The triple-glazed timber Passivhaus windows have arrived at Passfield Drive from Germany and are due to be installed in the next two weeks. Meanwhile, the new concrete floor slab for the rear extension is ready to be poured. Unfortunately, the contractor has laid Cellotex insulation to the area beneath the new slab where bere:architects specified Floormate. In order to keep the project on programme and to minimize disruption bere:architects have permitted the Cellotex to remain, however, the contractors have had to install an additional DPM above the insulation – the thermal efficiency of Cellotex is acceptable but it is not as resistant to damp.

Paul Jennings (one of the UK’s top air-tightness experts) conducted air-tightness training on site today in order to familiarise the contractor with the processes involved in producing a draught-free building. The air-tightness tests form an intrinsic part of building to Passivhaus standards – these guarantee that the contractor is building to the required parameters in order to sufficiently minimize the amount of heat loss through uncontrolled air movement between inside and out. Such training is invaluable as the contractor gains a clear understanding of the various tapes, membranes and mastics that are required to ensure draught-free construction. bere:architects have specified the use of Illbruck window tapes, Orcon F mastic and Tescon No1 tape to seal Intello and Solitex membranes and to ensure a draught-free construction between the window and the structure.

A window opening before the window is installed. The contractor has placed a polythene sheet in to the structural opening so that the residents are affected as little as possible during the work.