WHY BUILD WITH HEMP
Return to OldBuilders Home page
Properties of Hemp-Lime
Superb thermal insulation performance
Negative Carbon build
Thermal Mass Insulation
Excellent sound insulation
High thermal inertia
Vapour Permeable (breathable)
Fire and pest resistant
Inherently air-tight structures
Design Flexibility, curved, thickness
Hemp-Lime is a sustainable material, it can be used as a solid wall insulation,
in floors and roofs. It can also be used as a plaster on old stone and brick
The hemp-lime mix is a combination of hemp shiv and lime, the lime is typically
a blend of hydraulic and hydrated lime, proprietary binders are also available
from St. Astier and Tradical.
The mix forms a bio-composite building material and insulation. It has excellent
thermal and acoustic properties and creates a healthy internal environment.
From a global environmental perspective hemp is a truly sustainable material,
that if widely adopted could have a significant effect on the greenhouse gases
produced by the construction industry. An average house produces over 50 tons of
carbon emissions, hemp building by contrast locks up over 50 tons of carbon,
approximately 110kg of CO2 per m3 of Hemp-Lime.
Built around a timber frame structure, the construction technique can deliver a
fast build out, with excellent levels of insulation, natural air-tightness and
good vapour permeability.
Hemp-Lime is a flexible and adaptable material, allowing builders, architects
and home owners huge flexibility for building layouts and design. Hemp-Lime can
be used with many structural framing systems, the timber frame supports the
hemp-lime wall. With on site custom framing additional benefits dealing with
cold bridging and air tightness can be obtained.
The nature of the wall is lightweight, which means fewer supports and lighter
foundations, saving time and money. Due to the vapour permeability the walls, it
is sufficiently dry to allow the use of untreated timber.
The building process involves casting into temporary shuttering, moulds or forms
around the timber frame structure, a lime plaster is applied just like concrete
or render, both inside and outside. The hemp-lime can cope with the flexural
nature of buildings. It is rodent, mould and fungus resistant, when it is
plastered. It has excellent fire resistance to conform to current building
regulations. Plaster and render finishes can be done in the same way as cement
or gypsum plaster, in addition to imaginative and artistic possibilities.
hemp-lime products are among the most ecologically sound of building products.
Hemp does not require chemicals in its cultivation. Like most plants, hemp
transforms carbon dioxide during its growth and captures the carbon, releasing
the oxygen to atmosphere. This has the effect in achieving the sequestration of
the principal greenhouse gas CO2.
Lime based binders are produced using lower energy methods in the manufacturing
than Portland cement. Lime is burned at a lower kiln temperatures reducing
emissions considerably from the methods used in producing Portland cements. In
addition, as the lime cures, carbonation occurs, and it re-absorbs carbon
dioxide in the process.
The considerable insulation characteristics of hemp-lime means lower heating
costs in winter and comfortable temperatures are maintained in hot weather. The
vapour permeability of the hemp-lime means a reduction or limitation of forced
ventilation and de-humidifying systems.
Hemp-Lime is comfortable to touch and feel, it can radiate warmth into a room.
The high vapour permeability avoids the development of condensation and trapped
moisture within the building. This improves the air quality and naturally
controls the humidity. A low humidity level reduces the likelihood of irritant
moulds and fungal growth, mould can affect the health of occupant's. The natural
materials means the absence of solvents, glues and plastics, most the most
dangerous building materials, such as particle board, waferboard, carpet, foams,
paints. The importance of breathability for a healthy indoor environment.
Statistical Information (Courtesy of Tradical®)
1 Hectare will produce up to 10 Tons of hemp in France and about 8 Tons in the
UK and Ireland.
60% of the processed hemp crop is shiv,
1 Ton of shiv is approx. 50 bales
1 Bale of hemp shiv contains 200 litres when uncompressed
1 Hectare will produce 5 to 6 Tons of shiv (250 to 300 bales)
1 Hectare will produce enough shiv to build a small house
1 Hectare of hemp will absorb up to 18Tons of CO2
as it grows (total crop - shiv, fibre and dust)
The shiv from 1 hectare contains about 10 to 11T CO2
Hemp-lime wall mix contains 108kg CO2/m3 (Spray applied at a density of
Hemp-lime wall mix contains around 150kg CO2/m3
(Shuttered and tamped at a density of 460kg/m3)
Hemp-lime roof mix contains 155kg CO2/m3 , Hemp-lime wall mix contains 85kg
Walls of Houses
A small semi detached house of 48 m2 GFA with 300 mm thick walls, contains 33 m3
This is 165 bales of hemp and 7.25T of Lime
This will lock up 3.6T of CO2 in the walls
A small detached house of 52 m2 GFA with 300mm thick walls, contains 49 m3 of
This is 245 bales of Hemp and 10.8T of Lime
This will lock up 5.4T of CO2 in the walls
A larger detached house of 100 m2 GFA with 500 mm thick walls, contains 120 m3
This is 600 bales of hemp and 26.4T of binder
This will lock up 13.2T of CO2 in the walls
Thermal Performance - U-Values
300 mm wall gives 0.30 W/m2.K
400 mm wall gives 0.22 W/m2.K
500 mm wall gives 0.18 W/m2.K
Testing carried out by the BRE on the Haverhill houses,
performance vs. theoretical performance might suggest that the thermal
performance of hemp-lime is up to 40% greater than its u-value would indicate.
This is due to the effect of thermal mass and humidity control. This would
suggest that a 400mm thick wall would give you the thermal equivalent of 0.13
W/m2.K. In order for you to make an important decision like this you should
read the BRE reports and other studies to understand the effects of thermal
Testing carried out by the BRE on the Haverhill houses see
showed that hemp-lime construction met the acoustic requirements of the building
regulations. Further ongoing research shows that it has the ability to absorb up
to 90% of air-born sound. This research is continuing in order to maximise the
potential of hemp-lime to be used in sound-proofing applications.
Compares HEMP built with MASONRY built, clearly shows less heat loss from the
This top picture is the Hemp house, blue is cold outside wall = less heat loss
Bottom Picture is Masonry house, red is warm outside wall = MORE heat loss
SOME HEMP BUILDINGS BUILT BY OLDBUILDERS These photos show the process of hemp
building, note the mixing, barrows, shuttering and hand tamping used by us until
recently here in Ireland, we now also use the machine mix and blown method like
in pictures above used in France.
Hemp building area on website for more information
Hemp building area on website for more