Concrete-like blocks made with hemp and lime have been used as an insulating material for construction. Such blocks are not strong enough to be used for structural elements; they must be supported by a brick, wood, or steel frame.^[1] However, hemp fibres, called hemp hurd, have been shown to be a replacement for concrete for many jobs, including creating durable and breathable homes.^[2] The most common use of hemp lime in building is by casting the hemp hurd and lime mix while wet around a timber frame with temporary shuttering, and tamping the mix to form a firm mass. After the removal of the temporary shuttering, the solidified hemp mix is then ready to be plastered with a lime plaster.^[3]

The first example of the use of hempcrete was in 1986 in France with the renovation of the Maison de la Turquie in Nogent-sur-Seine by the innovator Charles Rasetti.^[4] In the UK hemp lime was first used in 2000 for the construction of two test dwellings in Haverhill.^[5] Designed by Modece Architects,^[6] who pioneered hemp's use in UK construction, the hemp houses were monitored in comparison with other standard dwellings by BRE. Completed in 2009, the Renewable House is one of the most technologically advanced made from hemp-based materials.^[7] The first US home made of hemp-based materials was completed in August 2010 in Asheville, North Carolina.^[8]

A panellized system of hemp-lime panels for use in building construction is currently under test in a European Union-funded research collaboration led by the University of Bath. The panels are being designed to assure high-quality construction, rapid on-site erection, optimal hygrothermal performance from day one, and energy- and resource-efficient buildings. The 36-month work program aims to refine product and manufacturing protocols and produce data for certification and marketing, warranty, insurance cover, and availability of finance. It also includes the development of markets in Britain, France, and Spain.^[9]

Hemp is used as an internal plaster and is a mixture of hemp hurd (shive) mixed with larger proportions of a lime-based binder. Hemp plaster has insulative qualities.^[10]

Hemp as a building construction material provides solutions to a variety of issues facing current building standards. Its light-weightiness, mold resistance, breathability, etc. makes hemp products versatile in a multitude of uses. ^[11] Following the co-heating tests of NNFCC Renewable House at the Building Research Establishment (BRE), hemp is reported to be a more sustainable material of construction in comparison to most building methods used today.^[12] In addition, its practical use in building construction could result in a reduction of energy consumption costs and the creation of secondary pollutants.^[12]

The hemp market was at its largest during the 17th century. Shortly after, at the end of the 18th century and on, it saw a decline during its rapid illegalization in many countries.^[13] It has recently resurfaced in green building construction, roughly 25 years ago in Europe.^[14] The modern-day disputes regarding the legality of hemp lead to its main disadvantages; importing and regulating costs. Final Report on the Construction of the Hemp Houses at Haverhill, UK conducts that hemp construction exceeds the cost of traditional building materials by £48per square meter.^[15]

The use of hemp-lime panels for building construction is currently under test in a European Union-funded research collaboration led by the University of Bath.^[16] The panels are being designed to assure high-quality construction, rapid on-site erection, optimal hygrothermal (pertaining to both humidity and temperature) performance from day one, and energy- and resource-efficient buildings.^[16] The 36-month work program aims to refine product and manufacturing protocols and produce data for certification and marketing, warranty, insurance cover, and availability of finance. It also includes the development of markets in Britain, France, and Spain. ^[16]

The most common use of hemp-lime in building is by casting the hemp-hurd and lime mix while wet around a timber frame with temporary shuttering and tamping the mix to form a firm mass. After the removal of the temporary shuttering, the solidified hemp mix is then ready to be plastered with lime plaster.^[17]

Hemp is classified under the green category of building design, primarily due to its positive effects on the environment.^[18] A few of its benefits include but are not limited to the suppression of weed growth, anti-erosion, reclamation properties, and the ability to drain soil from poisonous substances and heavy metals.^[18]

The use of hemp is beginning to gain popularity alongside other natural materials. This is because cannabis processing is done mechanically without any harmful effects on the environment. A part of what makes hemp sustainable is its minimal water usage and unreliability on pesticides for proper growth. It is recyclable, non-toxic, and biodegradable, making hemp a popular choice in green building construction.^[18]

Hemp fiber is known to have high strength and durability, and has been known to be a good protector against vermin. It has the capability to reinforce structures by embossing threads and cannabis shavers. Hemp has been involved more recently in the building industry, producing building construction materials including insulation, hempcrete, and varnishes.^{[11][19][20][21][22][23][24]}

Hemp has low embodied energy compared to most building construction materials overflowing the market today. It has the ability to absorb large amounts of CO2, providing air quality, thermal balance, creating a positive environmental impact.^[19]

Hemp’s properties allow it to resist mold, and its porous materiality makes it breathable. In addition it possesses the ability to absorb and release moisture without deteriorating. Hemp can be non-flammable if mixed with lime and builders can apply it on numerous aspects of the building (wall, roofs, etc.) due to its lightweight properties.^[18][19]

Hemp is commonly used as an insulation material. Its flexibility and toughness during compression allow it to be easily implemented within structural framing systems. It could also be easily adjusted to different sizes and shapes by being cut during the installation process. It does not settle and therefore avoids cavity development, lowering its need for maintenance.^[24]

Unlike many other insulants such as fiberglass insulation, hemp insulation is naturally lightweight and non-toxic. It allows for an exposed installation in a variety of spaces, including flooring, walling, and roofing. Compared to mineral insulation, hemp absorbs roughly double the amount of heat and could be compared to wood, in some cases even overpassing some of its types.^[24]

Hemp insulation's porous materiality allows for air and moisture penetration, with a bulk density going up to 20% without losing any thermal properties. In contrast, the commonly used mineral insulation starts to fail after 2%. It evenly distributes vapor and allows for air circulation, constantly carrying out used air and replacing it with fresh ones. Its use on the exterior of the structure, overlaid with breathable water-resistive barriers, eases the withdrawal of moisture from within the wall structure.^[24]

In addition, the insulation doubles as a sound barrier, weakening airborne sound waves passing through it.^[24]

Main article: hempcrete

In addition to the absorbed CO2 during its growth period, it repeats during the creation of the concrete. The mixture hardens when the silica contained in hemp shives mixes with lime, resulting in the mineralization process which extracts the CO2 from the air, purifying it. It continues to do so in the application during its touch with water.^[23]

Hemp is most commonly used as concrete in building construction due to its lightness (roughly seven times lighter than common concrete). It is made of hemp herds (shives), hydraulic lime, and water mixture varying in ratios.^[22] The mix depends on the use of concrete within the structure and could differ in physical properties. Surfaces such as flooring interact with a multitude of loads and would have to be more resistible, while walls and roofs are required to be more lightweight.^[22] The application of this material in construction requires minimal skill.^[22]

The most common variation of this building style is hempcrete; made of concrete-like blocks. Such blocks are not strong enough to be used for structural elements and must be supported by brick, wood, or steel framing.^[12] The first example of the use of hempcrete was in 1986 in France with the renovation of the Maison de la Turquie in Nogent-sur-Seine by the innovator Charles Rasetti.^[21] In the UK hemp-lime was first used in 2000 for the construction of two test dwellings in Haverhill.^[20] Designed by Modece Architects,^[25] who pioneered hemp's use in UK construction, the hemp houses were monitored in comparison with other standard dwellings by BRE.^[26] Completed in 2009, the Renewable House is one of the most technologically advanced made from hemp-based materials.^[26] The first US home made of hemp-based materials was completed in August 2010 in Asheville, North Carolina.^[27]

Hemp Oils and Varnishes:

Cannabis seeds have high-fat content and contain 30-35% of fatty acids. The extracted oil is suited for a variety of construction applications.^[19] The biodegradable hemp oil acts as a wood varnish, protecting it from mold, pests, and wear. Its use prevents the water from penetrating the wood while still allowing air and vapor to pass through.^[11] Its most common use can be seen in wood framing construction, one of the most common construction methods in the world. Because of its low UV-resistant rating, the finish is most often used indoors, on surfaces such as flooring and wood paneling.^[24][11]

Hemp-based insulating plaster is created by combining hemp fibers with calcium lime and sand. This material, when applied on internal walls, ceilings, and flooring, can be layered up to ten centimeters in thickness. Its porous materiality allows it to regulate air humidity and evenly distribute it.^[11] The gradual absorption and release of water prevent it from cracking and breaking apart. ^[28][11] Similar to high-density fiber cement, hemp plaster can naturally vary in color and be manually pigmented.^[29]

Hemp ropes can be woven in various diameters, possessing high amounts of strength making them suitable for a variety of uses for building construction purposes.^[23] Some of these uses include installation of frames in building openings and connection of joints. It is also used in bridge construction, tunnels, traditional homes, etc.^[23] One of the earliest examples of hemp rope and other textile use can be traced back to 1500 BC Egypt.^[14]

Cannabis geotextiles could be put in both wet and dry conditions. Hemp-based bioplastic is a biodegradable alternative to regular plastic and can potentially replace PVC (Polyvinyl chloride), a material used for plumbing pipes.^[23]

Hemp Wood:

Hemp growth lasts roughly 100 days, a much faster time period than an average tree used for construction purposes. While dry, it could be pressed into tight wood alternatives to wood frame construction, wall/ceiling paneling, and flooring. As an addition, it is flexible and versatile allowing it to be used in a greater amount of ways than wood.^[11] Similarly, hemp wood could also be made of recycled hemp-based paper.^[30]