Quality assured Passivhaus: Part 1

mark Siddall

In part 1 of a 2 part article, Mark Siddall of Low Energy Architectural Practice: LEAP  observes that there appears to be mounting confusion about the PassivHaus standard and PassivHaus Certification. Here he reflects upon the implications of such misunderstandings. It’s time to straighten out some the facts.

The Government has undertaken a legal commitment to reduce carbon emissions by 80% by 2050 and is developing tools and strategies to try and ensure that this commitment is satisfied. This has led to the rise of the Code for Sustainable Homes and a series of net-Zero Carbon targets for new build projects - whereby homes are to be net-Zero Carbon by 2016, schools and pubic buildings by 2018 and commercial buildings by 2019. However, recent research by Leeds Metropolitan University has found that homes built to energy performance standards, including Building Regulations, are not performing as required. This fact alone raises some important concerns. Quality Assured PassivHaus buildings have been proven to perform in accordance with theory. However, in the UK, there is growing number of projects that people claim to be PassivHaus buildings but upon closer analysis do not appear to satisfy the rigorous quality assurance requirements established by the PassivHaus Standard. This introduces risks that could damage the growing reputation of the standard before it has been properly established.


A quick recap

In case you didn’t know the PassivHaus Standard is the worlds leading energy efficiency standard and it can be applied to all manner of building typologies including homes, offices, schools, care homes etc. Of late I’ve been to a number of meetings and conferences where it has emerged that people tend to think that the PassivHaus Standard is “a number” or perhaps a series of “energy performance parameters.” The basic, well publicised, performance requirements that tend to be recited include:

• An annual energy consumption for space heating of ≤15 kWh/m2.yr
• A primary energy requirement of less than ≤120 kWh/m2.yr (best practice being less than 70 kWh/m2.yr) 1
• An air leakage of less than ≤0.6 ach @50pa when tested in accordance with EN 13829
• Perhaps they are also aware that the risk of overheating should be ≤10% (with best practice being less than 5 %.)

What is not recognised in these statements is the background to these standards. Supporting these basic requirements are a number of other less widely appreciated requirements that serve to deliver thermal comfort and energy performance all via a carefully structured quality assurance system.


Towards a need for Quality Assured Buildings

Rather than discuss the process of delivering low energy buildings people seem to have a fascination with design targets. The question is, do these targets turn into a reality? When asked how he got involved in working on low energy buildings Dr Wolfgang Feist, founder of the Passivhaus Institut, said

“I was working as a physicist. I read that the construction industry had experimented with adding insulation to new buildings and that energy consumption had failed to reduce. This offended me – it was counter to the basic laws of physics. I knew that they must be doing something wrong. So I made it my mission to find out what, and to establish what was needed to do it right.”

In this respect I personally find the above statement by Dr Feist rather intriguing for it indicates to me that in Germany, just as the UK, quality assurance is key to the delivery of truly low energy buildings.

In the context of a PassivHaus building what is meant by “quality assurance” needs to be clearly understood. Here it includes the correct building physics concepts, the correct application of these concepts during design and specification processes and finally the correct implementation on site. Various aspects of these quality assurance issues will be considered in more detail below but first it is useful to provide a little background as to why this quality assurance is required. A little bit of history will serve to make a point.


The History of the Low Energy Standard

In 1983 Sweden developed an energy performance standard that limited the space heating 50-60 kWh/m2.yr (the theoretical performance of the 2006 UK building regulations). In Germany it was recognised that the average German home uses 200 kWh/m2.yr for space heating and that if Swedish energy standard were to be adopted then a factor four reduction in energy demand could be achieved; this led to the rise of the largely unofficial voluntary “Low Energy Standard.” This eventually led to a tendency for architects and builders to make claims about having built low energy houses simply because they orientated the house in a southerly direction or applied an extra couple of centimetres of insulation. After a while newspaper articles began to crop up with statements such as “family uses more energy in their new low-energy home than in the old heritage building they previously occupied”, “mould problems in low-energy houses “, or “low-energy houses are only for the hardiest, as they stay quite chilly in winter to save on energy.” Anyway you get the point, the buildings were not delivering the required performance and the public felt duped as they understandably began to believe that there aren’t any real benefits from “energy efficient” buildings. In this context it is not surprising that German research into building physics found that low energy buildings did not always perform as expected – eerily, as recorded by Leeds Metropolitan University, this finding is reflected in UK experiences. As noted in the quote above it was with this in mind that Dr Feist set out to understand what was going wrong.

Later, in order to overcome the failures in quality assurance, RAL 965 was developed for the Low Energy Buildings. This simultaneously created a definition for low energy buildings, protected the design standard from abuse and, as a basic term and condition for delivery and sale, provided the people requiring low energy buildings with a quality assured product2 Interestingly the most recent version of RAL 965, issued in 2009, also includes the PassivHaus Standard and requires that both Low Energy buildings and PassivHaus buildings are designed using PassivHaus Planning Package (PHPP). In many respects the Energy Performance Standards delivered by the CarbonLite Programme, which was developed by the AECB: The sustainable building association, seek to establish a programme that is akin to the RAL standard both in terms of its numerical prescription and the development of trained and informed builders and designers.


Delivering Quality Assured Buildings

For a PassivHaus the use of PHPP is the most fundamental aspect of the quality assurance process. One of the principal benefits that PHPP offers is that the designer does not have to return to first principles as a number of assumptions have been researched, established and validated by PHI and then included in the design tool. In addition, not only does the tool include all the necessary aspects of building physics that need to be considered, but it also establishes a datum that allows one PassivHaus to be compared to another. In this respect it should be recognised that PHPP establishes a number of conventions which can simplify the design process and enable validation. At this time not all of the conventions in PHPP agree with UK methodologies, often for good reason. There are over 10,000 certified PassivHaus buildings. The heating energy demand, as calculated by PHPP, has been validated against the monitored heating energy consumption of more than 500 new homes.

For a PassivHaus the use of PHPP is the most fundamental aspect of the quality assurance process. One of the principal benefits that PHPP offers is that the designer does not have to return to first principles as a number of assumptions have been researched, established and validated by PHI and then included in the design tool. In addition, not only does the tool include all the necessary aspects of building physics that need to be considered, but it also establishes a datum that allows one PassivHaus to be compared to another. In this respect it should be recognised that PHPP establishes a number of conventions which can simplify the design process and enable validation. At this time not all of the conventions in PHPP agree with UK methodologies, often for good reason. There are over 10,000 certified PassivHaus buildings. The heating energy demand, as calculated by PHPP, has been validated against the monitored heating energy consumption of more than 500 new homes.

[Feist 2004] Feist, W. "Heat transfer losses with respect to building practise", in Heat Transfer and Distribution Losses, proceedings No.28 of the "Arbeitskreis kostengünstige Passivhäsuer" (German), 1st edition, Darmstadt, 2004, pp 123-156

Gerit Horn, in a paper on the legal aspects of designing and constructing PassivHaus buildings, remarked that the “agreement to plan and construct a “PassivHaus” means that the calculation methods used in PHPP apply for the determination of compliance with the PassivHaus Standard." 3 On this basis the requirement for a PassivHaus should form a part of the contractual obligations of the design team and the contractor, furthermore, these requirements should be clearly defined as otherwise the client will not be able to demand compensation based upon the PHPP calculations. This also can also be understood to indicates the fact that providing valid quality assurance systems have been in place certification of a PassivHaus building may not be a prerequisite.


Recent claims in the UK

Recently I have found that I have had the issue of quality assurance in mind when I the read various articles in the press where people (journalists, clients, architects or builders) have made claims about schemes that have been designed to the PassivHaus Standard or having completed PassivHaus buildings.

At first I always find the reports of a new PassivHaus very encouraging but after a while, as I read the article, I repeatedly find tell tale signs - errors and omissions - that suggest that the projects are not actually PassivHaus buildings at all.4 Worst of all in some cases there are even claims of building in accordance with PassivHaus “principles” - these projects are certainly not certifiable PassivHaus buildings. Whilst they are no doubt designed and built by well meaning individuals the projects have not been subjected to the same level of rigorous analysis (leading to inappropriate specifications), they have not used the correct design tools (leading to erroneous assumptions) and they have not been subject to the same standard of quality assurance (which means that errors can creep in and as a consequence theory and reality will not converge).

Now I can hear you, the reader, say “Do such claims matter?” To me the obvious answer is a resounding “yes.” For instance imagine if someone claimed to have a “BREEAM Outstanding” office. Would you expect them to have certification to prove it, or would you think it okay for them just to pass it off without actual substantiation - just because they tried harder than usual? At the moment what I have witnessed is that this kind of thing is happening with the PassivHaus standard - here and there people are making ill-informed, often unsubstantiated, and false claims. Whilst energy efficiency is the focus of the PassivHaus standard it is an over simplification to suggest that it is ‘simply’ an energy standard. It is in this respect that it should be recognised that PassivHaus is also a quality assurance standard. In order to deliver buildings that perform as predicted, as a quality assurance system, PassivHaus works on a number of levels and includes; certifiers, designers, components and ultimately buildings.

Is all this quality assurance required? Perhaps it is worth considering the need for quality assurance in the context of building performance. There is mounting evidence to suggest that buildings that are being designed to achieve thermal performance standards, including the Building Regulations, are in some cases consuming in excess of 70-100% more energy than the predicted values.5 InIn light of the recent discussions at Copenhagen, if there was ever a need for quality assured construction it is now. The old adage “you can not manage what you cannot measure” would seem particularly true here.

Certification schemes such as BREEAM and the Code for Sustainable Homes (CSH) are well meaning, however, by being broad-brush design tools they do not focus sufficient attention upon the key details that can influence a building’s design and ultimately its energy performance aspects. By not focussing attention on the important details it is unlikely to perform appropriately when the building is realised – leading to increased energy costs, increased carbon emissions and greater occupant discomfort. In this respect BREEAM and the CSH fail to offer a sufficiently rigorous quality assurance and, furthermore, this kind of tool has been shown to incorporate what can only be described as perverse incentives that can actually encourage designs that run counter to the greater ambition. 6

It was in this context that within the UK the AECB launched its CarbonLite Programme as a means of improving the quality of the buildings that are constructed. The programme has, to date, concentrated upon improving the quality of design skills, and though practical training for builders is yet to be commenced, much of the current course could be beneficial to contractors and sub contractors as it would serve to raise awareness of key issues.



Evolution or revolution?

The rise of the CSH has led to a dearth of “innovators” each with their own untried and untested super product/concept. Whilst it is great that the UK construction industry is finally thinking, there is an inherent danger of reinventing the wheel at great expense. Perhaps we could in fact be learning from projects that have already been developed, trailed, tested, verified and proven to work.

The Darmstadt PassivHaus was a research project funded by one of the state governments (Hessia). The building physics models for the project were complex and dynamic; much beyond what is required, affordable and replicable for normal construction. The physics was then tested by building a real house that was occupied by families for years, rather than weeks, and was rigorously monitored throughout this period (in fact the houses are still occupied). This is a far cry from the “demonstration” houses at the BRE Innovation Park.

After all this complex research and analysis the PassivHaus Institute went on to develop a simplified design tool that that would enable mainstream construction to replicate the results. This tool became the Passivhaus Planning Package (PHPP). Since then the PassivHaus Standard has been proven to be cost effective time and again in studies across Europe, meanwhile much of the UK construction industry is wasting time, and money, trying to corner a market and score a bit of brand recognition. I just find myself asking whether it would it be wiser to learn from experience. When given the choice of evolution or revolution, I’d choose evolution.


Why are such issues of building physics and quality assurance vital?

In light of the threat of climate change Government has undertaken a legally binding commitment to reduce the UK’s carbon emissions by 80% by 2050 and other issues deserving attentions such as fossil fuel depletion and fuel security there is a significant challenge to the status quo. This reduction target is not theoretical, to address climate change no amount of accountancy will solve the problem, this target must be achieved in reality.

It is in this context that the research by Leeds Metropolitan University becomes so powerful for they have found repeatedly that homes can, and are, failing to perform in accordance with design standards. As the theoretical targets become more stringent so the gap appears to widen. It is worth recognising the systematic errors that can occur in low energy or ‘superinsulated’ buildings designed to something akin to PassivHaus “principles”:

• The appropriate building physics design model is not used from the beginning of the design process i.e. not using PHPP – this leads to systematic errors
• The correct area and geometric conventions are not used to establish the energy performance – heat losses and energy consumption figures can be distorted
• Incorrectly calculated U-values lead to an under estimation of the heat losses (an error of 30% is possible)
• The notional PassivHaus U-values are used – leading to an increase in energy demand (using this method it is unlikely that the 15kWh/m2.yr target will be achieved)
• Thermal bridging is not accounted for appropriately which can lead to increased heat losses. (Poorly defined and inadequately designed details can result in 50-100% more heat loss than intended.)
• Incorrectly specified windows and doors can lead to heat losses being 60% higher than expected due to additional heat losses via the frame and spacer bar.
• Incorrectly specified heat recovery ventilation systems can lead to an increase in energy consumption of 25% (specifically by the use of uncertified heat recovery systems without due consideration for impact upon efficiency of the system as a whole – this will be discussed in more detail in part two of this article.)
• Pressure tests are not conducted i.e. actual performance can not be verified. The resulting error can mean that infiltration heat losses are >300% higher than required.
• It can be concluded that no space heating is required which leads to ludicrous claims of affordable “zero heating” and “going beyond PassivHaus” (there is not space here to discuss this matter in detail, but suffice to say that it was the recognition that the reality of “zero heating” was in fact impractical that lead to the PassivHaus standard being structured as it is. This matter was also explored in AECB/CarbonLite report “A Comparison of The PassivHaus Planning Package (PHPP) and SAP” as shown in the graph below.)

• Poor construction details (failure to design for construction and inability to design out defects that will impair thermal performance – thermal bridging, poor airtightness, thermal bypass etc.)
• Poor site quality assurance – poor airtightness, gaps in insulation leading to constructed thermal bridges, thermal bypass etc. Instances of poor workmanship are inexcusable for the simple fact that the skills that are required are, in their own right, not complex. All we are talking about is attention to detail which was once customary practice and takes no more time that a more sloppy approach.

These failings, many of which also are commonplace within the construction industry, have a number of impacts including the fact that the owners and occupiers of modern buildings are not reaping the full benefits of reduced fuel bills and improved thermal comfort. It also means that theoretical carbon emissions are not actually being achieved and as a consequence will not deliver the Government’s legal obligations. In this context it is notable to consider that where a building fails to satisfy the legal and/ or contractual obligations mandated by performance standards, i.e. PassivHaus or Building Regulations, designers and constructors may be exposed to claims of professional negligence. Certification processes such as those established adopted by the German RAL standard, and as endorsed by the PassivHaus standard, are a means of ensuring that such defects, and potential claims, are avoided.




Returning to Dr Feist’s quote it can be seen that the goal of PassivHaus standard is not simply to “design to a number.” It is much more than that. The ambition of the standard is to close the gap between design and practice; to have theory and reality converge. If the UK is to achieve an 80% reduction in carbon emissions by 2050 the quality of the buildings that it builds, and refurbishes, needs to be vastly improved. This may be achieved by introducing the appropriate quality assurance systems throughout the design and delivery process. Buildings without the rigorous quality assurance are far less likely to succeed in their aims and ambitions, particular in very low carbon/ energy buildings. It is in this context that the purpose of this article was shed to some light on the subject of the PassivHaus Standard and the quality assurance that is associated with delivering such buildings at a national level and on individual building projects.

Go to Part 2 of Mark Siddall's article >>>>>>>>>>>>>>




1 Incidentally with only the addition of solar hot water the Darmstadt Passivhaus achieves a measured primary energy consumption of about 58 kWh/m2.yr (including all domestic electricity; and 28 kWh/m2.yr for heating, ventilation and dhw).

2In the UK the RAL standard is typically associated with colour specifications but RAL is in fact the German Institute for Quality Assurance and Certification (this is a very traditional German institution, dating back to the 19th century). A RAL standard does not specifically ensure a quality management system but rather prescribes the absolute numerical values that need to be achieved in order to ensure that the performance has been met. By virtue of this numerical standard, to ensure that it is met, certain quality assurance measures must be in place. For a PassivHaus the RAL seal of approval can only be obtained if the quality inspector, and a third party assessor, are fully satisfied that all conditions are met. Also the assessor must be a part of a Guetegemeinschaft (a society for quality assurance) that is a member of RAL - such societies pledge to uphold the set quality standards. This involves not only checking the numbers, but also checking the actual building in its various stages. In addition, there is an obligation to document all critical aspects (like providing receipts for insulation material etc.)

3 Horn G, “Legal aspects in the Planning and Construction of Passive Houses”, International PassivHaus Conference, Nuremberg 2008.

4 Examples include
a) The Chewton Mendip project: This has appeared in the RIBA Journal (October 2009, pp 65-68) and Green Building Magazine (July 2009, Volume19 Issue no 1) – here the signs that these homes are not real PassivHaus building stems from the use of uncertified heat recovery system, the apparent failure to use PHPP and no report of a pressure test result.
b) The Boundary Close housing scheme: Here the design tool was SAP rather than PHPP, the pressure test results did not achieve the PassivHaus requirements, and timber framed windows with double glazing were used (unlikely to satisfy the comfort requirements)
c) Cardiff PassivHaus: Here the scheme failed to satisfy the pressure test requirements. The scheme did use PHPP. Though using the moniker of PassivHaus at least the scheme is honest about it’s errors and used the right design tool. Definitely a step in the right direction. http://www.sustainablebuildingresource.co.uk/home/cardiff_passiv_haus/initial_results/1568/
d) Learning from Passive Action, CIBSE Journal July 09

5 Lessons from Stamford Brook, Understanding the Gap between Designed and Real Performance, Evaluating The Impact Of An Enhanced Energy Performance Standard On Load-Bearing Masonry Domestic Construction, Partners in Innovation Project: CI 39/3/663, Report Number 8 – Final Report, Leeds Metropolitan University, 2008

6 Good Homes Alliance says Code could be better, N Grant, N May, P Warm, Green Building Magazine (Autumn 2008)
Water and the Code for Sustainable Homes, C Hassell, Green Building Magazine (Autumn 2008)
Rainwater harvesting systems: Are they a green solution to water shortages, J Thornton, Green Building Magazine (Spring 2008)

Go to Part 2 of Mark Siddall's article >>>>>>>>>>>>>>

About the author:
Mark Siddall, principle at low energy architectural practice LEAP, is an architect and energy consultant specialising in low energy and PassivHaus design. He was project architect for the Racecourse Passivhaus scheme and has a keen interest building performance. In addition to architectural services his practice provides project enabling and education for clients, design teams and constructors.

LEAP website: www.leap4.it