The Denby Dale home project draws to an end

Today the Denby Dale Passivhaus gets its official certification - one of the first three projects to be certified today by Pete Warm of WARM: Low Energy Building Practice (and verified by the Passivhaus Institut in Germany). We had a party at the house on Monday in anticipation of this, attended by all the team (architect, clients, builders) as well as supportive local councillors and officials from our progressive council, Kirklees, presided over by the mayor of Kirklees herself. Much cake was consumed and tea drunk and it was great to be able to see the house looking lovely and fresh and bright, without scaffolding and building site mess. There will be an official Passivhaus plaque and certificate coming our way soon and it will be very nice for me to wave a copy of it at the Passivhaus conference in Dresden when I go there in May.

Certification processPassivhaus is a clearly defined standard for low energy building developed by the Passivhaus Institut in Germany. There is now a handful of Passivhaus certifying bodies in the UK - BRE, Inbuilt, Scottish Passive House Centre and WARM. To become a certifier, you need to have experience of Passivhaus construction and design, to have undergone an internship with the Passivhaus Institut in Germany and consequently become approved by the institute as a certifier. Once are approved, a certifier’s first three certified projects need to be checked by the Passivhaus Institut and thereafter certification would be checked on an annual basis to ensure quality is maintained. Our certifier in this case is Peter Warm of WARM, who also did our original PHPP calculations.

Because we are also using WARM for certification, Peter had to have his PHPP calculations peer-reviewed by energy consultant Alan Clarke. Alan is an experienced building services engineer and independent energy consultant, who as well as running his own consultancy, is one of the key energy advisors to the AECB. For the certification process, the project had to be completely re-entered into PHPP, which Alan has done alongside checking calculations, thermal modelling and the like.

The Passivhaus Institut has a long checklist of data we needed to provide for certification, such as: details of all the junctions; Therm modelling; photographic evidence; product certificates proving U-values and performance; detailed MVHR specification; documentation of airtightness and so on. The certifiers also needed to double-check which materials we did use in the end to see if they’d changed at all.

The Denby Dale Passivhaus was one of the first three projects to be certified by WARM and so has also had to be verified by the Passivhaus Institut - confirmation of which came through today!

Final figuresAirtightness: 0.33 ach @50 Pa measured using the Euronorm and Passivhaus method

Passivhaus requirements are 0.6 ach @ 50 Pa

For Passivhaus certification (and Euronorm methodology), the volume of all internal partitions, stairs, floor void etc are discounted in the airtightness calculations, resulting in a lower overall internal volume (in this case internal volume is calculated as 277m3).

Space heating: 15 kWh/m2/annum (actually it was probably lower than this but the certification process only verifies final PHPP figures as meeting Passivhaus standard of 15 kWh/m2/annum).

Partnership workingThe success of the Denby Dale Passivhaus is all down to the building team on site. They made it happen and they really took on board what needed to be done and why. I can’t imagine how we would have got this level of performance using the usual procurement method of subcontracting common in the construction industry. You need a connection between trades and knowledge of every stage of the build. You need those on site to understand who know every facet of the build and to have an understanding of, for example, why you have to be careful about puncturing the airtightness barrier.

It is possible to get a building to reach at least modest levels of airtightness with conventional mastics, silcones and gaffer tape - which is the traditional way that the British construction industry has done it -but these are all measures that break down quickly. Passivhaus design in PHPP requires quality materials and quality methods. I feel confident that the Denby Dale Passivhaus’ performance will last the lifetime of the building - it is a very solid house.

The relationships between all the team have been vital - us, the clients, the building team, the architect and product experts within Green Building Store. It comes down to a good working partnership. Our clients Geoff and Kate have been brilliant and have followed every stage with great interest. I will miss our bi-weekly meetings with them over homemade lemon drizzle cake and quality coffee.

The futureWith the knowledge that we have gained at Denby Dale, we are keen to develop both new build and retrofit projects within West Yorkshire. We are very excited about the prospect of applying Passivhaus principles to existing buildings - because obviously they are the majority of buildings in the UK. We are in the research stages of a possible Passivhaus refurb project on a thirties detached house in West Yorkshire, using PHPP. The principles of Passivhaus new build and retrofit are the same. You put your money into making the thing perform better. You would need to use PHPP - you might not get down to the levels that a new build might take but if you’re getting down to something like 20kWh/ m2 you are making a massive dent in CO2 emissions.

We at Green Building Store are also expanding and strengthening our Passivhaus products and services to include: construction; consultancy; training; and Passivhaus products. Interest in all things Passivhaus seems to be growing almost by the day, and we have recently had approaches from housing associations, local authorities, and individuals all interested in furthering their understanding of the Passivhaus approach, and particularly in our experience of cavity wall construction.

As I said in the previous blog, I am very keen that the growing interest in Passivhaus design translates into high quality design and construction. This is why Passivhaus certification is so important and why I keep banging on about training and partnership working. We must try to ensure that anything claiming to be a Passivhaus, really is one. Quality assurance is vital. That is also why we are now active in supporting the work of the newly established Passivhaus Trust. This is a not-for-profit initiative of the AECB, which is receiving support from some of the key players in the industry. As chair of the AECB, my business partner and technical adviser on Denby Dale Chris Herring, has been very active in getting all of this off the ground, and is now first chair of the Passivhaus Trust.

The Passivhaus diariesFor me it is an honour to be able to play my part in promoting and developing Passivhaus in the UK, and to support a construction methodology which I believe can really play a part in addressing the urgent issue of climate change. I have really enjoyed the experience of writing the Passivhaus Diaries blog itself and it has been great that Building has given this spotlight to this particular corner of the burgeoning Passivhaus movement in the UK. It has been both nerve-wracking and a great honour to have our small West Yorkshire project under scrutiny and I really appreciate the comments and support of those who have followed the blog.

It won’t be the end of our blogging activity though - Geoff and Kate have said that they are up for a monthly blog on “Living in the Denby Dale Passivhaus”, which will probably start in June - look out for it on our website (, which will cover their experiences of living in the house, and experiences of low heating bills and MVHR etc. Leeds Met will be measuring energy usage of the house post-occupancy to see if it is performing as predicted by PHPP. Building will also be looking at how Denby Dale is performing from the clients’ perspective in a few months - so watch this space!