performance standard

Quality assured Passivhaus buildings: It's more than a number – Part 2

Mark Siddall of Low Energy Architectural Practice:  LEAP

Mark Siddall of
Low Energy Architectural Practice: LEAP

In part two of his two part article on quality assured Passivhaus buildings, Mark Siddall [], who specialises in sustainable building design, explains the certification process in a little more detail.

In the last article I explained that the Passivhaus standard is much more than an energy performance standard, it is also a quality assurance standard that closes the gap between theoretical performance and reality. I also highlighted the importance of using the appropriate design tool (the Passivhaus Planning Package) when designing Passivhaus buildings, and I discussed the ways in which buildings that are not subject to the same quality assurance system have been found to fail to satisfy their performance targets.

In this article I will discuss the accreditation of approved certifiers, Passivhaus designers, products and buildings and the fact that, in order to assist with delivery of its Passivhaus projects, Devereux Architects has developed a stringent quality assurance methodology known as the Passivhaus Delivery System. To assist with the dissemination of the lessons that the practice has learned, it is to become a founding member of the Passivhaus Buildings Trust, a new organisation established by the AECB and committed to assisting the UK with the delivery of buildings that perform as intended.

Approved certifiers

The Passivhaus Institute regulates who is able to certify Passivhaus buildings. In order to become an approved certifier, applicants must work at the Passivhaus Institute for two weeks undertaking training and checking proposed Passivhaus designs. Currently there are four approved certifiers in the UK. Peer review, a well respected tradition in academic circles, serves to ensure errors are eliminated and that quality is maintained.

One of the issues that can put people off the certification process is the cost, particularly if it means that dual certification is required; say Passivhaus and Code for Sustainable Homes. In this respect the risks need to be weighed against the losses. Do you want to achieve the carbon reductions in theory or in practice? Do you want to be exposed to claims of negligence or not?

If the designer has not built a Passivhaus of your building typology before, albeit a house, school, hospital or office, then they may not have an adequate quality assurance system. For this reason I would tend to offer a cautionary note and would suggest that certification is a wise choice, after all you want to be sure that you're getting the energy and carbon savings that you are paying for.

If, as a client, you employ a certified Passivhaus designer you can be assured that they have a certain level of competency, certainly higher than average; but once again if they have not delivered a Passivhaus they may not yet have all the tools in place. Perhaps, in this case, a client could proceed at risk and decide that there is no need to go through the certification process, but ultimately certification is the surest way of ensuring success.

Experiences at the Passivhaus Institute (PHI) have shown that the certification process can actually serve to focus the attention of the design team and can, with a little coaching, actually end up a lot less complex whilst also achieving the end goal. In this respect the certified buildings become less expensive than would otherwise have been the case; so in essence certification more than pays for itself.

Certified Passivhaus designers

There are two means by which a designer can become a certified Passivhaus designer. The first is to build two Passivhaus buildings and get them certified. This is a particularly challenging approach but has been achieved. Until recently it was the principle method of proof (in fact it was the initial approach that I embarked upon and, given the paucity of information in the English language, required a great deal of research). However, of late the Passivhaus Institute has established a training course to allow people to become certified Passivhaus designers (I attended the first UK course late last year). The intensive ten day training course covers the design and specification of the building fabric, ventilation, heating and of the requirements of the standard. The course is then followed by a rigorous three hour exam.

If a client desires a Passivhaus building there is no technical requirement to employ a certified Passivhaus designer, However, there are distinct advantages insofar as they have proven that they have the basic knowledge and the skills. Having passed an exam should not of course be confused with experience, and ultimately experience is the surest way to avoid any of the pitfalls that can catch the Passivhaus designer unaware.

Certified designers can, dependent upon their background, contribute to a project by undertaking the design first hand or by coaching a less experienced design team. An experienced certified designer, or a certifier for that matter, can help to streamline the design, avoid abortive work and advise upon optimisation of the design and construction process. By undertaking these roles they can assist with the delivery of robust solutions and help to minimise, and even reduce, both the capital and the running costs without compromising the ambition of the project.

Certified components

Passivhaus certified components can be recognised by the use of the Passivhaus Institute logo. Components include windows and ventilation heat recovery systems. The first, and most reasonable, question that can, and should, be raised is, is there a need for certified components? You could say that the unfortunate answer is 'yes'. Let's take a look at the reasons why each of these components require certification.


The Passivhaus standard requires that windows have a whole window U-value of 0.8W /m2K. The thermal performance requirement is not a whimsical number. Like everything in Passivhaus design it is supported by an understanding of building physics and the desire to satisfy human comfort requirements under a given set of design conditions. The whole window U-value has to be calculated in accordance with EN 10077 and includes the frame, the spacer bar and the glazing. Furthermore when designing a Passivhaus, using PHPP, the thermal performance of each window component must also be considered - experience has shown that such data is not readily available from most manufacturers and suppliers. Certification makes sure that manufacturers have such information available and that it was verified.

Provided the design parameters that underpin the U­-value requirement are met, with sufficient knowledge and understanding of building physics, it is possible to design certified Passivhaus buildings without using certified windows. In theory this can save money. However if the manufacturer is not familiar with Passivhaus and can not readily provide the supporting data, this process can be more trouble than it is worth as the design fee is likely to increase to cover the additional workload. There is a nice little anecdote to support this. Some years ago, at the 7th International Passivhaus Conference, one lecturer presented analysis that suggested the best option for reducing costs was not to use Passivhaus certified windows. A year later the same lecturer came to the conference to present his views about Passivhaus design. The difference was that this time, now that he had a little more experience and had worked on a couple of Passivhaus buildings in Vienna, his message was now "Only use certified windows! All the other stuff is substandard. And it's difficult and expensive to check!"

Heat recovery ventilation (HRV):

Compared to windows it is more difficult to avoid the need for certified heat recovery ventilation (HRV). One of the reasons for this is the fact that glazing systems can be thoroughly specified by the designer and can then be batch processed by the manufacturer on a project by project basis. The same design flexibility is not available with heat recovery systems for, whilst they are relatively simple components, their design relies upon a great deal of careful and skilful engineering.

The Passivhaus Institute uses a different testing procedure to that described in EN 13141 (Ventilation for Buildings) - the standard which is used for SAP Appendix Q assessment. The reason for this alternative testing method stems from the fact that when the Passivhaus Institute (PHI) started their research they found that air could leak from one side of the heat exchanger to the other. This not only inhibits the thermal performance of the heat recovery system but also compromises thermal comfort as the supply air is colder than comfort standards would recommend. The PHI also recognised that the thermal envelope should be described in a realistic manner, i.e. what is really needed is the performance of the heat recovery unit in a building and not in a laboratory - something that the EN standard also fails to do.

Passivhaus design

When the PHI undertook lab tests and ran through the physics they found that there was, on average, a 12% difference between the calculated performance using the EN standard method and monitored values based upon the PHI's alternative method. In effect the EN standard overestimates the performance of heat recovery units because it counts losses from the laboratory and into the exchanger as if they were heat gains, and because it does not properly account for air leakage within the unit - which are again incorrectly treated as gains. Worryingly, on the basis of recent on-site measurements from installed but uncertified HRV units, Dr. Rainer Pfluger from the University of Innsbruck reports that, the differences in performance can be even more extreme.

For a worked example I'll take two HRV systems, one Passivhaus certified and one EN tested. For convenience both have an apparent efficiency, of say 87%. Using the EN tested unit in a building, rather than a laboratory, it has an efficiency of about 75% in the specific case. I then tested these two units on a Passivhaus modelled in PHPP and found that the house using the EN tested unit, would consume about 25% more energy than the Passivhaus certified unit. (If you were to address energy performance deficit, by improving the opaque thermal envelope alone, you would need about 125mm more insulation!)

Delivering Passivhaus buildings

Stating what is required for the delivery of a Passivhaus, at the first Passivhaus Schools conference, former Deputy Chief at the Energy Department of Frankfurt, Axel Bretzke said; "You need architects and other design team members with an obsession for good quality, simple and creative solutions, a knowledge of building physics and some prior experience of energy efficient buildings". From this statement it can be appreciated that a Certified Passivhaus is greater than the sum of its parts and is only made possible by employing the right people, and quality assurance tools, and having a thorough understanding of the requirements. Sadly it is here that the supposed 'Passivhaus' buildings that were discussed in the previous article seem to fail.


For the last eighteen months I have been working with our client, Gentoo Homes, on a residential development that incorporates 25 Passivhaus standard homes at the Racecourse Estate, Sunderland. From day one we have worked very closely with Alan Clarke, our energy and services engineer, to develop the design. This close working relationship has been instrumental in our ability to get this far. Judging by my experience to date, and having recently completed the first English language version of the certified Passivhaus designer course, I have reached the personal conclusion that, whilst the course is pretty robust, it does not yet take into account the quirks of the UK building industry; as a consequence there is still a potential knowledge gap, albeit much reduced, between theory and practice. It is for this reason that Devereux Architects has undertaken an extensive three year research programme and developed its own Passivhaus delivery (PHD) system.

If this gap is to be bridged on a large scale there is still a substantial amount of desktop research that is required before being able to realistically deliver a certified Passivhaus that performs as intended. For instance, there are a few scant scientific reports on the phenomenon of thermal bypass - unaddressed heat loss can increase by over 150% - and very little information on delivering truly airtight buildings. With this in mind my last few years of painstaking investigation, which now forms a part of the PHD, should be sufficient. I am looking forward to learning about how the buildings perform in reality - as they are to be studied by the EST and the Good Homes Alliance, time will tell whether all the efforts have paid off and whether we have succeeded in delivering a Passivhaus.


The Passivhaus delivery (PHD) system is a totally new kind of quality assurance system that is focussed upon delivering low energy buildings. The operating procedure has a number of phases. The first phase occurs during the briefing process. Here we deliver and facilitate Passivhaus workshops to improve the understanding by the client and the design team.

During this process we raise general awareness of what it means to procure a Passivhaus building and highlight the fact that some new approaches to brief development are required. The second phase occurs during the tendering process, here we run a workshop to inform the contractor about Passivhaus, the requirements that it places upon the scheme and we also work to dismiss a lot of myths about buildability (if the project is being managed through a partnering process or as design and build contract, this workshop may occur earlier in the process). The third phase occurs post tender. Here we provide workshops to the contractor's project manager and the sub-trades.

Our system also includes a new quality assurance tool, the purpose of which is to assist the construction supervisor and the site staff with ensuring that the buildings are constructed to the required standards. The quality assurance process also includes the requirement for the commissioning of heat recovery systems and heating systems. In addition to this we also require that the construction supervisor reports any deviations from the design drawings so that we can assess the impact upon the buildings performance - this process is critical as workmanship can make or break the scheme.

The purpose of this exercise is to assist the contractor with ensuring that the building is constructed in the appropriate manner. Whilst the project is on site we regularly inspect the site and photographically record the progress of the work, to address specific concerns, and we continue training for each new sub-trade that arrives on site and find design solutions to any unresolved issues.

During the first year or two the systems begin to bed down and settle in. They can have a tendency to begin to drift away from their settings, and whilst certain gremlins come to light, others can go undetected for years - decades even. Seasonal commissioning should be a necessary part of the annual maintenance schedule. Strictly speaking, this particular process lies outside of the requirements of the Passivhaus standard - but it is not outside the recommended approach to quality assurance. After all, which building owner would, after having made a substantial capital investment, willingly turn their back on it and then squander money on the energy bills that they had sought to mitigate? In buildings it is import to ensure regular maintenance is undertaken. There are a growing number of proven strategies for delivering successful long term building maintenance - once again these are reviewed as a part of Devereux's PHD system.

Post construction

In order to help ensure that the building will perform well in reality, aspects of human behaviour and building usage must also be considered. For this reason the role of the PHD continues beyond the construction phase and engages with building occupants, maintenance personnel and facilities managers. Once again workshops are used to inform people about the new building and how they can get the most out of it. Building occupants are briefed about the control systems for thermal comfort, lighting and acoustics whilst the people that manage the building (which may or may not be the occupant) are briefed about maintenance schedules and the like. To ensure that these valuable lessons are not, in time, forgotten, two simple manuals are prepared that explain the key features, facts and requirements of the building.

It should be recognised that the focus of the PHD differs between non-domestic buildings and residential ones. The reasons for this change of tack are that non­domestic buildings tend to be larger and more complex - thus requiring greater explanation and understanding, and also the fact that non-energy considerations can have a substantial impact upon the total lifecycle cost of operations - often even greater than that of the energy costs. It is apparent here that the interest, as with most good Passivhaus, is in providing multiple benefits from single expenditures.

Is it necessary to certify a Passivhaus building?

At the start of this article I ventured to suggest that the only real Passivhaus is a certified Passivhaus. Strictly speaking this may not be the case, provided that certain assurances are in place. For example, as fellow AECB member Nick Grant of Elemental Solutions explains; "If a Passivhaus building is not to be certified one party or another must be willing to stand by the claim if challenged; this may be the architect, a clerk of the works or the constructor". For example a person buying a home described as a 'low energy eco-building' could expect high levels of comfort and low energy bills. However, if they find that the building uses more fuel than expected, and because in the UK 'low energy eco-building' is not an established performance standard, they would have little foundation for a claim (like the German 'low energy' homes from the 198O's, some so called eco-buildings are unable to achieve comfortable temperatures in cold weather). If this building had been described as Passivhaus the owner could ask to see the PHPP calculations, the results from the blower door test, construction details and specifications.

If these documents were in order then further investigation could be carried out. It may suggest that the owner could be enjoying a higher than normal indoor temperature or may be leaving windows open all winter. If this is denied then it should be a relatively simple matter to determine whether or not the building has been constructed appropriately, even if it would be too difficult to identify exactly where the heat is being lost.

Passivhaus Buildings Trust

Due to differences between certain UK and German national standards, and differences in construction technologies, there is a need for a platform, a centre for excellence that can assist with the integration, coordination and delivery of the Passivhaus standard within the UK context. Such a platform would also ensure that the quality of the Passivhaus standard is not compromised. To assist with these integration issues such a platform has now been established by the AECB, the Passivhaus Buildings Trust. This not-for-profit organisation will work for the public good and recognises that reducing energy use and carbon emissions from the UK's buildings is a major challenge. The Passivhaus Buildings Trust aims to:

• Be a centre of excellence for information, knowledge and skills.

• Develop accreditation schemes for individuals,

companies, products and services which can deliver low energy buildings.

• Help to generate flagship low carbon developments throughout the UK.

• Assist with the coordination of approved certifiers and to certify Passivhaus buildings.

The rapid introduction of the knowledge, skills and products to deliver low energy, low carbon buildings requires focused leadership. For a number of years Devereux Architects has had an interest in promoting the low energy, low carbon agenda. The practice is proud to announce that it is to become a founding member of the Passivhaus Buildings Trust.


In this series of articles I have identified, and then clarified the reasons for, the chain of quality assurance mechanisms that run throughout the Passivhaus certification and delivery process. Each one is necessary; each one is a critical link in the chain. I hope that the next time you read an article on a building that is claiming to be, or perhaps need to make a decision about procuring, a Passivhaus you will be able to ask yourself a few questions and determine whether or not the project could really be what it says it is.

Accessed online: 7th August 2014

The Lightbulb Moment

Did you ever have a really good idea about how to save money?  Paul McAlister (Passive House Architect), Richard Bell (Solmatix Renewables) and Eamonn Connolly (SIPFIT ltd) are three local house experts who have had their lightbulb moment and have discovered the secret of building a house which reduces heating costs by 80%.  They shared their knowledge with 85 delegates last Thursday at a Passive House seminar in Belfast’s Ramada Hotel.

left to right - Eamonn Connolly, Paul McAlister, Richard Bell

“The Passive House is the fastest growing energy performance standard in the world with over 30,000 Passive House buildings built to date.  It’s a very simple approach and it is based on excellent thermal performance, exceptional airtightness and mechanical ventilation,” explains Portadown architect Paul McAlister, one of the keynote speakers at the seminar.

“It’s a lovely house to live in.  In winter, there is a comfortable indoor climate with fresh air, less dust and no condensation problems – that’s definitely good news for any allergy sufferers.  The bank balance also benefits as heating costs are reduced by a staggering 80%.  Government grants are available too, such as those from Land & Property Services which offer free rates for five years to the occupier of a new zero carbon home and two years to the occupier of a new low carbon home.”

Almost 400 new homes were started in Northern Ireland between January and March 2011 according to the National House Builders Federation.  An increasing number of new homes are being designed with some Passive House features and with the change in building regulations this will become more popular.

Using the right building components is key in designing a Passive House.  “By including features such as triple-glazed windows and super insulation, it’s possible to make significant long-term savings in fuel costs.  It’s estimated that it costs £2,600 to heat a traditional house each year but by including the “Passive House” low energy features, fuel costs can drop to as little as £220 per annum,” continues Eamonn Connolly from Warrenpoint’s SIPFIT Ltd who specialise in pre-fabricated insulated wall panels.

Renewal energy is the icing on the cake of a Passive House.  Local company Solmatix Renewables are very experienced in this area and their owner Richard Bell is very passionate that this is a must-do for all new home owners.

“Fuel costs rocketed last winter and we have to look at new ways to heat homes in Northern Ireland.  An air source heat pump is a renewable low cost alternative to a traditional oil boiler.  Add to that some solar panels and significant extra savings can be made to household fuel costs,” explains Richard.

So now is the time to have your lightbulb moment.  “Think Passive House” as you plan your dream home so that you can switch on to savings in your bank balance, better health and lower CO2 emissions.