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What is a Passivhaus and should we all be building them?

When you build your own home, you are in the unique position of being able to decide on not only the design and layout, but also its standard of energy performance.

How far you wish to go in the pursuit of energy efficiency is a personal decision, but it can dramatically affect both the running costs of your home and its impact on the environment.

While the minimum building regulations requirements have increased over the years, many choose to go far beyond them and create much higher performance homes.

Passivhaus (English: Passive House) is the most well known, and highest, standard for energy efficient homes. It is something to which many aspire, without perhaps knowing exactly what it entails.

A Facit Home designed to Passivhaus principles.

What exactly is Passivhaus?

Passivhaus is a voluntary building performance standard. The brainchild of a Swedish academic, Bo Adamson, and Dr Wolfgang Feist of the German Institute for Housing and the Environment, it is a set of rigorous requirements for house designers and builders to meet in order to create a Passivhaus certified, low-energy home.

Recognised around the world, it seeks to all but eliminate the home's need for dedicated heat generation. It relies predominantly on passive heat gain from the occupants and the sun, and its retention within the building.

A specific software package is used to calculate the predicted energy demand of the design, which needs to be less than 15kWh/m²/yr. By way of comparison, that is about 10% of the energy a standard home uses for heating.

The 5 key elements used to achieve this are:

  • Super-insulated building envelope - U-value lower than 0.15W/mk2

  • Airtight construction - air leakage lower than 0.6m3/h/m2@50pa

  • Triple glazing - U-value lower than 0.8W/mk2

  • No thermal bridges - removing conduction of heat from inside to out through careful detailing

  • MVHR system - bringing in fresh air and retaining heat from the stale air it extracts

Beyond this, meeting the standard mainly comes down to manipulating the design.

As a methodology that focuses on energy preservation or ‘passive’ energy principles, meeting a Passivhaus' specific requirements can affect the overall appearance of the home. Designing for the rules is often only possible with the right site and orientation. It can be complicated and limit the home’s architectural potential. For example, a Passivhaus typically needs south facing windows to optimise solar gain and many are designed with a very functional form in order to achieve the strict standards.

A Facit Home with large, south facing windows for solar gain - and solar shading to keep it cool in summer.

Is it necessary to build to Passivhaus certified standard?

There is no doubt that all new homes should be seeking to reduce energy consumption, so with Passivhaus being the gold standard it has clear merit.

However, whilst it’s a great aspiration, when we consider the UK’s climate (where the average winter temperature is around 5-7 degrees) you can question whether it is necessary to go to such lengths. It is possible to get too focused on hitting Passivhaus targets and lose sight of your main intent; building a highly energy efficient home that suits the context in which it will sit.

Achieving Passivhaus standard can have significant upfront cost implications that only really result in incremental gains, as well as constraints and compromises on the design. It is also debatable whether it is worth going the extra mile to have your home formally certified as a Passivhaus, which itself is a chargeable service (and not something everyone who builds to the standard even actually does!)

Spot the photovoltaic panels added for energy generation on this south facing Facit Home.

What standard does Facit Homes build to?

The 'fabric first' approach that we take is the bedrock of Passivhaus and delivers most of the performance with none of the box ticking requirements. By adhering to the key principles above, and in some cases exceeding Passivhaus levels, we create high performance, energy efficient homes that do not compromise on design.

Using our fully customisable timber structure, the Facit Chassis, we can create the home you want whilst being confident of always having a super-insulated, airtight building envelope to keep you warm. With triple glazing and MVHR as standard too, our well considered fabric first approach will perform to a similar level as Passivhaus on all but the coldest few days of the year in the UK.

What else should you consider?

The environmental cost of embodied energy is not considered as part of the Passivhaus standard. Embodied energy is the sum of energy required to produce a product or material. In this case, it is the energy used to design and build a home. A Passivhaus can be built with concrete or brick, materials that have a much higher embodied energy than timber.

A 2011 research study that Facit Homes undertook investigated the cost of embodied energy in creating homes with Passivhaus standard U-values using various materials. It found that a customer would have to live in a masonry home for an extra 100 years for the operational energy savings to even out the embodied cost, when compared to a Facit Home.

That is why we use sustainable, FSC certified timber for our structure. Campaigns such as ‘Wood CO2ts less’ by Wood for Good website promote timber as a renewable resource, a carbon trap and a great substitute for CO2 intensive materials like concrete.

A Facit Home in construction. FSC certified plywood is used for all Facit Chassis™.

So should you build a Passivhaus?

A highly respected standard, Passivhaus is achievable if you have the budget and dedication, and are happy for it to potentially define the design of your home.

However, not meeting it doesn’t stop you from creating an environmentally friendly and energy efficient home that will work perfectly for you, as we have proven over the years for our customers.

For more information about the fabric first approach of a Facit Home, have a look at our previous article.


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