The Cotswolds is a beautiful region in England known for its picturesque countryside, quaint villages and historic buildings. However, as more people move to the area, there is a growing need for sustainable housing that integrates well with the natural surroundings. One solution is the construction of a sustainable residential annex, designed with environmentally friendly features that reduce its impact on the environment. Such buildings can be built using locally sourced materials, such as Cotswold stone, to minimise transportation costs and support the local economy. To ensure energy efficiency, the annex will incorporate solar electricity generation, triple-glazed windows and insulation made from recycled materials. These elements help to reduce energy consumption and lower the ’embodied carbon’ footprint of the building. Water conservation is achieved through rainwater harvesting systems, which collect water for use in irrigation and flushing toilets. Additionally, low-flow plumbing fixtures and water-efficient appliances reduce water consumption and minimise wastewater production. To ensure a healthy indoor environment, the annex incorporates natural ventilation systems and non-toxic building materials, as well as super-insulation and heating via air-source heat pump. These features help to maintain good air quality and minimise exposure to harmful chemicals, while keeping the building cool in the summer and efficiently heating it in the winter. The building is approximately 110 square metres in floor area and replaces a disused farm outbuilding.