While energy efficient homes are gaining in popularity, many homeowners still wonder what they actually entail. Expert in the creation of high-performing, energy-efficient homes, Andy Mitchell, Managing Director at 21°, demystifies the concept. Good planning means you can secure the benefits and the best features that make these properties low energy, comfortable, healthy and sustainable.

Through practical elements like airtightness, thermal insulation, and efficient ventilation, Andy explains how energy-efficient homes are far more accessible than many people realise.

Core components of an energy-efficient home

An energy-efficient home comprises three main pillars – minimal air leakage, effective ventilation, and a thermally-efficient core building shell (wall, roof, floor, windows, and doors) and connections between them. All of these elements must work together in synergy for optimal results.

In fact, these ‘optimal results’ provide a level of health and comfort that often far exceed what most people have experienced. It’s therefore essential these components are carefully considered as a whole system, rather than being viewed in silo, to guarantee their overall effectiveness.

For example, installing thermally-efficient windows and doors is not enough to foster a comfortable indoor temperature if there is uncontrolled air movement throughout the house.


Airtightness is crucial in preventing uncontrolled air leakage, which can lead to energy loss and increased heating costs. Airtightness is often overlooked, yet accounts for approximately 30-40% of a home’s heat loss. An airtight home helps to maintain a stable indoor temperature and improves energy efficiency.

From tapes and membranes to advanced sealing solutions, airtightness products are essential for creating a well-sealed building envelope.

These solutions should also extend to products such as windows and doors – where not only the frame is well-sealed to the building, but the opening element has gaskets that ensure an airtight seal when shut. Class 4 (BS EN 12207) is the best grade of airtightness for windows and doors These products prevent air leakage which can typically account for as much as a third of a home’s heat loss.


Effective ventilation is essential for maintaining indoor air quality and comfort while also being energy-efficient. Although making our homes airtight is key to improving efficiency, some air changes are still required to stop the moisture buildup. If this is not done correctly it can lead to mould and dust mite issues, as well as the accumulation of other toxic gases such as VOCs.

Mechanical ventilation with heat recovery (MVHR) systems are engineered to provide continuous fresh air while recovering heat from exhaust air, maintaining a comfortable indoor environment and alleviating the need for additional heating, further reducing energy consumption.

MVHR systems provide optimal ventilation, ensuring properties remain fresh and healthy – without compromising on energy efficiency.

For example, in addition to providing triple-glazed windows and doors, we designed and supplied the MVHR system in a new build Passivhaus home project, utilising a Zehnder ComfoAir Q MVHR unit with rigid steel ducting.

For this project 21° worked with oak frame specialists, Oakwrights (also a NaCSBA member), to develop an MVHR system that would work alongside the encapsulation system. The client cited the quality of the products and the precise installation as being “crucial for the airtightness of the project, ultimately contributing to the Passivhaus certification”.

Thermal efficiency

The thermal efficiency of the building elements is integral to overall energy efficiency, reducing the need for artificial heating and cooling by maintaining a consistent indoor temperature. High-quality insulation materials and solutions ensure every part of the home, from walls and the roof to floors and the foundation, is well-insulated.

High-performance doors and triple-glazed windows are also an essential factor in a properly insulated property, as they’re designed to minimise heat transfer and ensure warm air stays in during the winter and out during the summer. Windows and doors should also contribute to the overall airtightness of the home, furthering energy efficiency.

A whole house retrofit in Cambridgeshire springs to mind in highlighting the role of windows and doors as part of wider thermal performance considerations. Here, our client chose inward opening windows, a lift and slide door, a fold-aside door, and two entrance doors (styles PA2 and GR1) from the GBS78 triple glazed timber range. The result was a comfortable, sustainable home that came as near as possible to Passivhaus standards.

Achieving exceptional energy efficiency with integrated solutions

At 21°, we believe that energy-efficient homes are not just for the eco-conscious few, but for everyone. By combining high-performance products with the right specifications and integration, homeowners can achieve remarkable energy savings, improved comfort, and a healthier living environment. Whether building a new property or retrofitting an existing one, solutions are available to meet the highest standards of energy efficiency and sustainability.

Energy-efficient homes are characterised by airtightness, thermally efficient building elements, and efficient ventilation, all working together to create a comfortable, healthy, and sustainable living space.

Through advanced construction techniques and technologies, energy-efficient homes are becoming more practical and accessible to all. As an industry leader, we are committed to advancing the knowledge and application of these solutions, helping to build a more sustainable future for all.


NaCSBA member SIP Build UK has scooped a prestigious award in the brand new Making Better Homes Awards, run by national builders’ merchant Jewson. The awards recognise those creating energy-efficient, safe, and comfortable homes across the UK. SIP Build UK’s commitment to sustainability ensured SIP Build UK won in the Best Building Fabric category for its self build, Munoz House.

For the winning project SIP Build UK was commissioned to create a highly insulated and airtight envelope using Structural Insulated Panels (SIPs) for a self build in Colchester. The panels minimise heat transfer and energy loss through walls, providing excellent thermal performance.

The judging panel was impressed by the use of modern methods and fabric-first approach. Judge Matthew Handley said: “This high energy efficiency build is a great example of how SIPs can add value. The fabric-first method and renewables have delivered a wonderful living space.”

Ian Still, SIP Build UK National Sales Director said: “It’s fantastic to win Jewson’s Building Better Homes Award. Working closely with the homeowner from the start helped ensure this dream Passive Haus Certified SIP home was a success. Seeing the family now enjoying the benefits of their thermally efficient SIPs home makes this project even more special.

“We are immensely proud of this project, as it shows the perfect balance between energy efficiency and aesthetics. We entered the awards to showcase our dedication to quality, efficiency and sustainability in construction. This award is not just an achievement, but a responsibility to keep providing excellent sustainable solutions.”

About SIP Build UK

SIP Build UK is a highly accredited award-winning SIP company that designs, manufactures & installs SIP superstructures. We work nationwide to exact standards and take great pride in delivering our customers fabulous homes and buildings.

Words: Duncan Hayes

Self builders interested in creating a sustainable home won’t want to miss the Passivhaus Open Days from 28-30 June. Organised by the Passivhaus Trust, the event sees homes nationwide welcoming visitors to find out more about Passivhaus.

This annual event sees owners of Passivhaus buildings around the world opening their doors to visitors to educate and inspire others about the benefits of Passivhaus design.

The Passivhaus Open Days are a unique opportunity for self-builders and professionals to find out more about how the designs work, from principles to the lived-experience and how this translates to running costs. Meeting and talking to the owners or professionals involved offers useful insight and inspiration.

Projects listed to date include new build homes and retrofit refurbishments, including a Victorian church in Northumberland, and more projects will be added over the coming weeks.

Booking for the event is essential as space is limited – find out more and book on the Passivhaus Trust website.

The Passivhaus Trust is a membership organisation bringing together expertise and professionals involved in the construction sector working to promote the adoption of Passivhaus in the UK.

Buildings contribute to 35% of total global energy consumption, and Passivhaus embraces a range of proven solutions to optimise new and existing buildings to create better energy efficiency for heating and cooling to create more comfortable living conditions.


The Passivhaus Trust is calling for Scottish Government to stick to its commitment for a Scottish Passivhaus Equivalent Policy for all new build homes, in light of the fact that ministers recently scrapped their target to cut carbon emissions by 75% by 2030.

Scottish Government had previously said it would pass subordinate legislation to introduce a new minimum environmental design standards for new housing. This will create a national Scottish equivalent to the Passivhaus standard for all new builds, which, the Passivhaus Trust states, would cut heating demand in new homes by 79%.

The Passivhaus Trust call to government comes in light of pressure from mainstream house builders who are calling for a review of the plans.

Data for 2023 showed that completions across all sectors fell by 11% in 2023 in Scotland, while starts fell by 24%, figures that indicate the size of the crisis.

The Passivhaus Trust maintains that improving energy efficiency standards will not adversely affect housing delivery, but will dramatically improve the quality of the homes delivered. It estimates that building to Passivhaus will create additional initial costs of between 4-8%, which will come down with economies of scale.

However, it does conceded that the new build market is operating in difficult conditions, and is consequently proposing a transition period for the new policy to come into force.

What is Passivhaus Standard?

Passivhaus is an international energy performance standard based around reducing the requirement for space heating and cooling of new homes. Collectively, buildings contribute 35% of total global energy consumuption, and Passivhaus is a solution for this.

Adopting a Passivhaus approach means a fabric-first solution that plans for your homes build fabric and energy usage – something that many self builders adopt. Not everyone building to these principles opts to have their home approved as meeting the Passivhaus Standard – find out more on the Passivhaus Trust’s website about what this means for you on your project.


Words & Image: Duncan Hayes

After 30 years of trading as Green Building Store, the building products supplier and high-performance homes specialist has rebranded itself as 21°. The new name reflects 21°’s vision to support customers to create life changing homes that are healthy and comfortable, secured by optimising energy performance.

21°’s supports self builders by advising and supplying a range of products and services to help make their build as airtight as possible, such as by incorporating triple glazing and MVHR.

By concentrating on airtightness, the home benefits from fewer draughts and air that’s free from outdoor pollutants. This enables the home to maintain a year-round ambient temperature with the added benefit of ensuring that the building is ultra low energy.

Andy Mitchell, managing director at 21°, commented, “We’re thrilled to announce the rebrand of Green Building Store to 21°, and our customers can enjoy the same exceptional service and expertise they’ve relied on from us. While we’ll continue to offer advice and guidance for obtaining Passivhaus certification, we’ll also support those not able or looking to achieve full accreditation, but who still want to create a home that’s designed with wellbeing at the forefront.”

“When specified correctly with one another, windows, doors, and MVHR, along with airtightness and insulation, are the core products for optimising for energy efficiency and comfort. It’s this interconnected specification that is key, and central to what we do.”

Image, from left to right: Paul McGurk, MVHR designer, Mark Redmond, windows estimator, Luke Gilman, windows department manager, Tom Heywood, MVHR department manager, Mike Shufflebotham, sales manager.

21° is a NaCSBA member meaning you can trust them on your project.
Find all our members in the – and you can find all our members in the Membership Directory

The National Self Build and Renovation Centre (NSBRC) in Swindon has launched a new event called Market Day, where many of its exhibitors will be encouraged to be on stand to chat to self builders in a relaxed and informal setting.

Kicking off on Friday 8 March, 10am-3pm, the Market Days will be on the second Friday of each month. The event is being organised following requests from visitors, to give people the chance to discuss projects in detail away from the busyness of the traditional show days.

Plus, visitors will be able to join a free guided tour of the NSBRC’s new-build educational zone at midday.

A list of exhibitors who will be on stand for the next upcoming Market Day is available on the NSBRC’s website, so you can plan you trip to speak to the right companies for your project.

Find out more about the NSBRC’s Market Days

The Right to Build Task Force has published new data that illustrates that not only are self build homes more sustainable than the average new build, but they have a greater beneficial local impact in terms of spend on materials and labour.

This is welcome news that adds weight to the case for a site when it is submitted for planning, contributing to the argument about a site’s impact versus its harm locally.

The National Custom and Self Build Association (NaCSBA) has long known anecdotally that individuals invest more in their own homes in terms of green tech and sustainable methods than mainstream builders, but welcomes the news that for the first time there is data-based evidence to support this.

In terms of building greener, this is mainly due to the fact that self builders invest more than a mainstream builder would as they want a home that’s more energy-efficient and in which they intend to live in for a long time. Equally, they don’t need to factor in a profit margin, unlike speculative builders.

NaCSBA also welcomes the news that the model contributes more locally than speculative building does, as it feeds into local economies – boosting SME businesses and offering training opportunities.

About the research

The analysis was conducted by Chamberlain Walker Economics, which used five local authority areas for the research, chosen as they represent a range of types and sizes. These were Breckland Council, Durham CouncilFolkestone and Hythe District CouncilHerefordshire Council and South Gloucestershire Council.

Sustainability of self build homes

The Energy Performance Certificates (EPCs) of self build homes in the five areas were reviewed to compare energy usage, in comparison to new builds in these areas.

The research looked at two metrics: average energy consumption and average CO2 emissions. This found that the average energy consumption of custom and self build homes was significantly lower, by 8-42%, while CO2 emissions were also lower, by 7-43%, in comparison to new build local averages.

This adds to the growing evidence of custom and self build as a greener route to housing, such as the survey that showed that more than 50% of self builds have a renewable energy source as their primary heating system.

Local economic impact

Using the same five areas, the research examined the economic factors around the local impact of labour and materials for custom and self build. It found that these homes roughly doubled the economic impact of mainstream housebuilding, as self builders buy more materials locally, and also source SME trades for their project.

This equated to self build spending nearly double, at £45 in every £100 spent, as opposed to mainstream housebuilders, who spend £22 on local materials and labour.

This is good news for local authorities, as well as providing a pool of work for SME housebuilders, a group that government is keen to see grow.


NaCSBA member Air Craft Southern has added the innovative Heliomotion system to its suite of heating, cooling and solar solutions. Ideal for any self builder interested in improving sustainability, Heliomotion is a solar power plant for residential and commercial use, that moves to track the position of the sun, thereby maximising efficiency.


Easily installed by DIYers, once in place the configuration follows the sun in two-axes, which means the solar panels can deliver between 30-60% more energy annually, in comparison to a conventional roof-mounted system.

It uses GPS to calculate the sun’s location from its position to maximise the energy produced from solar power. This can be used to power the home, or stored in batteries for later use.


Not every roof is suitable for solar, and Heliomotion is a great solution for those with sufficient outdoor space for this clever alternative to solar generation. 

Produced by Bee Solar Tech, tracking systems can increase productivity, meaning that you can secure the same energy output with few panels than a fixed system. Heliomotion won Best Sustainable Technology or Product category in the 2022 Build It Awards

Government has announced a plan to scrap the stranglehold that nutrient neutrality has had on house building. This saw a complete ban on any new housing in wide areas across England. The announcement is great news for builders, not only self builders but for custom build developers who have been impacted.

Housing Secretary Michael Gove announced a major deregulation of the rules around Nutrient Neutrality which led to 74 councils setting up moratoriums for all new building, following requirements made by Natural England.

Gove commented that cutting the red tape will unblock up to 100,000 stalled homes, which is worth £18 million in activity for the economy.

In the announcement government squarely blames ‘defective’ EU laws for the problem of Nutrient Neutrality, although it was the government quango Natural England that made the requirements that halted building. Most councils enforced a ban in affected areas as not doing so would have left them open to legal challenge.

What is Nutrient Neutrality?

Nutrient Neutrality refers to run off of excessive nutrients from the land, which pollutes water courses and damages river habitats. But new housing is believed to cause minimal additional run off, with farming and out-of-date water treatment plants being the main forces contributing to pollution.

An amendment to the Levelling Up and Regeneration Bill will bring about the announced change, and building could commence immediately on many sites as a considerable number have planning permission in place.

Housebuilders welcomed the announcement, but environmentalists have criticised government for its stance.

However, government also announced new environmental measures to improve habitats and reduce pollution, including more funding for Natural England’s Nutrient Mitigation Scheme, which offsets any negative impact from house building.

Michael Gove MP said: “We are committed to building the homes this country needs and to enhancing our environment. The way EU rules have been applied has held us back. These changes will provide a multi-billion pound boost for the UK economy and see us build more than 100,000 new homes.

“Protecting the environment is paramount which is why the measures we’re announcing today will allow us to go further to protect and restore our precious waterways whilst still building the much-needed homes this country needs.

“We will work closely with environmental agencies and councils as we deliver these changes.”


The Building Performance Network (BPN) has published three free modules to support a range of stakeholders, including self builders, to help them get sustainability right. The guides are designed to support stakeholders to understand the gap between planned energy performance and the actual reality of living in the home.

At NaCSBA we know self builders often become semi-professional in the level of knowledge they develop as they pursue their own build. As such, while these guides won’t be relevant for all, there will be many self builders researching sustainability who will find them insightful as they work to create an energy home that performs as well as promised.

What is Building Performance Evaluation (BPE)?

BPE refers to the performance of a home and its systems. Understanding  around this area can be complicated, drawing on various data sources, but is necessary to support the emergence of more homes better able to reduce their carbon footprint.

The Building Performance Evaluation modules:

The guides , the first three of five, will support your understanding of what it’s like living in buildings where sustainability has been factored in, in comparison to their predicted performance. This in turn will help you when it comes to making decisions about fabric and systems for your own build, helping you to cut through the greenwash.

The new guides are available at the BPN’s Resource Hub, which is sponsored by Ecology Building Society, and are designed to be entry level for those who are new to BPE and want to understand how to avoid building inefficient homes.