EDUCATION
We believe that sharing knowledge about integrating healthy materials into our built environment is just as important as building healthy homes. We are passionate about empowering individuals, builders, and designers with the practical skills, technical understanding, and confidence needed to create healthier, more sustainable buildings.
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Whether you're looking to explore the benefits of hemp-lime (hempcrete), dive into hands-on learning through our workshops, or expand your knowledge with some free resources and videos, this is the place to get started. Our goal is to make the powerful potential of natural building more accessible, giving you the tools and support to bring your own projects to life.
Why
HEMP-LIME?
Hemp-Lime (aka Hempcrete) is one of the most environmentally building materials available today, actively offering measurable reductions in environmental impact throughout its entire lifecycle. From cultivation to construction and beyond, hemp-lime provides a a Non-toxic, low-waste, carbon-negative, and regenerative alternative to many conventional building materials.
CLIMATE IMPACT
Hemp is a powerhouse for carbon sequestration. As one of the fastest-growing plants on Earth, it can reach heights of 6–10 feet in just 90 days, potentially producing multiple harvests per year and absorbing up to 15 tons of COâ‚‚ per hectare (2.47 acres) annually. This rapid growth cycle makes hemp one of the most efficient natural carbon sinks in the agricultural world.
Hemp cultivation is remarkably low-impact. It requires minimal water and thrives without the need for chemical fertilizers, herbicides, fungicides, or pesticides. These characteristics allow hemp to be integrated into regenerative agricultural systems that improve soil health rather than deplete it.
When Hemp hurd is combined with a lime-based binder to create hemp-lime, the carbon captured during plant growth is locked into the building envelope. . Over time, the lime binder undergoes carbonization, a chemical process in which it reabsorbs atmospheric COâ‚‚ as it cures and hardens. This secondary carbon uptake further improves the material’s overall carbon balance.
Unlike many conventional construction materials that rely on numerous petro-chemicals, synthetic additives, and energy-intensive manufacturing processes, hemp-lime is composed of natural, mineral-based ingredients. It does not emit toxic byproducts during production, installation, or long-term occupancy.
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Because of these combined processes, hemp-lime can continue offsetting carbon emissions after installation, contributing to buildings that reduce environmental harm and, in some cases, actively reverse it.
WASTE
The environmental benefits of hemp-lime extend beyond carbon performance. The hemp hurd used in hemp-lime mixes is an agricultural byproduct derived primarily from hemp grown for food and fiber production. This allows construction to utilize material that would otherwise have limited use.
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Construction waste is minimal. Unused hemp-lime can often be reconstituted and reused during installation. At the end of a building’s lifespan, hemp-lime can be broken down and composted, returning to the soil without introducing persistent pollutants or microplastics. This stands in contrast to many synthetic insulation and wall systems that contribute long-term landfill waste and environmental contamination.
LONGEVITY
The lime binder in hemp-lime plays a critical role in long-term durability. As carbonization progresses, the binder gradually hardens and mineralizes, effectively turning the composite material into a stone-like matrix. This process results in an increased strength of the hempcrete mixture over time.
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When properly detailed and protected from prolonged liquid water exposure, hemp-lime wall systems can last indefinitely with minimal maintenance. This longevity reduces the need for frequent repairs or material replacement and lowers the cumulative environmental cost of the building.
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By eliminating toxic chemicals, reducing construction waste, and providing a durable and high-performance building envelope, hemp-lime addresses many of the most pressing environmental and health challenges present in contemporary construction.
THERMAL INSULATION
Hemp-lime provides effective thermal insulation due to the highly porous structure of the hemp hurd, which traps air within the material matrix. Depending on mix design, density, and installation method, hemp-lime walls can achieve thermal resistance values of approximately R-2.0 to R-2.1 per inch.
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While this R-value is lower than that of some conventional insulation materials, hemp-lime performs differently than lightweight insulations that rely solely on trapped air. Its insulation value works in combination with thermal mass and moisture regulation, resulting in reduced heat loss, improved temperature stability, and enhanced occupant comfort. In many climates, hemp-lime walls are designed with increased thickness to further improve thermal performance and reduce heating and cooling loads.
THERMAL MASS
Hemp-lime exhibits high thermal mass and specific heat capacity, allowing it to absorb, store, and slowly release heat energy. This property helps moderate indoor temperature swings by delaying heat transfer through the building envelope. As a result, interior spaces experience smaller and slower temperature fluctuations throughout the day and night.
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When paired with passive solar design strategies or conductive heating systems such as masonry heaters or radiant tube heating, hemp-lime can significantly improve overall energy efficiency. Stored heat is released gradually, reducing peak heating and cooling demands and supporting more consistent interior comfort over time.
MOISTURE REGULATION
Most conventional wall assemblies rely on vapor barriers and moisture control layers to prevent water intrusion. While effective in some contexts, these systems can trap water vapor within wall cavities when detailing or installation is imperfect. Trapped moisture can remain undetected, creating conditions conducive to mold growth, material degradation, and long-term structural issues.
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Hemp-lime behaves fundamentally differently due to its hygroscopic properties. It can absorb and release moisture vapor without loss of performance or structural integrity. Hemp-lime can temporarily store up to approximately 20% of its weight in moisture, then gradually release that moisture back into the surrounding air as conditions change. This buffering effect helps regulate indoor relative humidity and reduces the risk of condensation within wall assemblies.
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Similar to how thermal mass flattens daily temperature fluctuations, hemp-lime moderates diurnal humidity cycles, contributing to improved indoor comfort and durability. As the lime binder continues to carbonate over time, it becomes increasingly moisture stable, further supporting long-term performance and resilience of the building envelope.
Hemp-lime is a highly adaptable building material that can be used across a wide range of building types, scales, and architectural aesthetics. It is commonly employed in wall, floor, and roof assemblies, and integrates effectively with many structural systems and design approaches. Its flexibility allows it to be used in residential, commercial, institutional, and retrofit applications while maintaining consistent performance characteristics related to durability, moisture regulation, and thermal stability.
CONSTRUCTION METHODS
Hemp-lime walls can be installed using a variety of construction methods, allowing builders and designers to select an approach that aligns with project goals, labor availability, and construction sequencing:
• Cast-in-place: The most widely used method, where hemp-lime is mixed on site and placed between temporary formwork. This approach allows for continuous insulation and custom detailing.
• Spray-on: Hemp-lime is applied pneumatically, typically onto prefabricated panels or existing wall substrates. This method can increase installation speed in certain contexts.
• Blocks & Prefabricated Panels: Factory-produced components that reduce on-site labor and improve consistency. These systems are often used where construction speed or standardization is a priority.
Each method offers different advantages related to construction efficiency, thermal performance, and integration with other building systems.
STRUCTURAL COMPATIBILITY
Hemp-lime is compatible with a wide range of standardized structural systems, making it suitable for both new construction and retrofit applications:
• Concrete & Masonry Structures: Hemp-lime can function as a breathable, insulating enclosure around reinforced concrete or masonry walls. In some systems, hemp-lime blocks are designed to be filled with concrete, similar to conventional concrete masonry units, providing structural capacity while maintaining vapor permeability and thermal performance.
• Wood Framing Systems: Hemp-lime integrates effectively with post-and-beam, timber frame, and light wood framing. In these systems, hemp-lime provides insulation, fire resistance, and long-term durability without relying on synthetic materials.
• Metal Framing Systems: Steel and aluminum frames can be paired with hemp-lime to create non-combustible wall assemblies with improved thermal and acoustic performance.
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With appropriate engineering and detailing, hemp-lime can be used in projects ranging from small residential buildings to larger multi-story structures, as well as in the retrofit of existing and historic buildings where improved indoor air quality and thermal performance are desired.
CUSTOMIZABLE AESTHETIC & FINISHES
Hemp-lime supports a wide range of finish options, allowing designers to achieve varied architectural expressions while preserving vapor permeability and long-term durability. Common finishes include breathable plaster systems such as clay and lime, as well as exterior cladding systems including:
• Masonry veneers such as brick, stone, or tile
• Wood or composite rain screens
•Ventilated facades using cement board, metal panels, or similar materials
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These finish options allow hemp-lime assemblies to meet diverse aesthetic requirements without compromising building physics or material performance.
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SPECIAL CONSIDERATIONS
Hemp-lime requires informed design and detailing to perform as intended. Wall assemblies must remain vapor permeable to support moisture regulation, and structural systems must be designed to accommodate the material’s thickness and weight. Proper engineering is required to address vertical and lateral loads, particularly in seismic or high-wind regions.
When these considerations are addressed through thoughtful design and coordination, hemp-lime provides a durable, resilient, and adaptable building solution suitable for a wide range of climates and building types.
Hemp-lime exhibits excellent fire resistance without the use of chemical fire retardants or additives. Unlike many conventional building materials that can ignite, melt, or release toxic fumes when exposed to high temperatures, hemp-lime maintains its integrity under extreme heat conditions.
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Hemp-lime assemblies have been shown to withstand temperatures of up to approximately 1,700°C (3,092°F), which exceeds the peak temperatures typically reached in residential and wildland fires. Rather than combusting, hemp-lime undergoes a controlled surface charring process that significantly slows flame spread and heat transmission.
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Fire testing conducted under both European and North American standards demonstrates hemp-lime’s strong performance. Under the ASTM E-84 Steiner Tunnel Test, hemp-lime has achieved a Flame Spread Index of 0 and a Smoke Development Index of 0, representing the highest possible fire performance classification within this standard. Under the EN 13501-1 European fire classification system, hemp-lime has received a Class B-s1,d0 rating, indicating no combustibility, no smoke production, and no flaming droplets during the course of this test.
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Unlike synthetic insulation materials that can emit hazardous gases when exposed to fire, hemp-lime is composed of mineral and plant-based constituents that do not release toxic fumes. Independent testing and real-world fire simulations conducted by organizations such as the BRE Group (UK) further confirm hemp-lime’s ability to delay fire spread and maintain structural stability during fire exposure.
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These characteristics make hemp-lime particularly well suited for use in fire-prone regions and in buildings where occupant safety, material resilience, and non-toxic performance are critical considerations.
Hemp-lime exhibits strong natural resistance to pests due to its dense monolithic structure, high alkalinity, and lack of digestible organic nutrients. Unlike many conventional wall systems that rely on framed cavities filled with soft insulation materials, hemp-lime walls form a continuous solid matrix with no large voids or concealed spaces that can serve as nesting areas for rodents or insects.
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MATERIAL CHARACTERISTICS
The lime binder used in hemp-lime creates an alkaline environment with a pH typically above 12 during curing and remaining highly alkaline over time. This chemistry is inhospitable to insects, rodents, fungi, and microbial activity. As the lime carbonates, it mineralizes the hemp hurd and any adjacent materials it contacts, gradually forming a stone-like composite that is neither palatable nor penetrable to pests.
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Unlike cellulose-based insulation, foam products, or batt systems, hemp-lime does not provide food value, nesting material, or protected pathways for infestation. The absence of internal cavities significantly reduces the likelihood of concealed pest activity that often goes undetected in conventional assemblies.
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NON-TOXIC RESISTANCE
Conventional construction frequently relies on chemical treatments such as insecticides, fungicides, and biocides to manage pest risks. These compounds can degrade over time, introduce additional indoor pollutants, and require reapplication. Hemp-lime achieves long-term pest resistance through its inherent physical and chemical properties rather than through applied chemical deterrents.
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As a result, hemp-lime provides durable biological resistance without relying on toxic additives, contributing to a healthier building envelope and reducing long-term maintenance and exposure concerns.
Hemp-lime exhibits strong natural resistance to mold, mildew, bacteria, and fungi due to its high alkalinity and vapor-open structure. Lime-based binders typically maintain a pH of approximately 12.4, creating an environment that is inhospitable to most microorganisms. This high alkalinity inhibits biological growth without the need for added fungicides, antimicrobials, or chemical treatments commonly found in conventional building products.
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In addition to its chemistry, hemp-lime has a high hygroscopic capacity, allowing it to absorb and release moisture without degrading or losing structural integrity. Rather than trapping moisture within sealed wall cavities, hemp-lime moderates fluctuations in indoor humidity, reducing the conditions under which mold and microbial growth typically occur.
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Research conducted by the University of Bath has demonstrated that hemp-lime wall assemblies naturally buffer indoor relative humidity within the range of approximately 50–60%, which is widely recognized as the optimal range for preventing mold growth and maintaining healthy indoor environments. This moisture-buffering behavior reduces condensation, surface wetting, and prolonged damp conditions that can lead to microbial colonization in conventional wall systems.
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By combining vapor permeability, moisture buffering, and alkaline chemistry, hemp-lime provides a passive and durable approach to mold prevention that enhances indoor air quality while avoiding reliance on toxic chemical additives.
Modern construction relies on a vast array of synthetic chemicals. Today, there are over 80,000 chemicals in commercial use, yet only an estimated 1% have been thoroughly evaluated for long-term human health and environmental impacts. Many of these substances are present in standard building materials, where disclosure requirements are often limited and ingredient transparency is not mandatory. As a result, occupants are frequently exposed to chemical compounds without clear knowledge of their composition or cumulative effects.
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CHEMICAL EXPOSURE
Common building materials routinely contain substances known or suspected to be harmful to human health. These include formaldehyde-based adhesives used in engineered wood products, heavy metals present in gypsum wallboard, PFAS compounds used in house wraps and weather barriers, and VOCs such as benzene, ammonia, and formaldehyde found in many paints, sealants, and finishes.
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Insulation products often introduce additional chemical loads through the use of fungicides, insecticides, and synthetic fire retardants. Many of these compounds are designed to remain chemically active over long periods, which increases the likelihood of continuous off-gassing into indoor environments.
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In tightly sealed modern buildings, these emissions can accumulate rather than dissipate, contributing to degraded indoor air quality. Long-term exposure has been linked in scientific literature to respiratory irritation, neurological stress, endocrine disruption, and increased sensitivity in children and immunocompromised individuals.
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NON-TOXIC SOLUTION
Hemp-lime is composed of hemp hurd, lime-based binders, and water, without synthetic resins, petroleum-based foams, added fire retardants, or chemical preservatives. Its mineral-based chemistry remains stable after curing and does not off-gas harmful compounds over time.
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Because hemp-lime does not rely on chemical treatments to achieve fire resistance, pest resistance, or durability, it avoids many of the toxic additives commonly found in conventional wall assemblies. This makes it well suited for applications where long-term indoor air quality and occupant health are primary concerns.
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LONG-TERM STABILITY
Unlike materials that degrade chemically and increase emissions as they age, hemp-lime continues to stabilize through carbonation, gradually converting lime back into limestone while remaining inert and non-toxic. This process does not introduce new chemical byproducts and supports consistent indoor environmental quality over the life of the building.
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By eliminating sources of chemical exposure at the material level, hemp-lime enables a fundamentally different approach to building that prioritizes health, transparency, and long-term environmental responsibility.
Hemp-lime, also known as hempcrete, is a breathable, non-toxic, bio-composite building material made from three primary ingredients: the woody core of the hemp plant known as hurd, a lime-based binder, and water. Despite its name, hemp-lime is not a substitute for concrete and is generally not load-bearing. Instead, it is used as a high-performance infill material for walls, floors, and roof assemblies, where it provides insulation, thermal mass, moisture regulation, and long-term durability.
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A typical hemp-lime wall assembly finished with lime or clay plaster can replace many conventional materials, including exterior paint, siding, house wrap, sheathing, insulation, drywall, and interior paint. Many of these conventional products contain synthetic chemicals that off-gas over time, degrade with age, and contribute to poor indoor air quality. Hemp-lime assemblies eliminate the need for these materials, resulting in a simplified, mineral-based enclosure that supports stable indoor humidity, improved air quality, and consistent thermal performance.
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Beyond health considerations, hemp-lime offers strong environmental and performance benefits. The material is durable, energy efficient, and carbon-negative, as it stores biogenic carbon within the hemp hurd while the lime binder reabsorbs CO2 through carbonization over time. Hemp-lime also exhibits high resistance to fire, pests, and mold, contributing to long service life with minimal maintenance.
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While hemp-lime requires a structural frame for load-bearing support, it integrates readily with wood, masonry, concrete, and steel systems. With appropriate design and detailing, it can be adapted to a wide range of architectural styles, climates, and building types.
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When properly designed and installed, hemp-lime addresses many challenges associated with conventional construction, including material toxicity, moisture management, durability, and environmental impact. Its exceptional performance characteristics make it an increasingly relevant material within modern, sustainable building practice.
Indoor air quality is a critical and often underestimated component of building performance. Modern construction often emphasizes airtightness and energy efficiency while relying on materials that emit volatile organic compounds, synthetic binders, and chemical additives. In tightly sealed buildings, these emissions can accumulate over time, contributing to respiratory irritation, endocrine disruption, and long-term health concerns.
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Hemp-lime offers a fundamentally different approach to indoor air quality, based on material chemistry, vapor permeability, and long-term stability.
AIR PURIFICATION
Research has shown that hemp-lime can actively improve indoor air quality by adsorbing and neutralizing airborne pollutants. A study conducted by the University of Bath found that hemp-lime wall assemblies were capable of reducing airborne VOC concentrations by up to 85%, including formaldehyde and other common indoor contaminants.
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NON-TOXIC MATERIAL COMPOSITION
Hemp-lime is composed of hemp hurd, lime-based binders, and water, without synthetic resins, petroleum-derived foams, chemical fire retardants, or added biocides. As a result, it does not introduce VOCs such as formaldehyde, benzene, or ammonia that are commonly associated with conventional insulation, composite wood products, and synthetic finishes.
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Once cured, hemp-lime remains chemically stable and does not degrade or off-gas over time, contributing to consistent indoor air quality throughout the lifespan of the building.
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MOISTURE REGULATION
Hemp-lime is vapor open and highly hygroscopic, meaning it can absorb, store, and release water vapor without losing structural integrity. It can hold up to approximately 20% of its weight in moisture, releasing it gradually as conditions dry.
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This moisture buffering moderates indoor relative humidity and helps maintain levels within a healthy comfort range, typically between 40% and 60%. By flattening daily humidity fluctuations, hemp-lime reduces condensation risk and limits the conditions that support mold, mildew, and bacterial growth.
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Unlike conventional wall systems that rely on vapor barriers and chemical moisture control strategies, hemp-lime manages moisture through physical and chemical processes rather than containment.
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MOLD RESISTANCE
With a pH above 12 the lime binder used in hemp-lime is strongly alkaline, creating an environment that is naturally resistant to mold, fungi, and pests. This resistance is achieved through mineral chemistry rather than through fungicides or insecticides, which are common in conventional insulation products.
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As a result, hemp-lime walls remain inhospitable to biological growth even in humid conditions, further supporting long-term indoor air quality.
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CLAY PLASTER FINISHES
When finished with clay plasters, hemp-lime wall systems gain additional moisture-regulating capacity and surface-level adsorption of airborne pollutants. Clay plasters are also valued for their ability to store and release humidity rapidly, improving short-term indoor comfort.
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Clay surfaces are known to emit low levels of negative ions, which may contribute to perceived air freshness and occupant comfort. While research into their interaction with electromagnetic fields is ongoing, clay plasters are widely recognized for their role in creating stable, low-toxicity interior environments.
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INDOOR AIR STABILITY
Many conventional materials degrade over time, increasing emissions as they age. Hemp-lime becomes more chemically stable as it carbonates, gradually converting lime back into limestone while continuing to absorb CO2 from the atmosphere. This process does not generate harmful byproducts and contributes to long-term material durability and indoor air consistency.
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By combining non-toxic composition, pollutant adsorption, vapor permeability, humidity buffering, and biological resistance, hemp-lime supports indoor environments that are measurably healthier, more stable, and more resilient than those built with conventional materials.
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