LIME HEMP.. A Low Carbon Solution?

I recently read a very interesting article by Joseph Little Architects,

which discussed the potential for using Lime-hemp as a potential solution to Carbon sink global problems.

I found the article fascinating and have provided a direct link to the article on his website.

The link is as follows:

http://www.josephlittlearchitects.com/documents/hemp_lime_paper.pdf

I have also copied some of this article in the following page, without any of the attached  images. I trust you will find Mr. Little’s article as interesting as I did.

A provocation
“We can’t solve problems by using the same kind of thinking we used when
we created them.”
Einstein
This article is intended to act as an exploration and provocation. Why do we
build the way we do, what effect does that have? Could we for instance,
design and specify buildings that actually benefit the Environment rather than
burden and pollute it as currently. Is it possible that the construction of a
house could absorb CO2 thereby transforming new housing estates or
apartment buildings into giant absorbers of carbon dioxide? Imagine Ireland
being able to count commercial constructions or new housing among its
‘carbon sinks’, in place of Siberian forests or the carbon credits that the
Government will have to trade for at tax payers’ expense, to meet the Kyoto
Protocol targets? Why not? It’s all possible!

Cement in the limelight
Cement and its derivatives (mass and re-inforced concrete, concrete blocks,
mortars and renders) are ubiquitous. Concrete, clear float glass and steel
have become the badges of modernity. High-rise New York, the great bridges
of Denmark, the Three Gorges Dam of China or the masterpieces of Mies,
Foster or Ando are inconceivable without them. The Developed World uses
these materials without question, without stop, and the business people,
politicians and town builders of the Developing World see them as the mark of
civilisation and progress.
Ordinary Portland Cement (OPC) was invented as an artificial hydrated lime
that allowed mortar (made from it) to set under water. It was patented in 1824
and was an expensive specialist product till the first decade of the Twentieth
Century due to requirement and cost of grinding it in industrial plants. Initially
cement mortars were as flexible as lime mortars but over time their specialist
use for engineering structures encouraged stronger mixes. Today it is a very
different material to hydrated lime or other lime-based products.
Lime has been used as the preferred binder of building materials in many
cultures throughout history. Up till the middle of the last century it was the
base ingredient of mortars and renders everywhere because it could be made
almost anywhere using local limestone sources in local kilns. This advantage
had the attendant drawback of quality varying from place to place. In general
lime production remained a cottage industry. The requirements of ‘total war’
and the new world order that followed WWII created a bias towards industrial
processes and an insatiable demand for large scale civil engineering and
housing projects. Everything was to be uniform, strong, progressive and
modern. OPC fitted this view but lime did not. It would appear that by the
early 1960’s lime was totally supplanted in the Western World and knowledge
of its uses and application had begun to be forgotten.
At what cost success?
The Irish Concrete Federation, which will be giving a paper at the forthcoming
Irish Sustainable Building Show, is correct in stating that ‘After water,
concrete is the most used material on earth’ (go to seminars at
www.sustainablebuildingshow.com). But at what cost has this growth
occurred?
The Green Building Handbook, Volume 1 (edited by Professor Tom Woolley
of University of Ulster) states that cement manufacture is the only significant
contributor to CO2 emissions besides fossil-fuel burning and is responsible for
8-10% of the world’s annual CO2 emissions and rising. Ian Pritchett of Lime
Technology Ltd states that 280 billion tonnes of CO2 have been released into
the atmosphere from the consumption of fossil fuels and cement production
since the start of the Industrial Revolution, more than half of this since the
mid-1970’s.

As we all now know CO2 emissions and climate change are directly linked.
The Intergovernmental Panel on Climate Change recommends a global
reduction of more than 50% in CO2 emissions by 2050. The International
Symposium on the Stabilisation of Greenhouse Gases, based in the Hadley
Centre (UK), reported in early 2005 that ‘large scale, irreversible system
disruption’ was likely after a 3° rise in temperature. Various sources estimate
that within 4-10 years time the volume of CO2 particles in the atmosphere will
be sufficient to result in a permanent rise of 2°C worldwide. This means
action in all sectors of society is needed now, particularly in the energy
generation and construction industries. It clearly can’t be put off for a further
decade.
The gravity of The Green Building Handbook’s information in this context
seems wholly at odds with the Irish Concrete Federation’s claim that there is a
‘negative perception of concrete which has been carefully cultivated by
various interest groups’ with regard to concrete‘s sustainability (see weblink
above). OPC Concrete may be an amazing material but it is not sustainable.
Surely all of us, even those who currently specify it, must form part of the
‘interest group’ that wishes to curb climate change.
Across the Irish Sea the British Cement Association (BCA) is beginning to
face up to its role in environmental degradation. Its report from 2002,
‘Cement, Concrete & Sustainability, A report on the Progress of the UK
Cement and Concrete Industry towards Sustainability’, comprehensively lists
various effects of cement and concrete production from employment, to
transport to emissions. It also explains how they are trying to reduce a wide
range of negative effects. The extract from Table 1 of that report, for
instance, shows a 10% reduction in CO2 emissions in 7 years.
BCA’s efforts are a good example of an organisation trying to incrementally
reduce the negative effects of its products. While their efforts are laudable,
they are only intermediate steps and not fast enough in the context we are
facing. Indeed the whole Construction Industry must strive to adopt beneficial
practices and materials, and not be content to focus on reduced negative
effects. It is easier for all of us to continue doing what we know: we just can’t
afford to.
So what are alternatives?
I agree with Ian Pritchett’s view that as a first step cement and concrete
should be restricted to their unique selling point: high-strength and specialist
uses. Even in that niche use reduced cement content and reduced emissions
are possible. As I hope to show there are other low-energy alternatives to
OPC in concrete that could become the mainstay of commercial masonry
construction, especially where that construction is low-rise or mass housing.
Directly comparable alternatives include ‘eco-cements’, limecrete, geopolymeric
cements and magnesium carbonate compounds. Among the brand
names of these are ‘Carbunculus’ and ‘Tececo’. In recent years Ecocem a
DublinPort-based company is manufacturing a strong, white-coloured cement by grinding granulated blast furnace imported from the Low Countries. As the
blast furnace slag is a waste product from steel manufacture the CO2 penalty
has already been paid. Its real value is the OPC production it can offset.
Further alternatives are timber, bamboo, lime-hemp, cob, adobe bricks and
rammed earth. All of these could also be developed as lower energy,
sustainable alternatives for various characteristics of cement-based products.
Lime-hemp composites seem to be particularly exciting alternatives to
concrete. Pat Borer in Wales, Tom Woolley in Northern Ireland, Ian Pritchett
near London, Lawrence Brown in Normandy are just some of the people
investigating lime-hemp in wall construction in this part of the world.
Given the conservatism of the mainstream construction industry one
strategically-sound approach to effecting change is to relate it to current
building and design practices. An example of this is retaining blockwork
construction as a construction methodology, but moving to low energy or low
emission ingredients. In that way for instance blockies need only minimal retraining
to lay lime-hemp (or other) blocks, engineers need adapt the figures
they input, but not their understanding of transfer of load in a wall, and
quantity surveyors can still estimate volume of masonry per length of wall etc.
This is the approach Limetec are taking. They are currently conducting trials
into engineered, load-bearing lime-hemp blocks. They hope these will be
commercially available within a year.
Materials in construction- cement
In cement’s early day it shared many characteristics of hydraulic lime, it was
less strong than the blocks it bound and it had some flexibility. However as
civil engineering projects grew more ambitious and as the ready-mix concrete
industry developed cement was made to be increasingly strong, and with that
increasingly brittle. While my parents’ solid wall house, constructed in the
early 1950s of cement mortar and concrete blocks, has never cracked or
leaked, the same design would have been at risk by the early 1970s due to
this change in cement composition.
For the first time mortar joints were found to be stronger than the blocks
themselves. This meant that where movement occurred it could crack the
blocks as quickly as the mortar joint. The lack of flexibility also meant that
even small amounts of wall movement could lead to permanent cracks.
Increasingly during the 1960s cavities became popular in blockwork wall
construction to reduce the risk of water penetration to the inside face of the
wall.
Expansion joints were introduced into blockwork walls, and into the cement
render finish even where a movement joint in the blockwork was not required
due to this inflexibility. A whole range of new ties, restraints, de-bonding
sleeves, expansion joint beads, external leaf lintels etc were invented and
popularised to accommodate these changes. After the second Oil Crisis
insulation was increasingly inserted into these cavities and the partial- and
full-fill insulated cavity wall systems were born. I have ample experience that
these forms of construction are difficult to build right and have read studies of their poor thermal performance. Perhaps we need to re-discover solid wall
construction?
Materials in construction- lime
The following are some of the reasons lime lends itself to solid wall
construction. It is weaker than masonry blocks which means it
accommodates whatever movement is necessary. When cracks do occur
they occur as multiple tiny fissures, not one large crack. Debris, dust and tiny
pieces of mortar lodge in these fissures over time, which coalesce back into a
solid lime mortar with the help of the next rainfall. This ability is called
‘autogenous healing’. Because of its hydroscopic characteristics walls
breathe through the lime mortar and lime render. It has been shown that
masonry in walls with cement mortar have a shorter life span because the
only way the wall can breath is through the masonry not the mortar.
Ian Pritchett of Limetec also highlighted three environmental characteristics of
lime mortar:
1) It has approximately 30 to 50% lower CO2 emissions than OPC overall.
This is because it is fired at a lower temperature, but it also re-absorbs
back a greater amount of the CO2 it emitted than cement.
2) It also has a lower embodied energy input than OPC. Between 50 &
70% less energy (depending on lime type used) goes into making a
lime-based standard type IV masonry mortar compared to a cementbased
one.
3) He feels one of its greatest advantages is its ability to act as a binder of
low energy, sustainable materials such as earth, woodwool (from
timber chippings) and hemp.

Materials in construction- hemp, and lime-hemp
Hemp is another material with remarkable properties.
a) Hemp can grows from seed to 3 metres in six months, it therefore
grows faster than any other plant except bamboo. Per acre it
generates far more biomass than commercial forestry.
b) As it does not take from the soil, land does not need to lay fallow after
harvest. Irish farmers can therefore grow a crop, part of which
becomes a construction material and another part of which can
become clothing, cosmetics, paper etc in rotation with their usual
foodcrops. Imagine construction in urban centres having a direct
positive impact on nearby rural economies!
c) Hemp, like all plants absorbs CO2, it then emits the oxygen and uses
the carbon as a building block of its growth. Pritchett states that one
kilo of plant material typically uses 1.7kg of carbon dioxide in its
production.
d) Pat Borer’s team researching the best materials for the Centre for
Alternative Technology’s WISE Building has obtained a K-value of
0.10W/mK in the first stage of development of their lime-hemp blocks.
They have high hopes that they will obtain a value of 0.07 W/mK. In
my calculation I use 0.10W/mK in relation to Pritchett’s blocks which
may be an over-simplification as denser lime-hemp blocks will be
physically stronger but thermally weaker.
[research since this article was published has shown that a wall of
350mm thickness of hemp-lime sprayed or cast around a timber frame,
finished with render and plaster will give a U-value of ~0.27W/mK2.
Note that decrement delay, due to its thermal mass, should give a
thermal performance far exceeding this – see below]]
e) A final remarkable characteristic is that lime-hemp walls retain heat
longer due to their specific heat capacity, so they can have some of the
thermal characteristics of insulation and some of the thermal mass
characteristics of heavy mass materials, like concrete. This was seen
to good effect in a BRE study of the Haverhill lime-hemp houses in
Sussex.

CO2 Sequestration
In an as yet unpublished paper, Ecobuild Chapter on Lime and Low Energy
Masonry Pritchett posited the idea that due to lime and hemp’s special
characteristics lime-hemp masonry walls could act as carbon sinks. I found
this idea fascinating and, as Pritchett had sent me a lime-hemp block sample,
decided to work out how significant the absorption might be.
As a way of teasing out the environmental value of load-bearing lime-hemp
construction for mass housing, I endeavoured to:
1) Establish a wall construction that was buildable and could meet various
U-values, starting with the minimum thermal standard under the
Building Regulations.
2) Estimate the volume and mass of 1sqm of wall and then quantify the
associated CO2 emissions, using Pritchett’s figures.
3) Compare the walls of two houses of the same design, but different
constructions, for their effect on CO2: one being a concrete block cavity
wall, the other lime-hemp solid wall construction.
Image courtesy from TGD L
I deliberately chose the design of a typical two storey semi-detached house
shown on page 63 of Technical Guidance Document L (2002) to the Irish
Building Regulations (see diagram above). It features partial-fill cavity walls
on strip foundations. I designated this Version 1. I felt that if I were to
maximise the carbon sequestration benefits of hemp and the solid wall
potential of lime the second house, Version 2, should be of thick solid wall
construction. It therefore has the same design and external area but thicker
solid 450mm lime-hemp walls (see diagram below). These walls result in
6.4% less space internally (or 2.5sqm less per floor). I judged this could be a
reasonable sacrifice for a householder to bear if I could prove that the benefits
were sufficient.

Buildability & thermal performance
As you can see the bond I propose is a variation on the English Bond. Like all
good masonry bond patterns the first priority is to ensure a good overlap of
blocks and the reduction, wherever possible, of a line of vertical joints through
the wall. While there is more blockwork in this wall than a cavity wall, the
blocks are lighter and there is a complete lack of complication, i.e. the
traditional bug-bears of partial fill cavity walling (cavity cleaning, fixing of ties
and perfect positioning of insulation) are all absent. It must therefore be
simpler to build and possibly as fast.
From a supervision or certification point of view there is very little to go wrong.
The lower level of skill may suit it to the self-build market as much as mass
housing. It was even suggested to me that the technology may be suited to
wall-building machines. Finally the omission of various ties, and lintels to the
outer leaf should help to offset the cost of the greater number of blocks. A
detailed cost comparison would be interesting.
Using the U-value calculator ‘Uvaluate’ (freeware from Xtratherm Insulation
company) one can quickly establish figures for the two walls. The partial fill
cavity wall meets the 0.27W/m2K standard with no allowance for on-site error.
However using Pat Borer’s initial test results of 0.10W/mK, I found that the
lime-hemp wall had a U-value of 0.21W/m2K, without the thermal contributions
of insulation, render or cavity! The addition of only 60mm of Rockwool
insulation is enough to bring it to the ‘super-insulation’ standard of 0.15W/m2K.
For the sake of finishes and waterproofing an external render and internal
plaster would be used in any case.

Comparing the role of CO2 in the walls of the two houses
I immediately ran into the problem of verifying data. Several of my sources
differed, with the cement industry tending to give more conservative figures.
In some cases the opposite occurred: Professor Woolley wrote in a 1997
book that ‘the manufacture of cement from chalk or limestone involves a
chemical reaction in which carbon dioxide is given off at a rate of 500kg
tonne-1’. Due to BCA-reported improvements of 13% between 1996 and 2001
I had initially revised his figure downwards by the same amount. However
Pritchett informed me that a leading UK cement company told him recently
that they had just dropped below 1000kg CO2 per tonne.
I also was unable to get certain kinds of figures from anyone. Some kinds of
data, such as the embodied energy of lime-hemp, simply haven’t been
calculated yet. It must be seen therefore that my calculations (see Appendix
1 on the ‘Construct Ireland’ website version of this article) are illustrative
rather than conclusive.
It is worth noting that my focus has been on establishing the CO2 emissions
associated with manufacture of lime and OPC (including, mining, packaging
and initial transport), and the CO2 sequestration of hemp and lime-hemp. I
have relied heavily on Limetec’s information for this (see Appendices 2 & 3 on
website). I have not focused on the embodied energy of transporting these
materials to site, on actually building the houses or the CO2, or embodied
energy, of any other building materials that would be built into those houses.
This is due to the limited time, the imperative of dealing with CO2 and the
difficulty I experienced in getting figures for all the ‘actors in the play’. All of
this could do with a great deal more study. Obviously a truly sustainable
design approach would not stop at a 3 bed semi-D or a low-carbon
specification but would include orientation, building type, urban planning,
transport connections etc.

Results
I found in my quick study that the manufacture of blocks for the OPC
concrete block house (Version 1) emitted 6.44 tonnes of CO2, but the
manufacture of the lime-hemp blocks for the Version 2 house sequestered
between 14.2 or 4.7 tonnes of CO2. The latter figures depend on whether one
assigns the CO2 associated with the whole plant or the shiv (its woody core)
only to this construction material (see Appendices 1, 2 & 3 on website
version).
For the sake of argument it is therefore possible, due to the change in block
specification alone, that a 100-unit housing estate of the same 3 bed semi-Ds
could result in 2.06 KTonnes less CO2 in the Atmosphere. This is based on
the following simple calculation: (100 x 6.44T) + (100 x 14.2T) = 2,066T. This
is because the OPC-based emissions were prevented and the lime-hemp
substitute absorbed further atmospheric CO2.
But are these figures significant? Given that www.guardian.co.uk lists the
UK’s annual CO2 emissions as 556.9 Mtonnes, it can be seen that the blocks
of my 100 houses will not change current trends on their own. It would take
the manufacture of building blocks for ~270,000 housing estates to equal the
UK’s national emissions figure! What I think is powerful about lime-hemp as a
material is that the substitution creates (1) an environmental benefit, (2) an
easier form of construction, (3) a higher thermal performance and (4) even
gives local farmers the ability to grow ‘building supplies’ in rotation with food
crops. How many materials can boost equivalent advantages?
Moving Forward
Believe it or not a few materials can! Limetec is also conducting research into
compressing earth blocks on site from the material excavated during the build
process and significant research and test cases are underway elsewhere for
other materials such as cob and earth-hemp composites. Due to the
environmental penalty I believe we need to replace OPC-based concrete in
non-specialist applications as soon as possible. If Limetec’s trials proceed as
planned there will be reliable, commercial and environmental alternatives to
OPC concrete blocks available in the UK within 2 years and hopefully in
production in Ireland shortly after. The alternatives to OPC-based poured
concrete (listed above) are currently available as a niche market but this can
change if designers and clients start specifying them.
I hope this study shows that one can create an environmental design and
lower impact structure from the very first block on site. It is not necessary to
wait till expensive, high performance insulation, sophisticated claddings,
building management systems or energy generating devices are installed to
see an environmental benefit. We can get it right, indeed we need to get it
right, in every phase of the building, housing estate or town’s construction,
right from the first block or pour. While these materials could and should be
integrated into sophisticated low-energy (or low-carbon) buildings, heavy,
simple and dumb also has a lot to offer!