PH Open Days: Lena Gardens Victorian Retrofit

Lena Gardens Passivhaus retrofit (right)

During last month’s Passivhaus Open Days across the UK, Footprint visited 20 Lena Gardens Road, Hammersmith where a 120-year-old listed Victorian house was recently refurbished and accredited with a Passivaus certificate. It is the first retrofit in the UK to be accredited with the Passivhaus standard. The intention of its owner and passive system designer - Tom Pakenham of Green Tomato Energy - was to demonstrate that a refurbishment project can achieve the stringent German standard and at the same time to show the way it works.

New triple-glazed windows

Not much can be seen from outside, apart from the Passivhaus certification label next to the door. Even the new triple-glazed, airtight windows and front door were specially ordered to replicate to the smallest detail the original ones. The only visible exterior change is the addition of solar thermal and PV panels on the roof.

All thermal upgrading had to be done internally. To avoid potential thermal bridging with internal insulation, the house interior was completely stripped leaving only the exterior envelope which was then super-insulated; the floors were then ‘hung’ into their position with using perimetric metal ‘L’ beams.

There is heat exchange between the incoming and outcoming air which means that it takes less energy and time for the house to heat up - and that heat produced from cooking can be used to warm up the space.

Solar thermal water tank - solar thermal panels provide 50% of annual hot water needs

An MVHR unit is used for topping up space and hot water heating during winter, and the solar thermal panels provide around 50% of total hot water needs.

Currently the house achieves less than 120 Kwh/m² for primary energy, 15 Kwh/m²/year for heating and an air tightness of 0.49 Ach/h@Pa which is even less than the 0.6 required from Passivhaus Standards. The house maintains a temperature between 18-20 °C all year, and a relative humidity of 55%. To prove it, Tom Pakenham used a meter during our tour, checking every single room.

Loss of floor area due to internal insulation is not noticeable in the lower ground floor kitchen

The super-insulation provides sound-proofing as well; the house is really peaceful and quiet inside. The total floor area lost due to internal insulation was around 5m² which, due to the big open spaces inside the house, is not noticeable. The external wall, apart from the outside brick layer, contains 180mm of Kingspan phenolic foam insulation, a chipboard which provides airtightness, another 220mm insulation layer and the internal plasterboard. Airtightness in the junctions and slots between the insulation layers is provided with a special sticky tape. The chipboards are screwed on the insulation boards with low thermal conductivity screws to avoid thermal bridging.

Overall, Lena Gardens is an excellent example of what can be achieved in sensitive refurbishment. Opening the house to the public was a great idea so that people can observe first-hand both the design considerations and technical details of eco-refurbishment.

by Myrtia Fasouli, AJ sustainability intern

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