It is important to continually review materials and methods of construction to ensure the best possible results are being achieved. It is therefore possible to question the current structural frame that hemp-lime has to be applied within. Could the hemp stalk itself be used structurally and would it be a more environmentally friendly option compared to timber? Theoretically a hemp frame could provide a romantic concept of growing your own zero carbon home that adheres to modern standards of shelter.
There is an incentive to move away from oil based materials in order to reduce fossil fuel consumption. Fossil fuels are non-renewable, running out and damaging to the environment when burned. It is therefore important to develop alternative construction materials which are more sustainable in their production and application within the built environment. Lime-hemp offers a low embodied energy and negative carbon footprint, although the timber frame that supports it can be less environmentally friendly.
Globally there is also growing pressure to protect our tree stock for ecology as well as its importance in regulating the climate. Although timber in the UK is from managed forests, it still undergoes a relatively high amount of processing. If hemp were to be substituted for timber ‘as a tree-free fibre source, it could reduce harvesting of primary forests and the threat to associated biodiversities’(18). Hemp ‘yields four times more fibre per acre than trees do’(19) and as Woolley states, only 1% of the agricultural land in the UK would be needed to produce enough hemp for all the new dwellings built each year. It could ‘provide a source of material that can be replaced each year and grown as part of a well managed agricultural system.’(20)
Removing the timber structural frame of current hemp-lime construction by using structural hemp stalk instead, would reduce both the building’s embodied energy and the strain on our tree stock. It could also prove a more economical method of construction as such an agricultural crop would be far cheaper than timber.
As the world starts to turn towards a more sustainable approach to living it is important for architecture to facilitate such change. The first response has been to ‘bolt on’ or integrate active systems into the current standards of design. This strategy often includes the micro-generation of a house’s electricity demands via solar panels and wind turbines, the more efficient use of water and a reduction of waste. However, many of these technologies require a large initial input of energy for their manufacture, some even needing constant power during their use which then leads to long environmental pay-back times. There are similar issues with the construction of a buildings external envelope. The modern building envelope is made up of many layers, each performing a single function and each requiring a relatively large amount of processing in its manufacture. The wall therefore has a high embodied energy which negates the environmental benefits of the design. However, recently ‘greater awareness has developed in which the nature of materials and methods of building construction are seen as equally important.’(21)
Some new thinking attempts to achieve the same levels of insulation, ventilation and comfort by using passive design. This approach relies on the architectural design rather than active systems to achieve low energy buildings, therefore requiring little input for the running of the building. This is heavily rooted in the physical and microscopic understanding of the materials used and the physics of dynamical building design. The method often adopts fewer layers of materials with each material performing multiple functions, therefore producing a more monolithic building envelope with fewer connections between layers much like hemp-lime construction.
There is an emerging romanticism of self-builders who choose to build from the products of the land in the immediate vicinity. This Idea has its roots based in traditional methods of construction, utilizing surplus crop, managed woodland, coppicing or the local rock and soil types. Vernacular architecture largely had to make do with the local materials as transportation from afar was difficult. In the modern world this is not true, materials are shipped worldwide and an architect or builder can specify any material from any corner of the globe. The inherent cost of this is mainly transportation, which can also dramatically increase the embodied energy of a material. Therefore in the new age of environmental sensitivity we are starting to address these issues and once again re-evaluate the use of local materials.
With hemp it could become feasible to buy a plot of land, cultivate and harvest a crop and then build on that land with the materials produced. ‘One hectare of land can produce up to 10 tonnes of hemp’(22) which is enough to build one house. Using the material in its most basic state would remove a large part of the cost and embodied energy that is involved in processing. If situated in an area with limestone or near a lime mine, this could lead to a building which is fully rooted in its locality.
Currently, there is a high cost associated with the harvesting and processing of hemp due to a relatively robust crop that is hard to cut. With only one main processing plant in the UK the transport costs can also be high. A move to smaller localized processing facilities would drive down this economic and environmental cost.
The modern shelter is generally quality assessed and has to adhere to stringent regulations. ‘In many cases, appropriate lowtech natural building alternatives are rejected in new housing programs because they do not seem to fit with contemporary Western ideals and standards’.(23) This makes it increasingly difficult to use traditional methods of construction and materials as they do not appear to perform to the high standards required. The vernacular self build project is now often unattainable by the unskilled. However, some modern sustainable materials like straw bale and hemp-lime have been developed to meet the high standards of construction needed while still being possible to build by an unskilled workforce.
Another standard of the modern shelter is its design and form. Both traditional methods of construction and straw bale are limited in their form and design capabilities. A straw bale house is limited to the module of a bale, its depth and an inherent roughness to its surface. As with many of these methods it is difficult to construct a precise form, relying more on soft lines and moulding by hand. However, with the aid of formwork, it is possible to sculpt lime-hemp into any form desired; achieving smooth surfaces much like you can with concrete. This allows the architect or builder to specify exact geometries and crisp lines, making a more contemporary aesthetic attainable.
However, hemp-lime is currently limited by the structure that frames it, usually running in orthogonal lines between timber posts, caped at the top by a timber beam. Occasionally it has been curved in plan but this involves an exercise in smoothing out a faceted framework. It is difficult to achieve such a curve in one dimension let alone two. By re-evaluating the material and exploring the potential of the hemp stalk it may be possible to achieve such feats. This could liberate hemp-lime from the grid and allow a much more organic form to be produced, more akin to the material itself. A new found flexibility would allow the material to be used in any form desired, potentially increasing its use within the construction sector.