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.

The company began by developing its own range of windows and doors – the Ecoplus system – since superceded by the triple glazed PERFORMANCE, ULTRA and PROGRESSION ranges. Thermal efficiency was a major priority from the start with use of low emissivity glazing used from the start. This commitment has culminated in the company’s recent decision to switch to triple glazing as standard. The company has been at the cutting edge of responsibly-sourced timber with FSC® certified timber introduced as standard for all its in-house window and door ranges (FSC-C008220).

Before forming Green Building Store – and its construction division Green Building Company – Bill Butcher and Steve Slator had also undertaken the design and build of the ‘Longwood low energy house’ in Huddersfield, which has been 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 corresponds to the AECB CarbonLite Silver standard. In 2023, Green Building Store rebranded to become 21° and continues to be involved in energy-efficient building projects throughout Yorkshire and the north-west and has built the pioneering Denby Dale Passivhaus and Golcar Passivhaus projects and the award-winning Stirley Farm EnerPHit project.

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, which it believes offers the most effective and rigorous solution to low carbon construction in the UK.

Passivhaus design includes features such as: maximising use of passive solar gain; super insulation; stringent airtightness standards; and use of mechanical ventilation and heat recovery systems. Passivhaus design has been widely established in Europe for over 20 years and offers a cost-effective and proven approach to low carbon construction.

21° has been developing its understanding and expertise in Passivhaus design 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. Bill Butcher The company has also been a member of the Passivhaus Trust since 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