energy performance

Windows and Overhangs in Passive Solar Heating

Windows and Overhangs in Passive Solar Heating

As part of any passive solar home design, the choice and design of windows and overhangs is important. You want your house to admit as much heat and light as possible in the cold season, but not overheat during summer. And you also want them to help protect your home from the cold in the winter.

Thermal Mass - Understanding its benefits

Thermal Mass - Understanding its benefits

Thermal mass 'Thermal mass' describes a material's capacity to absorb, store and release heat. For example water and concrete have a high capacity to store heat and are referred to as 'high thermal mass' materials. Insulation foam, by contrast, has very little heat storage capacity and is referred to as having 'low thermal mass'.

Thermal Bypass - What is it?

Thermal Bypass - What is it?

The Government's legally binding objective of achieving an 80% reduction in national CO2 emissions and the drive for zero carbon homes and buildings is focusing attention upon building design and procurement.

Power from renewables surges to high as emissions fall

Power from renewables surges to high as emissions fall

Nearly a quarter of Britain’s electricity was generated from wind turbines, ­solar panels and other renewables last year. Output from renewables rose from 19.1 per cent in 2014 to a record 24.7 per cent in 2015, according to the Department of Energy & Climate Change.

Embodied Energy of Materials

Embodied Energy of Materials

Total primary energy consumed from direct and indirect processes associated with a product or service within the boundaries of cradle to gate. This includes all activities from material extraction (quarrying / mining / harvesting), manufacturing, transportation and fabrication until the product is ready to leave the final factory gate.

Passive homes move is active step towards carbon neutral future

Passive homes move is active step towards carbon neutral future

It’s a glorious day: Dun Laoghaire-Rathdown county council has passed a motion to make the passive house — and its equivalent — mandatory for all new buildings.

Dún Laoghaire council defies Alan Kelly on passive houses

Dún Laoghaire council defies Alan Kelly on passive houses

Dún Laoghaire-Rathdown County Council could be on course for a clash with Minister for the Environment Alan Kelly after councillors voted in favour of an energy-efficient building standard over which his department has serious concerns.

Criteria for the Passive House, EnerPHit and PHI Low Energy Building Standard

Passive House is a building standard that is truly energy efficient, comfortable and affordable at the same time.  Passive House is not a brand name, but a tried and true construction concept that can be applied by anyone, anywhere.

Pennine Farmhouse marries traditional style with passive performance

Pennine Farmhouse marries traditional style with passive performance

Steel Farm is the first certified passive building in Northumberland, and the first cavity wall passive house in the north east of England. It is located near Hexham in the North Pennine area of outstanding natural beauty (AONB)

The design and construction of an exemplar Zero-Carbon Primary School

The design and construction of an exemplar Zero-Carbon Primary School

In 2008 the Department for Children, Schools and Families (DCSF) identified funding for pilot/exemplar projects under the Zero Carbon Task Force (ZCTF).

Delivering Low Energy Buildings for Real

Delivering Low Energy Buildings for Real

This Guide is a unique publication which combines professional guidance from a range of suppliers and industry experts, which, when combined together, can deliver a low energy building. A variety of systems are presented ranging from ventilation systems to a range of insulation, airtightness, windows and water treatment systems. 

Invisible Fuel

Invisible Fuel

The cheapest and cleanest energy choice of all is not to waste it. Progress on this has been striking yet the potential is still vast. Improvements in energy efficiency since the 1970s in 11 IEA member countries that keep the right kind of statistics (America, Australia, Britain, Denmark, Finland, France, Germany, Italy, Japan, the Netherlands and Sweden) saved the equivalent of 1.4 billion tonnes of oil in 2011, worth $743 billion.

BREEAM Environmental Assessment Method

BREEAM Environmental Assessment Method

BREEAM is the Building Research Establishment’s (BRE) Environmental Assessment Method first launched in the UK in 1990. It sets best practice standards for the environmental performance of buildings through design, specification, construction and operation.

A Beautiful Solution - An argument for Passive House by architect Justin Bere


The government's cynical recent energy policy announcements represent a dereliction of duty to the vulnerable and to future generations. There is an alternative, argues award-winning passive house architect Justin Bere - and it's beautiful.

Many of the UK's elderly citizens and low income residents cannot afford to maintain healthy conditions or basic levels of comfort in their homes, while those who are better off often cosset themselves in over-heated homes burning excessive amounts of precious and polluting fossil fuel. Everyone complains about the cost of energy, politicians wring their hands and try to sound as if they have a plan, but little is done to improve the UK's domestic and non-domestic buildings to make them more affordable to run.

"Those who peddle minor gestures in sustainability as if they are an al­ternative to passive house are either lacking in real knowledge, or simply playing confidence tricks on the public."

In a world where there is a rapidly growing population demanding a share of ever fewer resources, it is unrealistic folly and indeed utterly foolhardy to think that the answer to the high fuel consumption of our buildings is simply to outsource new power stations on guaranteed repayments to meet the unchecked projected future growth in demand. Yet this is exactly what the UK is currently doing. Through sloppy thinking, the UK is mortgaging the future; locking the younger generations into a level of expenditure on fuel that will most likely be completely unaffordable for them. Effectively they will be trapped in a situation with no affordable way out. What is utterly unforgiveable is that the reason for this is that the current generation doesn't want to feel any of the pain of transition. But transition will have to happen in the end and the longer we leave it, the more painful - or catastrophic - it will be.

Yet those of us in the passive house community have demonstrated that there is a solution that can deeply reduce overall energy demand in both new and existing buildings by 80 or 90% while at the same time creating ex­ceptionally healthy and comfortable buildings. New passive house buildings can be built for little or even no extra cost if design priorities are realigned with an energy saving imperative. But even where there are additional costs, such as in passive house retrofits, the costs can be paid back in a lifetime so that future generations are handed an affordable and beautiful solution.

The UK can look back with pride at how its population pulled together and responded effectively to national emergencies in the 20th century. Once again, and as much as at any time before, we need to respond with effective action to what I believe is an even bigger emergency than those faced by previous generations.

Effective action will include re-building the respect for vocational skills, the passion for making things to the best of our ability and to world-beating levels of excellence. It will include renewed respect for world-class engineers and engineering businesses. It will include a transformation of the construction industry from one focussed on what it can take from society, to one focussed on what it can give to society.

All this requires an honest, clear vision which I believe all of us in the passive house community have, and which we must promote. We must point out that those who peddle minor gestures in sustainability as if they are an alternative to passive house are either lacking in real knowledge, or simply playing confidence tricks on the public.

In An Introduction to Passive House (RIBA Publishing, £27.99), I present facts and arguments that attempt to show why passive house is the best form of building for people's health, comfort and general well being, for every age group, for fantastically low energy use, for very low whole-life costs, for the environment as a whole and for the future of the planet.

Embracing passive house technical methods does not mean that we have to turn our backs on beautiful architecture or light-filled, flowing spaces. Passive building techniques give us the opportunity to hold on to the uplifting aesthetic tenets of the very best 20th-century buildings, while at the same time transforming our technical abilities to make social progress and beauty possible in a world where excessive consumption is no longer tenable.

An Introduction to Passive House shows that the economics of passive house are clear. While shifting priorities is a simple lifestyle choice for many, for others the help of responsible, in­telligent and forward-looking govern­ments is needed in order to make it easy for individuals and organisations to make steps now, for the benefits of both themselves and of society at large, now and in the future.

Passive house is emphatically not a product, nor does it require designers to use particular products. The Passive House Institute offers manufacturers technical assistance to improve their products, and provides quality assurance certification, but passive house buildings can be built without any certified products. Passive house is a standard and an advanced method of designing buildings using the precision of building physics to ensure comfortable conditions and to deeply reduce energy costs. It does what national building regulations have tried to do. Passive house methods don't affect "buildability", yet they close the gap between design and performance and deliver a much higher standard of comfort and efficiency than government regulations, with all their good intentions, have managed to achieve.

The in-use performance data from passive house buildings shows that to provide comfort, to save energy, to reduce bills, to protect people from fuel poverty, to reduce excess winter deaths, to save money in the long run and, arguably most importantly, to reduce CO2 emissions, it is difficult to escape the conclusion that deep, energy-saving passive house retrofits and new-builds must become the norm. A deep, energy-saving retrofit programme will create jobs now at the same time as saving money on fuel imports, both now and long into the future. Vast amounts of money can also be saved by reducing the need for new power stations and for long-term storage of nuclear waste, and by reducing the serious impact upon the National Health Service of the UK's dreadful, damp and draughty buildings.

In concluding I will repeat the question that visitors to passive house buildings seem to ask more than any other: Why aren't all buildings built like this?

An Introduction to Passive House by Justin Bere (RIBA Publishing) is available now at RIBA Bookshops (

Bere, J. (2014) ‘A Beautiful Solution’, Passive House + , Issue 5, UK Edition, pp. 20.


Zero carbon targets and the construction industry

The new definiation of Zero Net carbon occurs after allowable solutions are introduced.

The new definiation of Zero Net carbon occurs after allowable solutions are introduced.

Zero carbon is great as a political aspiration but will it stack up effectively as a policy? Richard Hillyard examines Government aims to impose zero carbon targets on the construction industry. Back in July 2007 the Government published the Building a Greener Future statement. This policy document announced that all new build homes would be zero carbon from 2016.

The definition of zero carbon requires new dwellings to take into account:

  • emissions from space heating, ventilation, hot water and fixed lighting,
  • exports and imports from the development (and directly connected energy installations) to and from centralised energy networks.

Note:- Expected energy use from appliances is excluded from zero carbon definition.

By following this policy the Government expects new buildings to have net zero carbon emissions over the course of a year.

The definition of zero carbon consultation subsequently introduced by the government, sought views on the Government's proposals. This consultation ran from 17 December 2008 to 18 March 2009 and goes on to explain how to achieve net zero carbon emissions.

The Government also announced that from 2019 all non-domestic new builds will also be required to have zero net carbon emissions, with earlier dates for schools (2016) and public sector buildings (2018).

Wisely, the government set boundaries to what it meant by zero carbon. The embodied energy content of construction materials is not covered, and neither is the transportation of materials. Additionally, transport emissions associated with developments are not included as the government intends to deal with these through other policy instruments.

Given these omissions, it could be argued that Government's proposals do not equate to zero carbon. Even if it is not possible (nor cost-effective) to construct a building without generating any greenhouse gases, how far could we get by dramatically improving the efficiency and sustainability of construction methods?

In any case, does it really matter? Less than one per cent of the UK's existing building stock is replaced every year, and it's been estimated by the Department for Communities and Local Government (CLG) that 87 percent of the current housing stock will still be around in 2050. That means that the UK cannot meet its carbon reduction targets without a far-reaching retrofit programme for existing buildings.

The UK Green Building Council's proposal for a Code for Sustainable Buildings will play an important role in improving the focus on energy efficiency in existing buildings. But this is just one of a hierarchy of measures that the Government says will be needed.

The consultation document proposes a three-stage hierarchy for designers to achieve zero-carbon. The first step for energy efficiency requires compliance with Part L of the Building Regulations. This stage may also encompass other regulatory instruments, such as a mandatory requirement to design to Level 6 of the Code for Sustainable Homes.


The second stage proposed by Government is something called Carbon Compliance', which essentially is the use of on-site micro-energy generation. A report by the UK GBC Zero Carbon Definition Task Group believe over 80 per cent of homes in the UK to be unable to achieve zero carbon targets this way. The development of near-site and off-site low and zero-carbon energy generation is also being proposed.

Initially there were reservations over whether the use of biomass technologies could be included in the zero carbon strategy. However, the government appears to be in full support of using biomass systems both within new homes and as a source of direct heat from nearby off-site generation.

The third stage in the zero-carbon strategy is what is known as ‘allowable solutions', which is a buy-out fund or form of carbon offsetting through high quality international investment in low and zero carbon projects.

This third way will, it is believed, only be permitted where energy efficiency and carbon compliance are unable to be achieved totally through on-site and near-site measures achieve the goal of zero carbon - in other words the residual emissions.

The government is proposing a system of credits to permit off-setting to occur. Credits will be awarded to developments that have a range of energy-saving criteria. For example, energy-saving appliances and low and zero-carbon technology capable of exporting energy to the grid will earn credits to enable an offset of residual carbon emissions.

The government would prefer off-site low and zero carbon technologies to be included in this part of the hierarchy by feeding into the national grid.

So will the policy work? The first two parts of the hierarchy - energy efficiency and carbon compliance - are signs of forward thinking. With a few tweaks, off-site low and zero carbon energy generation could play an integral part of reaching the zero carbon target, but only if the contribution from the grid can be guaranteed to be clean.

Other questions remain to be answered. For example, with allowable solutions, will off-setting contribute to reducing carbon dioxide emissions enough for claims of zero carbon to stack up - not just initially but over a sustained period? Or is it, as some might argue, just a way of covering up holes in the system, and easing collective guilt?

Off-site low and zero carbon energy generation technologies sounds like reasonable measures, but if they are supplying to the grid as opposed to supplying directly to a development, what guarantees will there be that this clean energy will not be lost in the overall electricity generation? This is a key issue, especially when it's mixed with the output from the proposed eight new coal power stations (each potentially generating eight million tonnes of CO2 per year) that the Government is keen to build.

These questions highlight the credibility gaps that still exist between intention and delivery in Government's push for a low carbon and sustainable energy future. Whatever transpires following the zero-carbon consultation, tackling the issue effectively will not only significantly affect the environment, but also our pockets.

Zero carbon targets on the construction industry, [Online], Available: [18 March 2014].

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

Quality assured Passivhaus buildings - Part 1

Mark Siddall of Low Energy Architectural Practice:  LEAP

Mark Siddall of
Low Energy Architectural Practice: LEAP

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 are 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 world's 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 s 15kWh/m2.yr

• a primary energy requirement of less than 120kWh/ m².yr (best practice being less than70kWh/m2.yr)

• an air leakage of less than O.6ach@50pa when tested in accordance with EN 13829

• perhaps they are also aware that the risk of overheating should be s 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 (PHI) 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 50-60kWh/m².yr (the theoretical performance of the 2006 UK building regulations). In Germany it was recognised that the average German home uses 200kWh/m².yr for space heating and that if Swedish energy standards 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 product. 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, 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

After the successful completion, and perhaps more critically, the validation of the original Passivhaus project in Darmstadt (1991-93) Dr Feist and his team at the Passivhaus Institute began to develop the PHPP. This design tool is a simplified means of ensuring that all the requisite aspects of the comfort criteria and building physics are addressed in the appropriate manner and in the necessary detail. Whilst detailed discussion of these criteria is beyond the scope of this article, suffice to say that PHPP carefully considers heat losses and gains associated with airtightness, ventilation, thermal bridging, solar gains, internal gains and the like.

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. The heating energy demand, as calculated by PHPP, has been validated against the monitored heating energy consumption of more than 500 new homes.

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.' 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.

Recent claims in the UK

Recently I have found that I have had the issue of quality assurance in mind when I read the 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, Worst of all in some cases there are even claims of building in accordance with Passivhaus 'principles' - these projects are certainly not 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 OK 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. In light of the recent discussions at Copenhagen, if there was ever a need for quality assured construction it is now. The old adage 'you cannot 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 focusing 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.

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. 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 the government has undertaken a legally binding commitment to reduce the UK's carbon emissions by 80% by 2050 and other issues deserving attention, 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 'super-insulated' buildings designed to something akin to PassivHaus 'principles':

• the appropriate building physics design model is not used from the beginning of the design process, ie. 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 1 5kWh/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, ie. actual performance cannot 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.)

• 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 than 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, ie. Passivhaus or Building Regulations, designers and constructors may be exposed to claims of professional negligence.


Returning to Dr Feist's quote it can be seen that the goal of the 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, particularly in very low carbon/energy buildings. It is in this context that the purpose of this article was to shed 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.

Accessed online: 7th August 2014