Eco renovation on a budget

Case Study

Louise renovated her old Welsh stone cottage, using passive solar design principles and natural materials such as sheep's wool. She managed to create more room and reduce heating bills - and all that on a very tight budget.

Added: April 29, 2010

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Louise and her partner were living in a standard "two-up, two-down " Welsh stone cottage. When they needed a bigger place for their growing family, they had the choice to either move into a new house, or to renovate and extend the old one. Rather than leaving the old cottage behind and building yet another new house, they decided to turn their existing building into a bigger and more energy efficient home.

The house: This is the old stone  cottage Louise renovated (click    to enlarge).Their renovation project was carried out with the aim to

  • -increase the amount of space available for their family, to enable them to stay in their old house rather than move into a new one
  • -reduce the amount of energy consumed in the building for heating and lighting, to reduce their bills and their impact on the environment
  • -use sustainable building materials which have a low environmental impact in their production and, where possible, use renewable resources

In the end, they nearly doubled the amount of floor space available in their house, got the insulation to a much higher standard than that of the surrounding houses - and did all that for a fraction of what it would have cost to buy a new house!

triple glazed windows minimize heat lossPassive solar design principles: A triple-glazed solar space
Louise and her partner built their extension on the south-east facing side of their house. This allows them to apply what is known as passive solar design principles to actually use incoming sunlight to help heat their home. By using a large amount of high quality glazing window space, they let a lot of sunlight into the building. Once inside the room, the sunlight hits the floor or the old slate stone wall and turns into heat. High quality windows will stop heat from leaving the building, so the heat is "trapped" inside and absorbed by the thick slate wall. As this heavy internal wall has a high thermal mass it can absorb a lot of heat during the day and then release it into the building during the night, reducing temperature fluctuations inside the building. To make sure their windows let a lot of sunlight in but don't let the heat get back out, Louise and her partner have chosen triple-glazed windows which have the spaces between the window panes filled with argon gas. This reduces the heat transfer through convection as argon molecules are heavier and less mobile than air. The windows have a U-value of 1.2, which means their heat loss rate is less than half that of normal double glazing. Such windows are standard in many Continental European countries, especially in Scandinavia.

DIY timber frame
The walls of the extension consist of a timber frame structure. Timber frame walls make use of a sustainable and renewable resource that can often be sourced locally, and you can even do it yourself - Louise and her partner built their extension after attending a course on timber frame building at the Centre for Alternative Technology. The walls have a cavity that can easily be filled with an insulation material, in this case sheep's wool, another renewable building material which uses local resources (though the wool needs some processing before it can be used, so it is generally easier to buy ready-made sheep's wool insulation material).

Roof insulation: Keeping the snow
PU foam board insulationTo create two extra rooms in their house, Louise and her partner had to convert the loft into a habitable space  - and that required putting enough insulation under the roof to keep the attic warm.  They filled the space between the roof rafters with sheep's wool, but as the rafters were only 5 inches deep, this would not have given them enough thickness for sufficient insulation (at least twice as much is recommended). Louise in the converted loft spaceAdding more sheep's wool insulation would have been difficult and would have taken away valuable room height, so they had to make a compromise: While they generally tried to use renewable, organic materials wherever possible, Louise and her partner decided to add a polyurethane (PU) foam board with a tin foil surface onto the rafters as an additional insulation layer. PU foam is a synthetic material typically made from fossil fuel products, and as such it is not a renewable building material. However, PU foam has very good insulating properties, and so a relatively thin foam board can add as much insulation as a significantly thicker layer of wool. As Louise explains, this was a necessary compromise: "I would have preferred not using this material, but I considered having good insulation, and preserving the loft as a usable living space, more important". For proof that her roof insulation works, Louise only has to look at her roof when it snowed: While the snow melts on the roofs on either side in her terrace, her own roof stays white as the heat stays inside the building and doesn't escape through the roof.

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Related questions


  • AECB: the Sustainable Building Association - - 0845 456 9773
      Network of builders, architects, manufacturers, and organisations. Aims to develop, share and promote best practice in environmentally sustainable building. There is a list of members on the website.
  • Energy Saving Trust - - 0300 123 1234
      Gives advice on saving energy in the home and local funding opportunities for renewable energy.