UK’s Greencore Homes Goal: 10,000 Hempcrete Homes by 2035

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Written By Jean Lotus

Greencore Construction works with the British government to build high-permforming “Better than Zero” Passive House homes with hemp panels. Image courtesy Greencore Construction

UK’s Greencore Homes Goal: 10,000 Hempcrete Homes by 2035

By Jean Lotus

Greencore Homes, one of the largest hemp-lime builders in the UK, recently announced two large British housing development projects featuring the company’s “Biond panels” totaling more than 130 new “Better Than Net Zero” homes in Oxfordshire and Buckinghamshire. The UK government’s Homes England will provide £8 million to “turbocharge housebuilding for small and medium-sized enterprise (SME) builders,” the company said.

HempBuild Mag recently spoke with Greencore founder, Ian Pritchett – a physics major by training – who shared his journey from historic preservation to revolutionizing sustainable construction with prefabricated hemp-lime panels.

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Ian Pritchett, co-founder and innovation director of Greencore Homes. Courtesy of Greencore Homes

From Lime Mortar to Hemp-Lime: A Natural Evolution

Pritchett's foray into sustainable building began in the early 2000s, driven by a desire to reintroduce traditional materials into new construction in the so-called “Lime Revival” movement in Britain.

"We started looking at that quite seriously and set up a company in 2002 called Lime Technology, which was to promote the idea of using lime mortar instead of cement mortar for new buildings," he said. 

His company developed pre-blended lime mortars – easy to use on construction sites. The company’s big break came with the rebuilding and refurbishment of St Pancras Station in London, which utilized a thousand tonnes of their lime mortar.

This success led Pritchett to explore other environmentally friendly applications for lime, eventually leading him to hemp. He credits architect Ralph Carpenter in Suffolk, UK, (considered to be the “grandfather of UK hempcrete”) as a pioneer in using hemp and lime, having learned from French techniques. 

"I was impressed with what Ralph was doing," Pritchett said. The company also worked for about 12 years with building science researchers and engineers at the University of Bath to nail down the properties of hemp-lime that would work best in the UK.

Adnams Brewery in Suffolk was built with Pritchett’s Lime Technology hempcrete blocks in 2006. Photo courtesy Adnams Brewery

After years of balancing historic building repairs with new construction, Pritchett made the pivotal decision to sell his historic building business and focus entirely on new builds, especially with lime and hemp. "That's what I've been doing for the last twenty years," he said.

“We have known Ian for about 20 years and he is probably the most commercially successful hempcrete builder in the world,” Tai Olson of Chicago-based US Heritage Group told HempBuild Mag in an email. 

A Greencore duplex community in Oxfordshire. Photo courtesy of UK Construction Blog

Greencore panelized system. Photo courtesy UK Construction blog

Scaling Up: The Shift to Panelized Systems

Early on, Greencore steadily built houses and non-domestic buildings, completing 150 to 200 houses and about 50 non-domestic buildings over five years, Pritchett said. The pandemic slowed them down, but so did the wet-mix, on-site application of hemp and lime, particularly during inclement weather. A harsh winter in 2010, where 85 houses were being cast simultaneously, caused significant delays. Bad weather and a wet mix meant the company incurred a substantial weekly penalty on a project for Marks and Spencer's at Cheshire Oaks.

"That focused our minds," Pritchett recalled. This experience led to a crucial decision: to adopt a panelized system. "We would make the panels in a factory, cast the lime of hemp into them, and we would dry it in the factory as well. And that was probably the best decision we ever made." This shift eliminated weather-related delays, dramatically increasing efficiency. Fifteen years ago, a panel would take six weeks to make and dry; now, the process takes only 24 to 48 hours.

Greencore's "Biond panels" feature a 120-millimeter (five-inch) layer of hempcrete combined with seven inches of wood fiber insulation, resulting in a 12-inch thick panel. "Overall, you've got a panel that's 12 inches thick," Pritchett explained. The company's factory currently has the capacity to produce 200 houses a year, with plans to scale up to that rate by early next year.

Greencore Homes’s 30,000 sq. ft. facility in Bicester, England manufactures enough Biond panels to build 200 homes per year. Photo courtesy of Greencore Construction

Growth and Collaboration in the UK Market

Pritchett said he doesn’t mind competition in the hemp building industry, because success for anyone is success for all. Regarding the high-profile Phoenix Project in Lewes, East Sussex, he said, "I think it's great whether we build it or somebody else builds it. The world is big enough for competitors. We see competitors as very important because it's validating. It's spreading the word. It's increasing the size of the market." He praised Jonathan Smale, the former head of Greenpeace and visionary behind the project, for successfully securing planning approval for the 700-home conversion of a former industrial site.

Greencore is actively working on several new developments in Oxfordshire. A project for 42 homes in Milton Heights secured £8 million in financing and is currently under construction, with the first 10 houses nearing completion and an expected finish for the entire project by mid-next year. Of these, 14 will be affordable homes. Additionally, a 65-house project in Launton is commencing groundworks. These two projects alone account for over 100 houses under simultaneous construction.

“This partnership with Homes England represents a pivotal moment for Greencore,” said Jon Di-Stefano, CEO of Greencore Homes in a press release.  “As we continue to drive housing delivery to reach our target of 10,000 homes by 2035, partnerships such as this with Homes England will be essential. “

Another project in Haddenham, Buckinghamshire will feature 89 Better Than Net Zero homes, of which 27 will be affordable. Greencore has a pipeline of 200 houses in the planning system and 200 more on sites being acquired.

Pritchett said the company’s audacious goal of 10,000 Better than Net Zero homes in the next decade is just a small percentage of the 3 million new homes to be built in the UK.

Greencore homes in Springfield Meadows, Oxfordshire. Photo courtesy of Greencore Homes

Greencore homes in Springfield Meadows, Oxfordshire. Photo courtesy of Greencore Homes

Hempcrete and Passive House: A Powerful Combination

Pritchett emphasized the benefits of combining hempcrete with Passive House principles. While hempcrete is a good insulator, he noted it's not the "best insulation material" on its own for achieving Passive House standards without extremely thick walls. The company’s composite biopanel, with both hempcrete and wood fiber, addresses this by improving thermal performance and significantly reducing drying times.

"If you bring the two things together, you get the best of both worlds," Pritchett said. Other Passive House methodologies Greencore uses are optimal house orientation for solar gain; minimizing surface area to reduce heat loss and sufficient shading to prevent overheating in summer. 

Pritchett also highlighted hempcrete's natural phase-change property, which means "the real thermal performance is better than the steady-state thermal performance." This results in houses that perform "much better than the Passive House software predicts."

Each Greencore home has a 262 kWp roof-integrated solar PV system. Coupled with good insulation, airtightness, and mechanical ventilation with heat recovery, these elements contribute to "a fantastic house." 

Greencore homes in Hook, Oxfordshire. Photo courtesy of Greencore Homes

Dispelling Myths and Looking Ahead

Pritchett acknowledged the challenges of promoting hemp building, particularly in the US, where building costs and energy costs are generally lower – making the argument more difficult for higher-performing, but potentially more expensive, construction.

Pritchett’s advice to his US counterparts starting out? He suggests focusing on the whole-life cost and performance, especially in commercial construction where climate control is critical.A hempcrete-renovated archive for the National Museum of Denmark led to significant savings on mechanical and electrical equipment due to the building's passive performance, he said.

Emphasizing hemp’s building performance and industrial use

“I don't think it's helpful to link hemp building with marijuana,” Pritchett said. “We use hemp because it produces better buildings, more energy efficient buildings that are lower embodied carbon.”

All in all, Pritchett's journey from historic preservation to leading a modern hemp-lime construction company has been a pragmatic approach to sustainable building. He noted that the UK has no regulations about embodied carbon in housing and no subsidies for hemp building.

"Everything we've done has had to stack up commercially," he said. 

Correction: The headline of this article has been corrected because of a typo to “10,000 Hempcrete Homes by 2035.”

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Jean Lotus
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