Wherry Housing Association wanted its Mayfield Road development in Huntingdon to be a showcase for the local district council to “promote sustainability”. As a result its Code for Sustainable Homes (CSH) level 5 status is clearly signposted. The 29 houses and apartments are clad in ‘thermowood’ and Trespa, and the main roof areas are decked out with solar thermal and PV panels, while others are planted with sedum to reduce water run-off.
At the same time, said architects PRP, the objective of the project was to come up with more than a green statement. It wanted to include features that departed from ‘standard’ eco-housing, even if that made CSH compliance more demanding.
“The easiest route is to base everything on airtight square boxes,” said project architect Mark Bell. “But we wanted to show you can deliver more flair and still achieve higher levels of the Code.”
The key to meeting this goal, he agreed with Dr Paul Newman, technical director of Kingspan Potton, which supplied the development’s core TEK structural insulated panels (SIPs) shell, was close liaison between everyone involved. “We did a lot of work with the architects and contractor Hills Partnerships at the front end and everyone listened to each other from the start, which was key,” said Newman.
“You don’t meet the CSH by throwing everything together last minute and dealing with problems on site,” said Bell. “You have to spend time on design and build processes in advance.”
This groundwork, he added, included producing an energy strategy report, sustainability statement, full SAP and EPC, computer-simulated thermal modelling and embodied energy calculations.
Mayfield Road is based on Passivhaus principles to minimise energy use for lighting, heating and cooling. That means combining mainly south-facing living areas with the right-sized windows, adequate ventilation and shading. Each property is also equipped with an Itho mechanical ventilation and heat recovery unit and Ecoplay grey water recycling system, plus energy monitoring devices and “highly efficient gas boilers”.
The choice of SIPs, as opposed to the straw bale structure initially proposed, was down to their combination of flexibility, insulation performance and speed of erection.
“The structural shell was completed in 14 weeks and the envelope alone meets CSH level 3, with the combination of 142mm panels and 62mm of Kingspan Therma insulation externally giving U-values from 1.3,” said Hills sustainability manager Warren Sparkes.
SIPs were also used for main roofs to create vaulted ceilings.
“This is the kind of architectural feature you might not necessarily advocate under the CSH, but working with Kingspan, we showed it could work,” said Bell.
For the green roofs, SIPs were switched for Kingspan trussed rafters, which are better suited to the warm build-up needed. A different structural approach was also used for other design twists that challenged code-compliant norms; namely drive-through porticos in the two-storey terraces and first floor overhanging extensions on the houses.
“These made life more difficult, because we had to switch to Kingspan timber frame, creating the challenge of maintaining uniform airtightness and thermal performance between this and SIPs,” said Sparkes. “But, again, addressing this early resolved the problems.”
Other lessons reinforced by Mayfield Road on CSH compliance were that it demands “effective interfacing” between trades and “education in the use of new materials and methods and the level of quality control and monitoring needed”.
“It has to be stressed that, if it’s not checked, it’s not signed off and you can’t leave issues on site to the next trade; the message is ‘if you drill it, fill it’,” said contracts manager Jon Thistlethwaite.
Despite the challenges, however, Mayfield Road left those involved with the view that meeting upper levels of the CSH needn’t cramp creativity.
“It limits design to an extent,” said Newman. “But this project showed that, as we learn about compliance and develop new approaches, it will become less of a constraint.”
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The wooden shutters help to cool the houses |
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The houses comprise a SIPs shell supplied by Kingspan Potton |
