Recognising the need for affordable, low-energy housing, self-builder and low energy retrofitter, Andrew Gill, has undertaken an ambitious project to prove that cost-effective refurbishment of existing housing stock is a viable possibility.  Challenging himself with the complete renovation of a dilapidated terraced house in Manchester, he turned to Knauf Insulation to supply extensive insulation measures throughout the property.

There are approximately 7 million solid wall domestic properties in the UK, many of which are poorly insulated and highly energy inefficient.  Acknowledging that a large proportion of these properties are in low-income areas, Andrew, who has an MSc in Architecture: Advanced Environment and Energy Studies, from the Centre of Alternative Technology in Wales, set out to explore the ways in which low value properties can be economically refurbished without making them unaffordable.

Adopting a fabric first approach, Andrew’s key objectives throughout the project were: increasing insulation, improving air tightness, managing ventilation and limiting embodied energy within the refurbishment.  Most importantly, he was adamant that improved insulation and air-tightness must work in tandem, to ensure maximum efficiency.

He commented: “It’s essential that insulation and air-tightness work hand-in-hand and throughout this project I have focused on eliminating air leakage, so that the thorough insulation measures installed within the building are able to deliver optimum performance.”

The main insulation component was Knauf Insulation’s ThermoShell® Internal Wall Insulation System (IWI), which was used throughout the property at a thickness of 65mm.  Specifically designed to upgrade the thermal efficiency of solid walls, Knauf Insulation’s ThermoShell IWI system can accommodate wall imperfections or fixings for fittings such as radiators, and can be adapted around openings such as windows and doors, making it perfect for Andrew’s needs.

In addition, as it is a full-fill solution the ThermoShell IWI system minimises air movement and reduces air leakage – a key consideration for Andrew and his goal of achieving maximum air tightness.

ThermoShell IWI comprises EcoStuds – extruded polystyrene laminated to Oriented Strand Board (OSB), which are mechanically fixed to the internal wall to create a frame to accept the insulation.  As the system uses an insulating material to form the frame, rather than timber or metal, it reduces cold bridging and allows for a thinner system to be used to deliver the thermal performance required.

Earthwool EcoBatt water repellent glass mineral wool slabs are then friction fitted between the EcoStuds and faced with a vapour control layer and standard plasterboard, which provide the best solution when considering airtightness.  The Earthwool EcoBatts fully fill the insulation zone and are in intimate contact with the EcoStuds and the vapour control layer, thereby preventing any air movement within the system.

As well as the IWI system, Andrew installed Knauf Insulation’s highly versatile Earthwool Loft Roll in varying thicknesses around the house, including 440mm at ceiling level in the roof, 100mm in the intermediate floor, 100mm beneath the stairs and 200mm in the suspended timber ground floor, which was combined with 25mm of Polyfoam ECO Floorboard Standard.  Finally, Andrew installed Knauf Drywalls, Thermal Laminate Plus in 27mm and 35mm thicknesses along the party walls at the junction with the exterior walls, and around the window and door reveals, to further minimize cold bridging.

Andrew has conducted analytical modelling of the property, which suggests an energy reduction of 62 per cent and carbon reduction of 57 per cent compared to its previous condition.  In addition, the property is expected to achieve a band ‘C’ Energy Performance Certificate rating, a significant improvement on the band ‘F’ that it held previously.

“I am pleased with the results of the insulation and with the simplicity of the ThermoShell IWI system,” Andrew continued.  “The property has been air-tightness tested with excellent results that sit firmly at the top end of retrofit best practice, short of attaining Passivhaus standards.  In addition, I’ve achieved excellent levels of thermal efficiency – the U-value in the loft, for example, is just 0.10 W/m2K, which is a fantastic improvement and a big step towards my ultimate aim of proving that cost-effective energy refurbishment is a realistic goal.”

Andrew has been blogging about the refurbishment throughout the project and has amassed a wealth of useful information on his website, for full details visit

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