Passivhaus: how to insulate your home against soaring energy bills

'The Deerings' Passivhaus home by Gresford Architects. Main Contractor: Husker. Location: Harpenden

Coldwells Building Company are now certified Passivhaus builders, and with high energy prices here to stay, there’s never been a more compelling case to build an affordable, low-energy, high-quality home.

Over the past nine months, the Coldwells team have been studying, sitting exams and taking part in specialist training to become certified Passivhaus tradespeople. It makes us one of the few building contractors in Scotland with a qualified and committed workforce in Passivhaus construction.

So what is Passivhaus? How much does it cost? What's it like to live in a Passivhaus home? We've got all the answers in this consumer guide,  so read on to learn about Passivhaus in Scotland and how it can reduce your energy bill to the cost of a cup of coffee per day.

What is Passivhaus?

Developed in Germany, Passivhaus (or Passive House in English) is not actually a type of brand or product. In fact, it’s the world’s leading building standard, which guarantees affordable homes with amazing levels of comfort and radical reductions in energy use.

Homes built to the standard are so well designed, constructed, insulated and ventilated that they require minimal heating and maintain an almost constant temperature. Cool in the summer and warm in the depths of a Scottish winter.

For people with allergies and asthma, Passivhaus homes are among the world’s healthiest and most comfortable to live in. There are no draughts, no cold spots, no mould, no condensation and no excessive overheating. Fresh clean air is constantly supplied to the home and this all happens with minimal energy.

In fact, Passivhaus homes use around 75% less energy than the average UK new build. It might sound like magic, but the Passivhaus Standard is based on sound science. 30 years of studies, testing and intensive monitoring have proved Passivhaus delivers what it promises - sustainable, healthy, comfortable and easy to heat buildings with lasting quality and guaranteed performance.

Passivhaus delivers what it promises - sustainable, healthy, comfortable and easy to heat homes with lasting quality and guaranteed performance.

Dr Wolfgang Feist with his family in front of the first Passivhaus home in Germany, which continues to perform optimally. Photo: Peter Cook.

How Did it Start?

When most people think of German and Scandinavian engineering and design, they think of quality. Passivhaus is the brainchild of the German physicist, Dr Wolfgang Feist and Swedish construction engineer, Professor Bo Adamson.

In 1988, they set out to investigate why low energy buildings often didn’t deliver on their expected energy saving potential and later applied their findings to create a physics-based approach to better quality construction. The result was Passivhaus – an affordable method to minimise a building’s energy demand while maximising comfort.

The first Passivhaus home was built in Germany in 1991 and there are now 65,000 certified Passivhaus buildings worldwide, including a nursery in Aberdeen.

Passivhaus has caught on in Scotland, with schools planned in Edinburgh, new housing developments underway in Fife and scores of other projects in the pipeline or already successfully built. It’s the way of the future, and for good reason.

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'The Deerings' Passivhaus home by Gresford Architects. Main Contractor: Husker. Location: Harpenden

Scotland’s Energy Challenge

Scotland, like the rest of the UK, is suffering from an energy crisis, with millions of homeowners struggling with a recent £700-a-year rise in energy bills and bracing for a further £600 increase in October 2022.

A whopping 87% of UK households rely on gas for heating. Such overreliance means we’re vulnerable to huge swings in global prices, and the problem is exacerbated by our leaky homes. The UK has the worst insulated houses in Europe, meaning heat disappears through walls, windows and doors, quickly after leaving our radiators.

Conversely, Passivhaus homes are designed to use minimal energy. In Scotland, they are generously insulated, with triple glazed windows, high levels of airtightness and ventilation systems. Insulation and airtightness seal the home, like a vacuum flask, keeping the house quiet and cosy year-round. The ventilation system supplies fresh air to each room, but the windows can also be opened to let nature in.

Passivhaus buildings are warmed by ‘passive’ sources. They’re heated (mainly) by the sun and from activity within the house, ie - people and pets living inside, cooking dinner and boiling the kettle. Very little additional heating or cooling is needed.

For you, the homeowner, this translates to huge savings in energy bills and a home which provides energy security for the future.  Passivhaus homes are ideally set up to meet all their energy needs from renewable sources. This means they will require little or no upgrading as Scotland’s housing standards push towards net zero.

Over the next eight years, more than one million Scottish homeowners will be required to upgrade or install energy-efficient heating systems, and by 2045, all homes in Scotland must have significantly reduced their energy use.

So, if you’re considering building a new home, Passivhaus offers an easy solution for low energy bills and the massive cuts in CO2 emissions we need to make - urgently. This protects your investment for your legacy while offering a comfortable, more healthy living experience for you and your family.

Benefits of a Passivhaus Home

  • Radical reductions in energy bills
  • Quiet and comfortable thanks to superior insulation & airtightness
  • Affordable
  • High standard of indoor air quality
  • Better value for money over time
  • Higher sales value than a standard new build
  • Built to standards which exceeds UK building regulations
  • Helps Scotland reach Net Zero by 2045
  • High levels of satisfaction amongst homeowners
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'The Deerings' Passivhaus home by Gresford Architects. Main Contractor: Husker. Location: Harpenden

How Does it Work?

Rather than rely on expensive, bolt-on eco-technologies to generate energy, Passivhaus concentrates on reducing the amount of energy required to operate a home in the first place.

It takes a ‘fabric first’ approach to energy efficiency, meaning the building itself does the work. Super-insulated and airtight, it requires little energy to run, because it’s effectively sealed against the elements.

Passivhaus design centres on five main principles, and these must be integrated into your home to achieve the standard:

1. High-quality insulation

Passivhaus design starts with continuous, high-quality insulation wrapped around the home’s entire shell, insulating the walls, roof and floors. This creates an ‘envelope around the building, like a giant thermal sleeping bag. This plays a big role in reducing heat loss, making it possible to warm the house without a conventional heating system. It also keeps the house cool in summer. Fortunately, high-quality insulation options are also natural and environmentally friendly, including wood fibre, sheep’s wool and cellulose insulation. There’s no need for toxic chemicals or plastic insulation in your Passivhaus home.

2. Airtight construction

The Passivhaus standard focuses on creating an airtight building envelope, 15 times more demanding than the minimum building regulations. Quite simply this means there are no draughts coming in and no leaks going out. The standard takes precautions to tape and seal all gaps around doors and windows, electrical outlets, pipes and lights. Essentially, anywhere an air leak could occur, Passivhaus construction makes the extra effort to plug it.  An airtight home limits heat escape cuts down on energy costs and promises the very best comfort, with no draughts, condensation, or cold spots.

3. No thermal bridges

A thermal bridge is a weak spot in the insulation where heat transfer is much higher. This could be due to a break in insulation, less insulation, or if the insulation is interrupted by a material with higher thermal conductivity, such as wood. This weak spot then creates a path of least resistance for heat to escape.

A useful analogy is to think of a flowing stream. Water will always follow the path of least resistance as it carves its way through the landscape. Similarly, the heat inside a building will always try to move the cooler air outside the walls of a home, using the easiest path.

Imagine a well-insulated home where the builders forgot to insulate a particular corner of the roof. Despite the high-performance insulation in the rest of the building, the heat would rush toward that defined area of least resistance. Thus, creating a thermal bridge, which acts as a heat highway headed straight to the outdoors, and impacting the home’s energy efficiency.

Passivhaus requires careful detailing to eliminate thermal bridging that allows heat to escape through gaps in insulation or building junctions.

4. High-performance windows

Windows can often be the weak link in a home, either through heat loss or heat gain. For this reason, using energy-efficient windows is vital to achieving the Passivhaus Standard. This typically means using triple-glazed windows that are as high quality as possible.

The size and position of windows are also essential. Passivhaus homes are optimally orientated and designed to make the most of the available natural light and heat.

5. Ventilation system that can recover heat

Now that the home is air-tight and air leakage has been stopped in its tracks, you need to implement a way of flushing the stale air out and replacing it with fresh, filtered and temperature-managed air. The answer? A mechanical ventilation with heat recovery (MVHR) system. The MVHR does exactly that, avoiding any stuffiness in the home and eliminating the potential for condensation in colder weather. It’s a nifty thing, and it does this through a heat exchanger which ensures any incoming air is near enough the same temperature as that which has been pushed out.

These five principles come together to create Passivhaus homes which are comfortable to live in all year round, no matter what the weather is doing outside!

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'The Deerings' Passivhaus home by Gresford Architects. Main Contractor: Husker. Location: Harpenden

What’s it Like to Live in a Passivhaus Home?

In 2011 Dormont Estate, near Lockerbie, became one of the first developments in Scotland to build homes to the Passivhaus standard. Below you can hear from the residents about what it’s like to live there.

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Designing Your Passivhaus

To achieve the Passivhaus Standard your home needs to be designed correctly from the outset.

At the heart of the standard is the Passive House Planning Package (PHPP) software. It’s a necessary part of Passivhaus design which enables a certified designer to accurately plan, optimise and calculate how much energy is needed to keep your house comfortable before it’s built.

The physics-based software uses site-specific weather data and takes account of the building’s orientation. It even factors in shading from the trees on-site to provide a detailed analysis of how the building will perform year-round.

The fact that analysis begins at the design stage means changes can be made to ensure the building performs optimally prior to construction.

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Image from Scott Brown Rigg

The Certification Process

To qualify as a Passivhaus home, a building must meet a compliance process with an independent expert consultant who is an accredited certifier.

The certifier supervises the process from the beginning, firstly checking the design drawings and calculations in the PHPP software.

They then check what’s built on-site, ensuring it matches the design accurately.

Finally, the completed house has an airtightness test to confirm there are no leaks, and the ventilation is tested to ensure it runs effectively and quietly.

When the certifier is satisfied that everything is in place, you, the homeowner, receive a certificate and a plaque, which you can fix to your home.

These steps add up to a robust quality assurance process, much more rigorous than the typical building regulation inspections. Designers and builders are more vigilant knowing their work will be checked and verified and any honest mistakes can be picked up sooner.

Is Certification Worth It?

Yes. Certification proves your home performs as it has been designed.

The ‘performance gap’ (where the final build doesn’t meet the design criteria) is a huge problem and many UK new builds underperform, largely due to poor build quality and lack of quality control.

On the other hand, Passivhaus homes incur energy demands and costs which are very closely aligned with their design. In a 2020 study of 97 UK Passivhaus homes, the University of Bath found the standard delivered ‘low energy homes with no performance gap.’

This compares favourably to Energy Performance Certificates (EPCs), which have a reputation for having a large performance gap.

A Passivhaus certificate demonstrates to others that the home has achieved the required design performance and this removes uncertainty if it’s sold or rented.

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'The Deerings' Passivhaus home by Gresford Architects. Main Contractor: Husker. Location: Harpenden

Beware of Cheap Imitations

The main reason we love Passivhaus is that no other building standard delivers results so reliably and the fact it can be verified and benchmarked against a set of criteria can’t be overstated.

The construction industry is full of greenwash. Claims of “eco-home this” and “green home that” are bandied about, but these terms are ultimately meaningless unless a building is independently tested against a rigorous standard. Without it, there’s no evidence or proof that claims of quality and performance are true.

In the UK, there are occasionally claims that a home meets or exceeds the Passivhaus standard simply because it might meet one or more of the requirements of the Passivhaus standard.

On other occasions, claims have been made that a home is designed using ‘Passivhaus principles’. For example, it achieves the air-tightness target or incorporates insulation to recommended levels.

However, it’s wrong to claim that such a building satisfies the Passivhaus Standard.  A building can’t be described as a Passivhaus unless it’s been modelled in the Passivhaus Planning Package (PHPP) and meets all the requirements of the standard.

We believe this matters most for our clients because Passivhaus provides certainty, which in turn ensures confidence. You know exactly what you’re getting.

Achieving the Passivhaus standard demonstrates your building team have really understood Passivhaus principles and that your home will perform as expected.

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Passivhaus home by Gresford Architects. Contractors: Husker. Location: Chieveley

Where to Get Advice: Designers & Contractors

So, you’ve done your research and you’re convinced a Passivhaus home is for you. But where do you start?

Firstly, you’ll need the help of a certified Passivhaus designer/architect who’s been trained and passed a comprehensive exam. The designer will use the Passivhaus Planning Package (PHPP) to model and calculate how your entire house will work before it’s built.

The design calculations must then be translated into precise construction, which means you’ll need a contractor who’s committed to building to the Passivhaus standard. A contractor who doesn’t understand what they’re being asked to deliver is a recipe for disaster.

Exemplary construction is required for a Passivhaus home to perform appropriately. This means diligence and excellent standards of craftsmanship must be employed at all times.

Certified Passivhaus builders,  like Coldwells Building Company, demonstrate their knowledge of Passivhaus construction by passing an exam. After five years, contractors must provide evidence they’ve maintained and advanced their existing knowledge by documenting their work on a Passivhaus project.

A perfect Passivhaus design can be implemented badly.  It’s important your builder understands Passivhaus construction, so they don’t end up having to do costly rework.

The Passivhaus Trust has a map detailing the locations of its UK members, including certified contractors and designers. Getting the right people on your team is key, as Passivhaus projects require collaboration and joined-up thinking.

Am I Limited With My House Design?

No. Passivhaus homes come in all shapes and sizes and can accommodate any budget. They can be built using different materials and can sit in any context, from Aberdeen city to isolated plots in rural Aberdeenshire.

But as physics tells us, the bigger a surface area, the more heat will be lost. So if your design is long and low, has numerous overhangs or extensive glazing, it will be harder to achieve the necessary standard. The walls may need to be thicker, the doors and windows higher spec – and all that comes at a cost.

On the other hand, a smaller surface area means fewer building materials. And you save money and energy, reducing the building’s impact on the planet’s resources.

 

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Passivhaus home by Gresford Architects. Contractors: Husker. Location: Chieveley

Does Passivhaus Cost More?

Investing in a well-planned Passivhaus home isn’t much more expensive than investing in a standard new build, costing around 4% to 8% more initially, but less overall in the long term.

But here’s a question:

Is costing more the same as costing too much?

After all, should a high-quality, high-performance, future-proofed home cost the same as a home that barely meets legal minimum building standards?

When you consider that Passivhaus can achieve 75% cuts in occupants’ energy bills, without the need for any expensive, bolt-on eco-technologies, the investment is clearly justified.

A 2019 study found that costs associated with early Passivhaus projects are now reducing as the standard becomes more widely adopted in the UK.

This is evidenced in Brussels, where Passivhaus was mandated as the building code in 2016. In the five years leading up to the mandate taking effect, costs came down so much that it was sometimes cheaper to build Passivhaus than not to.

Passivhaus can be designed and built cost-effectively to match your budget. There are many examples of this from around the world.

Other Benefits – sales price, mortgages, quick planning permission

Sometimes Passivhaus projects can even help win planning permission. Local authorities committed to cutting carbon have been known to favour new homes which are exemplars of low-carbon construction.

And although there are no official statistics, the Passivhaus Trust  (the organisation that supervises the awarding of the Passivhaus standard in the UK) says they’ve seen Passivhaus homes sell for between 5% and 10% more than similar properties built to normal energy efficiency standards.

If you’re considering building a Passivhaus, you may be able to fund it with a green mortgage. These mortgages reward you for owning an energy-efficient home, typically by offering you discounts or cashback.

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Passivhaus home by Gresford Architects. Contractors: Husker. Location: Chieveley

Final Thoughts – Should your home and legacy include higher standards? 

We are delighted that more people are looking for ways to reliably build low energy homes and finding the answer in Passivhaus.

Although the standard is currently voluntary in the UK, there’s a growing campaign to mandate it in Scotland, as it’s the perfect starting point to meet the country’s commitment to being Net-Zero by 2045.

We build Passivhaus homes because we want to change Scotland’s housing for the better. Energy bills shouldn’t absorb an obscene amount of people’s incomes. We want brilliant, high-quality housing to be available to all.

This will take time, but we’re dedicated to pursuing our vision of a Scotland where all houses are truly energy efficient.

So, if you want to do the right thing for the planet and your pocket, building a Passivhaus home has much to recommend it. The Coldwells team can talk you through everything you need to know about building to the gold standard in low energy eco homes.

We only build a limited number of homes each year, so our clients are assured of the highest level of service. If you have a timeframe in mind, start the discussion far in advance.

We offer consultations for those wanting true craftsmanship and the integrity of a certified Passivhaus builder. Take advantage of our willingness to share knowledge with you and schedule a strategy conversation today.

hello@coldwellsbuilding.com

Tel: 01975 223011

Editors note: This article was last updated September 29, 2022

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