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Lena Gardens – Certified Passivhaus retrofit


This was greentomatoenergy’s first project. A Passivhaus retrofit of an 1870s mid-terrace in West London (Enerphit didn’t exist then).

Due to planning restrictions in the local conservation area, the exterior of the house had to be kept unchanged in appearance. All insulation was applied internally on floors, walls and ceilings. This gave the final external wall a U-Value of 0.1. Our Passisash triple-glazed sash imitation windows and a Passisash triple glazed door were installed as it is a conservation area.

An Integrated solar thermal system for hot water was installed, backed up by air-source heat pump which is hoped to boost the solar percentage of
annual hot water requirements to more than 70%. 2 panels are almost flush to the slate on the front roof-slope and a third panel was placed on the flat roof,
6 photovoltaic panels were installed with a 1.1kWp output.

To avoid thermal bridges, the floor joists were rehung and the steel I-beam was placed in a insulating foamglass pocket. A continuous airtight layer was formed within the insulation build-up of the house. This was formed of an OSB layer taped at all joints and running continuously within walls, under floors and over ceilings.
The air coming into the building is pre-heated by going through an underground heat exchanger below the basement, as the ground temperature stays at 12°C. The incoming air is then preheated again in the Mechanical Ventilation Heat Recovery system using the heat from the stale outgoing air. An air to air heat pump then takes more heat out of the outgoing air and further heats the incoming air. This eliminates the need for a boiler to heat the house.

An extensive wild grass green roof was created. Green roofs have many environmental benefits including; creating natural environment s for plants and animals, adding extra thermal insulation and alleviating flooding.

Watch this for more https://www.youtube.com/watch?v=0-jfgiZyN68

  • Street view of London's certified Passivhaus retrofit
  • Front Bay Triple-glazed Passisash windows of London's certified Passivhaus retrofit
  • Plaque certifying the Passivhaus retrofit
  • Interior of front bay triple-glazed Passisash windows at the Passivhaus retrofit
  • Tilt-and-turn triple-glazed Passisash windows at the Passivhaus retrofit
  • Tilt-and-turn triple-glazed Passisash windows at the Passivhaus retrofit
  • Flat garden-style roof area in central London
  • Solar thermal technology provides hot water to the Passivhaus
  • Airtightness application technique is crucial for Passivhaus certification
  • Energy-savings made at Lena Gardens