sustainable building? WitH FlaX and HeMP!

gROW 2 build

Flax and hemp are two important renewable resources that are

used as components in biobased construction materials. The

European project Grow2Build wants to bring all parties involved

in the flax and hemp chain, i.e. agriculture, primary processors,

industry, construction sector, and end consumers into contact

with each other. By exchanging information and bringing parties

together, Grow2Build endeavours to help improve these building

materials and to put them (back) on the market.

a HOuse OF 120 M2 OF WHiCH Walls, FlOORs, and insulatiOn COnsist OF HeMP, enCaPsulates MORe tHan 1 1 tOns OF CO

2.

building in a sustainable ManneR FOllOWing biO-eCOlOgiCal PRinCiPles

The building construction sector is a significant source of green-

house gas emissions and one of the biggest consumers of non-

renewable and renewable natural resources. For this reason,

all developments in sustainable building materials and solutions

have potentially significant impact.

CO2 emissions can be reduced by energy conservation and be-

gins with an energy efficient living space improvements, namely

airtight construction, improved insulation, correct ventilation and

installation of renewable energy sources such as solar energy or

solar water heating system (SWH), thus reducing your home gas

and electricity consumption.

Additional benefits arise from building with resource-efficient

and environmentally friendly construction materials. Renewable

resources, e.g. wood, reed, straw, flax and hemp absorb CO2

from the air in the course of their growth and transform it into

carbon compounds constructing the plant in photosynthesis pro-

cess using solar energy. Therefore, the CO2 is being stored in

the environmentally efficient building materials, which has a posi-

tive effect on the greenhouse gases balance. After a lifetime of

such construction, the materials can be reclaimed, reused (CO2

remains stored), recycled for energy or disposed, (CO2 emission

is delayed by 60 or 100 years).

From a bio-ecological point of view, building materials based on

renewable (cultivatable) resources are an interesting alternative

for a part of construction materials. Wood was used for building

purposes from time immemorial and is still popular today. Other

well known bio-based resources, like hemp, flax and sheep wool

are gaining interest of the building industry with material research

developments and environment-oriented legislations.

Renewable resources are inexhaustible and thus not posing

a threat to the environment if managed in a sustainable way. A

well-thought replanting allows for the production and consump-

tion period to beat least as long as the development period of

the resources. It is also important that the ecological and health

impact of the manufacturing process and use are limited and that

the technical and functional quality remains guaranteed.

In a lot of cases, the transport of building materials and products

provides a not to be underestimated contribution to the global eco-

logical impact of the material or product. If the locally cultivated

resource, such as flax and hemp, are also processed nearby, then

transport related energy consumption is kept to a minimum, thus

additional emissions and environmental impact can be greatly

reduced.

CultiVatiOn OF FlaX and HeMP

Northwestern Europe is known as the most convenient flax cul-

tivation region in the world, which is related to the appropriate

soil, favourable climate conditions, and the expertise of the grow-

ers refined in centuries of this industry. The same environmental

reasons and growers expertise causes industrial hemp to regain

its popularity.

From antiquity to the 18th century, flax and hemp have been used

in making clothing, ropes, sails, food, and medicine, among other

things. At the beginning of the 20th century, hemp and flax started

to be replaced with cost-competing imported fibres like cotton and

later on, since the Second World War, by synthetic fibres.

Industrial hemp, a drug free variety of Cannabis genius was linked

to the inherently different drug-containing varieties, and its culti-

vation was banned among the most of Europe until 1992. Some

species of Cannabis genius contain THC (tetrahydrocannabinol),

a psychoactive compound. Cannabis Sativa Indica (commonly

known as Marijuana) has a THC content between 2% and 10%.

Cannabis Sativa Sativa (Industrial Hemp), indigenous to our re-

gions, has a THC content of about 0.05%, which is well below the

European legislation limit for industrial hemp of 0.2% THC.

There is, a renewed interest in industrial hemp and the possibili-

ties it bears:

1992: A European regulation allows the cultivation of industrial

hemp. France, the Netherlands, Switzerland, Spain, and Ger-

many passed legislation concerning the cultivation of low THC

(industrial) hemp.

1999: 10 states in the US allowed the cultivation of industrial

hemp. In practice, no industrial hemp was cultivated because the

DEA (Drug Enforcement Administration) has not yet given permis-

sion for this.

The benefits of flax and hemp can be seen in various applications

among automotive, food, cosmetics, textile, and building materi-

als industries. These renewable resources have a great potential

in the development of a sustainable living space.

PROCessing FlaX and HeMP

Flax and hemp are interesting crops from an agricultural point

of view. Both can be used as rotation cops because they leave

behind a favourable soil composition after harvest. Hemp grows

faster than weeds and doesn’t need crop protection agents or a

lot of fertilizers.

The steps in processing hemp and flax fibres:

Harvest - Harvest happens between June and August. The plants

are left lying on the field in rows.

Retting - Is a process in which solar UV radiation and micro-

organisms, in the moist conditions of a regular alternation of dry-

ing and soaking, dissolve carbon compounds, which keep fibres

together, thus separating them from the stalks.

Turning - Turning rows of straw enhances consistency of the ret-

ting process.

Bundling - After retting, the hemp straw is pressed together into

balls, flax straw is rolled.

Breaking - In order to remove fibres optimally from the stalk, the

straw is broken into small pieces.

Scutching - The last timber parts are scraped away from the fi-

bres.

Hackling - This is the splitting of the fibres: short and long fibres

are split and fibres are being aligned.

building MateRials Made FROM FlaX and HeMP

Flax and hemp are basic ingredients for ecological building ma-

terials. Because of the many possibilities offered by these crops

and their relatively easy cultivation, there is renewed attention

given to flax and hemp use. Both the stalks and the fibres are

processed into construction materials.

The fibres are extremely strong and the stalk woody material is a

moisture absorbing medium.

There are two main types of flax: fibre flax and oil flax. Oil flax is

intended for extraction of linseed (flax seeds), which is pressed to

extract oils. Oil flax seeds contain about 40% of oil, which can be

converted into multiple products such as furniture, floor oils, paints

or linoleum. They are extraordinarily strong and very light at the

same time. Flax fibres have high rigidity, great vibration dampen-

ing, and a low density (1.4 p (g/ cm³)),in comparison, for instance,

with glass fibres (2,54 p (g/cm³)). They also do very well as ther-

mal and acoustic insulators. The fibres from fibre flax are perfectly

recyclable, biologically biodegradable, and compostable.

Similarly, each part of the industrial hemp plant has its useful ap-

plication. The hemp stalk consists of long and sturdy fibres, inner

core has moisture absorption and insulation properties, the seed is

a source of oil and protein and the leaf is suitable as cattle-fodder.

Hemp stalks are often used as animal bedding. Hemp possesses

three characteristics that are useful in the construction industry: its

insulation capacity, the mechanical resistance of the fibres, and

the low density (110 kg/m3). Additionally, hemp shives can also

absorb a large quantity of water (3.5 to 5 times their own weight).

neW natuRal COnstRuCtiOn MateRials COMbine duRabilitY and liVing COM-FORt

Insulation materials

The short fibres of both hemp and flax, which are not used in the

textile industry, are processed into insulation material. These natu-

ral fibres are hygroscopic, which means they absorb and maintain

a certain amount of water without getting wet. The short fibres re-

sist both heat and cold. Flax and hemp insulation are damp open

and bear up to an optimal living climate. Insulation is available in

bulk, in rolls and in panels for floor insulation.

For the production of hemp and flax insulation the fibres are sepa-

rated from the stalks, after which the short fibres are pressed into

bales for further processing.

Manufacturers often bind the natural fibres of the insulation ma-

terials with polyester fibres or starch. About 10 to 15% fire resist-

ant agent is also added, an agent that often also gives protection

against fungi. No extra mixtures are added to blown hemp fibres

and loose fill insulation made of hemp.

The production processes of insulation materials made out of flax

and hemp carries a low environmental burden.

Composites

Fibre reinforced polymer composites (FRP) consist of two main

components: reinforcing fibres and a polymer matrix. The most

commonly used composite in the construction industry is glass

fibre reinforced polymer (GRP), which in building construction are

mainly used in structural and architectural applications such as

roof construction, door frames, canopies, dormers, chimneys and

coping systems. Natural fibre reinforced polymers (NFRP) offer

a potential alternative to GRPs and could prove to have a lower

embodied environmental impact.

Hemp and flax fibres display high tensile properties, and are of-

ten compared to glass fibres. Therefore, once extracted from the

plant, natural fibres are used for reinforcement in similar process-

ing methodologies as glass fibres, by incorporating reinforcement

in forms such as yarns, woven or nonwoven mats and chopped

fibres with hand or automated processing techniques. Some other

benefits of processing with NFRP include lowered abrasion to ma-

chinery and potentially lower impact of human respiratory system.

The density of natural fibres (cellulosic fibres - 1.5g/cm3) is sig-

nificantly lower than that of glass (2.5g/cm3). Hence, the specific

mechanical properties of NFRPs are comparable to that of GRPs.

The weight of a material is a key consideration in application as a

lower density material can reduce costs in some areas of manu-

facture, fabrication, transportation and construction. The low den-

sity of natural fibres also results in a lower thermal conductivity in

certain configurations, suggesting that an NFRP could perform

well where thermal bridging is a concern, such as window frames

or secondary structural elements such as wall ties.

When natural fibre reinforcement is combined with a bio-de-

rived polymer such as cashew nut shell liquid oil (CNSL) a fully

biodegradable composite or ‘biocomposite’ can be produced,

which further reduces the environmental impact of such material.

As such, research into biocomposites has garnered much atten-

tion recently and biocomposites in the construction industry could

soon become a reality.

There is already NFRP leisure equipment available on the mar-

ket like kayaks, tennis rackets, and professional racing bikes etc.

made from composites incorporating flax fibre reinforcements

available on the market.

Wall render

Flax shives are often added in lime or clay plasters. The flax straws

reinforce the plaster coat and provide added aesthetic value.

Reinforcement nets are also made of flax fibres. Moreover, plas-

ter work must be reinforced to prevent crack formation at the

joints or for use in various grounds.

Hempcrete (lime hemp mixture) is used as plaster material or as

construction material, depending on the composition of the mix. A

thick layer of hempcrete on cold, thick walls can raise the comfort

of a home significantly. A coat of 4 to 6 cm ensures the thermal

regulation of the wall and can also correct unevenness. The in-

ertia of the wall is maintained and the moisture balance is not

disturbed. The introduction of a lime hemp mix to the inner side

is a technique that is applied in the renovation of old buildings.

Hempcrete as construction material

As a construction material, hempcrete (or lime hemp concrete)

combined with a timber frame can be used for walls, roofs and

floors, each with a slightly modified compound. It can also be

applied to the outer side of an existing home as outer wall insula-

tion. The lime hemp mix is applied by spraying, deposited in a slid-

ing casing or built with prefab pressed bricks. The outer walls can

then be finished with a coated wooden cover or with a plaster mix

of lime and sand.

A case has shown that hempcrete houses score at least as good

as traditional brick constructions when it comes to constructive life-

span. It has also shown that the energy consumption for heating

is the same in hempcrete houses as in traditionally built homes.

There is less condensation in the lime hemp houses and there are

less cold bridges as well.

The use of prefabricated hempcrete blocks is the same as tradi-

tional way of building with bricks at the construction site. Hemp-

crete blocks are laid with plaster or lime and finished with plaster

or lime (brush, spraying machine). The larger bricks can also be

laid on shingles as floor filling. The bricks have high fire resist-

ance properties (B, s1, d0): they spread no flames, maintain their

mechanical properties, and create little smoke.

Chipboards

Flax chipboards are made with shives and a binding agent. Pro-

cessing boards with such material allows for constant quality,

homogenous constitution, low density and fine structure. These

boards are used in furniture manufacture, ceilings and wall pan-

els. In the case of wall panels, plaster carton boards are attached

both sides with the main benefit in the insulation properties of such

sandwich structure.

Linseed oil and natural paint

Linseed oil is gained by pressing the seeds of oil flax, which contain

approximately 40% of oleic substances.

Linseed oil can be used for protecting wood or for making bio-

based paints. Natural paint from linseed oil is often biodegradable

and consists of renewable raw materials, in contradiction to most of

current paints from petrochemical materials.

Linoleum

Linoleum is a wear resistant floor cover usually few millimeters

thick. It’s a natural product that is highly durable and resistant to

dents made by furniture.

The production process goes as follows: first the linseed oil is

boiled, which causes it to oxidize and makes it harden faster later

on. Thereafter, it is mixed with resin, filler (cork or wood dust) and

colorant. This is then rolled on the back of jute cloth. After this treat-

ment linoleum must first be hung in drying towers for the linseed oil

to dry and harden before it can be used.

did YOu knOW?

The original chip boards were made from flax straw and not from

wood, which explains why the chip board industry today can still be

found in areas where flax used to be cultivated. The cores of some

acoustic internal doors are made with flax straw.

Plumbers use flax fibres on a daily basis to seal threaded pipe

joints?

© het StroBuro cvba

sOuRCes

• Jan van Dam, Martien van den Oever: Catalogus biobased

bouwmaterialen; het groene wonen. Wageningen UR. Propress,

Wageningen, 2012,118 p.

• Ir. Danckaert Freya, ir. Verbeke Paul, ir. Delanote Lieven, ir. De

Cubber Katlijn: Inleiding tot de biologische teelt van hennep.

PCBT (Interprovinciaal Proefcentrum voor de Biologische Teelt).

Rumbeke. 2006, 34 p.

• Thoelen Peter: Hennep/kemp voor de bouwsector. VIBE vzw.

Antwerpen, 2008, 18 p.

• Wervel: Kemp voor een koel klimaat. Wervel. Brussel, 2008, 9 p.

• www.wtcb.be - ‘ecobouwen en duurzame ontwikkeling’ - Docu-

menten

• www.kennisakker.nl/kenniscentrum/handleidingen/teelthandlei-

ding-vezelvlas

• www.procotex.com - ‘producten’ - vlas composieten

• www.milieuadvieswinkel.be

• www.ikgabouwen.be

© Peter Steen

WWW.gROW2build.eu

Bas