Paul Newman from Potton talks through the construction of the UK's first Passivhaus show home.
Interview with Paul Newman
Paul Newman is the Self Build Director at Potton. Potton, which recently celebrated their 50th anniversary, have helped design and build over 6000 homes and have a portfolio of over 12,000 different designs. The Potton approach to custom build is to work with landowners to secure outline planning permission on their sites, with design left as a reserved matter. They find customers for those sites who then buy the land from the individual landowners. Potton then work with the customers to provide their normal self build package.
At their site in St Neots they have a show centre of completed houses, where they are currently adding a Passivhaus. They have been sharing progress of this build with video updates and have also allowed members of the public to experience it being built.
Building a Passivhaus show home was an obvious step
Potton have four complete show homes at their St Neots site and one at the National Self Build and Renovation Centre. Moving with the changing market and increased demand for low energy homes, their last show house was constructed to achieve level 4 of the Code for Sustainable Homes. Wanting to move their business on and offer customers something new, they decided to construct a further show house, with a Passivhaus being the obvious choice.
Their experience over the last 8 years has been that they're being asked more and more often about energy efficiency and low energy homes and hope that this Passivhaus and the lessons they have learnt from it will put them in good stead for the future.
The design aimed to push the Passivhaus standard hard!
In coming up with the design Potton were keen to challenge the reputation that Passivhaus buildings sometimes have of being simple, boxy designs. They expect to evolve different design forms based on this Passivhaus, while not necessarily directly repeating it.
The building form is quite complicated and has a valley roof, so from a thermal bridging perspective the junctions have been tricky to resolve. Paul also thinks their life would have been much easier if they'd taken 18 inches of height off the design!
Something they found encouraging was the use of an innovative self adhesive breathable membrane which has contributed positively to the building's airtightness. The first airtightness test had a figure of 0.68 but after some alterations they managed to get it down to 0.5.
The SIPs system took a matter of days to install
The house has been constructed with Kingspan Tek – a product which is certified by the Passivhaus Institute – and Potton have been using it for the last 10 years on both their self build and volume contracting business. It provides a thermally robust solution and can be erected on site very quickly. One consideration, however, is that once installed it is hard to make changes to room layouts, etc.
Use PHPP modelling from day one to see how the building is performing
Paul explains that early modelling in the Passivhaus Planning Package was an important lesson for them when designing the Passivhaus. By doing this, something that showed up early on was that the building had a tendency more than was desirable to overheat. They were able to experiment by changing the overhangs, reveal depths and specification of the performance of the glazed units within the windows to make a considerable difference.
Engage with suppliers early in the process
There are two main lessons that Paul feels they have learned from the Passivhaus self build process. The first is the need to engage early on with suppliers to make sure they understand what you're trying to achieve, have the right products available and certifications in place where appropriate. While they did try and engage early with their supply chain, their lesson was that they actually should have engaged even earlier and placed some of their orders earlier too.
Secondly, Potton worked with sub-contractors who they have used on hundreds of other Potton houses in the past. What they found was more attention to detail was required to achieve Passivhaus performance, and they needed to have their hands held tightly throughout. Paul thinks this is something that won't be unique to their build, as there just aren't enough experienced Passivhaus sub-contractors out there.
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