To work properly, a Passive House needs continuous insulation together with a continuous air tight membrane. No gaps. Gaps allow heat to escape and cold to enter. This is challenging but achievable in a new building, when you're starting from scratch. It's much, much harder to achieve with a retrofit like the EcoBungalow when you're modifying an existing building.
So - before we got down to the detail of how the kitchen would work, what the steps to the garden might look like and so on - Russel needed to figure out how to achieve as continuous an air tight membrane as possible. The two sketches below show how the strategy has evolved.
© Hesketh Hayden Architects
We'll be improving the EcoBungalow with thick external insulation with a rendered finish. The initial approach was to put the air tight membrane between this external insulation and the outer face of the external wall. This results in a gap where the floor meets the wall.
We ran the initial drawings past Alex, our builder. He suggested that the air tight membrane went on the inside face of the existing external wall, so avoiding the gap. This approach would mean that all internal walls would need to be stripped out to avoid having to fiddle the membrane around them. It sounded radical but - as it's a bungalow - none of the internal walls are structural. It does mean a very small loss of internal floorspace but - as it massively simplifies the build and improves the design - we decided this was the right solution. An excellent demonstration of why involving the builder early in the design is a good idea!
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