This is a Passivhaus Basics blog post that gives an overview of a specific aspect of the Passivhaus Standard.

The international Passivhaus Standard is a clearly defined and rigorous standard for energy efficiency, comfort and quality assurance of buildings. Designing a building to achieve the standard requires detailed knowledge and a rigorous methodical approach to design and documentation. To ensure this happens, it is possible to train and qualify as a Certified Passivhaus Designer or Consultant.

The route to certification is the same for a designer or a consultant. It is only the individual’s prior qualifications and experience that determines if they qualify as one or the other. For clarity, this post will only refer to a Certified Passivhaus Designer, but for all intents and purposes, ‘designer’ is interchangeable with ‘consultant’ in this context.

A Certified Passivhaus Designer, regardless of their prior qualification, works across disciplines on a Passivhaus project. Their role integrates architecture, structure, building services, building science, energy modeling and construction detailing. They will at times both support and challenge the other designers on a Passivhaus Project.

The Certified Passivhaus Designer on a project doesn’t need to be completely independent. They can also be the architect, structural engineer, building services engineer, or another consultant on the team. And the same person fulfilling two roles does have advantages. However, in many cases combining two roles requires more time and work than one individual has available. Regardless, it is best if the Certified Passivhaus Designer is an integral part of the design team rather than just an occasional consultant.

The Passivhaus Building Certifier must be independent of the design team.

A Certified Passivhaus Designer brings the detailed knowledge and rigorous methodical approach needed to design buildings to the international Passivhaus Standard.

What is Passivhaus Design?

A Passivhaus Designer is trained in the fundamentals of Passivhaus design. This includes the ‘hard requirements’ – 10W/m2, 15kWh/m2.a heating/cooling demand, 120kWh/m2.a Primary Energy, 0.6ach, etc – that Passivhaus is often described in terms of, the ‘soft requirements’ (comfort and hygiene criteria) and the functional definition of a Passivhaus building.

With a good knowledge of the fundamentals, a Passivhaus Designer is able to communicate the benefits of Passivhaus to a client, as well as the advantages and features. They are also able to communicate the impact on the design process and design outcomes to other designers such as architects and engineers.

Passivhaus fundamentals also include the history and development of the international Passivhaus Standard and why the required metrics are important. For example, why specifically target the heating demand?

A key to Passivhaus design is identifying the aspects of heat energy balance that the building design can influence – that is, where heat is gained and lost due to the design of a building. Aspects include building shape / mass, glazing, shading, insulation / thermal bridging, airtightness and ventilation. These are important for both energy efficiency and comfort.

Quality control is also key to Passivhaus design. The design of the thermal envelope needs to be rigorous to ensure that insulation and the airtight barrier is continuous and effective when built. U-values need to be robust and reliable. Thermal bridges need to be eliminated by design or thermally modeled.

A Passivhaus Designer is also trained in space planning for Passivhaus. How internal rooms and spaces relate to solar heat gains, internal heat gains, ventilation and building services all need consideration as early as possible. Space planning can have a considerable impact on the ease and cost effectiveness of achieving the Passivhaus Standard.

The final aspect of Passivhaus design is the building certification process. A Passivhaus Designer can guide a client and team through the process, but cannot certify a Passivhaus building. Only an independent Passivhaus Building Certifier can certify that a building meets the international Passivhaus Standard requirements.

Passivhaus design encompasses all aspects of building design that can influence heat loss and heat gain, as well as space planning and certification requirements.

Passivhaus Designer or Building Scientist?

Passivhaus design is essentially about building science. The training to become a Passivhaus Designer reflects this. Passivhaus building science includes thermal comfort, energy balance, heat transfer through opaque and transparent elements, thermal bridges, ventilation, infiltration, solar gains, internal gains, heat load and climate.

For each section of building science, a Passivhaus Designer is trained in the basic science and in the detailed applied building science. Passivhaus design applies the science very specifically and transparently.

The training and the exam require long hand calculations, however, in most project situations a Passivhaus Designer will use the Passive House Planning Package (PHPP) for calculation purposes. The calculations carried out within the PHPP are clearly set out on the relevant worksheets. As data is entered, the equations get populated with the relevant entries. Sometimes, however, it will still be necessary and beneficial for a Passivhaus Designer to undertake manual calculations.

Of course, building science isn’t just equations. Airtightness and infiltration, for example, require an understanding of how and why to test a building using a blower door. Ventilation, for example, requires an understanding of the issues and benefits of different types of systems, the effects of CO₂ concentration on indoor air quality and the importance of indoor relative humidity.

Passivhaus design is very climate specific. A design that meets the requirements of the international Passivhaus Standard in London could have almost twice the heating demand in Stockholm and therefore not meet the standard. Knowing how to optimise a design for the specific local climate is an important skill in a Passivhaus Designer’s toolbox.

A Passivhaus Designer puts applied building science to work as an integral part of the Passivhaus design process.

Can it be Built and will it be Airtight?

Most buildings suffer from a performance gap between the design predictions and the actual building performance. Passivhaus effectively eliminates the performance gap. Part of this success is due to the care and attention to construction detailing. This ensures that what is designed can and will be built as intended and that it meets the requirements of the Passivhaus Standard.

Many aspects of a design are fixed during the design stage and ideally never get changed during construction. Regardless of design, several critical aspects are still dependent on good construction quality, though. These include;

• Glazing – weather proof and airtight installation without thermal bridging is needed.
• Airtightness – a continuous, unbroken, air barrier is needed.
• Insulation – continuous installation without thermal bridging or gaps is needed.
• Ventilation – correct, high-quality installation and commissioning is needed.

Too often architects and designers draw details that aren’t easy to build. This can result in compromised quality and performance when constructed (as well as headaches for the builder), or in site changes being necessary. Neither of these outcomes is ideal for any project and part of a Passivhaus Designer’s role is to help avoid them. A Passivhaus Designer should review all construction details with an eye for how the continuity and integrity of the building envelope will be delivered. They will be looking at the weather proofing, the insulation, the air barrier and the buildability of the detail.

Choice of product and material is also important to ensure buildability and realistically how well they will perform when installed. For example, rigid insulation materials can offer very high thermal performance. In practice, though, rigid insulation can be difficult to install well to ensure there are no gaps between or behind boards. Even very small gaps can significantly reduce the performance of the insulation. Complicated details can make it even harder to get the best performance out of any form of insulation.

Airtightness often needs additional care and attention as the Passivhaus requirement of 0.6ach is still perceived as a challenge by many in the industry. It is, therefore, critical, that the design, detailing, and documentation makes it as simple, straightforward and clear as possible to understand the airtightness strategy and to achieve it on site.

A Passivhaus Designer’s role with regards to airtightness may extend to providing toolbox talks and installer briefings on site. Explaining the purpose and methodology to achieve an airtight building envelope often helps to raise aspirations on site. It also reinforces the important contribution each trade can make to the quality and performance of a building.

A Passivhaus Designer should provide site support, visiting the site and observing construction progress. With their specialist training and understanding of what details matter for Passivhaus, a Passivhaus Designer may spot something critical that an architect or clerk of works doesn’t. They should also be able to assist in resolving any issues that arise.

A Passivhaus Designer helps to eliminate the performance gap by design.

Building Services, even for Architects

Integrated design is vital for successful Passivhaus design. And building services are an important part of any building design. A Passivhaus Designer, even if they are an architect, is trained in the design of building services for Passivhaus.

Building services include ventilation, heating, hot water, lighting, and appliances. Ventilation is the most important of these and given the most detailed consideration.

For ventilation and heating, the starting point is the comfort (and hygiene) requirements of the international Passivhaus Standard. Ventilation is needed to provide fresh air and to remove odours, pollutants (CO₂, VOCs), water vapour (humidity control for comfort and to avoid mould etc) and excess heat (summer cooling). Additionally in Passivhaus buildings, the ventilation system preheats incoming fresh air (via the heat exchanger) to avoid cold draughts and filters out dust and pollen. In some but not all Passivhaus designs, the ventilation also delivers the heating.

A Passivhaus Designer is trained in designing the ventilation system and the related duct sizing and layout. This is an important part of an integrated design and a very useful skill for an architect to have if they are also a Passivhaus Designer. The ventilation system design is ideally developed at the same time as the architectural design. This way spaces for the equipment and ducting can be intentionally allowed for rather than shoehorned in later. It also means both energy and cost effective locations for equipment can form part of the design.

For example, the MVHR unit needs to be located close to an external wall so the fresh air and exhaust air ducts, which must be insulated, are short and direct. If these ducts are relatively long, they get expensive and the MVHR efficiency starts to drop. A lower efficiency MVHR increases ventilation heat losses which must be balanced somewhere else by reducing heat losses. This might mean additional insulation and therefore, additional cost. For more about MVHR read this blog post: What is Mechanical Ventilation with Heat Recovery (MVHR)?

Early design decisions relating to the building services can have a big impact on the cost-effectiveness of a Passivhaus design. A Passivhaus Designer can help ensure intelligent design decisions are made.

One of the key premises of the international Passivhaus Standard is that a Passivhaus building can be heated via the ventilation air only. This eliminates the need for a boiler, heating distribution pipework and radiators, along with the associated costs. However, this isn’t the only way to heat a Passivhaus building and it’s not always the right way either. A variety of heating options should be considered for a Passivhaus project and the appropriate system selected. The heat source and system controls need consideration also.

Hot water makes up a noticeable part of energy consumption in a Passivhaus building. User choice and patterns of use can have a huge impact on this and are out of a designer’s control. Heat loss from the distribution of hot water is less dependent on actual use patterns and can, therefore, be minimised through Passivhaus design. This is important to reduce energy consumption. It is also important as heat loss within the thermal envelope may contribute to summer overheating risks.

Artificial lighting also makes up a noticeable part of energy consumption in a Passivhaus building. The first approach a Passivhaus Designer will take is to minimise the need for artificial lighting by good daylight design. After that, it comes down to efficient layouts, sensible light levels and selection of energy efficient fittings.

The energy consumption of appliances is entered into the PHPP and contributes towards the total Primary Energy consumption. The project’s Passivhaus Designer needs to know the details of all appliances that will consume energy, including IT and entertainment systems. They can provide guidance on selecting energy efficient solutions.

Building services: critical for Passivhaus comfort and energy efficiency.

Designing with the PHPP

An important part of a Passivhaus Designer’s training (or self-learning) is in the use of the Passive House Planning Package (PHPP). The PHPP is a design tool and it is also used for Passivhaus Building Certification. For more about the PHPP read this blog post: What is the Passive House Planning Package (PHPP)?

Early in a project, even before a final design has been agreed, a Passivhaus Designer can build a simple and interactive model in the PHPP. This can include orientation, climate, rough building geometry, approximate windows sizes and conservative estimates of wall, roof and floor assemblies. This can form the basis of a Passivhaus feasibility study. It will quickly establish what aspects of the design are critical for it to achieve the Passivhaus Standard. It also allows various options to be quickly explored in an informed manner. For example, window sizes and shading options can be explored with instant results displayed for each option.

The PHPP model should then progress in parallel to the design development – ideally as an integral part of the design process. Options and solutions can be iterated and explored using the PHPP model to instantly see the impact. It is possible, and desirable, to eliminate the traditional approach of investing considerable time in developing an option and then waiting for another consultant to feedback on the feasibility and impact of the options.

To use the PHPP intelligently as a design tool the Passivhaus Designer needs to be an integral part of the design team. This can be achieved with the architect or an engineer also being the Passivhaus Designer. Or the Passivhaus Designer can be independent of the other design roles, but still an integral part of the design team and process.

Finally, the PHPP is developed in full detail and submitted to the Passivhaus Building Certifier. They will assess the PHPP and in most cases build their own PHPP model to compare and check against. This forms a critical part of the Building Certification process and documentation.

The PHPP: integral to Passivhaus design and the key tool of a Passivhaus Designer.

A final hurdle: the Passivhaus Designer Exam

To qualify as a Certified Passivhaus Designer or Consultant, a person must either submit a certified Passivhaus project that they designed and documented, or undertake suitable training and sit a written exam. Most people take the latter route.

The written exam is a challenging three hours, despite being open-book. The general consensus seems to be that the hardest part of the exam is simply completing all the required questions within the three hours.

The content of the exam covers all aspects of the Passivhaus Designer training. The type of questions fall into a few different categories:

• Multichoice questions – these sound straightforward but can actually be very challenging, especially as marks get lost for incorrect or unanswered questions. It’s not a matter of selecting A, B, C, or D, rather there are several correct answers to select from a list.
• Short form questions – these give a scenario and ask a question, or several questions, that require some calculations to be able to select a correct answer. Both the calculations and the answer get marked.
• Long form questions – these give a scenario and then a series of questions that require detailed written explanation and calculations. The questions are often multi-part and latter parts may depend to a certain degree on the answer to earlier parts.
• Design questions – these give a scenario and require designing or sketching for an answer. Typically there is one major design question which can be worth around 30% of the total marks in the exam.

Although the PHPP is not used for the exam, screengrabs from a project PHPP file are sometimes included with related questions.

Obviously, in most real-world project situations, a Passivhaus Designer isn’t going to be under exam conditions. This is recognised with a strong emphasis in the exam on showing all workings, calculations, units etc to encourage a thorough clear methodical approach to Passivhaus design.

Please note that these are general descriptions only based on my experience of studying and sitting the exam. Exam papers cannot be retained and past exam papers are not available for revision.

The Passivhaus Designer exam: a challenging three hours of thinking, calculating and designing by hand.

A Passivhaus Designer brings an integrated cross-discipline design approach.

Passivhaus design is integrated design.

A Passivhaus Designer is trained and knowledgeable in the fundamentals of the international Passivhaus Standard, the building science of Passivhaus, the construction of Passivhaus, and building services for Passivhaus. They bring all these aspects of the design together across multiple disciplines. A Passivhaus Designer can also be the architect or engineer on a project, or they can be independent. In either case, it is best that they are an integral part of the design team and process.

It can be beneficial to a project if the architect and engineers are trained as Passivhaus Designers, even if they don’t carry out the role of the Passivhaus Designer on the project. The knowledge and the mindset of a Passivhaus Designer brings considerable benefit to their way of designing within their own discipline.

The key Passivhaus design tool is the Passive House Planning Package. A Passivhaus Designer can use the PHPP at every stage of the design process to inform and iterate the design as it develops. However, a Passivhaus Designer shouldn’t be solely reliant on the PHPP and where necessary or useful should be able to carry out long hand calculations.

It is important for a Passivhaus project that a Passivhaus Designer is an integral part of the design team and design process.

Some additional resources:

• The Passivhaus Designer’s Manual: A technical guide to low and zero energy buildings. Read my detailed review here.
• Passivhaus Planner site from the Passive House Institute – everything you need to know about training and qualifying as a Passivhaus Designer or Consultant. Also includes a searchable global register of Certified Passivhaus Designers and Consultants.
• Learning Targets for Certified Passivhaus Designers and Consultants: PDF download.

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