EWI is used to augment the thermal insulation performance of existing external walls by improving their thermal resistance value.

EWI is the preferred method of insulating a solid wall property, refurbishing non-traditional housing or that which requires external repair work, or to improve a building that has severe heating problems. It should only be applied to walls that do not suffer from pre-existing rising damp.

An EWI ‘system’ comprises an insulation layer fixed to the outside of the wall and covered with a protective and decorative render, brick effect or cladding finish.

The insulation layer can be expanded polystyrene (EPS), phenolic foam or polyurethane foam boards; or mineral wool (MW) batts. A render finish is a cement based, mineral or synthetic base coat reinforced with mesh; and over-coated with a primer. A top coat render is then applied and finished to a smooth, textured, painted or pebble-dashed finish. Dry cladding includes timber boards and aluminium panels; whereas brick effect finishes can be stone or clay tiles or brick slips.

Benefits of EWI include ​improved protection of external walls against rain penetration to the inside, reduced heat loss, reduced CO2 emissions and lower heating/energy bills, reduced draughts through walls and around window frames, improved sound resistance and an enhanced appearance (i.e greater “kerb appeal”).

Warmer walls reduce the risk of condensation on internal wall surfaces and help with damp problems; and increase a property’s energy efficiency (EPC) rating.

EWI will change the external appearance of a property. In most cases planning permission or consent from local council planning authority is needed before undertaking any work. EWI must be installed in accordance with the national Building Regulations. The reaction to fire classification of EWI (which is largely determined by the materials selected for use) may restrict its use in terms of location and height.

Prior to installation each property to be treated must be surveyed to establish suitability, as incorrect treatment can be detrimental the building fabric in the longer term. Where appropriate, a condensation risk analysis must be undertaken by a competent specialist. If the ‘dew point’ will occur between the wall and the insulation, or within the insulation itself, a vapour barrier must be included between the wall and the insulation.

The project specific choice of EWI is determined by the existing wall type. For example, solid stone walls may be breathable and allow moisture to penetrate a little and be evaporated away. Using a breathable MW insulation with a breathable non-acrylic external render or other finish will allow the wall to maintain its breathability.

Solid brick walls may be impermeable to moisture penetration and non-breathable. Any rigid foam insulation will suit such a wall.

Window trickle vents and extract fans in high humidity areas need to be installed to meet room space ventilation requirements.

As with all property fabric related work, a high standard of installation is required. Poor detailing e.g. around eaves, allows water to pass behind the insulation where it can become trapped and cause hidden damage to the property in the longer term.

Simon Lloyd is Technical Project Manager working for Kiwa Building Products on construction Product and Systems for 3rd party certification with regard to fitness for purpose.

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High performance webertherm XM External Wall Insulation (EWI) by Saint-Gobain Weber has been specified for the showcase Skyline regeneration scheme in Stevenage, Hertfordshire. This landmark building, once occupied by HM Land Registry and known as Brickdale House, has been carefully re-designed and converted by Chase New Homes, of Waltham Abbey, Essex. A variety of 150 contemporary, well-proportioned residential suites and apartments designed to appeal to first time buyers and investors has been created. Skyline is superbly positioned in the town, close to all shopping and leisure facilities, and just two minutes from the main line station to London’s Kings Cross.

Designed by architects Corstorphine & Wright, Stourbridge, for Chase New Homes, the refurbishment work has dramatically transformed the building with major internal and external improvements. Visually, aesthetics have changed for the better with the application of webertherm XM, a lightweight render protected external wall insulation system, which has created a striking and stylish appearance that has modernised the building from a grey and tired-looking mid-1900s commercial block. Weber’s EWI has also improved the thermal performance of the building to a comfortable and sustainable 0.27W/m2K U-value. The application of webertherm XM EWI was carried out by Build-Therm Services of St Albans, Hertfordshire, a company familiar with Weber’s EWI systems.

The application of webertherm XM EWI system provides efficient thermal insulation for this refurbishment with the render coat and surface finish delivering excellent water shedding capacity to protect the building fabric. The system specified 120mm mineral fibre insulation applied to Cement Particle Boards fixed to a MetSec frame construction. This has been protectively covered with a 6mm meshcloth reinforced coat of weberend LAC, a polymer-modified, cement-based mortar. This is applied in two passes before being decoratively finished with webersil TF to achieve a textured render finish in Iced Blue offering a bright and welcome change to the streetscape.

Julia Wathen, of Build-Therm Services Limited, St Albans, Hertfordshire, was operations manager on the Skyline project “We really enjoy working with the Weber EWI systems as the materials are always of very high quality. We had 1000m² to apply and the result is a crisp, bright finish which adds to the modern style of the apartments.”

Since 2005 Chase New Homes, an independent and entrepreneurial company, has successfully developed new homes, building a reputation for excellence. Skyline is another showcase in the company’s varied portfolio which ranges from studio suites to £4m mansions. The company has several projects underway for a further 800 homes in Central London and throughout the Home Counties.

For more information about this product, or for technical support including award winning training courses, please contact Saint-Gobain Weber on 08703 330 070, or visit
A free download of the Weber App for iPhone and iPad users is also available from iTunes and from Google Play for Android smartphones and tablet users. Follow Saint-Gobain Weber on Twitter @SGWeberUK for the latest company news and updates.

The Insulated Render and Cladding Association (INCA) Awards 2018, which showcase exceptional projects and special achievements in external wall insulation (EWI), are open for entries. The INCA Awards celebrate accomplishments in technical standards, energy efficiency, carbon reduction and tackling fuel poverty through cutting-edge EWI.

INCA is excited to announce two new awards for 2018. The Heritage Award will recognise projects that have stood the test of time, to promote the benefits of installing EWI as a long-term solution. Also being introduced is the Component Supplier of the Year Award. Voted for by Systems Designers, this recognises the important contribution that component suppliers make in EWI.

There are two main project categories, New Build and Refurbishment. Regardless of the project, from high-rise and low-rise to residential or zoological, there are plenty of opportunities to enter. Other categories include awards for Installer of the Year, Innovation, Training and Outstanding Achievement.

Winners will be selected by an independent judging panel of leading industry experts who assess projects on thermal performance, technical difficulty, aesthetics and workmanship. They will be looking for individuals and companies that have proven outstanding ability.

INCA Executive Chairman Mitch Gee, said “I am particularly excited about the Awards in 2018 with the introduction of our Heritage category, which will help promote the long-term durability and benefits of external wall insulation. Those who have been in the industry for 10 years or more should be able to point us to some projects which demonstrate the exceptional track record our products and services have.”

INCA may sub-divide projects in the New Build and Refurbishment categories, according to the number of entries received. The closing date for entries is Friday 13 April at 5:00pm.

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