Maximising airtightness Passivhaus buildings require very high levels of airtightness 0. An adhesive-backed airtightness tape was then attached to the plywood with a fleece wrapped into the wet plaster, making the junction between the plywood and plaster airtight. Another airtightness tape was used to seal the gap between the window and the plywood box. Super insulation Super insulation is fundamental to Passivhaus construction, along with close attention around junctions of these elements. It allows for sufficient and comfortable ventilation to all areas of the house whilst minimising the loss of heat gained from the sun, human activity, cooking, showering, electrical appliances etc. This is achieved by use of a sophisticated heat exchanger driven by two very efficient fans.
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The rationale behind this decision was mainly due to the wealth of resources provided compliment of Green Building Store on this Passivhaus project. This project was the first certified Passivhaus in the UK to be built using cavity wall construction and has pioneered the combination of British vernacular construction methods with the German low energy Passivhaus design methodology. The Foundation The foundation used on this Passivhaus build is very similar to the traditional Irish Strip Foundation however it differs in one main area - its elimination of thermal bridging within the structure.
When we examine the traditional Irish strip foundation U value of 0. The Denby Dale foundation eliminated the thermal bridges by completing the following steps: Installing Insulated blocks on the inner leaf between the floor slab and the foundation to prevent any thermal bridging down the inner leaf.
Installing mm of insulation beneath the floor slab to prevent heat loss through the floor. Installing mm insulation in the cavity which continues down to the foundation to ensure there is no thermal bridge through the walls or from the foundation. The insulation in the wall below the dpc tray red is expanded polystyrene or EPS; this is rigid and closed cell. This means that it will not soak up any water and its rigidity is to compensate for lateral loads below ground.
To provide you with a deeper understanding and familiarity with the Denby Dale Passivhaus foundation; I have provided you with a simple sketch of the cross sectional detail of the foundation. To register for a free 40 page technical briefing on the Denby Dale Passivhaus, go to: The Door Threshold The door threshold is one area in which eliminating thermal bridges is particularly difficult.
When we examine the standard Irish block cavity door threshold we can determine that there is a huge amount of heat loss by means of thermal bridging; this is evident from the sketch on the left.
In order to eliminate these thermal bridges the Denby Dale project aimed to eliminate heat loss by super insulating. Like in the previous foundation detail, there is mm closed cell EPS insulation in the cavity; providing moisture resistance and rigidity.
Furthermore, the blocks on the inner leaf are lightweight insulated blocks and there is mm of insulation under the floor just like in the foundation detail. However, this alone was not enough to eliminate the thermal bridging as there would have been a thermal bridge through the floor slab. To solve this problem, the concrete slab was cut back and in its place a mm x mm fibreglass box section filled with polyfoam insulation was inserted.
This box was mechanically fixed to the edge of the slab by means of a resin grouted stainless steel threaded bar. To minimise heat loss the door step itself was created from EPS and covered with chequered galvanise for grip and durability.
The sketches below clearly portray the comparison in terms of detailing between traditional Irish construction and what is needed to achieve the passivhaus standard.
Denby Dale Passivhaus: Derrie O’Sullivan
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