By Sophie Neaves on Fri 19 May 2023
Passivhaus Guide: Everything you Need to know about Passive House
According to the World Green Building Council, buildings account for 39% of global energy-related carbon emissions. Around 11% of this comes from materials and construction. The remaining 28% comes from operational emissions – the energy needed to heat, cool and power buildings.
Passive house aims to change this scenario. It’s a concept in construction and a standard for energy efficiency in buildings. Owing to its origins at the Passivhaus Institut (PHI) in Darmstadt, Germany, it’s also known as passivhaus.
Early passivhaus projects took their inspiration from 1970s builds in North America, which aimed to minimise the need for energy use. That 1970s construction trend was a response to the oil embargo imposed by OPEC, which saw oil prices increase by 300%.
Now, with geopolitical factors once again pushing energy prices up – and public opinion turning firmly against fossil fuels – focus is returning to the potential of energy-efficient buildings.
But exactly what is passive house as an idea – and how does it work in practice?
What is a Passive House?
Simply put, a passive house is one that follows – and meets – the Passive House Standard. The standards prioritise energy efficiency and aim to minimise a building’s impact on the environment.
That minimal ecological impact is where the term passive comes in. The idea is that the building is almost just part of the natural background, rather than actively affecting the environment as traditional houses do.
Passive houses are ultra-low energy buildings that require minimal energy for heating or cooling. They use clever design and engineering to both generate heat and avoid losing it. Common features include triple-glazed windows, high-quality insulation and a near-perfect level of airtightness.
In addition, instead of intensively heating and cooling the building, a passive house system achieves comfortable conditions by heating or cooling fresh air entering the building. This is called post-heated or post-cooled air. In a passive house, this air will go through a MVHR (mechanical ventilation with heat recovery) system, to ensure it’s both clean and effectively recycling heat from outgoing stale air.
Energy costs in passive houses can be up to 90% less than in traditional houses. And they can even be 75% less than in new-build homes. Passive house designs consider every little detail and take advantage of every single opportunity to save energy.
What is the Passive House Standard?
The Passive House Standard is designed to deliver comfort, quality and lower running costs – in any type of building. In the UK, the UK Passivhaus Trust promotes these standards and is an official affiliate of the wider International Passive House Association (iPHA). Certification from the UK Passivhaus Trust guarantees that the work undertaken was of the highest quality possible – and also that the building will perform to expected energy efficiency levels.
Some of the basic ideals of passive house construction include:
- No draughts
- Highest levels of insulation
- Warmer indoor conditions in winter
- Cooler temperatures in summer
- A constant supply of fresh air
- High-performance windows that open
It’s a whole-building approach, where several solutions come together to deliver optimal benefits. For example, airtightness in passive house buildings works hand-in-hand with a mechanical ventilation with heat recovery system.
Airtightness is a key principle of passive house since the emphasis is on retaining heat inside the structure. To qualify for passive house certification, airtightness of 0.6m³/hr/m² or less must be achieved, at 50Pa.
Airtightness and ventilation explained
Modern new-build properties are now designed to be as airtight as possible. Whereas older houses experience natural leakage and ventilation, new homes are intended to retain as much heat as possible, by being almost entirely airtight. In a passive house dwelling, the level of airtightness can be up to 20x that of a standard-build house.
However, being airtight will inevitably lead to undesirable, unhealthy conditions, if a building is left insufficiently ventilated. Mould, damp and other issues will always result if ventilation is absent or ineffective. As well as cosmetic and potentially structural damage to the property, its occupants will also suffer if exposed to such conditions.
So, ventilation is non-negotiable. You cannot simply seal a property up and isolate it from the surrounding environment. Fresh air is a basic requirement – for both the building itself and its inhabitants.
The dilemma is how to accommodate the need for ventilation, even as you seek to eliminate energy escaping from a building.
One answer is MVHR, which actually works much more effectively when a building is airtight. This is a method of introducing fresh air into a building while simultaneously removing stale air and moisture. This system employs a heat exchanger to transfer heat from the outgoing air to the incoming air, which reduces the amount of energy needed to heat or cool the building.
However, it’s only in an airtight building that MVHR can exert complete control over the flow of air. Plus, MVHR systems are only capable of extracting heat from air that flows directly through them. They can’t recover heat from air that escapes through a building's structure or vents. And if they can’t recover and recycle heat from the humid, outgoing air, the systems aren’t reaching their potential for energy cost savings.
Passive house buildings are the ideal environment for MVHR systems – precisely because they’re so airtight. Very little heat escapes passive house buildings, giving an MVHR system all the warm, stale air it needs. This air is taken to the heat exchange unit, where it transfers its warmth to incoming fresh air, before being pushed out of the building. All this happens without compromising the building’s airtightness. Instead, MVHR facilitates the building’s airtightness, allowing it to stay almost hermetically sealed and well-ventilated at the same time.
Passive House principles explained
There are carbon-neutral buildings and there are passive house buildings.
Carbon-neutral buildings use a combination of energy-efficient measures and renewable energy generation to offset any necessary use of less sustainable fuels. Passivhaus buildings, meanwhile, are designed to use less energy to begin with. The high degree of airtightness in a passive house building is meant to prevent the elements from getting in, thereby greatly reducing the need for heating or cooling.
Some passive houses use just 30% of the primary energy required by other, non-passive house new-builds. What little primary energy they do use can comfortably be produced by renewable methods – as well as occupants’ body heat and heat from appliances. As a result, passive houses’ impact on the environment comes only from the materials that go into constructing them. Even this embodied energy cost is insignificant compared to the energy savings a passive house will make throughout its lifetime.
Passive houses only have minimal energy requirements because of five core principles they all follow:
1. Quality insulation
In a passive house building, continuous ‘super-insulation’ coats the whole outside of a building. Consisting of materials such as stone wool, this super-insulation creates an envelope that traps as much warmth as possible. Insulation is particularly important where cold spots can form, around windows, doors and places where walls meet roofs and the floor.
2. No thermal bridging
A thermal bridge is a part of an object that has higher thermal conductivity than the surrounding materials, meaning it transfers heat easily. These bridges create a path by which heat can leave a building, particularly when it’s colder outside. To deny the possibility of a thermal bridge forming, super-insulation creates a thermal break instead.
3. Superior windows
Passive house windows are triple-glazed and made of high quality materials, with the spaces between each pane sealed and filled with gases like krypton or argon. This is because gases are poor conductors of heat, so they won’t pass much heat on to the outside world.
Warm-edge glass spacers can also be used to insulate the edges of windows, which is usually a weak spot for heat loss. While a ‘low-emissivity’ coating on the windows reflects external heat away during the summer and keeps internal heat in during the winter.
4. Mechanical ventilation with heat recovery
MVHR plays an absolutely vital role in passive houses, not least because it makes sure they’re always well-ventilated. Without it, polluted, damp air would reign inside these airtight buildings.
The way that MVHR systems generate heat is also extremely energy efficient. By taking heat from outgoing stale air, they make certain nothing is wasted.
Plus, higher quality MVHR units come with 100% summer bypass modes, making sure outgoing heat is not retained during the warmer months.
5. Airtight construction
There can be no uncontrolled airflow between the interior and exterior of the building. If heat were to escape from natural ventilation through the fabric of the building, the MVHR’s heat exchange unit would be starved of the warm air it needs and heat wouldn’t be directed to where it’s needed.
How to become Passive House certified
Before a passive house project can attain certification, an independent certifier must sign off on it. The certifier should not be part of the primary design team and must offer unbiased confirmation that all Passivhaus Institute requirements have been met. In the UK, there is a certifiers circle of organisations that work with developers or homeowners throughout the road to certification.
To become a certified passive house, a building must meet several criteria:
1. Primary energy
One of the main ideals behind passive houses is that they require very little primary energy. To test a building’s commitment to this efficiency, certifiers will check that all domestic applications (such as heating, electricity and hot water) use no more than 60 kWh/m2 of living space per year.
2. Space heating
Passive houses work on the principle of retaining heat, but that heat must first come from somewhere – and occasionally be topped up. This can be done through methods such as solar panels, electric post heaters and ground source heat pumps. However, to qualify for certification, the energy demand for space heating cannot go beyond 15 kWh/m2 of living space per year, or 10W/m2 at peak demand. In a traditional house, this figure is around 100W/m2, on average.
To prevent that hard-earned heat from exiting the building, passive houses must be extremely airtight. Certifiers will measure just how airtight a building is by recording how many air changes it allows in an hour. To be classified as a true passive house, no more than 0.6 air changes per hour (at 50Pa) are permitted.
4. Thermal comfort
The concept of a passive house is closely tied to achieving a consistent temperature, all year round, by keeping the elements at bay with airtight insulation and sustainable climate control methods. Passive house certification requires that the building’s temperature cannot rise above 25°C for more than 10% of the hours in a year.
How to design and build a Passive House
Naturally, every construction project requires in-depth planning and research. But this is especially important when creating a passive house building. To meet the exacting demands of the Passive House Standard, a building must be incredibly energy efficient.
For one thing, a flawless envelope of insulation, with no gaps whatsoever, is usually required. Only then can passive houses achieve the almost-complete airtightness they need to retain so much heat. For passive house certification, the level of airtightness must be 0.6m³/hr/m² or lower, at 50Pa.
To gain that certification, different projects use different methods. And any good architect can design a passive house building, using almost any combination of energy-efficient features. But here are some golden rules that all passive house builds, wherever possible, should follow:
1. Detail your energy efficiency aims
Setting out key objectives – such as energy savings, indoor air quality and cost savings – focuses everyone on achieving them. It’s also useful to create key performance indicators, allowing professionals to chart progress as the build goes on.
2. Select the right location
Passive houses are intended to live in harmony with their natural surroundings – and use natural resources without damaging the environment. Locations with plentiful solar exposure and no prevailing winds are preferable for maximum energy efficiency. Spending time studying the local climate and weather patterns at the start of the project will pay dividends later on.
3. Design in detail
If you want to know how to build a passive house, detail is everything. To save the huge amounts of energy that they do, passive houses need to consider fine details.
When planning insulation, leave no gaps at all. When designing the windows, remember low-emissivity coatings. And when positioning MVHR vents, keep the intake and exhaust apart to avoid air pollution.
Architects should also choose the optimal orientation for the building. In the northern hemisphere, the southern facade should be oriented toward the equator, so the most-used areas of the house receive more energy from the low winter sun.
4. Choose the right materials
Passive house builds use high-quality materials that are as energy-efficient as they are durable. Insulation materials, windows, doors and other elements should all be sustainably sourced and actively help the building retain energy.
5. Work with the experts
Passive house construction needs specialised knowledge and previous experience. The end results rely upon finding a contractor who’s committed to energy efficiency and high-quality finishes.
6. Test and analyse
Once the building is up and running, it’s vital to test and monitor its performance. Then an independent certifier can verify that it meets the Passive House Standard.
Can you retrofit a Passive House?
It’s easier to apply passive house principles to a new-build property, where key passive house features can be planned in from day one. In existing properties, on the other hand, it’s harder to be sure of exactly which energy efficiency measures will work and which won’t.
In some cases with new-builds, you might even be able to choose the orientation of the property – to attract less sun in summer and more during the winter. Controlling the amount of sunlight in new-builds is also simpler because you can decide where windows go and how big they are, right from the blueprint stage.
Another important factor is how much easier it is to install ventilation systems like MVHR in new-build properties. They require extensive networks of ducting – particularly in larger properties – which can be difficult to accommodate in existing properties. Ideally, this would be semi-rigid ducting hidden within ceiling voids or the walls, where it’ll be both well-insulated and hidden from view. But in some properties, this either isn’t possible or is very costly to achieve. Similarly, a suitable location needs to be found for the heat exchange unit.
So, when retrofitting MVHR and related systems into an existing property, it’s especially vital to have a thorough site survey first. Then the ductwork can be carefully planned to minimise the complexity of its route, which will, in turn, minimise pressure resistance. The result will be a more efficient ventilation system, with a smaller price tag.
All told, a passive house retrofit won’t usually reach the same levels of insulation as can be achieved with a newly built property. Nonetheless, it’s always worthwhile to adapt older properties to incorporate passive house principles. Even if it becomes quite a complicated project, with some unexpected costs, the energy savings of a passive house retrofit will soon justify the initial outlay.
Plus, the UK Passivhaus Trust Standard includes a special retrofit standard called EnerPHit. It takes the limitations of retrofitting into consideration and is less demanding in terms of some certification criteria. However, any property that meets this standard will still be more energy efficient and comfortable than a non-passive house new-build property.
What is the difference between Passivhaus and EnerPHit?
Recognising that some existing buildings cannot meet its Passive House Standard without great difficulty, the Passivhaus-Institut in Germany created the EnerPHit Standard in 2010. The institute wanted to encourage the renovation of existing buildings to become more energy efficient, without requiring prohibitive financial investments.
EnerPHit is also an acknowledgement of practical considerations that might mean meeting the full Passive House Standard isn’t possible. These can include planning and conservation issues, disruptions to occupants or neighbours, and the inability to change the orientation of a property or where its windows are positioned. And in some properties, it’s extremely difficult to find space to accommodate extra insulation and/or ventilation systems.
The EnerPHit Standard is less demanding than the Passive House Standard, but still sets exacting targets for energy consumption, airtightness and indoor air quality, among other criteria. These targets must be met through effective insulation, ventilation, and heating and cooling systems.
When compared to the Passive House Standard, EnerPHit makes greater performance allowances for specific space heat demands and pressurisation, and allows for water activity on interior surfaces (up to 80%). An alternative route to certification for retrofitted properties is by meeting minimum requirements for passive house features like ventilation systems, an airtight building envelope and energy-efficient windows.
Benefits of passive house
Whether focusing on a new-build project or an existing property, the benefits of passive house design are compelling and long-lasting. Here are just a few of them.
At a time when costs are high and global energy supply is unpredictable, passive house energy costs can be up to 90% lower than in traditional houses. Passive house buildings can also avoid alarming fluctuations in energy prices because they lose and use so little energy. Allied to this, high energy efficiency ratings can contribute to property value.
Of course, one of the primary motivations behind passive houses is their negligible impact on the natural environment. As far as Mother Nature is concerned, passive houses are hugely preferable to more traditional, energy-hungry buildings.
Around a quarter of the UK’s carbon emissions come from heating buildings. By making the fabric of buildings less liable to lose heat, passive house principles can make significant contributions to our carbon-cutting goals. For example, over its lifetime, a passive house home from 2022 will emit 86% less than a comparable non-passive house new-build with a gas boiler.
Comfort and noise reduction
The systems used in passive house buildings aren’t just gentle on the environment: they also make the building a pleasant place to be. MVHR and similar set-ups maintain a comfortable temperature, at any time of year. In schools and workplaces, this will translate to better levels of concentration.
If ventilation systems like MVHR are chosen and set up correctly, occupants will experience minimal noise – and less need for noisy boilers, extractor fans and air conditioning. Plus, because passive house buildings are so airtight and well-insulated – without any weak spots – neighbouring occupants will notice very little noise from these properties. And occupants of the passive house will enjoy a sanctuary free from road noise, neighbouring construction, flight noise or whatever else might disturb their peace.
Because they rely upon intensive mechanical ventilation systems, passive house buildings feature exceptional air quality.
It’s vital to remove moisture-laden, stale air from living and working spaces, regularly replacing it with fresh air. If we don’t do that, the result is poor air quality, leaving occupants at risk from virus transmission, allergies and all manner of respiratory infections.
Respiratory infections tend to affect children more due to their faster breathing rate, which makes them more prone to inhaling harmful particles. On the other hand, poor air quality increases the risk of cardiovascular diseases and strokes in older people. Plus, when rooms aren’t well-ventilated, growths like mould and damp can exacerbate and even cause respiratory infections and long-term conditions.
By maintaining high air quality, businesses can reduce staff absenteeism due to such infections and illnesses – and the same principle applies to attendance in schools. Plus, studies have shown that better air quality – particularly through reducing levels of carbon dioxide – helps students to concentrate and improves workplace performance.
Passive house homes are generally lighter and more open-plan in design, with large windows letting plenty of sunlight in. Not only does this kind of home match modern design ideals, but higher levels of sunlight have been found to promote mental wellbeing and better cognitive function.
Passive houses use high-quality materials in their construction. But their design is just as important to ensuring the integrity of the building. ‘Thermal bridge-free design’ means insulation in passive houses is always extremely comprehensive, meaning there are no weak spots in any part of the building. As a result, there are no cold corners where damp, mould or other issues can take root and threaten the structure of the building. High-quality ventilation systems also safeguard against such threats.
How do passive houses save energy?
Based upon clever principles of sustainability and designed with great skill, passive houses save energy in numerous ways. The high-quality materials and craftsmanship they’re constructed or retrofitted with further guarantee their energy-saving credentials.
In some cases, passive houses require just 30% of the primary energy needed by conventional new-builds. Only minimal amounts of energy go into heating and cooling these properties, thanks to their extreme efficiency when it comes to retaining heat.
Little heat can ever escape these airtight structures, which almst entirely eliminate natural air leakage. High-performance insulation covers every part of the external walls, further helping to minimise heat loss during winter and heat gain in the warmer months.
Triple-glazed windows, insulated around the edges, add to this effect. Low-emissivity coatings on these windows reflect warm sunlight away in the summer and reflect internal heat back into the house during the winter. The placement of windows is also in tune with the seasons, reducing solar gain throughout the summer and encouraging it during the colder months.
While these measures minimise the need for heating and cooling, they can’t eliminate it entirely. To generate heating and cooling in a sustainable way, passive houses use MVHR systems. They retain and redistribute heat from the outgoing stale air in the winter, while a summer bypass function means the incoming fresh air isn’t heated when outside temperatures are higher.
The effect of all this energy conservation is that passive houses are just that: they’re passive parts of the environment, with little need to use natural resources to create energy.
How is Scotland leading the way on Passive House & Passive House legislation?
With some of the UK’s most unspoilt, wild landscapes, Scotland has great interest in protecting the natural environment. And when it comes to passive house, Scotland is certainly doing that.
The Scottish government has announced that starting from 2024, all new residential buildings constructed in Scotland must adhere to the Passive House Standard – or a similar Scottish standard that is currently being designed.
Following a proposal by Alex Rowley, Labour Member of Scottish Parliament (MSP) for Mid Scotland and Fife, the Scottish Parliament has fast-tracked the necessary legislation.
Rowley said: “We have the knowledge and technology to build houses fit for the future, with occupant comfortability as a priority, at a fraction of the heating costs of a standard build house now – it simply seems obvious to me that we should be doing this.”
“This will help future-proof housing stock, save people money, and tackle our climate emergency – a very welcome move! It is time to ensure we are building to the highest energy-efficiency standards possible and that those standards are verified during the building process so that residents can be assured of the quality of their homes.”
The move is part of Scotland’s efforts to reach net zero for greenhouse gases by 2045.
How does Passive House relate to Building Regulations Part F & L?
Ventilation is a crucial ingredient in passive housing and Part F of the Building Regulations details government requirements for ventilation. As well as mandating airflow checks after the installation of ventilation systems, it also stipulates different minimum ventilation rates for different types of rooms. Systems like MVHR can easily achieve these required ventilation rates, helping developers, homeowners and others to meet the Building Regulations.
Part L meanwhile, covers the conservation of fuel and power. Through high levels of airtightness and insulation – as well as smart measures like strategic shading and triple glazing – passive house buildings provide best-practice examples of energy-saving construction in action.
How does Passive House relate to the Future Homes Standard?
The Future Homes Standard comprises energy-efficiency rules to cover all new buildings from 2025, working towards the government’s Net Zero by 2050 target. Part of this Future Home Standard requires new builds to generate 75% less carbon than existing regulations allow them to. Passive house properties, however, are already there.
When compared to some regular new-builds, passive houses will generate up to 86% less carbon during their lifespan.
The Future Homes Standard also sets out minimum requirements for airtightness. The rules use U-values, which measure how effective a building’s fabric is in preventing heat transmission between its interior and its exterior – a crucial factor in air loss. The lower the U-value the more difficult it is for heat to escape.
Passive house u values already satisfy the requirements of the Future Homes Standard. So, for both carbon output and airtightness standards, developers and construction companies using passive house principles are well-prepared for the coming changes.
In fact, the Future Homes Standard will mean more developers and construction companies will have to embrace passive house methods.
Are passive houses expensive?
The case for passive houses is strong. As well as the energy savings, the health benefits and the quality of the build, momentum is firmly behind more environmentally-friendly living and working environments. Now is the time to consider passive house construction.
But how much does a passive house cost to build?
Well, there are a great many variables that affect the cost of building a passive house, or retrofitting one to follow passive house ideals. It’s important to note that passive house design principles aren’t just for large, expensive houses or offices. They can apply to buildings of any size and the ideas behind passive house can be adapted to suit various budgets.
Here are some of the common factors that affect how far passive house budgets will go:
- The size of the property: larger properties will require more materials, labour and specialist, energy-efficient systems
- Location: passive houses in colder climates will generally need more insulation, while those in warmer climates will need more shading features
- Materials: passive houses use high-quality, durable materials, including high-performance windows, doors, insulation and ventilation systems
- Design: simple designs will cost less, while angles and curves can make insulation more problematic and costly
- Labour: since passive house construction requires specialist knowledge, architects, certifiers and tradespeople will likely charge more for their services
Because of the many variables involved in passive house construction/retrofitting, it’s difficult to calculate an average cost. However, Checkatrade estimates that for certified retrofitting in the UK, the average cost per square metre is around £2,150. For a 150m2 house, the cost would be about £322,500. Once the work is all finished, the cost of passive house UK certification is an additional £1,500.
As passive house principles become more widely adopted in response to energy efficiency drives, the costs of passive house projects are coming down. Construction companies and personnel are now much more familiar with the requirements and processes.
According to Passivhaus Trust analysis from 2018, building to the Passive House Standard was 8% more expensive than building a new property without incorporating passive house features. However, once the build is finished, the energy savings soon come into effect. Homeowners will notice the difference from their very first gas or electricity bill, particularly if it comes during the winter, when usage is obviously higher. Plus, they’ll always be more self-sufficient when it comes to energy usage, leaving them almost entirely unaffected by future price hikes.
Is Passive House the future?
Governments around the world are rightly focusing their energies on energy efficiency and carbon reduction. According to the UN, more than 70 countries have set net zero targets, accounting 76% of global domestic emissions.
All kinds of businesses, local councils and property developers now – or will soon – have to construct buildings in a more environmentally-friendly manner. The groundswell of support for counteracting climate change will also lead countless individual homeowners to desire a greener home.
When all these different parties look for green building solutions, passive house will be an obvious candidate. It employs state-of-the-art design and engineering, using ultramodern materials and construction practices. Yet, at the same time, it means we’re more in tune with nature and sustainable ways of living. Passive house is an elegant, logical solution to the central issues of our time.
If you have any questions at all about ventilation solutions, please contact our expert team.