Hemp-lime – contemporary usage of traditional materials

Abstract

Hemp-lime is a comparatively unknown building material in Estonia. Scientific interest in this material is increasing remarkably quickly around the world, yet practical competence regarding its usage is lacking in Estonia, as far as construction is concerned.´

Hemp occupies an important place amongst crops that have traditionally been cultivated in Estonia, but its use has not been typically associated with the construction industry. Owing to its strong fibre, hemp has primarily been seen as raw material for the production of textile products, particularly rope, and the inner core of the plant, or ‘hemp hurd’, has been cast aside as a by-product. Since the porosity of hemp hurds results in relatively low thermal conductivity, hemp lime, the composite material made by mixing hemp with lime, is suitable for insulating pre-existing building envelopes as well as for installing insulation for new buildings during construction. Lime creates an alkaline environment around hemp hurds, making it difficult for fungi and pest insects to thrive. Compared to other natural insulation materials, hemp-lime therefore has a rather good balance between durability and cost-effectiveness.

The essential feature of hemp-lime relevant to construction engineering is that the material is monolithic – any occurrences of sparsity and the resultant risk of thermal bridging in building envelopes is kept to a minimum, since the hemp-lime filling that surrounds the load-bearing structure forms a solid external surface when properly installed. Owing to its high level of air-tightness, external structures made from hemp-lime can reduce the risk both of excessive cooling and of overheating. In addition to creating a comfortable indoor climate for residents, mitigating any sharp fluctuations protects the wooden construction elements surrounded by the hemp-lime, which also reduces the risk of moisture accumulation and frost damage.

Reducing the annual energy consumption of buildings and ensuring healthy indoor air quality pose significant challenges to the construction industry, since according to the current building code, the energy performance indicator of buildings constructed from 1st January 2021 should not exceed the limit established for nearly zero-energy buildings. In short, this calls for more efficient use of resources, including the production, transport, installation, and recycling of materials. Compared to the majority of contemporary building materials, hemp-lime is relatively eco-friendly, and its energy content is low.

Keywords: industrial hemp, lime, clay, hemp-lime, sustainable building materials