Why is passive house design so good? (reason No.1: it means a warmer house)

In this blog, you’re going to learn about:

  • What the passive house concept means
  •  The 5 principles of passive house buildings
  • The main benefits and problems
  • Expert views

So, if you are keen to live in an energy efficient home, dive in to find out all the facts!

What is the passive house concept?

Energy efficient construction is at the heart of the passive house design technique. By making maximum use of the sun and high levels of insulation and airtightness, an energy efficient building is created and a living space with high levels of thermal comfort.

The Energy Saving Trust describes passive houses as the gold standard in energy efficiency, creating buildings to rigorous design standards so that they maintain an almost constant temperature for space heating; they retain heat from the sun and need little additional heating or cooling.

The design process involves strategic orientation of the dwelling to maximise passive solar gain and enable precise window placement. All of the passive house components must be linked in the design of a new home which must be viewed in its entirety; no single element can be left out.

Passive house standards create sustainable buildings, with a low energy demand, aimed at reducing energy consumption.

Passive houses are orientated to face the sun.

The origins of passive house buildings go back to the 1980s, when physicist Professor Wolfgang Feist and construction engineer Professor Bo Adamson set out to design buildings with more insulation which were energy efficient.

Their work followed research into why low energy buildings often failed to deliver anticipated energy savings and lower carbon emissions, and the initiative was developed by The Passivhaus Institute in Germany.

While the majority of passive houses are built in German-speaking countries and Scandinavia, they can be seen in a range of buildings across Europe, Japan and the USA.

Anyone building an energy efficient house can apply to have it certified by The Passivhaus Institute; certified passive houses must comply with the planning system which enables the design to be altered until the house reaches the required building standard of energy efficiency.

The principles can also be applied to older houses, although it may be harder to reach the same levels of insulation as a newbuild.

The Passivhaus Institute has a separate certification recognising appropriate retrofitting work which has a lower level of acceptance than for a full passive house building, called the EnerPHit Standard; effectively it has the same criteria as passive house standard with a higher space heating demand of 25kWh/m2/year, rather than the passive house level of less than 15kWh/m2/year.

Passive house construction involving glass wool thermal insulation.

The 5 principles of the passive house standard

High standard of insulation

Low conductivity materials are installed within the wall and roof to minimise temperature loss and reduce energy demand; they also provide sound insulation, durability and building resilience, and can retain heat in a power cut.

The insulation is ideally uninterrupted, but where this is not possible and another material bypasses the insulation, a thermal bridge can occur; this reduces the effectiveness, especially when a conductive material like metal is involved.

Airtight construction

Mechanical ventilation provides fresh air. When tested, the building needs to have less than 0.6 air changes per hour to achieve passive house certification. 

The air barrier must be continuous through the use of effective air barrier materials, which will reduce domestic electricity costs and condensation problems. A suitable ventilation system with heat recovery strategy must be used to deal with excess humidity.

Double or triple glazing

Windows are where most heat can be lost, so high-performance glazing systems are needed such as Passive House-certified windows. Passive house windows can include non-conductive framing or large thermal breaks, insulated framing, double or triple glazed windows, argon or tryptone filled units, multiple low e-coatings, warm edge or non-conductive spacers.

Passive houses takes advantage of the sun; solar heat gain through strategically sited windows can help offset the heat a house needs in winter: in summer, this must be counteracted with shading. For every project, there will be an ideal number of windows to balance the advantage of free heat with minimising the amount of heat lost from too many windows.

Another consideration is surface temperature as low temperatures around the windows can result in higher condensation risk, and a colder feeling near a window. A certified passive house window can be identified to provide an allowable surface temperature around the window. For more about triple glazing, visit 24housing’s blog on triple glazing.

Triple glazing units provide high levels of insulation and reduce energy consumption.

Minimise thermal bridges

Thermal bridging can create cold spots and reduce warmth retention. To maintain a constant temperature, passive house buildings aim to be thermal bridge free where different architectural features meet, such as where a window is attached to walls, or a wall meets a floor.

Heat recovery ventilation

As passive houses are airtight, a ventilation exhaust air system is needed to bring in fresh air and extract CO2 and pollutants. In winter, warm exhaust air must be taken out and used to warm the cold air entering the house.

Passive house ventilation techniques involve a heat recovery ventilator to continuously remove stale air and deliver fresh air. During this process it extracts heat from the outgoing warm air, using it to heat air entering the house, without mixing the two.

At least 75% of the heat needs to be recovered in an efficient passive house heat recovery system. In summer, the system features a summer bypass dampener which ensures incoming air is not heated.

While the aim is to eliminate the need for a conventional heating system by reducing heating demand, a small heating element is often attached to the system; this uses very little energy and will be only be used in extreme freezing temperatures.

A design may also incorporate low carbon technology such as solar water heating or an air source heat pump, both of which use less energy than conventional methods.

Air ventilation being installed to passive house standards.

The benefits of passive houses

Passive house buildings are energy efficient; they are comfortable in winter and summer due to their constant temperature and dry building fabric. The design creates an even space heating temperature throughout house, the air quality is consistent, there are no draughts or temperature loss through leakage, which is reduced to less than a tenth of that in conventional buildings.

They can cater for the heating demand for domestic hot water, offer health benefits from being warm and well-ventilated, and significant total energy savings from the use of renewable energy. For more on energy efficient houses, visit https://24housing.co.uk/tips-to-get-your-house-in-the-best-shape-to-counter-rising-energy-bills/

Problems with passive house buildings

The higher costs of passive house construction make it unviable for large scale commercial builders. In the UK, the construction costs are 5% more than conventional buildings, due in part to increased insulation, triple glazing and the ventilation equipment which can cost between £4,000-£6,000 according to Grand Designs.

Solar panels provide renewable energy in this passive house.

Outstanding energy efficiency and consistent performance

Architect and certified Passive House designer Phil Simpson of  People & Place Architects said:

Passive house is one of the most measurable standards I’ve seen regarding the link between design performance and actual performance. While it may be seen as too costly to implement on a mass scale, as costs come down, the picture changes and more retrofitting will happen.

Passive house homes could be viable in the future, and we are currently looking at affordable housing projects which can be done at scale. There is a lack of awareness and there is also the problem that passive house doesn’t take embedded carbon into account (the emissions associated with the original construction). There should be wider promotion of the need for greater energy efficiency more generally.

Can the passive house concept be applied to any house?

Mr Simpson commented:

The EnerPHit retrofit certification, the passive house retrofit brand, is useful when dealing with older houses as the targets are a bit less onerous; with older houses it is harder to achieve benefits.

Obviously, it is easiest to install retrofitting measures when you are working on a wreck or gutting a house. The cost of certification puts some people off slightly, although some houses are fitted to EnerPHit standards but do not then incur the cost of getting certification.

Mr Simpson added that there are some common myths about passive house design.

One is that you can’t open windows due to the presence of a heat recovery ventilation system. Of course, opening windows is normal, the system is constantly carrying out the ventilation, which results in a very healthy house. Another misconception is that as passive houses are described as being airtight, people think it must be like living in a polythene bag, whereas, in fact, the controlled ventilation is actively cleaning the air.

Super insulation in passive house buildings

Improving space heating through insulation in the houses we build is vital, and Mr Simpson said:

Any form of insulation can be used in a passive house design, provided there’s enough of it to insulate properly and comply with safety and insurance requirements. I advocate using natural material as an insulator, such as wood fibre, sheep wool, hemp and recycled denim – while a greater thickness is required to match the qualities of man-made standard insulating materials, natural materials hold onto temperatures for longer, increasing the heat lag.

This highly insulated, timber frame building incorporating a 14th century wall, is being improved to passive house standards by People & Place Architects.

The Passive House Standard

The Construction Leadership Council (CLC)’s Housing and Net Zero Workstream lead commented:

It is likely there will be an increased use of passive house design as we move forward and implement the Future Homes Standard from 2025, which will bring minimum building performance standards much closer to passive house specifications.

While Building Regulations would not mandate passive house buildings, it would be one option for meeting future Building Regulations requirements; however, the detailed compliance and certification process that official passive house certification requires is a disincentive to widespread adoption.

From a retrofit perspective, there are currently no regulations requiring interventions to a passive house standard. The EnerPHit (retrofit) levels of energy intensity (25kwh/m2/yr) require a deep retrofit that is not considered to be cost optimal.

The fabric first approach is nonetheless favoured as a first step in decarbonisation, but a sweet spot is viewed (in discussions with BEIS, the Department for Business, Energy and Industrial Strategy which aims to promote home-grown energy) as being above 50kwh/m2/yr.

Fabric first is encouraged in the retrofit programmes such as the ‘Social Housing Decarbonisation Fund’ which supports local authorities and landlords when investing in retrofit, usually with matched funding from the local authority or housing authority.

Energy savings

However, the standard to which improvements are being made relate to Energy Performance Certificate (EPC) levels (usually a minimum of C) which is calculated using RdSAP methodology (used to assess the energy efficiency of existing dwellings) which considers energy cost rather than energy intensity. 

EPC minimum values are likely to be introduced for the private rented sector (2025 level C) but there are no minimum levels recommended for owner occupier homes.

Nevertheless, the CLC submitted a detailed report to government highlighting the importance of retrofitting in delivering the decarbonisation of buildings, this is known as the National Retrofit Strategy.

Whilst BEIS accepted the need for such a strategy based on the scale of the challenge, it did not support the ‘interventionist’ approach (based on PAS 2035 which provides specification for the energy retrofit of domestic buildings, and retrofit passports providing each home with a whole house assessment and a pathway to net zero).

We continue to work with BEIS to support them in the development of policies that can deliver the action needed to address the 29 million dwellings in need of energy efficiency measures to reduce their energy demand.

An insulated façade promotes air tightness.

Passive house benchmark

The Construction Industry Council’s champion for Modern Methods of Construction, Nick Mead, believes that passive house and EnerPHit should be more widely promoted in the UK as they allow a higher standard of build quality in the construction process and a level of measure to benchmark against. He agreed that cost is one problem, adding:

The principle part of passive house is the façade system. Cost is partly a problem due to the management of the installation and the materials which add a premium. However, the key issue is the problem of fire rated materials in façades and their testing as a system.

Getting the industry to recognise buildings are a system and not a sum of products is difficult. Many tests are purely for individual products and do not lend themselves to be certified when put together. There is also a lack of understanding what through wall means as a complete external building envelope.

As well as benchmarking, he said the main advantages of the passive house concept are the building standard, construction of the façade system and its sign off.

The future for passive houses

Passive house building techniques could help the UK to meet its net zero targets. Some of its key principles can be applied to our existing housing stock such as improved insulation and ventilation which would create warmer, healthier, more energy efficient homes.

While the increased costs attached to it are currently a barrier to widespread take-up, these costs could reduce as passive design becomes more popular, making it a more mainstream option.

However, already the significant cost saving, and possible energy security benefits for years ahead is making passive house buildings of interest to local authorities, housing associations (the low energy costs mean that tenants are less likely to fall into arrears), and those keen to create cost-effective new buildings.

Did I miss anything?

Maybe I didn’t mention something that you know about passive houses?

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