Thomas Vale Construction has recently completed two new Passivhaus primary school buildings, the first in the UK, for Wolverhampton City Council.
Despite having come close to achieving Passivhaus certification on previous projects, the company had not aimed for full certification until working on the schools.
Architects Architype took the idea to the council and Thomas Vale built on its experience to embrace the concept (Architype and Thomas Vale have announced a joint venture to win schools work based on their Passivhaus design).
“From our previous work on projects that used the principles of Passivhaus, and with the expertise of Architype, we were fairly certain we could construct a building in the UK to Passivhaus standards,” says Thomas Vale Construction environmental manager Matt Wisdom.
“The challenge was that the client also said there was no extra money or time for the build programme. It had to come in on time, on budget and get Passivhaus certification.”
Oak Meadow Primary school has about 450 pupils, measures 2,600 sq m and had a budget of £5.1 million, while Bushbury Hill Primary School, at 1,900 sq m and 240 children, had a budget of £4.2m.
Both began on site in October 2010 and the first phase, the new school buildings, was completed in October 2011. Overall completion for both sites is February 2012. Phase two, which includes demolition of the old schools and external works, has commenced on both sites.
Many projects aspire to become Passivhaus-certified or BREEAM Outstanding, but they are aspirations rather than obligations. This was not the case at these schools. Passivhaus certification was a ‘must’, increasing the pressure on the team to get it right.
“The Passivhaus element was a contractual requirement – we had to achieve certification,” says Thomas Vale senior contracts manager Kevin Zamur.
To familiarise themselves further with the principles of Passivhaus, the operational team went to Germany to visit the Pro Climate training centre.
“In Germany they have been working on Passivhaus for over 20 years. Our visit enabled us to get more of a feeling for all the details needed to achieve the certification – the taping and sealing methods, the various gaskets and so on,” says Mr Zamur.
To gain Passivhaus certification, a building needs to have excellent thermal performance, use minimal energy for space heating and the envelope must be highly insulated.
Both schools were constructed using a timber frame and timber panel system. The insulation was manufactured by Warmcel and made from recycled newspaper.
“We collected the newspaper in the schools during construction. It went to the Warmcel factory to create the insulation for the new school buildings,” says Mr Wisdom.
The windows are triple-glazed timber-frame windows, assembled in the UK by a subcontractor who sourced the components from the Continent. “Most of the windows and doors that are Passivhaus standard need to come from Europe, but these were assembled in the UK, which is unique,” says Mr Wisdom.
The insulation for both schools was also unique, as it was wrapped around the entire structure, including the building slab. “A duvet layer surrounds the entire building with insulation,” explains Mr Wisdom.
“There was 250 mm of insulation under the slab, which is not standard, and the insulation that went around the walls was another 300 mm. A typical building probably has about 150 mm on it.”
One of the requirements for certification is an air-tightness of 0.6 cu m/h/sq m@50Pa or lower, so the team carried out various intermediate tests during the build programme.
“We did the intermediate air-tightness test when the timber frame was erected, the roof was on, the windows were in and the flooring was down. We needed to be sure at the point we started closing off walls that we were achieving the required levels of air-tightness,” says Mr Wisdom.
The intermediate test received a score of 0.34 cu m/h/sq m@50Pa – much lower than required. Once the tests showed the building envelope was adequate, the biggest challenge for Thomas Vale was ensuring this was not compromised by any of the work carried out by subcontractors.
“When the M&E contractors came on board and started doing the M&E for the fixed installations, we managed the process so that everybody was fully aware they had to stick to the required routes for the services,” says Mr Wisdom. This included appointing “air-tightness champions” for both sites, who monitored and managed the whole process.
Alongside the work of the air-tightness champions, the design team ran other initiatives.
“When we began work on site it became obvious that many of our supply chain had not dealt with Passivhaus before either, so we ran workshops throughout the build programme,” says Mr Zamur.
“The workshops would include details of the timber frame, the windows and doors, the roof and the M&E installations generally.”
The final test results that have gone forward for the certification are 0.48 cu m/h/sq m@50Pa for Oak Meadow and 0.53 cu m/h/sq m@50Pa at Bushbury, both acceptably below the required limit.
“We were delighted with this result,” says Mr Wisdom. “We worked closely with the entire project team, the architects, the Passivhaus consultants Elemental Solutions and our supply chain.”
Following construction, Thomas Vale and Architype remain involved with both schools to ensure the buildings are performing to standard.
“The lead architect and I are in the schools weekly, so if there are issues that the staff, the teachers or the children have, we can deal with them quickly and make sure the school is being managed properly,” says Mr Wisdom.
“Teachers who don’t know anything about construction are educated about it; we hold their hands through the whole process while they are trying to settle into a new building, and they can rely on us to deal with any issues.”
These visits will decrease in frequency to become monthly for the first 12 months following construction.
The success of projects such as these hinges on the whole team, from the client to the smallest subcontractor, understanding and embracing the principles of Passivhaus.
“If we’d got into contractual arguments with our supply chain or design teams, the focus on achieving the standards and quality of construction would have disappeared, so it has been critical to have that team spirit throughout the process,” says Mr Wisdom. “The quality of the relationship across that team has been amazing.”