Grass construction has long been used for traditional buildings, providing a locally-sourced material to insulate, protect and enhance the aesthetics of dwellings. But as the world looks towards more eco-friendly and sustainable means of building, grass is getting a second look.
The History of Grass Construction
Across the globe, grass has provided a source of building material for both indigenous and non-indigenous communities to work with, being readily available and a renewable resource. The indigenous Aboriginal people of Australia used spinifex grass construction on their dome-shaped shelters as a durable thatching material, while in Africa’s arid Sahel region, grass-woven mats are often constructed into tent-like structures which provide a cooler alternative to their mud brick houses. Throughout the South Pacific, traditional bures made from bush timber frames have been designed with thatched grass, palm or reed roofs and walls, while on the Indian Subcontinent, vetiver grass construction has long been woven into mats that are hung in doorways to help cool the passing air, while at the same time emitting a natural perfume aroma.
With such a strong history to draw on, many architects of the biological building school are looking to reintroduce grass as a building material. While some methods have been used for centuries and are experiencing a revival, others are new innovations that are addressing modern building concerns.
Grass roofs were first used by the Vikings in Scotland and Ireland to help naturally insulate their homes. They helped to keep the cold out during the bitter northern winter months and maintained a cool temperature during the summer. But there are other benefits to grass roofs which make them a green solution to modern building needs, including the absorption of rainwater, the creation of a natural habitat for wildlife and the lowering of urban air temperatures. They are also aesthetically quite pleasing for those living around you and less intrusive on the overall landscape. They have proven to be a good sound insulator in densely packed urban environments (as seen in the implementation of a green roof at the Chicago City Hall), as well as mitigating and filtering the artificial pollutants that are increasingly being released into our surrounds.
There are two types of green roofs: intensive roofs which are thicker, heavier and can support a wider variety of plants, and extensive roofs which are shallower and require less maintenance. While they can be expensive to install and maintain, grass roofs tend to increase the overall lifespan of roofs by protecting them against the elements and tax reductions in some countries make them a sensible investment. With the increasing effects of climate change and a movement towards green design, grass roofs have gone from being a Viking tradition in northern Europe to a modern trend across the world.
Grasscrete Grass Construction
While grass roofs have been around for centuries, grass flooring constructions are a more modern innovation, combining a strong and durable load-bearing paving with an environmentally friendly and aesthetically pleasing natural material. Grasscrete is a method of laying concrete walkways, pavements and driveways in open patterns where grass or other plants can grow in between. It reduces the amount of concrete that needs to be used overall (and in turn diminishes the carbon emissions which result), while at the same time providing a load bearing up to 40 tonnes gross vehicle weight.
Grasscrete is cast on-site to create a cellular reinforced system using styrene void formers. Compared to precast concrete solutions, it provides a far improved drainage system for managing storm water, together with a reduction in greenhouse gas emissions. Grasscrete is a green landscaping option that doesn’t compromise on strength and durability, making it ideal for parking cars, walkways and roadside verges, as well as storm/drainage channels and reservoirs. The water which percolates to the base of Grasscrete surfaces can also be diverted and collected into a rainwater tank, providing a secondary water source for households in areas where rainfall is limited.
Hempcrete Grass Construction
While hemp (a variety of the Cannabis sativa plant) has long been used for industrial purposes and was one of the first plants to be spun into usable fiber 10,000 years ago (https://en.wikipedia.org/wiki/Hemp ), it may be in building that this natural material really shines. Hempcrete is made from the inner woody part of hemp plants, mixed with lime and water, and has great potential as a mold and pest-resistant insulator. Its flexible to work with and nearly fireproof, while only having a fraction of the psychoactive component tetrahydrocannabinol (THC) of medicinal and recreational cannabis products. Hempcrete blocks are not strong enough to stand alone as structural elements and require a supporting frame of brick, wood or steel, but they are durable and breathable, which makes them an ideal insulator.
But the aspect of Hempcrete that really makes it shine is that the material is both fast growing and carbon neutral. Growing hemp sequesters carbon dioxide from the atmosphere, while harvesting it reduces the amount that would otherwise be released during decay.
Hemp as an insulating material was first developed in France during the 1980s and later used by British designers in two test dwellings (https://en.wikipedia.org/wiki/Hemp#Building_material ). But the prohibition of growing hemp in the US since the 1930s has limited its use, meaning that those wanting to use Hempcrete need to import the raw material. Another downside of using hemp is that it requires thicker insulation than other building materials, but that’s a small price to pay for the environmental advantages it offers.
The potential of hemp as a building product is currently being assessed by a European Union-funded research project at the University of Bath with the hope that data for certification and marketing will see its use escalate in the future. Hemp-lime panels are being tested for their quality, hygrothermal performance, rapid assemblage and resource efficiency, while markets are being developed across Europe. At the same time, Tim Callahan who was responsible for building the first Hempcrete home in the US in 2010 is hoping to start building modular tiny homes from the material and eventually ship them across the country.