There may also be requirements for pull out tests to in order to specify the correct system fixings and wind loading calculations.

In the case of non-traditional constructed properties, whilst many non-trads can benefit significantly from EWI, again, it may not be an appropriate solution in every case and a structural survey should be undertaken prior to any such specification.

When EWI Can’t Be Used

Even if a property may appear suitable to benefit from an EWI upgrade there are times when it cannot be used:

    • EWI adds a thick, additional depth to external walls therefore where there is limitation in respect of access, boundaries and footpaths, then it may not be possible to use the system.
    • Certain substrates may not be of a quality good enough to mechanically fix an EWI system into (a fixing pull-out test will ascertain this).
    • You need to be aware of any local planning constraints on the use of the system and, in particular, any restrictions on specific finishes.
    • Specialist advice will be required in respect of any listed, historic and protected buildings.

External Wall Insulation
All You Need To Know

External Wall Insulation Systems And New Build

External wall insulation systems can be incorporated within and designed into the specification of any new build property, both residential and non-residential, in order to help achieve or surpass energy efficiency regulations and targets.

That said, there is one particular anomaly to be aware of and that is the fact that residential building which are constructed using a timber or steel frame are generally required (by the NHBC) to incorporate a drained cavity within the system. This means that an EWI system will need to be mounted on rails to allow for a minimum 15mm cavity (steel frame) or 20mm cavity (timber frame) to allow for the drainage of moisture.