HPH183 : How to achieve an outstanding airtightness result
Buckinghamshire Passivhaus has become one of the most airtight buildings in the UK. As such, we consider what factors contributed towards their exceptional result of 0.08 air changes per hour at 50 Pascals.
In this podcast we hear from key team members involved in the construction on this energy-efficient home.
Buckinghamshire Passivhaus timber frame
Following a PH15 build
As luck would have it, this is actually our second in-depth video case study for The Hub (the first being Long Barrow).
I'd got to know Janet Cotterell, author of The Passivhaus Handbook, quite well and been intrigued by the development of the PH15 system.
So since autumn 2016 every week or so we have been filming progress on site. Now the building is watertight and ready for its preliminary airtightness test.
The PH15 system aims to make Passivhaus affordable for everyone
The Passivhaus Homes PH15 system has been developed over time to address many of the challenges of achieving Passivhaus standard.
The system is manufactured off-site and delivered in packs as needed. With good carpentry skills, it is easy to assemble.
We spoke to Janet about it in episode 121 – the pros and cons of building with a kit or system.
A team effort helped them achieve an exceptional result
It's one thing using a ‘Passivhaus' system to meet the standard, but an outstanding result like this is only possible with a team effort.
At the heart of this is the relationship between client, architect and contractor.
There also needs to be buy in from everyone on the team.
Carpenter Wayne was determined to get an airtightness result of 0!
Not satisfied with merely meeting the Passivhaus criteria, foreman Wayne Kempster from Jigsaw Construction set himself the ambitious target of achieving 0 air changes per hour at 50 Pascal!
Despite being impossible Wayne wouldn't aim for anything else.
And let's remember this is Wayne's first ever attempt to build a Passivhaus.
Air leakage expert Paul Jennings' best ever result
With 30 years of experience, Paul knows a thing or two about airtightness. In fact he was the key contributor for the House Planning Help documentary The Future of Housing.
At Buckinghamshire Passivhaus he recorded a reading of 0.087 air changes per hour at 50 Pascals, his career best.
Paul points to the PH15 system as well as the team for achieving this result. “Fundamentally it's a very airtight system. You've got airtight boards, good tapes and quality control of people doing the works.”
Simple detailing increases the likelihood of a good result
Janet says: “If the detailing is complicated, however good the builder is, they're going to struggle.”
When it comes to sustainability it's amazing how often simplicity comes into play.
The PH15 system is designed in such a way that the airtightness layer is always easily identifiable.
Training before construction is vital preparation
Janet stresses that proper contractor training is essential in this process.
While it doesn't have to be a long session, it's extremely valuable to see how the system comes together.
The concrete basement contributes to this level of airtightness
Glatthaar is one of the few basement companies to guarantee Passivhaus performance.
Paul says: “Having the basement helps because you've got a concrete box which is going to be airtight, and it adds to the volume.”
In episode 163 Andrew McInulty helped us understand what makes an effective basement.
Everything coming together is the only way to get below 0.1
Buckinghamshire Passivhaus has a simple form and is built with a simple system. Exceptional care has been taken during the construction. There's a strong team with a lot of experience between them.
Overall, everything has come together.
