The main problem facing this retrofit project was leakage into the party walls and onwards to other maisonettes, the roof and underfloor voids. The volumes of air travelling through the party walls was far in excess of original expectations mainly due to the very poor build quality of the brickwork and the use throughout of paramount partitioning, which again was a source of major air leakage into the party walls.

Multiple means were used to address the issues including external parging, airtight taping, airtight foam, stitch drilling, spray foaming and airtight and fireproof composite sealing of vertical and horizontal service ducts through party and communal walls. Ongoing tests and training were carried out under the supervision of a trained Air Tightness Champion.Ironically, with this particular development, there was also an issue with the size of the glazing in both blocks that needed to be reduced. If left in their original sizes, it may have caused an overheating issue on the south facing elevations.

Designing the MVHR systems to fit into the maisonettes initially proved challenging for the team. Green Building Store’s MVHR department worked with Passivhaus mechanical & electrical expert Alan Clarke to design a system to fit the space available. The Zehnder ComfoAir 160 unit was chosen because of its compact form and performance characteristics, which enabled it to be located on the bathroom wall behind the bath. Green Building Store and Alan Clarke carefully designed and attenuated the system to ensure that the system operates quietly and with maximum efficiency. To ensure extra quality control, Green Building Store’s MVHR Technical Manager Andrew Farr gave a toolbox talk to ventilation installers on the project and he and Steve Clarke (Services Engineer at Green Building Store) commissioned the units after installation.