Green Building Store is now 21°


Founded in 1995 by three experienced building professionals and formerly Green Building Store, 21° continues to be involved in energy-efficient building projects throughout Yorkshire and the north-west.

Who we are

Founded in 1995 by three experienced building professionals, Bill Butcher, Chris Herring and Steve Slator, the company (then trading as Environmental Construction Products Ltd) grew out of their frustration with the poor availability of ecological building products.

Founded in 1995 by three experienced building professionals, Bill Butcher, Chris Herring and Steve Slator, the company (then trading as Environmental Construction Products Ltd and later as Green Building Store) grew out of their frustration with the poor availability of ecological building products.

The company began by developing and manufacturing its own range of timber windows and doors – the Ecoplus system.. Thermal efficiency was a major priority together with the use of ecologically responsible materials and finishing. The Company pioneered the use of advanced double and triple glazing and the use of responsibly sourced FSC certified timber. The current window ranges continue these commitments, with FSC timber throughout, triple glazing as standard and the highest levels of thermal performance including windows and doors suitable for Passivhaus buildings. 

Before founding the company, Bill Butcher and Steve Slator had also undertaken the design and build of the ‘Longwood low energy house’ in Huddersfield, which was at the time described as “one of the most energy efficient houses to have been built in the UK”. It remains an exemplar for low carbon construction even now, and is believed to be at a similar performance level to  the AECB Building standard which was developed later.

During the early 2000s the company developed a key focus on the Passivhaus standard and methodology, as the exemplar of what can be achieved in energy-efficiency and comfort in buildings. The buildings division, then trading as the Green Building Company, completed one of the very first Passivhaus homes, in Denby Dale near Huddersfield, in 2010 and went on to build a number of certified Passivhaus homes as well as refurbishing traditional buildings to exemplary levels of energy-efficiency. The award-winning Cre8 Barn, refurbished for the Yorkshire Wildlife Trust’s Stirley Farm in 2013, pioneered the Passivhaus retrofit standard.

In parallel with the building division’s work, the company developed the key supply chain for Passivhaus and energy-efficient buildings, with current departments offering advanced performance windows, mechanical ventilation with heat recovery and specialist airtightness and insulation materials. A combination of advanced products and excellent technical knowledge and support have combined to make the company well known and respected across the UK.

In 2024, Green Building Store rebranded to become 21°. The new brand reflects our aspiration for a wider reach as the company matures, building on the legacy of almost 30 years. 

About us


As buildings contribute to up to 50% of the UK’s carbon dioxide emissions, we believe the role of the construction industry in tackling climate change is pivotal. 21° is a passionate proponent of Passivhaus building design and methodology, which offers the most effective and rigorous solution to low carbon construction in the UK.

Passivhaus includes features such as: super insulation; stringent airtightness standards;  use of mechanical ventilation and heat recovery systems and optimising use of passive solar gain;. Passivhaus has been well established in Europe for over 25 years as well as in many other countries around the world.  Above all, Passivhaus offers a cost effective and proven approach to highly comfortable and healthy homes which are energy-efficient and low carbon. 

21° has been developing its understanding and expertise in Passivhaus design for over 15 years and offers a comprehensive range of Passivhaus products and services for the UK. By developing expertise in Passivhaus products, 21° hopes to facilitate the construction of Passivhaus buildings in the UK and to promote ‘best practice’ in low carbon construction. 21° has been a member of the AECB since its inception and actively supports the AECB CarbonLite Programme, which promotes Passivhaus design and training. The company is a Patron Member of the Passivhaus Trust, which it helped found in 2010.

See our awards and accolades

We’ve received major commendation awards for our pioneering approach to sustainability and for bringing cutting-edge sustainable products to the market for our customers.

Find out more



21° has also been a pioneer in introducing Forest Stewardship Council® (FSC) certified timber for fenestration products in the UK. FSC® certification indicates that the wood used to make a product comes from a forest which is well managed according to strict environmental, social and economic standards.

In 2005 21°’s relaunched Ecoplus range was the first UK manufactured window range to use certified FSC® 100% timber. In 2007 21° launched its Ecoclad range – the first FSC certified timber/ aluminium composite window available in the UK. In 2008 21° launched the Ecopassiv window and door range, which is the first certified FSC® 100% window suitable for Passivhaus buildings.

21° actively promotes FSC® certification as the most credible timber certification scheme available and the only one that is endorsed by all major environmental NGOs.

Please note: The Ecoplus, Ecoclad and EcoPassiv ranges have all now been superceded by our FSC® certified windows and door ranges.

FSC® welcomes the new Ecoplus System, the first UK manufactured FSC®100% range of windows and glazed doors. Construction and housing is a key sector for FSC® and is showing a strong and growing demand for sustainable materials. 21° has shown an outstanding commitment to offering products from well-managed forests.

Nick Clarke, former FSC® UK Director

Energy-saving products

Sustainable building products can play a key role in reducing CO2 emissions in buildings and 21° aims to offer products that are at the cutting edge of thermal efficiency. When we first launched our original Ecoplus range of timber windows and doors in 1995, it offered U-values at least 50% more thermally efficient than the then Building Regulations.

21° has constantly worked to improve its thermal efficiency even further – offering whole window U-values now as low as 0.68 W/m2K.

Sustainable design

Wider impact

By being at the cutting edge of sustainable design, 21° has led the way for competitors to imitate and follow. The original Ecoplus range can be said to have had a significant impact on the window manufacturing and construction products industry through its pioneering use of advanced glazing specifications and FSC® 100% timber.

Whilst 21° cannot take all the credit for the growing environmental awareness within the industry, the company has demonstrated to other manufacturers the consumer demand for sustainable building products.

21° products have been installed in schools, universities, housing associations, offices, factories, hotels, bus stations, visitor centres, sports centres and private homes throughout the UK.

How can we help?

Visit the showrooms

Visit us at our showrooms in Huddersfield and Swindon or catch us at exhibitions around the UK to see our windows and doors.

Request a quote

Tell us about your project, and we'll make sure you get a no-obligation quote from us. Take a step towards a more energy-efficient home today.

Get in touch

We offer a friendly and responsive aftersales service for our windows and door ranges, with a dedicated office and on-the-road aftercare team.

Life changing homes