Hemp Lime Research Articles

Thermal and Moisture Content Monitoring of a Full-Scale Load Bearing Hemp Lime Arch Prototype

Today, bio-sourced materials represent an important technological field of study, as they could sink atmospheric carbon dioxide into buildings. Little-processed construction materials would also reduce the environmental impact of the construction sector, which emitted more than 2.9 Mt of CO2 in 2020. Hemp-lime is a material that meets both these requirements. It is an insulating mix that can take different forms and be used in various parts of a building. The challenge is providing it with enough mechanical strength to make it loadbearing, at least to some extent. This research focuses on the construction and monitoring of a pointed arch, based on a previous experimental hemp-lime construction at Cardiff University in 2009, under the direction of architect David Lea. Since 2022, such an experiment on a possible loadbearing hemp-lime mix is being repeated at the Politecnico di Torino as part of a wider project called “experimental pavilions of vegetarian architecture”. The design and numerical analysis of the Cardiff prototype led to the modification of both the geometry and the composition of the mix using only pozzolanic air lime as the binder. The construction of the arch ended in December 2023. Observing the thermo-hygrometric conditions of this hemp-lime mix once in place is the main purpose of this article. A strong correlation is revealed between outdoor conditions with temperature and moisture content in the core of the arch. Building a full-size outdoor prototype allows for the avoidance of mathematical correction to the results obtained and allows the assessment the mix’s resistance in relation with environmental conditions. Due to some similarities of nature and function between lime and cement, many studies of lime mixes do not exceed a duration of 28 days, which cannot be considered the appropriate observation time for its curing. Therefore, we analysed this lime-based material for around 6 months, according to its own temporality and chemical kinetics. Through continuous monitoring at 10-min intervals, it was possible to highlight several significant aspects of rammed hemp-lime. The results show that the temperature within the mix is influenced by the outside temperature, but the sun exposure of certain areas drives up the corresponding temperature values more rapidly. Furthermore, while the absorption of water in the form of vapour is very rapid, desorption takes longer, as does re-establish a balance between the material and its context. Finally, solar exposure affects particularly 30-cm-thick elements, while elements that are 60 cm thick are not affected in the short term but only in long-term exposure conditions like season changes.

Lime Hempcrete Composites Based on Unfired Binders. A Review

AbstractHempcrete has emerged as a viable and environmentally sound building material based on hemp lime mixture, whose properties render it a low Embodied Energy and Carbon (EE and EC) building material. Additionally, it allows a hempcrete building to achieve low Operational Energy and Carbon (OE and OC) by moderating indoor temperature and relative humidity fluctuations through the year with minimal auxiliary heating or cooling. Hemp shives used in hempcrete are a waste product, yet lime is an energy intensive material. This paper summarizes a research project the purpose of which was to investigate the possibility of substituting the lime in hempcrete with unfired binders, in part of whole, thus lowering the EE and EC of the mixture even further. Results of this research have shown that this is possible without compromising any of the traditional hempcrete properties, e.g., compressive strength and insulating value. A comprehensive Life Cycle Energy Analysis (LCEA) and Life Cycle Carbon Analysis (LCCA) has shown total energy requirements for a prototypical building’s lifespan (50 years) to be between ~ 50–10% of an identical building with conventional materials, and total carbon emissions to be respectively ~ 50–10%.

Life cycle assessment of hemp-lime concrete wall constructions: The impact of wall finish type and renewal regimes

Using sustainable building materials is one of the key methods for minimising the negative environmental impacts of the global construction industry. Bio-based buildings building materials, such as hemp-lime concrete, are considered more sustainable, as they make use of a renewable raw material and can sequester CO2 from the atmosphere. Studies have shown that hemp-lime concrete can have a favourable global warming potential, though the life cycle of building materials affects a wide variety of negative environmental phenomena that should also be considered. Studies examining the life cycle of hemp-lime concrete have so far primarily focused on the material itself. Though the exterior surface of a hemp-lime concrete wall needs to be protected and have a finish applied to it, few studies have considered the environmental impacts of coated hemp-lime concrete wall constructions. Using life cycle assessment methodology, through a wide range of environmental impact categories, the study analysed the environmental impacts of applying lime putty and sand coatings to a hemp-lime concrete wall in pessimistic, average and optimistic scenarios, It also compared the environmental impacts of four types of appropriate wall finishes and the impacts of applying varying finish renewal regimes in the use phase. It was found that applying lime putty and sand finishes to the exterior and interior surface of a hemp lime concrete wall increased the total global warming potential by 19.054–30.793 kgCO2eq and had a noticeable effect on all other impact categories. It was found that while no one finish type could be considered globally superior to the others, in a majority of circumstances applying lime-based coatings resulted in lower embodied environmental impacts, than applying a ventilated façade with timber cladding.

Experimental Analysis of Moisture-Dependent Thermal Conductivity, and Hygric Properties of Novel Hemp-shive Insulations with Numerical Assessment of Their In-Built Hygrothermal and Energy Performance.

The use of lime as a binder in hemp-lime considerably increases the drying time of hemp-lime after casting. Furthermore, lime is a non-renewable mineral resource. As such, this paper explores the effectiveness of using an alternative non-mineral binder instead of lime to formulate a novel hemp-shive insulation. The moisture-dependent thermal conductivity, adsorption isotherm, vapour diffusion resistance factor, and in-built hygrothermal performance of four variants of a novel bio-based insulation were investigated. The hygrothermal performance of the novel hemp-shive insulation was compared with that of a previously developed novel hemp-lime insulation. No significant variation in thermal conductivity of hemp-shive insulations between the equilibrium moisture contents (EMC) at 0% and 50% relative humidity (RH) was observed, but there was a substantial increase in thermal conductivity hemp-shive insulations when the material reached the EMC at 98% RH. The average dry thermal conductivity values of hemp-shive and hemp-lime insulations were also similar. The adsorption isotherms of hemp-shive insulations were determined at 0%, 20%, 50%, 70%, 90%, and 98% relative humidity steps. At 98% RH, the moisture adsorption capacity of hemp-shive insulations was 4-to-5-times higher than that of hemp-lime insulation. Hemp-shive insulations' vapour diffusion resistance factor (µ value) was about double the µ value of hemp-lime insulation. Hemp-shive insulations exhibited 4-to-5-times higher water absorption resistance than that of hemp-lime insulation. Numerically determined porosity values of hemp-shive agree with the values of wood-based insulation materials of similar density. Finally, using all experimentally acquired data as inputs, dynamic whole-building hygrothermal simulations were carried out and the results show that novel hemp-shive insulation materials perform at a similar level to the hemp-lime insulation in terms of heating and cooling energy demand but require 45% less energy for humidification. However, the relative humidity inside the hemp-shive wall remains higher than 70%, which can potentially induce mould growth.

Thermal Transmittance in Roof–Wall Structural Junction Areas Insulated with a Hemp–Lime Mixture

The junction between the roof and the external wall is a sensitive area within the building envelope; here, increased heat flow often takes place. In the case of partitions insulated with materials based on plant ingredients, thermal bridges are particularly dangerous due to the possibility of condensation and, consequently, mold. The present article analyzed the connection of the roof with the knee wall made of a hemp–lime composite and the ridge in terms of the occurrence of thermal bridges. The following factors that may affect heat transfer in the junction were taken into account: the location of the load-bearing wooden frame, the roof slope, and the presence of internal plaster in the junction. Two-dimensional heat transfer analysis was performed based on the finite element method using THERM 7.4 software. All of the studied thermal bridges had ψ values below 0.10 W/(m·K). Calculations of heat losses through a roof with different slopes were also presented, taking into account the considered thermal bridges. As the roof slope decreases, the heat flow through the roof decreases, despite the increasing value of the linear thermal transmittance. The share of the considered thermal bridges in the total heat loss from the roof reached up to 15%. To verify the obtained results, in further analysis, it would be necessary to calculate the impact of the roof–knee wall bridge variants on heat losses throughout the entire building.

Hygrothermal performance of hemp lime concrete embedded with phase change materials for buildings

The use of biobased materials in building construction allows the reduction of fossil resource use and energy consumption. Among biobased materials, hemp lime concrete has been investigated in many studies highlighting its capacity to regulate interior relative humidity and its high insulation capacity. In order to design high-performance biobased concretes, a new hemp lime concrete combining the hygric regulation capacity of hemp lime concrete with the thermal regulation performance of phase change material was developed. This article focuses on the thermal and hygric performance of the new hemp lime concretes incorporating micro-capsulated phase change material (PCM) (named HL-PCM). Three hemp lime concretes that differ from formulation were developed and investigated. The thermal properties, moisture buffer values and its impact on interior relative humidity variation have been presented. Thanks to experimental works and numerical simulations, the results obtained showed that the thermal conductivity remain low, the heat capacity and thermal inertia increase considerably for hemp concrete with PCM, while the moisture buffering capacity remains excellent. Finally, numerical results showed that the used of hemp lime concrete (with and without PCM) reduce indoor relative humidity variation and improve indoor hygrothermal comfort.

Experimental investigation on the hygrothermal behavior of a new multilayer building envelope integrating PCM with bio-based material

Bio-based materials have strong hygrothermal behavior and phase change materials (PCMs) have high thermal inertia, but they have usually been studied separately in most research. In this paper, the hygrothermal behavior of a multilayer building envelope integrating hemp lime concrete (HLC) and PCM was investigated at experimental level. The envelope was flanked by a climate chamber and the laboratory ambient to imitate the outdoor and indoor environments, respectively. Four envelope configurations comprising a reference (without PCM) and three configurations with PCM (PCM placed on the outdoor and indoor side, in the middle of the envelope) were considered in order to study the effect of PCM and its position on the hygrothermal behavior of the envelope. The results showed that the PCM had a significant effect on the hygrothermal behavior of HLC, based on the high coupling between temperature and relative humidity. The characteristic time was considered to quantitatively evaluate temperature and relative humidity trends, and their value was increased with the participation of PCM. Moreover, PCM increased the heat store/release capacity linearly with its position. The closer the PCM was to the outdoor, the higher the heat store/release capacity and the lower the heating/cooling load from the envelope to the indoor environment. These phenomena were closely related to the PCM's temperature distribution and its corresponding specific heat capacity. Therefore, due to the envelope's thermal and hygric inertia on the indoor environment and the building's energy saving potential, it was recommended that the PCM be placed close to the outdoor side.

Influence of Hemp Shives Size on Hygro-Thermal and Mechanical Properties of a Hemp-Lime Composite.

Different fractions of hemp shives are used in the mixtures of the hemp–lime composite. The market offers shives of different granulation. It depends on the type of industrial hemp and on the capabilities of decortication machines. The aim of the research presented in the article is to check differences in the mechanical and hygro-thermal properties of composites with different shives fractions. The research part of the paper presents the preparation method and investigation on hemp–lime composites. Apparent density, total porosity, thermal conductivity, capillary uptake, vapor permeability, specific heat, mass absorptivity, flexural and compressive strength were examined. The results confirm that the shives fraction influences the individual properties of the composites. Hemp–lime composites with fine shives are characterized by higher water absorption, thermal conductivity, mechanical strength, vapor permeability as well as lower capillary-lifting capacity and specific heat than composites with thick shives.

The Heat Conductivity Properties of Hemp-Lime Composite Material Used in Single-Family Buildings.

The main goal of the paper is to calculate the heat conductivity for three experimental hemp–lime composites used for structural construction purposes with the use of the experimental stand inside two compartments. Due to current construction trends, we are constantly searching for eco-friendly materials that have a low carbon footprint. This is the case of the analyzed material, and additional thermographic heat distribution inside the material during a fire resistance test proves that it is also a perfect insulation material, which could be applied in addition of popular isolating materials. This paper presents the results of certain hemp–lime composite studies and the potential for using hemp–lime composite for the structural construction industry. Hemp–lime composite heat transfer coefficient, fire resistance, and bulk density properties are compared to those of other commonly used construction materials. The obtained results show that the material together with supporting beams made of other biodegradable materials can be the perfect alternative for other commonly used construction materials.

Hemp-lime – contemporary usage of traditional materials

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

A nearly Zero Energy Building in Mediterranean climate: a case study in Mesagne (Apulia)

This paper presents the case study of an nZEB building located in the municipality of Mesagne (Apulia, BR). It is a building of 309 m2 of usable floor space with two floors above ground. The building is a proof that a correct integrated design of the HVAC system and the building envelope can easily lead to an nZEB building with high performance in terms of energy consumption and comfort. The external envelope of the building is a structure in tufa blocks plus a mixture of hemp and hydraulic lime plus blocks of hemp and lime. Hemp lime is a mix of renewably sourced hemp shiv, a specially formulated lime binder and water. The air conditioning system is based on a controlled mechanical ventilation with air pre-treatment through an underground tube exchanger. A numerical simulation of the overall building-plant system performance was made with DesignBuilder in order to evaluate the energy consumption for air conditioning and the thermohygrometric comfort in the building. Several simulations were carried out to compare the incidence of different building-plant system on total energy consumptions: one without earth-to-air heat exchanger, one without heat-recovery and recirculation, one without solar shading.

Analysis of the Occurrence of Thermal Bridges in Several Variants of Connections of the Wall and the Ground Floor in Construction Technology with the Use of a Hemp-lime Composite.

This article analyses the connection of the two types of floors on the ground (floors on joists and self-supporting floors), with the external wall made of a hemp–lime composite for the occurrence of thermal bridges. Several factors that may affect the heat transfer in the junction were taken into account: the level of the floor on the ground, the wall thickness, the thermal conductivity of the composite, and the location of the timber frame construction. The technology of using hemp and lime is relatively new, and there is a lack of such analyses in the literature. The two-dimensional (2D) heat-transfer in the described construction joints was analyzed based on the finite-element method with the use of the THERM 7.4 software. The results were presented as averaged and linear thermal transmittance coefficients dependent on the above mentioned factors. The possibility of surface condensation was also checked. The differences in the values of the thermal transmittance of the junction between the two variants of ground floors reached around 0.13%–1.67% and the values of linear thermal transmittance factor reached approximately 2.43%–10.13%. The junctions with the highest floor level showed a decrease in the thermal transmittance value by about 3.00%–5.77% and in the linear thermal transmittance, by about 21.98%–53.83%, compared to the junctions with the lowest floor level. Calculations showed that almost all analyzed junctions are free from surface condensation causing mould growth, because the minimum temperature factors f0.25 were higher than 0.78 (except for junctions with the lowered floor levels). The junction with a floor on the timber joists showed better thermal parameters than the junction with a self-supporting floor in each of the analyzed variants. By increasing the level of floor insulation, it is possible to limit the thermal bridges and improve the thermal properties of the junction.

Environmental sustainability of the retrofitting of a vernacular dwelling in the Liguria seaside

In the Genova hinterland, a traditional rural dwelling has been completely restored with the addition of new buildings respecting the landscape and the relationship with the existing vernacular construction. The project, in compliance with all the bio-architecture criteria of intervention associates traditional natural materials such as stone and lime with cutting-edge materials and techniques such as raw earth and hempcrete.Both the recovery and the new buildings have been the subject of meticulous bio-design in terms of material choices and diversification of construction techniques according to the area of intervention and of the local material culture. The original stone walls have been preserved and consolidated with fibre-reinforced lime mortar applied directly on the stone wall after removing the old mortar. Timber beams and wooden floors have been almost completely renovated, but preserving and consolidating wherever possible the original structures. External walls have been re-plastered with thermo-plaster based on lime and diatomite. On the interior, a hemp lime mortar has been used.Environmental sustainability of the whole retrofitting has been assessed by using the Life Cycle Assessment (LCA) methodology in compliance with the international ISO standards 14040 and 14044. The scenario is from cradle to construction, i.e. A1-A5 in terms of European directive EN 15804. The study is fully compliant with this directive in terms of impact indicators and additional benefits.

Monitoring of a Hemp Lime External Building Insulation

In a context of promoting energy efficiency, building sector has undergone a notable evolution towards innovative construction insulation materials such as hemp concrete, in order to reduce buildings energy bills and environmental impact. Hemp-Concrete finds application as internal or external thermal insulator in wooden frame walls. In that context, a French building in Grand-Est region, employing Hemp-Concrete as an external insulator is selected and studied. An apartment is monitored for several months. Indoor temperatures, and relative humidities as well as external weather conditions are measured using sensors installed inside the apartment and a weather station placed at the building roof. Indoor comfort analysis shows satisfactory results according to ASHREA standards. Experimental approach is then coupled with a numerical validation at room scale using SPARK simulation tool. Investigations are conducted on indoor office air temperature and relative humidity. Results show a good agreement between numerical values and experimental measurements.

Experimental and numerical investigations of thermal performance of a Hemp Lime external building insulation

Hemp-concrete is a green material which has become nowadays highly recommended in the construction field. It finds applications as internal or external thermal insulator in wooden frame walls. At wall scale, studies proved that using Hemp-concrete in building envelope can improve indoor hygrothermal comfort. However, at building scale, hemp-concrete is scarcely studied. In that context, a French building in Grand-Est region, Champagne-Ardennes, employing hemp-concrete as external insulator is selected and studied. An apartment is monitored for several months. Indoor temperatures, relative humidities, thermal heat flux as well as external weather conditions are measured using sensors installed inside the apartment and a weather station at the building roof. Measurements underline the hemp-concrete ability to dampen external weather conditions by showing good results for both indoor temperature and relative humidity. Experimental approach is then coupled with a numerical validation at the wall and room scales using SPARK simulation tool. Investigations are conducted on thermal heat flux through the wall, indoor office air temperature, and relative humidity. Results show a good agreement between numerical values and experimental measurements.

Physical Properties of Building Blocks from Hemp Shives Aggregate and Cementitious Binder, Manufactured in the Expanded Clay (Vibro Pressing) Production Line

Scientific literature mostly aims at investigation of composites with fibre hemp shives (FHS) aggregate and lime binder, although, such materials are characterised by pretty low mechanical properties. In order to obtain higher mechanical properties of a composite, it is appropriate to use cementitious binder. This work investigates physical properties of blocks from hemp shives aggregate and cementitious binder, manufactured in the expanded clay production line using vibro pressing technology. Following properties of the blocks are determined: freeze-thaw resistance, compressive strength, thermal conductivity and density. Thermal resistance according to EN ISO 6946 for the block with cavities is calculated as well. It is found that compressive strength of FHS-cement blocks may be up to 3.18 MPa when the density is of ~850 kg/m3 and thermal conductivity up to 0.135 W/(m∙K). It is found as well that the decrease of compressive strength is 8.7% after 25 freeze-thaw cycles.

Development and hygric and thermal characterization of hemp-clay composite

This study investigates the use of clay as binder in hemp composite and compares hemp–clay composite to hemp–lime concrete. The clay is produced from washing mud from gravels production site. Two clay drying temperature are used. The thermal properties are measured with a hot wire method and the hygric characterization is based on the measurement of Moisture Buffer Value. Performances obtained on clay blocks, hemp–clay composite and hemp–lime composite are compared. The results show that the two clay drying temperatures do not impact on the thermal conductivity nor on the moisture buffer value of clay blocks. Hygric and thermal performances of hemp–clay and hemp–lime composites with the same density are close. These materials act as excellent hygric regulators. Performances measured separately on hemp and clay underline an interesting synergetic effect in the case of hemp–clay composite leading to a higher ability to the moisture buffering. Such material can be advantageously used in buildings to moderate indoor humidity variations.

Thermal properties of cob retrofitted with external hemp–lime

Insulating earth walls with an external layer of hemp–lime improves thermal performance in a sustainable way and could promote the wider use of earth in construction. Monolithic earth walls, known in Devon as cob, are widely used in many countries with temperate climates. Earth walls are a form of sustainable construction, but their thermal performance is poor when measured against current UK Building Regulations. Non-permeable, high-performance insulation materials may cause moisture-related problems in earth walling. Therefore, this paper describes the transient thermal properties of monolithic cob walls retrofitted with external hemp–lime insulation, which offers a permeable solution. The transient thermal properties of the walls are calculated using bespoke software developed for an earlier study of brick walls and the air-to-air thermal transmittance is determined for various thicknesses of hemp–lime insulation. Typical cob walls found in Devon have U-values >1 W/m2 K, or about three times the 0·3 W/m2 K UK Building Regulations target. For a 600 mm thick cob wall with 250 mm of external hemp–lime, a U-value of 0·3 W/m2 K is achieved. Five areas of concern are discussed briefly: caution, sustainability, acceptability, uncertainty in data and the possible energy and carbon dioxide savings.

Characterization and comparison of hygric properties of rape straw concrete and hemp concrete

The use of plant particles as aggregates in construction materials provide a very good hygric performance, and offers a real contribution to sustainable buildings. This paper focuses on the hygric properties of a new bio-based material called “rape straw lime concrete” in comparison with a “hemp lime concrete” which is used to validate the experimental protocol of this work. The tests are conducted on the sorption isotherm, the water vapor permeability, the capillary water absorption and the moisture buffer capacity which is estimated from the moisture buffer value determined under equilibrium condition. The results showed that the materials have very interesting hygric properties and exhibit an excellent moisture buffer capacity.

Predicting the long-term durability of hemp–lime renders in inland and coastal areas using Mediterranean, Tropical and Semi-arid climatic simulations

Hemp-based composites are eco-friendly building materials as they improve energy efficiency in buildings and entail low waste production and pollutant emissions during their manufacturing process. Nevertheless, the organic nature of hemp enhances the bio-receptivity of the material, with likely negative consequences for its long-term performance in the building. The main purpose of this study was to study the response at macro- and micro-scale of hemp–lime renders subjected to weathering simulations in an environmental cabinet (one year was condensed in twelve days), so as to predict their long-term durability in coastal and inland areas with Mediterranean, Tropical and Semi-arid climates, also in relation with the lime type used. The simulated climatic conditions caused almost unnoticeable mass, volume and colour changes in hemp–lime renders. No efflorescence or physical breakdown was detected in samples subjected to NaCl, because the salt mainly precipitates on the surface of samples and is washed away by the rain. Although there was no visible microbial colonisation, alkaliphilic fungi (mainly Penicillium and Aspergillus) and bacteria (mainly Bacillus and Micrococcus) were isolated in all samples. Microbial growth and diversification were higher under Tropical climate, due to heavier rainfall. The influence of the bacterial activity on the hardening of samples has also been discussed here and related with the formation and stabilisation of vaterite in hemp–lime mixes. This study has demonstrated that hemp–lime renders show good durability towards a wide range of environmental conditions and factors. However, it might be useful to take some specific preventive and maintenance measures to reduce the bio-receptivity of this material, thus ensuring a longer durability on site.