Compilation of relevent research


By Kim Brooks

August 2018

Hempcrete Natural Building is a privately held Canadian company, established in 2003. The following describes the hempcrete material, research results from testing from a broad variety of testing facilities globally, and a brief overview of the process by which we build our modular hempcrete houses.

Hempcrete is a lightweight fiber reinforced concrete material, a mixture of inner woody core as well as the long fibers of the industrial hemp plant, hydrated lime-based binder and water. This material is used internationally for construction, as wall infill system which offers insulation and moisture regulator. 

We have built 3 modular hempcrete houses to date; one in Alberta for a client, one on our property and a third on our commercial site on Bowen Island. This third unit has been sold and will be moved (by Nichol Brothers) onto a traditional foundation on Bowen Island.

The following describes our houses, and the properties of hempcrete material which has been researched extensively over the last 16 years.  Sources from the reference material at end of the document.

Properties of Hempcrete * (further details below )
Hygroscopic properties –
absorption and movement of moisture 
Vapor permeability:3.4 x 10-5 PSI.
Moisture Buffer Value 2 g/(m2.%RH)
Porosity 80% in volume
Thermal Performance
Conductivity and Thermal Mass Insulation  
R value2.4 – 4.8 per inch
Thermal Resistance  (typical U-value at 300 mm = 0.21 W/m2 K) 
Thermal transmittance (also measured in U value) 300mm wall (0.35 W/m2K) 
Thermal Conductivity 0.06-0.12 W/mK low thermal  conductivity  (λ  =  0.047  to  0.058W/m 2 K) low thermal  conductivity  (λ  =  0.047  to  0.058W/m 2 K) low thermal  conductivity  (λ  =  0.047  to  0.058W/m 2 K) (λ  =  0.047  to  0.058W/m 2 K)  
Air Permeability (air leakage rate per hour per square meters of envelope area)  <2:m3/m2 hr @ 50 pa 1.0 x 10-6 PSI 
Strength
Compressive strength
ranges, depending on the
casting process; 
  116 to 145 pounds per square inch (PSI) 29=>1006.56 (0.2 to 6.94 MPa ) 
Tensile    Composites made of 20% hemp fiber were found to display a tensile strength and modulus of 35 MPa and 4.4 GPa, respectively. 
Flexural strength:   44 to 58 PSI Flexural strength: 44 to 58 PSI
  
  Weight   15% that of traditional concrete
Dry density:270–330 kg/m3to 93.6 to 136.4 Kgs/M3 5.9 to 8.6 lbs/cf Concrete-150lbs. Hempcrete is 17=>20 times lighter than concrete 
 
 Fire ratingApproximately 60-120 minutes per 4 inches of thickness Limecrete, Ltd. (UK) reports a fire resistance rating of 1 hour per British/EU standards. Flame spread index = 0 Smoke Developed Index = 0 
 
Mean Acoustic
Absorption Coefficient 
0.69 NRC. It absorbs 90%
of airborne sound 
 
Carbon Negativity of
Hemp Concrete 
Test Wall of 1m x 1m x 0.3m sequestrated 82.71 kg of carbon dioxide. This
compensated for the 46.43 kg of carbon dioxide emitted during growing,
manufacturing and
construction processes such as manufacture of lime,
transportation of material,
etc., but also enabled an additional 36.08 kg of carbon storage
Carbon Sequestration     7 lbs/cf 108kg/M3 50 Kg /1 M2
Co2 emissions Significantly reduced (.545kg/kWh)

(HempLime) primary ingredients

Lime-Based binder

The high percentage of lime is an important due to the highly alkaline.  It is an excellent binder with unique binding properties to hemp due to the high silica content. Lime is poisonous to pests, fire resistant and prevents molds.

Hemp plant Chemical Properties

Hemp hurds componentContent (%)
Toluen-ethanol extract3.57
Holocellulose77.28
Cellulose44.5
Hemicellulose32.78
Lignin21.03
Ash3.04

As hempcrete is a natural product, performance can vary slightly. Due to this, when test results have varied, a range is included. Multiple researchers’ data is included- Please see reference sources below.

Hemp concretes have high levels of porosity enabling excellent thermal behaviour, hygric and acoustic advantages. Hemp lime provides a lightweight material with the characteristics of a heavier material which both insulates, stores heat and mediates fluctuations in external temperature. Although thermal conductivity is low relative to other high capacitance materials, the thermal transmittance is higher than walls with ample widths of classic insulation materials.

The thermal inertia characteristics of hemp-lime compensate and enable comfortable thermal indoor conditions and low energy operation. Future research will investigate dynamic thermal diffusivity evaluation to enable greater confidence in claims of hemp-lime as a material with optimum thermal inertia and mass characteristics.

Further information on the ‘Properties of Hempcrete’ table, above 

Hygroscopic properties -absorption and movement of moisture

Vapor permeability: 3.4 x 10-5 PSI.

Moisture Buffer Value of 2 g/(m2.%RH)

The breathability and ability to act as moisture buffer reduces the risk of damage from trapped humidity and the application technique prevents thermal bridges.

Hemplime concrete ‘works without any additional vapor retarder.’ (Hygrothermal Performance Assessment for Super SSR Modular Block Wall System. Smart Solutions Manfred Kehrer, President 171 Glassboro Dr. Oak Ridge, TN 37830 www.WUFI.us Date Prepared – November 2016)

Thermal Performance;

Thermal parameters of hemp-lime are increasingly well characterised with a proliferation of studies in recent years publishing performance results for a range of binder types, densities, moisture contents, and construction/application methods.

Conductivity and Thermal Mass Insulation

Thermal Resistance

The higher the R-value, the more thermal resistance the material has and therefore the better its insulating properties. Hempcrete has high Thermal Resistance

R value

Hempcrete ranges from 2.4 – 4.8 per inch of thickness

In comparison to other free-form construction materials has a much higher R-value. Concrete has a typical R- value of about 0.08 per inch of thickness compared to hempcrete

Thermal Conductivity:

(typical U-value at 300 mm = 0.21 W/m2 K)

0.06-0.12 W/mK

low

thermal  conductivity  (λ  =  0.047  to  0.058W/m

2K)low thermal  conductivity  (λ  =  0.047  to  0.058W/m2

K)low thermal  conductivity  (λ  =  0.047  to  0.058W/m

2K)(λ  =  0.047  to  0.058W/m

2K)  0.07–0.09 W/mK

0.09 – 0.115 W/mK

Thermal transmittance (also measured in U value)

300mm wall, 0.35 W/m2K (UK building code standards (0.21 W/m2K (domestic), 0.27 W/m2K). Evidence in the UK from a BRE study at Haverhill Housing Project indicates that the walls of a hempcrete house, performed at a better (lower) actual U value than the notional calculation. The monolithic nature of the wall construction in and of itself should also lead to lower thermal bridging, which may also have been a factor in the higher performances measured at Haverhill. The construction technique promotes good air tightness and minimal thermal bridging of the building envelope. All these factors combine to produce low carbon, hygrothermally efficient buildings that are low energy both in construction and in use, and offer opportunities for recycling at end.’Hygrothermal performance of an experimental hemp–lime building. (Andy Shea, Mike Lawrence, Pete Walker 2012/11/1JournalConstruction and Building MaterialsVolume36Pages270-275)

Thermal Mass or Inertia the capacity of a material to store energy.

Hempcrete has high thermal inertia and demonstrates all the characteristics of Thermal Mass with the added benefit of being lighter weight than concrete and other masonry building materials and is able to STORE and RELEASE ENERGY (heat) that gives hempcrete its superb ability to insulate.

Due to hemp concrete’s high porosity and Moisture Buffer Value of 2 g/(m2.%RH) moisture gets entrapped within the many pores of the material resulting in the material gaining thermal mass. This thermal mass prevents fluctuations in temperature of the indoor atmosphere much like phase change materials (PCM).

Materials like concrete cannot absorb and emit heat quickly and do not have the ability to buffer moisture. There is no other construction material on the market, which has such a high R-value to low production value ratio.

‘…hempcrete has serious ecological and energy credentials.’ Passive House

• Lower mechanical (HVAC) requirements. Our NotSo Tiny home requires 7,000 btu (relative to what, for comparison)

These properties also indicate a reduction in the requirement for air conditioning by a minimum of 10%

  • Air Permeability (air leakage rate per hour per square meters of envelope area)

 <2:m3/m2 hr @ 50 pa or 1.0 x 10-6 PSI

Hempcrete is inherently airtight. Better than best practices which is approximately 3:m3/m2 hr @ 50 pa.  A range of 5 -9 is common (https://www.cibse.org/getmedia/. Stroma-Air-Tightness-Presentation-Slides.pdf.aspx)There are air permeability benefits by the nature of lime hemp’s monolithic construction, (spray or infill around openings etc.) and plastering, rendering finishes.

  • Strength

Compressive

Compressive strength ranges, depending on the casting process;

116 to 145 pounds per square inch (PSI)

29=>1006.56 (0.2 to 6.94 MPa )

 ‘One of the most important parameters for a building material used as a walling material is

compressive strength. Researchers around the world that have worked with hemp concrete have

reported various values of hempcrete’s compressive strength.  The typical compressive strength is around 1 MPa, around 1/20 that of residential grade concrete. It is a low-density material and resistant to crack under movement thus making it highly suitable for use in earthquake-prone areas.

Unlike other organic concrete additives, wet hemp breaks down very slowly, enabling the cement to cure to maximum strength without cracks due to off gassing. Research also indicates a clear proportional relationship between density and compressive strength.

TensileComposites made of 20% hemp fiber were found to display a tensile strength and modulus of 35 MPa and 4.4 GPa, respectively. 

Flexural strength: 44 to 58 PSI Flexural strength: 44 to 58 PSI

  • Weight

Density:

dry density: 270–330 kg/m3to  93.6 to 136.4  Kgs/M3

5.9 to 8.6 lbs/cf

15% that of traditional concrete

Concrete-150lbs. Hempcrete is 17=>20 times lighter than concrete

  • Durability

the longevity of the structure made from the material Interestingly, hemp concrete, because of the lime content undergoes carbonation across a span of several years and turns into limestone, rendering strength to the structure and the micro bonds in the binder matrix (Cultrone et al., 2005; Lawrence, 2006). This gain in strength over time could possibly signify increasing durability with time and can lead to houses lasting for centuries; and afterwards they can even be recycled.

Mean Acoustic Absorption Coefficient

0.69 NRC. It absorbs 90% of airborne sound

  • Carbon

 Carbon Negativity of Hempcrete

Hemp shivs are composed of 45% carbon, meaning 1 kg of hemp shivs sequester about 1.6 to 1.8 kg of carbon dioxide through photosynthesis during the plant’s growth. A study conducted by Ip and Miller, 2012 indicated that a functional wall unit of dimensions 1m x 1m x 0.3m had sequestrated 82.71 kg of carbon dioxide, which not only compensated for the 46.43 kg of carbon dioxide emitted during growing, manufacturing and construction processes such as manufacture of lime, transportation of material, etc., but also enabled an additional 36.08 kg of carbon storage. This means that structures made of hemp concrete essentially compensate for all of the carbon emissions made from all other processes related to constructing the structures. Hence, if the goal is to achieve a carbon neutral building, hemp concrete must be used in a considerable quantum to offset the carbon emissions.

Carbon Sequestration

7 lbs/cf

108kg/M3

50 Kg /1 M2

A unique result of combining lime and hemp is their ability to act as a carbon sink. Data from Lime Technology Ltd in the UK estimate that a typical lime hemp house equates to roughly 50 tonnes of carbon per house, which in addition to embodied energy savings is a critical one-off carbon saving.

  Co2 emissions Significantly reduced (.545kg/kWh)

Human Comfort Model

Recent studies of standard and hempcrete buildings have shown that assessment of performance based on either R or U-values alone is unrepresentative of true performance. The interplay between the warmth, oxygen and moisture content plays a strong role in how comfortable humans feel, regardless of the R or U values.

A material with a high thermal inertia is one in which dynamic effects are prevalent, and one for which steady state analysis could prove inaccurate. It is a bulk material property related to thermal conductivity and volumetric heat capacity and can modulate the impact of varying environmental conditions. Constantly varying external environment conditions continuously impact the building envelope and don’t regularly allow for prolonged steady-state operation.

With respect of thermal performance characterization, studies have shown that hemp-lime exhibits high

moisture buffering capacity and a good balance between low mass and storage capacity. A recent

salient study of whole hemp-building performance presents insightful evidence of the ability of hemp to

attenuate oscillations in the external environment. Other studies have undertaken simulation based

investigation of dynamic whole hemp-building performance.

The majority of laboratory-based studies however have focused on steady state thermal characterization with less focusing on non-steady state situations. Transient behavior appears after an imposed change in temperature at a boundary of the material, as occurs during changing climate conditions or indoor environmental conditions. (A. Evrard and A. De Herde, “Bioclimatic envelopes made of lime and hemp concrete,” presented at the CISBAT, Lausanne, Switzerland, 2005.)

**********************************************************

References and Source details

Allin, Steve. Building with Hemp,2003

Amziane and Arnaud (Arnaud 2013)

www.Hemp-Technologies.com

Arnaud and Gourlay, 2011; Cerezo, 2005; Cigasova et al.,

2014; Elfordy et al., 2008; Evrard, 2003; Kioy, 2005; Nguyen et al., 2009).

Bevan R and Woolley T. Hemp lime construction: a guide to building with hemp lime composites. EP 85.

Bracknell, IHS BRE Press, 2008. BRE and University of Bath. Low-impact materials: case studies. Hemp lime: the Triangle. Available at: www.bre.co.uk/page.jsp?id=2669. NHBC Foundation.

Cultrone et al., 2005; Lawrence, 2006.

Garston, BRE, 2002. Available at: http://projects.bre.co.uk/hemphomes/index.html. Yong J and Morlidge 

 (PDF) Hemp Concrete – A Traditional and Novel Green Building Material. Available from: https://www.researchgate.net/publication/324647603_Hemp_Concrete_-A_Traditional_and_Novel_Green_Building_Material

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IIT Roorkee, Roorkee, Uttarakhand, India, March 7-8, 2018

International Conference on Advances in Construction Materials and Structures (ACMS-2018)

IIT Roorkee, Roorkee, Uttarakhand, India, March 7-8, 2018

Ip and Miller, 2012

Magwood, Chris, Essential Hempcrete Construction, 2017

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Ramsbury, The Crowood Press, 2006. Yates T. Natural building: a guide to materials and techniques.

Final report on the construction of the hemp houses at Haverhill, Suffolk. Client report 209-717 rev 1.

Thermographic inspection of the masonry and hemp houses: Haverhill, Suffolk. Garston, BRE, 2003. Available at: http://projects.bre.co.uk/hemphomes/index.html.

BRE, Garston, Watford WD25 9XX Tel: 01923 664000, Email: enquiries@bre.co.uk, www.bre.co.uk

BRE is the UK’s leading center of expertise on the built environment, construction, energy use in buildings, fire prevention and control, and risk management. BRE is a part of the BRE Group, a world leading research, consultancy, training, testing and certification organisation, delivering sustainability and innovation across the built environment and beyond.

Latif et al., 2015Fire Testing, example; ASTM E119-14 CAN/ULC S101-07
DATE(S) OF TESTING: June 22, 2018
TESTING REQUESTED: Testing to the mandatory requirements of the following criteria:
ASTM E119-14, Standard Test Methods for Fire Tests of Building Construction and Materials, and CAN/ULC S101-07,Standard Methods of Fire Endurance Tests of Building Construction and Materials
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Hygrothermal performance of an experimental hemp–lime buildingAndy Shea, Mike Lawrence, Pete Walker 2012/11/1JournalConstruction and Building MaterialsVolume36Pages270-275https://www.sciencedirect.com/topics/materials-science/hemp-fibers

Hygrothermal Performance Assessment for Super SSR Modular Block Wall System justSmartSolutions Manfred Kehrer, President 171 Glassboro Dr. Oak Ridge, TN 37830 www.WUFI.us Date Prepared – November 2016

Active research Centers;

The Université de Reims Champagne Ardenne in France

• The Université Catholique de Louvaine in Belgium

• The University of Bath in UK

• The University of Bristol (Interface Analysis Centre) in UK

• Collaboration of The University of Nantes (Institut de Recherche en Génie

Civil et Mécanique) with the University of Rennes (LGCGM – EquipeMatériaux

Thermo Rhéologie) and the Universitè de Bretagne Sud (Centre de

Recherche de Saint-Maudé, LIMATB)

(PDF) Performance of Hempcrete Walls Subjected to a Standard Time-temperature Fire Curve.. Available from: https://www.researchgate.net/publication/277533751_Performance_of_Hempcrete_Walls_Subjected_to_a_Standard_Time-temperature_Fire_Curve

[accessed Sep 17 2018]

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