We developed the design of the 2 storey house as a compact 10.7m X 7.4m south facing plan. This form has minimised the heat loss from the house and enabled gains to be received from its share of winter and summer sunshine. The Passivhaus PHPP planning design shows that the house achieves the required targets of space heating demand of: 15kWh/m²/yr, a heat load of: 10W/m² and a primary energy demand of: 112kWh/m²/yr. We worked hard to develop bespoke cold bridge free junction detail designs and Passivhaus carried out extensive Psi-Therm 2D modelling of all the key junctions to achieve a resultant calculated cold bridge PSI-value 0.02283W/mK, fRSi-value 0.91.
The Passivhaus standard requires an airtightness of ｲ0.6 ach (air changes per hour) @ 50Pa (current Building Regulations require 10.0ach @ 50Pa). This high standard ensures draught-free comfort, protects the building fabric from condensation Due to leakage of humid air, and ensures that the efficiency of the heat recovery ventilation is not bypassed by leakage ventilation. The completion air test by Paul Jennings of Aldas confirmed an airtightness result (at 50 Pascal’s): 0.58ACH or 0.52m²/m²/hr.
As a bonus to meeting the Passihaus standard criteria the house achieved an ‘as built’ EPC A rating and a numerical SAP figure of 104 making it eligible for a Level Six Code for Sustainable Homes rating. Tim and Sarah have now moved in, but are still finishing off certain superficial completion tasks and will monitor actual performance against design criteria over the next twelve months. We will report back in due course to let you know how it performs in reality.
Building fabric
Working with Viking and MBC Timber Frame we developed the low U-value, super-insulated, timber building fabric build ups as set out below:
Ground floor: 20mm reclaimed maple flooring, on 50mm battens with Knauf glass wool insulation between, on 100mm thick reinforced concrete floor slab, on 300mm Aerofloor EPS insulation, on Viking Passive Slab (PHI certified). U-value: 0.105 W/m²K.
Ground floor walls: 10mm thin coat silicone K render, on 100mm Masterblock recycled aggregate concrete block, on 50mm wide drained cavity, on Pro Clima Solitex WA wind-tight membrane, on 12mm thick Panelvent sheathing board, on MBC 300mm stud twin wall with full-fill Warmcel 500 cellulose insulation, on 12mm OSB with taped joints. The walls are finished internally with 50 x 50 battens to form service void insulated with Knauf glass wool insulation, on 12.5mm Gyproc plasterboard internal lining with plaster skim. Dulux Ecosure emulsion paint. (PHI certified). U-value: 0.112W/m²K.
