The house that hemp built

Irish Times

4 days ago

In Paris, public housing is being built with biomaterials. On Rue Marx Dormoy, in the 18th arrondissement, a terrace block of 15 social flats, by architecture firm
Barrault Pressacco
, has been made with timber frames and hempcrete; even the bay windows are hemp.
France is the largest producer of industrial hemp in the European Union, and has been using hempcrete in building construction since the 1990s.
However, while hemp farming and hempcrete production are growing across Europe, Ireland has been slow to nurture a domestic hempcrete industry, despite mandating its use, particularly in insulation, which could help meet our climate targets and develop new, sustainable agribusinesses.
Instead, our
national retrofit plan
, with a public spend of €8 billion to 2030, is predominantly insulation with carbon-intensive imported plastics.
As the environmental group
ClientEarth
put it, plastics are Plan B for the oil industry. Hemp, a crop that grows rapidly in most soil, is increasingly being seen as part of the solution to climate-resilient and climate-just buildings.
While concrete, construction's mainstay, contributes 8 per cent of global greenhouse gas emissions, three times that of aviation, hempcrete (a mixture of hemp and lime) is carbon negative across its life cycle, storing rather than releasing carbon.
As a non-toxic, lightweight building product, it boosts high thermal insulation, passive energy, breathable walls, good acoustic protection, carbon sequestration, and durability. While it sets hard and is long lasting it is not a load bearing material so is ideal for insulation and could replace some high carbon emitting materials we currently use in construction and energy retrofitting.
'Clients absolutely love it,' says Ronan McDermott, who runs
HempBuild
in Dublin and Meath. 'It's not just it's good for climate change, it's the whole pie; no chemicals, no toxins, regulates its own humidity, holds heats ten times better than concrete, hygienic, protects against pests, bugs, mould, lasts about 100 years and it's biodegradable.'
But while companies like HempBuild and
GráHemp
in Limerick are supplying hempcrete in Ireland, that hempcrete is being imported due to the lack of production and manufacturing here.
McDermott says the barrier in Ireland is the licensing steps required to farm hemp, which can put farmers off and the lack of manufacturing infrastructure to support industrial production. Ultimately, it is the negative association of hemp with its sister plant cannabis, which is illegal to grow here, that informs the barrier and although hemp has no psychoactive properties, and has been used for centuries in making textiles, in Ireland there has been a lack of public policy and support for the sector.
Earlier this year Teagasc, the State agency on agriculture and food research, hosted a seminar on industrial hemp production showcasing international and Irish businesses, like HempBuild, and made the case for investing research and development in hempcrete as a biomaterial product.
Teagasc senior research officer,
Fiona Thorne
, an agricultural economist, highlighted the benefits: 'Hemp can support Ireland's climate goals while providing farmers with new revenue streams, but significant investment in processing facilities and market development is required.'
Thorne sees the opportunities hempcrete potentially offers to Irish agriculture, climate action and the built environment as a 'no-brainer'.
'If you want to get momentum in this industry we need investment in research, we need the data to develop it,' she adds. At a time when Irish agriculture is facing significant change, particular in the impact of a potential loss of the nitrates derogation, and where Teagasc's research, in the last
National Farm Survey Sustainability Report
, shows only one third of the Irish farming community are economically viable, developing new climate resilient agribusiness solutions is urgent.
While Ireland has been slow to develop a hempcrete production base, hemp cultivation for fibre is growing across the European Union. There has been a 60 per cent increase in land use for hemp fibre cultivation in the past decade and the production of hemp has increased from 97,130 tonnes to 179,020 tonnes, by more than 84 per cent.
While France is the largest producer, with more than 60 per cent of EU production, it is followed by Germany and the Netherlands. We can learn from those experiences. 'It's not just Irish Government support that we should be looking at here, but also opportunities at the European level,' says Thorne. 'Our Cap [Common Agricultural Policy] strategic document for Ireland would be the vehicle for doing that.'
Hemp, as a crop, thrives with minimal reliance on chemical fertilisers, making it a sustainable alternative to traditional crops that are heavily reliant on inputs. This is particularly relevant in the context of the EU's targets for reducing agricultural chemical use, given its impact on rivers and biodiversity.
Hemp is therefore a good match for Ireland's bioeconomy strategy, published in December 2023, with its emphasis on a sustainable and circular economy. Hemp offers a match in developing native biomaterials for construction (as well as textiles, foods and biofuels). Yet Ireland remains slow to seize the opportunity.
The obstacle seems to be as much culture and mindset as vested interests. National policy is perhaps defined by what has always been done and the existing economic and dominant commercial business interests (concrete, plastic-based insulation, cladding etc) rather than adopting the systems-based transformative model climate action demands.
The siloed nature of Ireland's thinking on materials means the
Steering Group on Timber in Construction
, established in November 2023 and due to report recommendations, is solely looking at increasing timber use in construction rather than developing a holistic biomaterials strategy, including hempcrete.
In neighbouring EU countries, like France, timber and hempcrete work side by side delivering low-carbon solutions. The Irish Green Building Council (IGBC), in its roadmap
Building a Circular Ireland
, launched in May, calls for a bioeconomy strategy for construction that takes a holistic approach to developing timber and agri-crop supply chains and industries.
The roadmap brings together a reuse model for materials and existing buildings, tackling the significant issue of waste, where construction and demotion (C&D) waste is Ireland's largest waste stream – generating more than nine million tonnes a year. The roadmap is effectively a pathway to not just implement the
European Performance of Buildings Directive
but decarbonising construction and the built environment.
While it is expected that the steering group on timber will recommend removing regulatory barriers (timber is restricted due to fire regulations) and implementation of a national standard for the use of mass timber, similar progress on the development of an overall biomaterials in construction policy is absent. Across the EU, cross-laminated timber is safely employed in high-rise buildings, but it also forms part of an overall strategic approach to low-carbon building design, regulation and planning. Besides hempcrete, other complementary biomaterials, including straw from tillage farming and wool from sheep farming, can be used to develop products for the construction industry.
Natural insulations can be produced from hemp, wool, straw, reeds, verge grass, elephant grass, seagrass, flax, and mycelium. But if the lack of progress on hempcrete is puzzling, then the complete absence of any discussion around sheep's wool, something Ireland already produces in vast quantities, shows just how deeply entrenched the mindset is on materials and transformative solutions.
Ireland has 3.7 million sheep, yet sheep farmers say they have no market for the wool and often just burn it as waste. The few Irish businesses that offer sheep's wool for insulation are importing it from Austria or the United Kingdom.
At the IGBC conference in May, one of the main suppliers,
Ecological Building Systems
had five types of sheep's wool on display with the union jack stamped on it, while
Sheep's Wool Insulation
in Wicklow imports from Austria, where the wool is treated to prevent moth infestation. They say there's no supply chain in Ireland.
Thorne notes Teasgasc is engaged on hempcrete, but that's not the case with sheep's wool; there's no industry market development being done on sheep's wool as a biomaterial for construction. While we continue to maintain a national sheep herd (even if this is reduced to meet climate targets), developing new agri-business markets for waste wool is an obvious route to pursue.
Perhaps maintaining the status quo case of a dairy industry dependent on a nitrates derogation is potentially limiting our national ability to imagine innovative new agri-business that could be good for both farmers and climate action.
Helen Shaw is a climate solutions researcher and writer. She presented her work Imagining the Climate-Just City, at the recent International Social Housing Festival in Dublin