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Bedford Farm

When Tony Kelly bought Bedford Farm it was leaking heat. A thermal survey revealed that the cavity wall insulation had failed and that the double glazed windows had been badly fitted. The home owner investigated various possible solutions before arriving at the conclusion that Sto's external wall insulation system offered the most cost-effective and best possible technical solution.

What sold the ordinary-looking 1950s property to Mr Kelly seven years ago was the building's location. It was situated in an area of outstanding natural beauty overlooking a valley on the outskirts of the Surrey town of Godalming. "It's in a gobsmackingly amazing location, which is why we bought the place," he says.

While the location was stunning, conditions in the 4-bedroom single story building were far from ideal. "The house was incredibly cold in winter,". The building's remote location meant that the central heating was powered by Liquefied Petroleum Gas (LPG), which was costing over £2,000 a year.

What puzzled the homeowner about the high cost of heating was when the Kellys had bought the house seven years ago it had been refurbished. The original windows had been replaced with uPVC double glazed units, cavity wall insulation had been installed and the loft had been insulated. "I couldn't believe we were sitting in a house with modern double glazing, cavity wall insulation and a decent heating system, yet we were spending so much on heating – it just didn't make sense!" Mr Kelly says.

In the winter of 2010 the homeowner paid for a thermal survey of his chilly home using infrared photography. The survey showed that there were a large number of minor draughts, largely due to poor fitting double glazing. These were estimated to be less than 10% of the building's heating requirements. By far the biggest problem was with the blown mineral fibre cavity insulation.

The infrared images highlighted two problems with the cavity insulation. Firstly, it had been disturbed when the double glazed windows had been installed. As a result, it was missing from above the windows and had been shifted from the sides and beneath every one of the home's 20 windows. Secondly, in the sections of wall between the windows, the insulation had either slumped to the bottom of the cavity or it was missing entirely. "At best it was 15% effective," Mr Kelly says.

Finding a Solution

Having identified the problem, the next challenge was to find a solution. The homeowner considered three possible answers: fixing the cavity wall insulation, insulating the inside of the external walls or adding insulation to the outside of the property.

Fixing the cavity wall insulation was difficult since this would have involved cutting away sections of the outer brickwork in every wall to enable a vacuum pipe to suck out the defective insulation. An installer would then have to blow in replacement insulation. Because there is no way to ensure all the insulation has been successfully removed the replacement insulation contractor will not guarantee the thermal performance of the installation.

Internal insulation was another option, however, adding 100mm or more of insulation to the inside of the external walls would have significantly reduced the internal volume of the house. It would also have been disruptive and expensive because radiators and other fittings on walls would have to be moved.

By far the best solution was to apply insulation externally. "'When I'd done my homework, this proved to be the least disruptive, most cost-effective way of solving the problem," Mr Kelly explains. This option also had the advantage that the right solution would improve the external appearance of his home.

Installing Sto Insulation

Having scrutinised the alternatives, the homeowner concluded that the StoTherm Classic external wall insulation system was by far the best option. "The Sto system is contemporary, there are millions of square feet of it installed globally and it comes with a guarantee," Mr Kelly enthuses. What made up his mind, however, was the economic argument: "A Pound spent on the Sto system was more effective than on the other two options so in the end return on investment was the killer argument," he says.

The homeowner originally estimated the Sto system would improve the look of his home and add about £2,500 to its value, a figure he offset from the cost of the works when he calculated his return on investment. His calculations were based on a payback of 10 years, saving £700 a year or roughly a third of his heating bill. Sto also used its in-house expertise to help Mr Kelly obtain a government grant to contribute to the cost of the thermal improvements. This resulted in a £500 Carbon Emissions Reduction Target (CERT) grant being obtained from his utility provider.

Once the homeowner had decided on the system, Sto provided a list of approved contractors that could be approached to competitively tender for the work. P3 Projection Coatings was selected to install the system. "We fixed 100mm of expanded polystyrene insulation to the building's walls to get the required thermal performance of a U-value of 0.3w/m²/k for the walls," says Jason Smith, MD of P3 Projection Coatings. The insulation was attached using Sto-Turbofix quick-drying, pre-mixed polyurethane adhesive, supplied pre-mixed in a large can making it easy to carry round the site.

The building's refurbishment was relatively simple. The overhang of the eves was sufficient to cover the additional thickness of wall insulation on all but the gable walls. On the gable walls, the contractor adopted the standard solution of applying metal flashing to encase the top of the render. "It was a straightforward installation. The only major challenge was fitting insulation around the soil pipes, which cannot be moved," Mr Smith explains.

A Happy Customer

Once the insulation was attached, it was covered in a reinforcing coat complete with glass fibre reinforcing mesh before being finished in StoLotusan, a self-cleaning decorative render finish. The render also helped to seal the majority of minor cracks and gaps around the windows. "It took out 99% of the drafts," Mr Kelly says. A light green render was used, the colour of which had been agreed with the planners as part of the process of getting planning permission for the works.

Mr Kelly had concerns that adding 100mm of insulation to the outside of the property would make the windows look as if they were "hidden in tunnels", but careful detailing ensured this was not the case. The brick soldiers forming the existing window sill were covered in a thin layer of expanded polystyrene to prevent cold bridging, which was then finished with an aluminium sill. A 45° chamfer was also added to the insulation around the door edges as a finishing detail.

The homeowner says the difference was obvious as soon as insulation was attached to the building. "Within 48 hours of the job starting you didn't have to look at the heating system to know the situation had improved," he says. Over the following week temperatures in the rooms rose by 2 to 3 degrees so that the heating could be turned on slightly later and turned off earlier.

Mr Kelly is optimistic as far as getting a return on his investment, although he will not know for sure until he’s lived through a couple of winters. "What I can tell you is that I know we're spending less on heating because the heating is on for probably between 33% and 50% less time," he says.

Aside from a reduced heating bill, the real benefit has been the improvement to the home's appearance. Originally Mr Kelly had estimated Sto's external wall insulation project would add £2,500, to the value of his home, but now that the works have been completed he thinks the system had added considerably more. "It looks the business. I think it has easily put five or six grand on the house price simply by making it look smart," he says. "I think if we had to sell this place tomorrow, I could easily cover the cost of the works just by the value it has put on the property."