Passivhaus
Both the terms 'passivhaus' and 'passive house' refer to the voluntary low-energy construction standard developed in Germany, with the first monitored passivhaus being constructed in Darmstadt, in 1990.
The Passivhaus construction concept is a voluntary low-energy standard which is based on a set of identifiable and empirical criteria that a building can be measured against.
To ensure it remains open and transparent, the Standard is not legally protected, so theoretically any building can claim to be a passivhaus - however, only those that are Certified are verified by the Passivhaus Institute and so confirmed as such.
We encourage Certification on all of our projects for this reason.
The concept
Passivhaus buildings are defined as those that have an extremely low energy demand and yet meet high standards for thermal comfort and good indoor air quality, even in very cold winters (down to -10° C).
The word passive is used because the aim is to eliminate the need for an 'active' heating system: these buildings utilise the internal heat gains and solar energy entering through the glazed windows and doors, and simultaneously minimally heat the incoming fresh air, in order to reduce the heating energy demand to it's minimum level for the design in a given geographical location.
A 'fabric first' approach is adopted: there is no compensation available by relying on so called 'bolt-on' technologies in order to obtain a good energy 'rating' - the building itself must perform to a very high standard before any such things are added.
The Principles
1 - Super insulation throughout
All opaque elements of the external construction i.e. the ground floor, external walls and the roof, must be designed to limit the heat loss to a much higher standard than the current building regulations in the UK, and must be of a thermal bridge free construction.
2 - High performance glazing
This will typically mean triple glazed windows and doors with low-E coatings, a warm edge spacer where the glass meets the frame, and a cross-laminated and / or insulated timber window frame.
3 - An airtight building
The thermal envelope should be enclosed by one continuous airtightness layer to create as airtight a building as possible.
5 - Limiting energy consumption
All electrical consumption within the building is considered and reduced by the use of efficient appliances, and avoiding high consumption items like tumble dryers.
6 - Maximising solar gains
The glazing arrangement is designed to maximise the available solar gains whilst balancing and reducing the risk of overheating during times of the year when low sun angles are experienced, for example by incorporating shading elements if needed.
Overview of the Technical Criteria
There are three ‘classes’ of Passivhaus buildings: Classic, Plus and Premium. In all three classes some of the fundamental technical criteria remain consistent.
Classic
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What is now called the ‘Classic’ Standard is the original passivhaus criteria, where no renewable energy generation is required for compliance.
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Specific space heating demand: ≤ 15kWh/(m2.a) or
Specific heating load: ≤ 10W/m2
Airtightness level: 0.6 ach/hr at 50Pa
Frequency of overheating: ≤ 10% of the year at 25°C
(This may get reduced in the near future to ≤ 5% or lower.)
Primary energy Renewable: ≤ 60kWh/(m2.a)
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No energy generation required
Premium
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Passivhaus Plus Certified buildings not only drastically reduce their energy consumption, but also produce as much energy as the occupants use. The energy generated must come from renewable sources and be sufficient to operate the building throughout the whole year.
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Specific space heating demand: ≤ 15kWh/(m2.a) or
Specific heating load: ≤ 10W/m2
Airtightness level: 0.6 ach/hr at 50Pa
Frequency of overheating: ≤ 10% of the year at 25°C
(This may get reduced in the near future to ≤ 5% or lower.)
Primary energy Renewable: ≤ 45kWh/(m2.a)
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Renewable energy generation: ≥ 60kWh/(m2.a) – measured against footprint
Plus
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For Premium Certified buildings, far more energy is produced than is required to operate the building. This Standard is therefore well suited to grid-tied buildings, as they can then pass this excess energy back to the grid to be used by others.
This is a very challenging and ambitious goal.
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Specific space heating demand: ≤ 15kWh/(m2.a) or
Specific heating load: ≤ 10W/m2
Airtightness level: 0.6 ach/hr at 50Pa
Frequency of overheating: ≤ 10% of the year at 25°C
(This may get reduced in the near future to ≤ 5% or lower.)
Primary energy Renewable: ≤ 30kWh/(m2.a)
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Renewable energy generation: ≥ 120kWh/(m2.a) – measured against footprint
The Process
Components
There are many certified and non-certified components that can be used in a passivhaus building, from windows and doors to MVHR units.
Both certified and non-certified products can be used to create a passivhaus building, however generally the correct technical information is more readily available for certified components.
Whenever we are designing a new building or a renovation project we aim to select components that will be compatible with our low-energy, low-carbon aims.
Methodology
Under the Technical Standards a building's performance in terms of it's overall energy balance is calculated using the SAP methodology.
A passivhaus design is always verified using the PHPP methodology, which is a complex set of inter-related spreadsheets designed by the PHI.
We have been designing to the Passivhaus Standard since 2013; we will take care of all of the technical analysis for you in-house as our team includes a Certified Passivhaus Designer.
This makes for a more efficient design process for you: every design change we make is assessed and verified in the PHPP to ensure the best possible outcome for your project.
Certification
The journey of designing a passivhaus through to the final certification process can seem daunting at first, however with some careful organization it can be a straightforward process.
There is a considerable amount of information required and thorough checks to be made by the designer(s) at key stages: we aim to make this process as simple as possible by presenting your choices in a clear and concise manner, at the appropriate time in the development of the design.
If you would like more information about the process please contact us directly.
Three great reasons to adopt the Passivhaus Standard
Reduced costs
Rising energy prices are of concern to many people now, and no one likes to spend more money on something than they have to.
The lowered operational costs of a passivhaus building are a considerable incentive for many.
Durability
There are many research papers that highlight the importance of managing moisture within the building fabric, particularly when constructed with modern building materials. This is important in order to prevent long term damage to the construction.
Passivhaus can assist in this as the high level of airtightness demanded prevents the infiltration of unwanted moist air into the building fabric where it can become trapped, condense, and lead to degradation of materials and the formation of mould.
Sustainability
In the face of the climate emergency many people feel that if they can do their part to contribute towards a lower energy future then the world will benefit as a whole.
Passivhaus is an energy standard first and foremost, however it is very compatible with other sustainable agendas and ideas, such as vapour open (breathing) construction and natural (or minimally processed) materials and finishes.
We embed many sustainable design practices in all of our projects.
FAQs
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No. The standard is very versatile and applies to all building types. There are many different types of certified passivhaus buildings in existence in the world today, from schools and offices, to banks and swimming pools.
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Yes. Even without a conventional heating system, the design temperature for the whole of the indoor space is 20° C (maintained even when it drops to -10° C externally), however this can be adjusted either up or down according to the occupants preferences.
There are many examples of certified passivhaus buildings in many different climates that have been monitored and occupied for many years, proving that the standard is flexible and really does work, even despite a variety of occupant habits and lifestyles!
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Yes. Just like in a conventional building, opening the windows in a passivhaus simply lowers the indoor air temperature.
The principle difference is that in a passivhaus building there is no need to open windows to improve the air quality due to the MVHR system.
Opening windows is a key part of the design for additional ventilation in summer to counteract the risk of overheating.
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No. The ventilation system is very carefully designed and, when commissioned properly, should be installed to ensure very low air speeds at the various inlets and outlets within the building.
There is barely any perceptible air movement until within centimeters of the outlets, and consequently no noise.
This, coupled with the superior airtightness, ensures a draught free building.
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No. Although a more open aspect to the south is helpful in increasing the available solar gain, it is still perfectly possible to construct a certified passivhaus building on a north facing or urban plot - this will influence the design, and a small additional heating input may be required, but it need not kill the proposal!
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No. Passivhaus buildings can be any shape, be in any architectural style, and built using any construction method.
The important thing to remember is that the more protrusions, overhangs, dormers, etc. that the building has, the more potential area for thermal bridging there is, which means that this added heat loss has to be compensated for elsewhere, by adding more insulation to the walls for instance.
All of this can in turn increase the build cost, so it is worth considering the shape and form at a very early stage in the design process.
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No. We don't believe it has to be so, and there are an increasing number of completed projects built to the passivhaus standards here in the UK that demonstrate this.
The investment in higher quality building components is often off-set by the elimination of an expensive conventional heating / cooling system.
Just like on any construction project, the key to reducing build costs is to prepare and plan in advance of construction starting.
And of course, as with any other conventional building, the reduced running costs for the future have to be taken into account and balanced with the initial investment.
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No. It is possible to renovate some existing buildings to the EnerPHit standard, which is a slightly more relaxed set of values of the passivhaus criteria.
Still considerably better standards than the current building regulations, this set of reduced criteria does make an allowance for the difficulties faced when trying to bring existing and historical buildings up to date in terms of energy efficiency.
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No. The criteria remain the same.
The PHPP calculation is climate specific so a geographical location and altitude must be entered; the methods for meeting the criteria will vary depending on whether the building is in Siberia or Zimbabwe.