External Wall Insulation

EWI is designed as a system and therefore they are the sum of various component parts that have been tested to work together. Whilst foam and wood-based insulations may have a Euroclass fire rating of F or above and deemed to contribute to a fire or be easily flammable as a single element, when incorporated into a full system and tested in independent fire rigs, most of these systems will obtain an overall fire classification of B s3 d2 or higher. The European Fire Classification rating of B s3 d2 – B s1 d0 states that although the system contains combustible materials, overall, there is very limited risk to the contribution to a fire.

Click here to view IWCO21001 guidance on EN13501-1 Reaction to Fire Classification

Yes. there are systems that use mineral wool / stone wool as the insulation which generally have a The European Fire Classification rating of A2 s3 d2 or higher, therefore deemed as non-combustible.

Click here to view IWCO21001 guidance on EN13501-1 Reaction to Fire Classification.

EWI is very versatile and can be used on nearly every type of construction there is. Predominately used onto masonry, such as brickwork, new blockwork, over existing masonry and render in addition to timber and steel frame construction. The important thing to consider is that whilst solid wall insulation is generically suitable for many different substrates, each scheme should be assessed by the system manufacturer for suitability as there will also be requirements for pull out tests of the fixings to ensure that there is enough strength in the substrate as well as wind loading calculations. Some schemes may well require the specification of a drained system.

For non-traditional constructed properties, EWI can quite often offer a suitable solution, however it is recommended to seek structural advice first.

EWI is not the solution for all projects. Where there is limitation in the depth that the external wall can be installed, without encroaching onto boundaries and footpaths, then it may not be possible to use the system. Local planning can constrain the use of the system due to the requirement for specific finishes as well as the use on historic and protected buildings. 

Some substrates due to severe weathering may not be suitable for a standard EWI after pull out tests have been performed, however the use of a structural EWI system is usually accepted if this is the case.

New build residential timber and steel frame constructed buildings are generally required to have a drained cavity system by the insurance providers. This system is designed so that between the sheathing board onto the timber / steel frame and the insulation layer, there is a minimum 15mm (steel frame) and minimum 20mm (timber frame) clear cavity to enable any moisture to drain through a vented base track. These systems are generally created by using a rail or top-hat configuration with intumescent fire strips and fire barriers at compartment lines.

The use of EWI provides a high level of thermal enveloping and also increases the air tightness of the building. In new build construction the use of a ventilation system is specified as part of the package, however in retrofit this is not always possible. Going forward under the Building Regulations, both Part L – Conservation of fuel and power and Part F – Ventilation are being aligned for changes at the same time to reflect the importance of ventilation and air tightness in thermally efficient buildings. With retrofit it is important that the home occupier has a full understanding of the use of the property once EWI has been installed and that the opening of windows and good ventilation practice is important in maintaining a healthy indoor climate.

Nothing is maintenance free and your property is the same. Whilst many EWI systems are designed with low or minimal maintenance finishes, it is good practice to ensure that periodic checks are made on the system, detailing and junction points. Check with the EWI system manufacturer for the maintenance manuals and recommendations.

EWI is known as a cladding but most systems have a third-party independent certificate of assessment, such as BBA (www.bbacerts.co.uk), KIWA BDA (www.kiwa.com) or BRE (www.bregroup.com).  These independent certification assessments are designed to ensure that the systems meet the safety requirements and are fit for purpose for use in the United Kingdom.

Using the correctly specified system for the project, with fully trained and monitored installing companies will ensure the safety of the system meets the requirements of the scheme.

There is a wide range of variations in EWI systems, such as type and thickness of insulation, type of system, different finishes and colours, in addition to the complexity of the scheme installation itself. Costs obviously rise on single schemes to that of multiple properties or projects with greater areas to be insulated. As a guideline £65-£95 per square metre could be considered for a thin coat finish, such as silicone, silicate or acrylic and this would increase up to circa £120 per square metre for a brick slip system.

Traditionally the finishes for an EWI system are split into the following categories:

• Thin Coat Finishes – This includes silicone, silicate, acrylic, mineral and siloxane to name a few and these render finishes are all generally applied to their grain thickness which is usually around 1-3mm. The colour is in the product itself, however with the mineral finishes it may be necessary to finish with a low maintenance equalising paint.
• Thick Coat Finishes – This range would usually in a dash finish such as dry dash or wet dash as well as a brick render finish, which is created by cutting the brick design into the render coats.
• Brick Slip Finishes – This requires the use of either cut brick slips or flexible brick slips which are embedded into the render basecoats or inserted into an insulated framework.
• Stone Effect Finishes – In a rapidly developing industry we now have stone effect finishes which can be a created by using specialist finishing techniques to thin or thick coat finishes or by utilising flexible lightweight stone slips.

EWI can meet any requirement for the thermal requirements for an envelope. Most EWI systems have third party assessment approvals for using up to 250mm of mineral wool insulation and in some case up to 400mm of EPS insulation. These thicknesses of insulation will achieve an approximate U-Value of 0.13W/m²K and 0.09W/m²K respectively, but variations can be expected based upon the exact constructional build and system used.

Heat will try to escape, and where you a have thermal envelope then attention to small areas which do not have insulation or a reduced amount of insulation becomes important, as these are known as thermal bypass or cold bridging. Too many thermal bypass areas in a property can reduce the overall as built thermal performance of the EWI system; however, sometimes some form of thermal bypass cannot be eliminated.

Click here to view a range of thermal bridging risk details taken from External Wall Insulation Specification for Weathering and Thermal Bridge Control – Guide: August 2024

The installation of EWI systems should be by the system designer’s approved and trained installers, and most EWI system designers will be able to provide a list of their installers for a scheme.

The general rule of thumb for installing an EWI system is 5°C and above and below 30°C, however each system designer should provide their own specification for this. There are Thin Coat finishes which can be used during the winter months where these types of finishes can be susceptible to frost and rain wash-offs.

No. The answer is easy but the identification of what does require replacing and what does not is not so easy. Currently the requirement is that for an EWI system, if the top floor level is over 11 metres, the system should be a non-combustible system. If the top floor height is below 11 metres then the application of a system with very limited contribution to fire is fine, as long as the specification for the fire barriers has been specified correctly and installed to that specification. 

If the system has not been specified correctly or installed correctly then the requirements under the EWS1 forms will result in the recommendation for the removal of the system.

INCA – Trade Association for the EWI industry

INCA Website >

INCA Technical Information >

SWIGA – Solid Wall Insulation Guarantee Agency

SWIGA Website >