In the quest to reduce CO2 emissions and produce ‘nearly zero-carbon buildings’, most designers and builders focus on lowering operational emissions – even if it means emitting more CO2 in the construction process. There’s still very little thought put into reducing the CO2 emitted during the build stage and from the materials used in the building fabric itself.
There are, however, pockets of developments appearing across the UK – built by innovative SME builders harbouring a social conscience – that take a more holistic approach to sustainable housebuilding.
One such development currently under construction is Kings Farm Close. A collection of 15 new homes on the outskirts of the Oxfordshire village of Longcot, the development promises affordable, sensitively designed dwellings fit for 21st century living.
More significant, however, is that Kings Farm Close also claims to be the most sustainable housing development in Oxfordshire.
Modern methods of construction
Ian Pritchett, Managing Director of Oxfordshire-based Greencore Construction, has been championing a fabric-first approach to new homebuilding, using eco-friendly, modern methods of construction for some time. His approach is to build to the highest standards while also delivering comfort and quality at a great price.
Every Greencore home is built offsite in a factory using a timber frame panel system, which is insulated with a mix of hemp, lime and wood fibre. The hemp-lime mix provides exceptional levels of thermal performance – tests carried out by Bath University showed that this system stores nearly four times the amount of heat when compared with traditional insulation materials like mineral wool.
Meeting the double carbon target
This insulated panel system – branded as the Biond Building System – is manufactured almost entirely from natural materials. It means that Greencore’s homes, which are always built to Passivhaus thermal performance standards, can achieve the double carbon target of a low carbon footprint and low operational energy usage.
Ultimately, it means the homes’ occupants won’t need to use their heating as often. This is because the hemp-lime and wood fibre insulation in the superstructure – and a mechanical ventilation and heat recovery unit – help to maintain a comfortable indoor temperature all year round. The heating is provided entirely by underfloor heating, leaving wall spaces clear for furniture and decoration.
So, how is this possible? How does a humble plant-based insulation material like hemp-lime make such an impact on the thermal performance of a home?
Hemp-lime ‘phase change’ properties drive thermal efficiency
It’s all thanks to the natural ‘phase change’ properties of hemp-lime. The moisture naturally present in the cells of the hemp and in the pore spaces of the composite material can change from liquid to vapour and back again. When this change takes place, a lot of energy is either absorbed or released.
This phase change process can take place at a wide range of temperatures and means that energy entering or leaving one face of a wall is very different to the energy entering or leaving the other face. The reality is that the combination of good insulation and exceptional thermal inertia resulting from the natural phase change properties makes hemp-lime an extremely high performing material.
A little hemp-lime history…
Hemp-lime has been used as a building material for hundreds of years in central Europe, but was revived in the 1990s in France as a niche construction technique for new houses and for infilling the panels of historic oak-framed buildings. The new-build technique involves casting a wet mix of hemp and lime around a timber framed structure to form solid monolithic walls, normally finished with a lime render on the outside and lime plaster on the inside. This form of building has gained popularity in France and spread to the UK in the early 2000s.
Avoiding the delay of drying wet hemp-lime
Despite its rise in popularity, one major limitation hampers the use of wet cast hemp-lime in volume construction projects: it takes a long time to dry. In ideal weather conditions (warm, dry and breezy), drying can take as long as six to 12 months, which clearly isn’t practical for fast-track housebuilding in unpredictable British weather.
To tackle this, Greencore pre-fabricates the superstructure of each home at its factory – ready-filled with hemp-lime and wood fibre insulation – before it’s shipped out to be assembled onsite. This means the drying process can be managed in a controlled, indoor environment. Once onsite, the superstructure of each building can be erected in a matter of days. It’s modern methods of construction with a natural, sustainable twist.
Taking sustainability to the community
For Greencore and its partners, however, the sustainability focus doesn’t stop with the homes themselves. Back at Kings Farm Close, developer Oxford Advanced Living (OAL) – with support from affordable housing provider Sovereign – has made a concerted effort to build sustainability into the very fabric of the community.
“A fifth of the site’s total area will be shared green space,” says Martin Pike, Director of OAL, “planted and managed with native trees to support wildlife under a biodiversity plan. This project has really allowed us to put into practice all our ideas and determination to create a genuinely sustainable community in Oxfordshire.”
With 40% of the development given over to affordable housing, Greencore and OAL are keen to champion a ‘sustainability and quality for all’ approach to housebuilding.
“With these homes, the same high performance standards are available to everyone, regardless of whether you’re renting or buying a home,” says Martin. “We believe that all the residents will be able to enjoy greener and healthier lifestyles at Kings Farm Close, and we intend to work closely with them to help us with future projects.”
Alex Brooks, Development Manager at Sovereign, agrees. “These new affordable homes will not only be great places to live, they’ll also be good for the environment as well as keeping energy bills low for residents. It’s really important that we build homes and invest in communities that are fit for the future.”
Support from MPs
It’s an approach that hasn’t gone unnoticed in political circles either. In March this year, Ed Vaizey, the former culture minister and MP for the Oxfordshire constituency of Wantage, took time out of his schedule to visit Kings Farm Close and see the project first hand.
“The vast majority of new-build homes in the UK are of bland design, poor build quality and lack basic sustainability credentials,” he says. “Much of this is to do with national housebuilders refusing to embrace new technologies and construction methods.
“The Kings Farm Close development, however, is a shining example of forward-thinking, modern housebuilding from a team of people who are clearly very committed to bringing sustainable living to everyone – whether you own, part-own or rent your home.”
Recognition from sustainability leaders
In October 2018, Kings Farm Close was recognised by sustainability charity Bioregional for its national leadership in implementing One Planet Living, a comprehensive framework for planning, building and managing greener communities. Nicole Lazarus, Head of Bioregional Oxfordshire, praised the development, saying: “The Kings Farm Close team richly deserve recognition for their leadership in creating the kind of sustainable new housing we need so badly. We particularly love the natural materials used in the build system and the high-quality indoor environment that they make possible.”
There’s a lot to be said for the power of plant-based materials in construction. The fact is the more of these materials we incorporate into buildings, the more carbon we lock up – plain and simple.
Recent industry data shows that the construction of an average house produces 50 tonnes of CO2. On the other hand, construction of a Greencore home, using the hemp-lime timber frame panel system, produces very low or zero CO2 in the construction process.
With construction work at Kings Farm Close expected to complete in the autumn of 2019, it won’t be long before the final residents move in and the claim of ‘Oxfordshire’s most sustainable housing development’ can be put to the test.