Denise Freeman, head of marketing, Sto discusses how wsing External Wall Insulation Systems can address the big issue of inefficient housing stock.

We all know the figures: 80% reduction in carbon emissions by 2050; 30% of all carbon emissions come from housing; 80% of the houses that will be standing in 2050 are already built; 25% of these date from before 1919.

The biggest single challenge for the construction industry is therefore the upgrading of the existing housing stock to modern levels of energy efficiency. Just as the public sector is leading the way in new build, by routinely asking for new houses to be built to Level 4 of the Code for Sustainable Homes (well in advance of current building regulations), so it is experimenting to find the best solutions for refurbishment projects.

Broxbourne Housing Association the largest provider of social housing in the Borough of Broxbourne was faced with exactly this challenge when it fulfilled its promise to residents to improve two of its large 1970s estates. Coopers Walk and Fishers Close had been taken over from the council in 2006, and the housing association pledged to provide warmer, better looking homes and reduced fuel bills. A significant refurbishment was planned for the exterior of the buildings, with the tenants remaining in situ throughout the construction work.

Fishers Close consists of four blocks built of no-fines concrete walls with a pebble dash finish. The original building also included projecting plinths. These were removed to improve the aesthetic of the façade, but left a difficult surface to treat. The only way to improve the thermal insulation of the building was to use an
External Wall Insulation system and in this case, Woodward Ambrose Architects chose an adhesive fixed.

Using StoTherm Classic external wall insulation, the final U-value of the external walls is now 0.26W/m2K. For the residents, this has led to a dramatic improvement in the living environment, plus reduced heating energy requirements.

The durability of this treatment was an important factor for the architects, who were particularly attracted by the StoTherm Classic impact resistance: up to 60 joules.
It was also important to maintain the dramatically improved looks of the buildings, so the architects specified StoLotusan for the render finish. The unique Lotus-effect properties of this product actively repel dirt and function as a self-cleaning surface. StoLotusan is available in over 400 colours and in the Broxbourne project a range of colours was chosen to enhance the visual appeal of the buildings.

An External Wall Insulation System is possibly the simplest method to improve the thermal efficiency of solid wall structures, but the second estate in the Broxbourne project, Coopers Walk, was a cavity wall construction. However, close examination of the cavity walls revealed a significant problem with thermal bridging, which meant that filling the cavity with insulation would not have provided an adequate solution. EWIS was therefore used here too.

The impact on the energy efficiency of the two estates is impressive, and the project qualified for government funding through the CERT (Carbon Reduction Emissions Target) programme.

At the other end of the spectrum in terms of the scale of the project is Midmoor Road in Balham, south west London. This is another example of public sector innovation with the housing association, Family Mosaic, attracting Technology Strategy Board funding to investigate the best way to improve the energy efficiency of an Edwardian terraced house.

Like thousands of other properties around the capital, this house was built with solid brick walls and tight interior living spaces. The façade forms part of a uniform and aesthetically pleasing street, within 100m of a conservation area. The back of the building, on the other hand, offered both a bigger challenge and more options as the appearance is less significant.

The building was to be entirely refurbished, giving architects Prewett Bizley a blank canvass on which to plan their project. In this case, the practice set itself the challenging task of working towards certification under the new Passivhaus standard for refurbishments: EnerPHit. Under this standard the external walls must not exceed a U-value of 0.15W/m2K.

For the front elevation, an internal wall insulation system was used. At the rear a very large surface area of external wall combined with a less significant visual impact to make External Wall Insulation an obvious choice. The architects were particularly keen on this solution as it did not further reduce the living space in rooms that were already small.

The architects specified StoTherm Classic. The insulation is provided by 280mm thick EPS fixed to the walls using Sto-Turbofix adhesive. This fixing system masks minor imperfections in the face of the wall and also reduces the possibility of thermal bridging by minimising the number of mechanical fixings required.

For this project, a single mechanical fixing was used as a belt-and-braces insurance for each block of EPS.

The insulation layer was then coated with a robust off-white mineralic render. Around the window reveals (already splayed for better daylighting) the render was finished with a special smooth white to present a more refined appearance in sympathy with the Victorian/ Edwardian tradition. The render was overlapped over the window frames to further minimise the bulk of the frames and to alleviate thermal bridging. The U-value of the rear walls was measured as 0.12W/m2K.

Airtightness is another key characteristic of the EnerPHit standard and the finished house was pressure tested, revealing an airtightness 0.8M3/hr/m2. This is 12 times better than current building regulations.

The Technology Strategy Board criteria asked for the energy required to keep the building at 210C to be reduced by 90%. The project will be monitored over the next two years to assess the effectiveness of all the energy-efficiency solutions involved in the project.

Both these projects represent the pioneering approach of the public sector, actively looking for the best methods of improving the energy efficiency of existing buildings.

No doubt the lessons learnt in this sector will migrate to private sector projects. Either way, EWIS is becoming the widely accepted solution for improving the energy efficiency of existing buildings.