Park Lane residents Dave Pountney and Jo Bishop recently moved into their brand new Passivhaus where Val Robson was invited to take a look around and find out more about the story behind this innovative building project
The first Passivhaus was built in 1991 in Austria for Professor Wolfgang Feist, a physicist at the University of Innsbruck. Wolfgang Feist believed it possible that a house could be built which had no need for energy or fuel to maintain a comfortable living temperature all year-round. Worldwide, there are now over 70,000 Passivhaus buildings including Dave and Jo’s newly constructed detached house on Park Lane which they moved into last autumn after thirteen happy years overlooking the windmill in Impington.
Construction of a Passivhaus tends to cost approximately 20% more than a traditionally constructed house due to the high quality of materials used and the need to use specialist trades people for some elements of the work but it’s likely to be valued around 10% more than its traditional equivalent and the ongoing lower energy expenditure, especially in these current times, is an important benefit to be considered.
Keeping it natural
With over fifty years experience within the construction industry, Dave has been involved in the building of about twenty five Passivhaus structures standing him in good stead for the challenges that lay ahead. To be officially certified as a Passivhaus, a building must adhere to some basic principles which minimise heat loss and make maximum use of natural heat sources whilst also ensuring that fresh air is well circulated.


The building has to be free of thermal bridges which would allow heat to be conducted away from the building. Dave and Jo’s house is built on a 300ml thick polystyrene raft located underneath the concrete base while the walls are 325ml thick and pumped full of cellulose – basically chopped up newspaper. The roof has 300ml of cellulose with an extra 100ml of solid insulation on top to be sure it complies with the Passivhaus requirements.
The outside of the property is clad with Siberian larch, a hardy tree native to Western Russia, and, due to the intense cold in which these trees exist, they grow very slowly. This makes for a very tight grain giving great durability as well as an incredibly attractive finish. “When I ordered the Siberian larch”, Dave elaborated “the supplier told me that he did not expect to be able to source any more due to the impending war in Ukraine so to be sure that I ordered sufficient for the work needed”.
As required by the Passivhaus standard, all of the windows are triple glazed and there has to be extremely good airtightness so a special tape is used to seal all joints in the house including around the windows, between panels on the walls and any other joints such as around pipes and ducts.
A house with standards


The high standards of insulation and lack of air leakages mean very little heat is required to maintain the house at a comfortable living temperature. Dave explains “all the heat in the house comes from body heat, the sun and any appliances”. During my visit, the house was a very comfortable 20C and had a fresh, light and airy feel to it; attributable largely to the efficient ventilation. Another key element of a Passivhaus.
The air circulation is controlled by the MVHR (Mechanical Ventilation with Heat Recovery) unit located in the ground floor central plant room. A network of large ducts connect this to inlets and outlets in the ceilings of the house and the living areas have inlets in the ceiling which push fresh filtered warmed air into the room. The kitchen, utility room and bathrooms have outlets, sucking out air, which then goes through the heat exchanger where 85% of the heat is re-used to warm the incoming fresh filtered air. The stale air is then expelled. Alongside the fresh air feel to the house there is no sense of the air moving which makes for a very calming and quiet atmosphere.
Come in from the cold

For use during extreme cold, the house is fitted with underfloor heating on the ground floor and, shortly after my visit, this was put through its paces during a highly unusual period of sub zero temperatures which persisted for ten days. Dave reported back to me “I have to admit that, when it was -9C outside, we were incredibly grateful for this feature!”. A Passivhaus is allowed to have a heating system, but it has to use less than 15 kilowatt hours per square metre per annum to comply – the average yearly figure for existing houses in the UK is 200 kwh/m2!

The plant room is also home to the hot water tank. This is a very sophisticated piece of kit with its own diaphragm that moves up and down so that it is only containing the amount of water the occupants wish to heat. Dave controls this from an app on his phone and the LEDs on the side of the tank show the heating and water level statuses too.
Although the main construction is complete on the house there is still much work to be done before Dave and Jo get official Passivhaus certification on their home. Shading and overhangs will be added to the windows to ensure that they are not only protected from the elements during the cold months but also from the sun during hotter times. The orientation of a Passivhaus is also crucial with the majority of the windows needing to be facing south to catch the maximum sun. Dave and Jo were fortunate in that the plot is orientated in a way that allowed the house to be constructed in optimum orientation to make the most of solar energy. They also have fourteen solar panels which help with the energy bills.
The final test
There then remains one final, but very important, test that Dave has to commission in order to gain the coveted Passivhaus certification and this is to prove that the house falls within the Passivhaus standards of airtightness. Explaining what’s involved Dave told me “they will bring in a big fan which will be set up in one of the door or window openings. In order to pass the test there should be no more than 0.6 air changes per hour at a pressure of 50 Pascals. This equates to having no one hole, or several combined, which would total more than the size of a 20p piece throughout the entire house”.

Once this test is complete, and all the documentation is passed by the The Passivhaus Trust who are the official UK affiliate of the International Passive House Association, Dave and Jo will receive a plaque which can take pride of place on the wall of their fabulous new home!







































