Straw-Bale or Hemplime Construction Which is More Appropriate for an Environmentally Responsive...

GSE MSc Architecture: AEES Essay May 2010: Straw-bale or hemp/lime construction: which is more appropriate for

an environmentally responsive low-density housing development in Suffolk?

GSE MSc Architecture: Advanced Environmental and Energy Studies

Craig Embleton, 0750553, Group 15 (Lucy Cartlidge), C3 (CEM152)

(Environmentally responsive materials; practical examination) Essay

STRAW-BALE OR HEMP/LIME CONSTRUCTION: WHICH IS

MORE APPROPRIATE FOR AN ENVIRONMENTALLY

RESPONSIVE, LOW-DENSITY HOUSING DEVELOPMENT IN

SUFFOLK?

Word Count 2,724

[email protected]

http://www.greenfrontier.org

For the attention of Lucy Cartlidge

June 22nd 2010

Craig Embleton, 0750553, Group 15 (Lucy Cartlidge), C3 Essay [email protected] of 37

mailto:[email protected]

http://www.greenfrontier.org/




Table of Contents

TABLE OF CONTENTS .............................................................................................. 2

INTRODUCTION ........................................................................................................ 3

CRITICAL ANALYSIS ................................................................................................ 4

CONCLUSION .......................................................................................................... 20

GLOSSARY .............................................................................................................. 22

BIBLIOGRAPHY ...................................................................................................... 23

APPENDICES ........................................................................................................... 30





Introduction

This essay relates to several lectures of Module C3, ‘Environmentally responsive

materials’, particularly the ‘Straw-bale Building’ and ‘Hemp/Lime’ lectures.

The Housing and Regeneration Bill (now enacted) ‘Supports the delivery of three

million new homes by 2020’ (UK Parliament, 2008). The construction of this number

of houses could be environmentally devastating as production and transport of

construction materials uses 10% of UK energy consumption (EA, 2003).

However, the bill explicitly states that it ‘provides for the establishment of new

settlements like eco-towns and for simplifying the ways in which the Homes and

Communities Agency would facilitate delivery of these projects’ (UK Parliament,

2008). New settlements must be constructed using environmentally responsive

materials.

Suffolk County Council (SCC) is committed to ‘Creating the Greenest County’. Its

Environmental Action Plan (Appendix 1) for 2009-2010, includes the goal ‘to be an

exemplar in tackling climate change’ and ‘reduce its CO2 emissions by 60% by 2025’.

Theme 1 of the plan ‘Climate Change’ includes the sub-theme ‘Sustainable

Construction and Development’ (SCC, 2009). Using environmentally responsive

building materials will help achieve these ambitions.

This essay will compare hemp/lime to straw-bale construction, particularly embodied

and sequestered CO2, and ascertain which is more suitable for new low-density

dwellings in Suffolk.





Critical AnalysisSuffolkSuffolk is a largely rural East Anglian county of 380,000 hectares (Butterfield et al,

2003). It is one of the driest counties of the UK with ‘Sheltered and very sheltered’

driving rain indices (Nicholls, 2008). This is of benefit when considering straw-bale or

hemp/lime construction and the exposure of the walls to water permeation.

Agriculture

A good climate, good soils and flat low-lying terrain, endow Suffolk with prime arable

land. In 2009, 298,474 hectares of Suffolk were farmed, including 135,416 hectares

of cereals of which 96,105 hectares were wheat (DEFRA, 2009). Suffolk has the

potential to ‘grow-its-own’ building materials.

Housing need

Suffolk’s population density is less than half that of England’s, at 1881 people/km2

offering scope for low-density housing. Suffolk’s housing stock was 322,292 in spring

2009, up 25,519 since 2001. The Regional Spatial Strategy indicates should

complete 36,181 dwellings between spring 2009 and spring 2021 (Chown, 2009), an

average of 3,289 a year.

Building Superstructure

Brick-and-block

The standard low-density construction method used in the UK is brick-and-block.

The external weight-bearing walls consist of a ‘brickwork outer leaf, insulation, dense

solid blockwork inner leaf: cement mortar, plaster, paint’. (Anderson et al, 2009). This

building method is well understood by the building trade and the materials are

relatively cheap and reliable. The environmental responsiveness of the materials are

1 Suffolk has a population of 715,700 people (Audit Commission, 2009) and an area of 380,000 hectares (Butterfield et al, 2003). England has a population of 51,464,600 (ONS Centre for Demography, 2010) and an area of 130,439 sq km (Butterfield et al, 2003)





known (see appendix 2) but not prioritised. Harris and Borer call this ‘Developer’s

vernacular’ (2005).

Figure 1. Developer’s vernacular used in Durrant Road, Hadleigh, Suffolk. Not in

keeping with other buildings in the ancient market town.

Source: Google (2010)Woolley has criticised the weighting placed on the energy-in-use of houses when

considering ‘green’ credentials, arguing that the embodied CO2 of the construction

materials are not prioritised, even by the Passihaus standards (2006). Studies of

brick-and-block houses by Harris (1999), Brinkley (2006) and Asif et al (2007), as

summarised by Embleton show that minimising the use of concrete and plastics in a

house can reduce the embodied energy (2009). See appendix 3.

Straw-bale

Straw-bale building began in Nebraska in the nineteenth century. The bales are

simply stacked like Lego to form walls (Woolley, 2006). There are two basic types of

straw-bale construction: load-bearing and infill. With load-bearing houses, the bales

take the weight of the roof and no other super-structural support is used. With infill,

the bales insulate the frame of the house, which is usually timber (Jones, 2009).

Amazonails promote load-bearing straw-bale building, stating it is fast and easy for

non-professionals to follow (Jones, 2009). However, Snell and Callahan argue in





favour of the infill method stating that the load-bearing method exposes the bales to

damaging rainfall events. They also cite a major advantage being that adapting a

common structural system to straw-bales will allow easier co-operation with the

follow-on trades (2005). There is no timber reduction using the load-bearing method

(Jones, 2008). Woolley suggests infill is more acceptable to the public (2006).

Houses built with straw-bale and lime rendered would resemble Suffolk vernacular.

Figure 2. Shops in Hadleigh, Suffolk built in the vernacular. Rendered in lime.

Source: Author (2008)At 3.5 tonnes of wheat-straw/hectare (BEC, 2008), Suffolk’s 96,105 hectares of

wheat produces 336,368 tonnes/year. Building 3,289 straw-bale houses would

require only 5.5% of the wheat-straw harvest.

Hemp/Lime

Hemp/lime construction uses hemp hurds2 mixed with lime binder to form a kind of

concrete called “hempcrete”. This material was developed in 1990’s France. The

most usual form of Hemp/lime construction involves casting the material around a

2 Hurds or shiv is chopped hemp straw left after the fibre has been extracted.





timber frame with panels of timber stud. This forms a solid wall. External protection is

required; usually lime render (Bevan and Woolley, 2008). Internally, lime or clay

plaster is used. Novice builders can follow this technique.

Hemp

Historically Suffolk had a well-established hemp industry (Fordham, M) and the

county is home to the ongoing revival. Hemp Technology, a hemp processing plant

in Halesworth, Suffolk, has the world’s highest hemp production capacity, capable of

producing 25,000 tonnes of hurds a year (Hemp Technology, 2010).

Hemp yields average 5,500kg/hectare, of which 70% are hurds (3,850 kg). 8,000kg

of hurds are required to build a 2-bed terrace with 400mm walls (Rhydwen, 2010a).

To supply 3,289 properties requires 6,834 hectares of hemp – 5% of the land

currently down to cereals. Duel crops would also yield 1-1.6 tonnes/hectare hemp

seed. Currently Hemp Technology could produce the hurds required for 3125 houses

annually – 95% of Suffolk’s requirement.

Lime

The lime reserve is classified by Berge as ‘Very Large’ (2009). Suffolk, and the East

of England have major deposits of chalk, most of which lie outside National parks or

SSSIs.





Figure 3. Industrial limestone deposits in England, Wales and Northern Ireland,

showing National Parks, Areas of outstanding natural beauty and Industrial limestone

producers. Singleton Birch lime pit in North Lincolnshire and Needham chalk pit in

Suffolk are indicated.

Source: British Geological Survey (2006)Suffolk and neighbouring counties have large lime deposits, and an operational chalk

pit exists at Needham. While lime has lower CO2 emissions than OPC, they are still

fairly high and large-scale opencast mines destroy landscapes. Lime is abundant,

but finite and minimising its use is essential (Rhydwen, 2010b).


Singleton Birch lime pitNorth Lincolnshire

Needham chalk pitSuffolk




Figure 4. Singleton Birch lime pit in Barnetby, North Lincolnshire showing damage to

the landscape caused by mining. Singleton Birch is the UK's largest independent

manufacturer of lime products

Source: Google Earth (2010)

CO2 comparison of hemp/lime and straw-bale houses.Hemp sequesters CO2, but its processing into hurds emits CO2. Lime production

causes CO2 emissions, both through processing and transport and chemically as

CO2 is released during burning. Some will be reabsorbed during curing but not all.

Rhydwen suggests 25 –75% reabsorption (2010b).

One m3 of hempcrete contains 200kg of lime and 100kg of hemp-hurds. A

hempcrete wall requires 20mm (30kg/m2) of render, usually lime, inside and out

(Rhydwen, 2010b).

Straw sequesters CO2, but requires more render than a hempcrete wall due to

absorption into the straw. A straw-bale wall requires the equivalent of 35mm

52.5kg/m2 of render (Atkinson, 2008) inside and out.





CO2 Sequestration

Hemp

Hempcrete walls vary in thickness depending on house design. The Haverhill Hemp

houses’ walls are 400mm (Rhydwen, 2010b). The net values of CO2

sequestration/emissions vary more for hemp than for straw because hemp needs

processing into hurds whereas straw is a by-product of cereal production.

Rhydwen calculates that 1000m3 of hurds weighing 100kg sequester 127–181kg

CO2. Therefore a 400mm thick wall sequesters 50.8–72.4kg CO2/m2 (2010b).

Straw-bale

Atkinson estimated that one 1m*0.475m*0.4m 23kg straw-bale sequesters 31.28kg

CO2. Stacked, a wall sequesters 78.2kg CO2/m2 (2008).

CO2 Emissions

Rhydwen calculates that the net CO2 emissions from the lime in hempcrete are

63kg–162kg/m3. The lime in a 400mm hempcrete wall contains 25.2-64.8kg/m2

embodied CO2.

Lime plaster applied to one side of a hempcrete wall contains 9.5-24kg/m2

embodied CO2. Applied to one side of a straw-bale wall, it contains 16.6-42kg/m2

embodied CO2.

CO2 Sequestration minus Emissions for 1 m2 wall.

This section will attempt to ascertain whether straw-bale or hempcrete walls have a

better CO2 balance per m2.

Initially a 400mm hempcrete wall will be considered alongside a standard-width

straw-bale wall (475mm). The walls can either be plastered externally with lime (and

internally with clay) or externally and internally with lime.

This section will examine each end of the range of figures for embodied and

sequestered CO2 in the lime and hemp of a hempcrete wall. Only one value for the





CO2 sequestered in the straw of a straw-bale wall will be used, but two (high and low)

for the emissions associated with the lime plaster.

Where the application of lime plaster is to just the outer fabric of the walls, the inner

fabric is plastered with clay and is assumed to have zero emissions.

Table 1. Range of values for Embodied CO2, Sequestered CO2 and CO2 balance for

straw-bale and hempcrete walls (negative values indicate net sequestration).Embodied (E)

CO2 (Kg)

Sequestered

(S) CO2 (Kg)

Net CO2 emissions

Low E CO2 - S CO2 (Kg)

High E CO2 - S CO2 (Kg)Straw-bale

plastered one side

with 35mm lime

plastered.

16.6

to

42

78.2 -61.6

to

-36.2

Straw-bale

plastered both sides

with 35mm lime

plastered.

33.2

to

84

78.2 -45

to

5.8

Embodied (E)

CO2 (Kg)

Sequestered

(S) CO2 (Kg)

Net CO2 emissions

Low E CO2 - Low S CO2 (Kg)

Low E CO2 - High S CO2 (Kg)

High E CO2 - Low S CO2 (Kg)

High E CO2 - High S CO2 (Kg)400mm Hempcrete

wall plastered on

one side with 20mm

lime (hempcrete +

plaster)

34.7 (25.2+9.5)

to

88.8 (64.8+24)

50.8

to

72.4

-16.1 (34.7 - 50.8)

-37.7 (34.7 - 72.4)

38 (88.8 - 50.8)

16.4 (88.8 - 72.4)

400mm Hempcrete

wall plastered on

both sides with

20mm lime

(hempcrete +

plaster)

44.2 (25.2+19)

to

112.8 (64.8+48)

50.8

to

72.4

-6.6 (44.2 - 50.8)

-28.2 (44.2 - 72.4)

62 (112.8 - 50.8)

40.4 (112.8 - 72.4)

Table 1 shows that when comparing like-for-like values for embodied CO2 within the

lime, straw-bale walls sequester more net CO2 than all hempcrete wall scenarios,

and whether the straw-bale walls are plastered on one side or both with lime. E.g.





the best value for straw-bale walls plastered on one side was -61.6kg/m2 compared

to –37.7kg/m2 for hempcrete.

In order to ascertain whether a hempcrete wall would ever sequester more CO2 than

a straw-bale wall, a range of different thicknesses of hempcrete wall were

investigated. (The width of the straw-bale wall is fixed). The results are presented in

graphical format. Figure 5 compares walls plastered on one side with lime plaster

and figure 6 showing wall plastered on both sides with lime plaster. (See appendices

4 and 5 for data).





Figure 5. CO2 balance in hempcrete walls (plastered on one side with lime plaster) of

different thicknesses using high and low values for CO2 emissions for lime and high

and low values for CO2 sequestration in hemp. Negative values indicate

sequestration. Sequestration within a straw-bale wall of standard fixed width is also

shown with high and low values for CO2 emissions for lime.

24 22.1 20.2 18.3 16.4 14.5 12.6

2427.5

3134.5

3841.5

45

9.5

-2.3

-14.1

-25.9

-37.7

-49.5

-61.3

9.53.1

-3.3-9.7

-16.1-22.5

-28.9

-36.2

-61.575

y = -118x + 9.5

y = -64x + 9.5

y = -19x + 24

y = 35x + 24

-80

-60

-40

-20

0

20

40

60

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Thickness hempcrete walls m

Kg C

O2

High Embodied CO2 & High Sequestered CO2High Embodied CO2 & Low Sequestered CO2Low Embodied CO2 & High Sequestered CO2Low Embodied CO2 & Low Sequestered CO2Straw High Embodied CO2 Lime PlasterStraw Low Embodied CO2 Lime Plaster

Source: Author’s calculation based on Rhydwen ‘s hemp/lime data (2010b) and

Atkinson’s straw data (2008)

Figure 6. CO2 balance in hempcrete walls (plastered on both sides with lime plaster)

of different thicknesses using high and low values for CO2 emissions for lime and

high and low values for CO2 sequestration in hemp. Negative values indicate

sequestration. Sequestration within a straw-bale wall of standard fixed width is also

shown with high and low values for CO2 emissions for lime.





48 46.1 44.2 42.3 40.4 38.5 36.6

4851.5

5558.5

6265.5

69

19

7.2

-4.6

-16.4

-28.2

-40

-51.8

1912.6

6.2-0.2

-6.6-13

-19.4

5.8

-44.95

y = -118x + 19

y = -64x + 19

y = -19x + 48

y = 35x + 48

-60

-40

-20

0

20

40

60

80

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Thickness hempcrete walls m

Kg

CO

2

High Embodied CO2 & High Sequestered CO2High Embodied CO2 & Low Sequestered CO2Low Embodied CO2 & High Sequestered CO2Low Embodied CO2 & Low Sequestered CO2Straw High Embodied CO2 Lime PlasterStraw Low Embodied CO2 Lime Plaster

Source: Author’s calculation based on Rhydwen ‘s hemp/lime data (2010b) and

Atkinson’s straw data (2008)





Figures 5 and 6 show that only the scenarios where the lowest figure for embodied

CO2 in the lime plaster and the highest value of CO2 sequestration in the hemp are

used does the net CO2 sequestration near that of a straw-bale wall. This is true

whether plastered on one side or both sides with lime.

The formulae for straight line graphs obtained in figure 5 and figure 6 were used to

calculate exact thicknesses of hempcrete walls required to match straw-bale walls for

each of the four scenarios. Results are shown in table 2. See appendix 6 for data.

Table 2. Thickness of a hempcrete wall plastered required to sequester the same amount

of as a straw-bale wall.High Embodied

CO2 & High

Sequestered CO2

High Embodied

CO2 & Low

Sequestered CO2

Low Embodied

CO2 & Low

Sequestered

CO2

Low Embodied

CO2 & High

Sequestered CO2

Plastered outside with 20mm lime and inside with 20mm clayEquation y = -19x + 24 y = 35x + 24 y = -64x + 9.5 y = -118x + 9.5

Width in metres 3.17 -1.72

(unobtainable)

1.11 0.62

Including 40mm

plaster

3.21 -1.68

(unobtainable)

1.15 0.66

Plastered inside and outside with 20mm limeEquation y = -19x + 48 y = 35x + 48 y = -64x + 19 y= -118x + 19Width in metres 2.22 -1.21

(unobtainable)

1 0.54

Including 40mm

plaster

2.26 -1.17

(unobtainable)

1.04 0.58

It can be seen that after the addition the 20mm of lime plaster externally and 20mm

of clay plaster internally a hempcrete wall of 660mm would match a straw-bale wall

of 525mm. However this would rely on best-case scenario for emissions and

sequestration of CO2 in hempcrete. If the wall were plastered with lime on both sides

it would require a thickness of 580mm before it sequestered as much CO2 as a

straw-bale wall. A hempcrete wall with high embodied and low sequestered is a net

emitter of CO2. The other scenarios are over a metre wide.





Clearly a straw-bale wall sequesters more CO2 than a hempcrete one and minimises

the environmental damage caused by lime extraction, particularly if plastered

internally with clay. But what about other considerations?

Structural performance

The timber frame is the structural element in a hemp/lime wall. The hemp/lime forms

a no-cavity wall around the frame. Although the hemp/lime does provide support the

house does not rely on this (Thompson, 2010). Load-bearing straw-bale walls can

withstand loads of 48,826kg/m2. When used as infill, the weight is borne by the

timber frame (Jones, 2010). Structural performance does not differ for timber-framed

houses, whether non-load-bearing straw-baled, hemp/lime or brick-and-block.

Performance in use

Energy in use

Thermal performance: U-values, thermal mass

Building regulations require new external walls to have a U-value of 0.35 or less.

450mm wide straw-bales have a U-value between 0.13 and 0.20. W/m2K (Jones,

2009). However Andersen discovered that the U-value on sections of plastered

straw-bale wall was poor in comparison to thermal transmittance through a single

straw-bale, due to air penetration and natural convection flows. This was attributed to

poor construction (in Wihan, 2007). Atkinson’s estimated her lime-plaster/straw-

bale/clay-plaster wall to have a U-value of 0.13W/m2K (2008).

The U-value of Adnams brewery thick hempcrete brick walls are 0.18 W/m2K. Lime

Technology Ltd’s headquarter building has a calculated U value of 0.14W/m2K. The

walling is 500 mm thick Tradical® Hemcrete (Bevan and Woolley, 2008). However

the Haverhill houses did not perform as well as the conventional houses although

heating bills were the same (Rhydwen, 2010b).

Indoor air quality

Hemp/lime walls are breathable. They can absorb moisture, reduce humidity and

improve the air quality of buildings. Building can be airtight, so ventilation must be





considered (Bevan and Woolley, 2008), as with straw-bale buildings which are also

airtight (Jones, 2009). Air quality is greatly influenced by the finishes used. Lime or

clay internal plasters will reduce volatile organic compounds.

Acoustics

The Haverhill hemp homes ‘did not perform as well as the traditional (brick-and-

block) houses’ in terms of soundproofing (Rhydwen, 2010b). Jones claims that

Amazonails has ‘overwhelming experiential evidence that straw walls offer far more

sound insulation than 20th Century wall building techniques’ (2009). (Source material

not checked).

Economics and ethical considerations

The sale of straw for construction gives cereal farmers an extra income. Hemp hurds

production can be coupled with hemp seed and fibre, giving farmers three products

per crop.

Hemp/lime construction is currently more expensive than standard construction, but

this due to the current lack of skills in the building trade (Rhydwen, 2010b).

Straw-bale construction is less expensive than standard construction in terms of

materials, though labour needs vary. Both techniques are more accessible to self-

builders than brick-and-block construction.

Both hemp and straw are sustainable, renewable products that can be harvested

year after year and sequester CO2 in the process.





Comparing hemp/lime to straw-baleTable 3. Summary of the properties and merits of hemp/lime and straw-bale.

Embodied energy and U-value criteria also include lime plaster. Other criteria do not.

Environmentally

responsive criteria

Hemp/lime Straw Bale

Embodied Energy

Total content.

Negative value

indicated

sequestration

-37.7 to 38 kg CO2/m2 for 400mm

hempcrete wall externally plastered

with lime.

-61.6 to -36.2 kg CO2/m2 for

standard straw-bale wall

externally plastered with

limeExtraction Low for hemp is an annual crop.

High for lime as it must be mined.

Nil. Straw is a by-product of

grain production and energy

is already accounted for.Processing /

Manufacture

Low. Hurds must be extracted and

chopped, but done locally.

High for lime burning, but less than

cement.

None – already baled

during grain harvest so

energy is already accounted

for.Transportation Low. To and from Halesworth from

the rest of Suffolk. Lime can be

produced locally, but is often

trucked in from Lincolnshire.

Small. Already grown and

baled locally. May be

transport minor distances.

Environmental

legacySustainable

production

Hemp can be grown organically as

a break crop. Lime is very

abundant but not finite.

Sustainable if organic.

Whilst cereals are grown for

grain, straw is available as

a by-product.Deforestation Grown as a break crop, hemp

requires no additional land to be

cleared of trees.

Opencast lime mining strips the

land of vegetation including trees.

None. Land already farmed.

Toxic waste None with hemp.

Mining can cause heavy metal

pollution.

None with straw.

Pollution Some CO2 emissions- see

embodied energy.

Various water and land pollution

None. Pollution from

farming accounted for in

cereal production.





Environmentally

responsive criteria

Hemp/lime Straw Bale

problems due to lime mining.Health issues None if used correctly. None if used correctly.Waste None with hemp. Lime mining

causes spoil.

None.

End of life

(recyclability,

reusability,

disposability)

Hemp/lime can be broken up and

burnt to produce lime. Pozzolans

may cause issues.

Composts.

Performance in

useEnergy in use Variable results. Better and worse

than brick-and-block.

Good due to insulation.

Better than brick-and-blockIndoor air quality Excellent if correct finishes applied. Excellent if correct finishes

applied.Structural

performance

Same as a timber-framed brick-

and-block.

Non-load-bearing same as

a timber-framed brick-and-

block. Load-bearing walls

up to 48,826kg/m2.Thermal

performance: U-

values, thermal

mass

Thermal performance variable.

U-value 0.14-0.18W/m2K.

(Including plaster.)

Medium thermal mass.

Thermal performance good

when properly constructed.

U-value 0.13-0.20W/m2K.

(Including plaster.)

Low thermal mass.Acoustics Poorer than brick-and-block Better than brick-and-block

(source material not

checked).Availability of the

material

Hemp renewable

Lime abundant.

Straw renewable.

Ease of construction

(Labour intensive)

Non-specialist. No more labour

intensive than brick-and-block.

Non-specialist. Labour

intensive. Best with a group

of people.Length of

constructi

on

Initially longer than brick-and-block

for skilled craftsmen. Potential to

be quicker.

Quick with a group of

people and suits that

method.Economics and

ethical

considerations

Hemp production is a good

revenue stream for farmers and

sequesters CO2. Lime production is

less damaging than concrete.

Empowers self-builders.

Excellent second source of

income for cereal farmers

and sequesters. CO2.

Empowers self-builders.





ConclusionSummary of the case madeStraw is abundant in Suffolk and the county could grow enough hemp to supply its

housing requirements. Facilities exist in Suffolk to process 95% of the hurds required

to supply the entire housing need of the county. Suffolk’s climate is suitable for both

straw-bale and hemp/lime buildings, externally rendered with lime plaster.

Both building methods would bring local economic benefits, are suitable for amateurs

and professionals alike and produce structurally sound buildings. Both types of

building have similar air quality properties, but straw-bale buildings may have better

soundproofing and thermal performance than hemp/lime, and brick-and-block, but

results are inconclusive.

Minimising lime use minimises the environmental destruction caused by mining, and

the associated CO2 emissions. Straw-bale buildings used less lime than hemp/lime

buildings and usually sequester more CO2. Only the best-case scenario for a

hemp/lime building with very thick walls could match the net CO2 sequestration of a

straw-bale building.

Considering all factors, straw-bale building is more appropriate than hemp/lime for

the construction of low-density dwellings in Suffolk.

Existing OrthodoxyBrick-and-block is the default housing type in the UK. These materials have high-

embodied energy. However, sustainable building practice tends to focus on the

energy-in-use of new builds, assuming that this is the most important source of

GHGs. Low embodied-energy straw-bale and hemp/lime houses are unorthodox and

considered niche buildings suitable for self-building ‘environmentalists’.

This essay challenges these assumptions and focuses on the embodied CO2 of

environmental responsive building materials. It investigated whether the

superstructure of straw-bale and hemp/lime buildings could be CO2 sinks by

calculating how much CO2 each technique could sequester. The essay also





challenges the assumption that building materials must be mined and manufactured

by specialists remotely by showing that Suffolk could grow and process building

materials for its own needs.

Limitations of the essayThe essay was limited to comparing the properties of plastered straw-bale and

hemp/lime external walls for low-density housing. It did not investigate high-rise

dwellings, the use of the materials for constructing internal or party walls, or their use

for other purposes such as flooring or loft insulation.

Although the essay looked at a range of estimates for embodied and sequestered

CO2, it did not examine a continuum of values, or consider other GHGs associated

with cultivation, such as NO2. When clay plaster was considered it was assumed to

have no associated CO2 emissions, which may not be valid.

The essay concentrated heavily on the embodied/sequestered CO2/m2 within the

walls. It touched upon, but did not focus on other properties such as structural

performance or performance in use.

Further researchAn evaluation of the embodied/sequestered CO2 should be made for an entire

hemp/lime and straw-bale house of the same building style and floor space, rather

than for the external walls. Each section of the house, such as ‘Separating floors’

should be evaluated using a rating system such as the Green guide to specification.

Where the Green guide lacks information, such as the properties of hempcrete,

other sources should be consulted. Ideally primary data should be obtained,

particularly for the embodied CO2 of hemp, lime and straw, based on the location and

production of the materials. The straw-bale and hemp/lime house should also be

compared to conventional brick-and-block, and timber-framed houses.

A full LCA should be performed for each building type and energy-in-use should be

monitored as a long-term study comparing predicted and actual values.





Glossary

BEC – Biomass Energy Centre

BERR – Department for Business, Enterprise & Regulatory Reform

BIS – Department for Business Innovation & Skills

BRE – Building Research Establishment

BREEAM – Building Research Establishment Environmental Assessment Method

CO2e – Carbon Dioxide equivalent.

DECC – Department of Energy and Climate Change

DEFRA – Department for Environment, Food and Rural Affairs

EA – Environment Agency

EU – European Union

GHGs – Greenhouse gases

LCA – Life Cycle Analysis

OPC – Ordinary Portland Cement

OPDM – Office of the Deputy Prime Minister

SCC – Suffolk County Council

SSSI – Site of Special Scientific Interest

UK – United Kingdom of Great Britain and Northern Ireland





Bibliography

Anderson, J, Shiers, D and Steele, K (2009). The green guide to specification. 4th

ed. Bracknell: IHS BRE Press.

Atkinson, C. (2008). Energy Assessment of a Straw-bale Building. Unpublished

MSc thesis. University of East London

Embleton, C. (2009). Could new build houses in the UK be carbon negative in

terms of embodied energy? Unpublished MSc essay. University of East London

Audit Commission, (2009). Suffolk area assessment. Oneplace

Berge, B. The Ecology of Building Materials. 2nd ed. Translated from Norwegian by

Butters, C. and Henley F. (2009). Oxford. Architectural Press.

BERR. (2008). Strategy for Sustainable Construction. London: HM Government

Department for Business, Enterprise & Regulatory Reform (8731/2k/6/08/NP)

Bevan, R. and Woolley T. (2008). Hemp lime construction: A guide to building

with hemp lime composites. Bracknell: IHS BRE Press.

Biomass Energy Centre. (2008). Quantities of straw grown in the UK. [Online].

Available at: http://www.biomassenergycentre.org.uk/portal/page?

_pageid=75,17972&_dad=portal&_schema=PORTAL. (Accessed 29 May 2010).

Brinkley, M (2006). The Housebuilder's Bible. Huntingdon: Ovolo.



http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17972&_dad=portal&_schema=PORTAL

http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17972&_dad=portal&_schema=PORTAL



British Geological Survey. (2006) Limestone: Mineral Planning Factsheet. London:

Office of the Deputy Prime Minister

Butterfield, J., Summers, E., Holmes, A., Daintith, J., Isaacs, A. Law, J. and Martin,

E. (eds.) (2003) Collins English Dictionary. 6th ed. Glasgow: HarperCollins

Chown, J. (2009) Housing stock for Suffolk’s districts and parishes. Research

and Intelligence team Planning and Performance Improvement. Suffolk County

Council.

DEFRA (2009) June Survey of Agriculture and Horticulture: Land Use and

Livestock on Agricultural Holdings. London: Department for Environment, Food

and Rural Affairs

Environment Agency. (2003). Sustainable Construction: Position Statement.

Available: http://www.environment-

agency.gov.uk/research/library/position/41239.aspx. Last accessed 28 May 2010.

Forestry Commission (2002) National Inventory of Woodland and Trees England.

County Report for Suffolk: Forestry Commission. Edinburgh

Forestry Commission. (2010). Sitka spruce - picea sitchensis. [Online]. Available

at: http://www.forestry.gov.uk/forestry/infd-5nlej6. (Accessed 6 June 2010).

Google Earth (2010). Singleton Birch lime pit. Available at: 53° 35’ 48.48’’ N 0° 23’

6.72’’ W. [Accessed 7 June 2010].





Google Maps (2010). Durrant Road (Google maps streetview). [Online image].

Available at: (Accessed 30 May 2010).

Hafan Homes. (2010). Why construct in timber frame?. [Online]. Available at:

http://www.hafanhomes.co.uk/why-timberframe.php. (Accessed 2 June 2010).

Harris, C and Borer, P (2005). The Whole House Book. 2nd ed. Machynlleth:

Centre for Alternative Technology.

Harris, R. (2010). Is Timber a Sustainable Building Material? C3 [Lecture notes

notes]. Environmentally responsive materials; practical examination. MSc

Architecture: Advanced Environmental and Energy Studies Graduate School of the

Environment, University of East London, Centre for Alternative Technology,

Restaurant extension. 12 May 2010.

Hemp Technology. (2010). Hemp Technology history. [Online]. Available at :

http://www.hemcore.co.uk/history.htm. (Accessed 4 June 2010).

Holmes, S. (2009). Building Limes and Cements. C3 [Lecture notes notes].

Environmentally responsive materials; practical examination. MSc Architecture:

Advanced Environmental and Energy Studies Graduate School of the Environment,

University of East London, Centre for Alternative Technology, Restaurant extension.

15 May 2010.

Jones, B (2008). Building with straw-bales: A practical guide for the UK and

Ireland. 2nd ed. Totnes: Green Books Ltd.





Jones, B. (2009). Straw-bale Building. C3 [Lecture notes notes]. Environmentally

responsive materials; practical examination. MSc Architecture: Advanced

Environmental and Energy Studies Graduate School of the Environment, University

of East London, Centre for Alternative Technology, Restaurant extension. 13 May

2010.

Lawley, L. and Kearney, J. (2010). Natural materials for mortars, renders and

plasters. C3 [Practical notes]. Environmentally responsive materials; practical

examination. MSc Architecture: Advanced Environmental and Energy Studies

Graduate School of the Environment, University of East London, Centre for

Alternative Technology, Behind Builders Barn. 14th May 2010.

Met Office. (2008a). Wattisham 1971–2000 averages. [Online]. Available at:

http://www.metoffice.gov.uk/climate/uk/averages/19712000/sites/wattisham.html.

(Accessed 29 May 2010).

Met Office. (2008b). Lowestoft 1971–2000 averages. [Online]. Available at:

http://www.metoffice.gov.uk/climate/uk/averages/19712000/sites/lowestoft.html.


Met Office. (2008c). England 1971–2000 averages. [Online]. Available at:

http://www.metoffice.gov.uk/climate/uk/averages/19712000/areal/england.html.


Met Office. (2008d). UK 1971–2000 averages. [Online]. Available at:

http://www.metoffice.gov.uk/climate/uk/averages/19712000/areal/uk.html. (Accessed

29 May 2010).





Met Office (2008e). UK mapped climate averages. Rainfall amount annual

average 1971 – 2000. [Online image]. Available at:

http://www.metoffice.gov.uk/climate/uk/averages/7100_1km/Rainfall_Average_1971-

2000_17.gif (Accessed 29 May 2010).

Modcell. (2010b). A Carbon Bank. [Online]. Available at:

http://www.modcell.co.uk/page/balehaus/a-carbon-bank. Accessed 8 June 2010.

Modcell. (2010a). Modcell helping you build a more sustainable future. [Online].

Available at: http://www.modcell.co.uk/page/faqs. Accessed 4 June 2010.

Nicholls, R. (2008). The Green Building Bible Volume 2. 4th ed. Llandysul: Green

Building Press.

Thompson, H.O’D. (2010). Hemp/Lime (2) – Building with hemp-lime/hempcrete

– Practical aspects and specification details. C3 [Lecture notes notes].

Environmentally responsive materials; practical examination. MSc Architecture:

Advanced Environmental and Energy Studies Graduate School of the Environment,

University of East London, Centre for Alternative Technology, Restaurant extension.

13 May 2010.

ONS Centre for Demography (2010) Population estimates for UK, England and

Wales, Scotland and Northern Ireland - current datasets. Fareham: Office for

National Statistics

Ordnance Survey (2010). GB Coastline and administrative boundaries. [Online

image]. Available at:



http://www.metoffice.gov.uk/climate/uk/averages/7100_1km/Rainfall_Average_1971-2000_17.gif

http://www.metoffice.gov.uk/climate/uk/averages/7100_1km/Rainfall_Average_1971-2000_17.gif



http://www.ordnancesurvey.co.uk/oswebsite/images/userImages/misc/outlinemaps/o

utlineb.gif (Accessed 29 May 2010).

Rhydwen, R. (2010a). Hemp/Lime (1a) – History & Background to Hemp

(Cannabis Sativa. L.). C3 [Lecture notes notes]. Environmentally responsive

materials; practical examination. MSc Architecture: Advanced Environmental and

Energy Studies Graduate School of the Environment, University of East London,

Centre for Alternative Technology, Restaurant extension. 13 May 2010.

Rhydwen, R. (2010b). Hemp/Lime (1b) – Building with Hemp and Binder. C3

[Lecture notes notes]. Environmentally responsive materials; practical examination.

MSc Architecture: Advanced Environmental and Energy Studies Graduate School of

the Environment, University of East London, Centre for Alternative Technology,


SCC (2006). Green Procurement Guide. Ipswich: Suffolk County Council.

Snell, C. and Callahan, T. (2005). Building Green: A complete how-to guide to

alternative building methods: Earth plaster, straw-bale, cordwood, cob, living

roofs. New York: Lark Books.

United Kingdom Parliament. (2008). Housing and Regeneration Bill. Available:

http://services.parliament.uk/bills/2007-08/housingandregeneration.html. Last

accessed 28 May 2010.

Wihan, J. (2007). Humidity in straw-bale walls and its effect on the

decomposition of straw. Unpublished MSc thesis. University of East London



http://www.ordnancesurvey.co.uk/oswebsite/images/userImages/misc/outlinemaps/outlineb.gif

http://www.ordnancesurvey.co.uk/oswebsite/images/userImages/misc/outlinemaps/outlineb.gif



Woolley, T (2006). Natural Building: A Guide to Materials and Techniques.

Marlborough: The Crowood Press.

Woolley, T. (2009). Sustainable Construction Materials: An introduction to the

concept and analysis of their uptake in practice in the UK. C3 [Lecture notes

notes]. Environmentally responsive materials; practical examination. MSc

Architecture: Advanced Environmental and Energy Studies Graduate School of the

Environment, University of East London, Centre for Alternative Technology,


Word Count – 2,724





AppendicesAppendix 1. SCC Environment Action Plan 2009-2011 Theme 1.D Sustainable

Construction and DevelopmentObjective Action Timescale Responsibility Local Area

Agreement Target

or National

IndicatorD1. Improve the

environmental attributes

of buildings in Suffolk

and through this reduce

carbon emissions.

Lead a sustainable

construction working

group in Suffolk to look

at key plans, policies

and methodologies

including local

development

frameworks and the

Suffolk Design Guide

for sustainable

construction.

Ongoing Environment

and Transport

(Sustainable

Environment/

Sustainable

Development)/R

esource

Management

(Corporate

Property

Services)

Reduce the

amount of CO2

emissions for each

person in Suffolk

NI186.

Make sure

adequate plans are

in place so that

Suffolk can adapt

and respond to the

issue of climate

change NI188D2. In disposing of

property consideration

will be given to

promoting the highest

environmental

standards.

Continue to work with

partners and

developers involved in

the Chilton Woods

development to

discuss how this

development can

contribute to creating

the objectives of

Creating the Greenest

County.

Ongoing Resource

Management

(Corporate

Property

Services)

Reduce the amount

of CO2 emissions

for each person in

Suffolk NI186

Make sure

adequate plans are

in place so that

Suffolk can adapt

and respond to the

issue of climate

change NI188D3. Establish a culture

of environmental/

sustainable excellence

in the built environment.

BREEAM policy:

Where the council has

influence over a design

and build project it will

expect a standard of

BREEAM ‘excellent’.

Where this is not

Implement the

council’s BREEAM

policy by:

maintaining a website

resource for staff to

increase awareness of

the council’s BREEAM

policy, what BREEAM

is and how it can be

implemented;

implement the

End 2009

for strategy.

Action Plan

by 2010/11

Resource

Management

(Corporate

Property

Services)

Reduction in the

county council’s

CO2 emissions

NI185

Reduce the amount

of CO2 emissions

for each person in

Suffolk NI186

Make sure

adequate plans are

in place so that





Appendix 1. SCC Environment Action Plan 2009-2011 Theme 1.D Sustainable Construction and Development

Objective Action Timescale Responsibility Local Area

Agreement Target

or National

Indicatorpossible (in

circumstances agreed

by the Environmental

Panel) the council

expects a minimum

environmental standard

of BREEAM ‘very good’

(or equivalent) to be met

and will aim for

‘excellent’ in particular

aspects of BREEAM e.g.

energy or biodiversity.

council’s BREEAM

policy assessment

system for all

qualifying building

schemes. To be

overseen by the

Environment Panel;

develop energy, water

and environmental

minimum standards for

new builds.

Deliver the Property

Strategy for Fire

Stations which

includes environmental

criteria and then

develop an action plan

to implement the

Property Strategy for

Fire Stations.

Suffolk can adapt

and respond to the

issue of climate

change NI188

Working age

people with access

to employment by

public transport

(and other specified

modes)NI176

D4. Ensure that

sustainability is a key

element in the Building

Schools for the Future

programme.

Undertake the

procurement for wave

6 of Building Schools

for the Future with the

intention of ensuring

60% carbon reduction

on 2002 equivalent

builds.

Aim to include 1

carbon neutral school

in wave 6 of Building

Schools for the Future.

Commence

s in 2011.

Children and

Young People

(Building

Schools for the

Future

programme)

Reduction in the

county council’s

CO2 emissions

NI185

Reduce the amount

of CO2 emissions

for each person in

Suffolk NI186

Make sure

adequate plans are

in place so that

Suffolk can adapt

and respond to the

issue of climate

change NI188





Appendix 1. SCC Environment Action Plan 2009-2011 Theme 1.D Sustainable Construction and Development

Objective Action Timescale Responsibility Local Area

Agreement Target

or National

IndicatorChildren traveling to

school – mode of

travel usually used

NI198D5. Seek to minimise

the environmental

impacts of

developments that affect

Suffolk’s communities.

Continue to lobby

against the proposal

for a second runway at

Stansted Airport.

Minimise the

environmental impact

of any future nuclear

power station

development at

Sizewell whilst

maximising community

benefit.

Manage pressures

arising from the

Regional Spatial

Strategy’s growth

proposals in a way

which minimises

environmental impact

and delivers the most

sustainable outcome

for Suffolk.

Ongoing. Environment

and Transport

(Sustainable

Development)

Reduce the amount

of CO2 emissions

for each person in

Suffolk NI186

Make sure

adequate plans are

in place so that

Suffolk can adapt

and respond to the

issue of climate

change NI188

Source: Suffolk County Council, 2009





Appendix 2 – Green guide to specification rating system example

'External Walls' - 'Brick or stone and blockwork' cavity walls – ‘Brickwork outer

leaf, insulation, aircrete blockwork inner leaf’

Brick or stone and blockwork cavity walls:

All building types

Summ

ary Rating

Clim

ate change

Water extraction

Mineral resource extraction

Stratospheric ozone depletion

Hum

an toxicity

Ecotoxicity to freshwater

Nuclear w

aste (higher level)

Ecotoxicity of land

Waste disposal

Fossil fuel depletion

Eutrophication

Photochemical ozone creation

Acidification

Typical replacement interval

Embodied C

O2 (kg C

O2 eq.)

Recycled content (kg)

Recycled content (%

)

Recycled currently at End of Life (%

)

Brickwork outer leaf, insulation, aircrete blockwork inner leaf:

Cement mortar, plaster, paint

A+ A A+ A+ A A+ A+ A+ A+ A+ A+ A+ A+ A+ 60+ 73 0.6 0 83

Cement mortar, plasterboard on battens, paint

A+ A A+ A+ A A+ A+ A+ A+ A+ A+ A+ A+ A 60+ 74 3.5 2 86

Cement: lime mortar, plaster, paint

A+ A A+ A+ A A+ A+ A+ A+ A+ A+ A+ A+ A+ 60+ 72 0.6 0 83

Cement: lime mortar, plasterboard on battens, paint

A+ A A+ A+ A A+ A+ A+ A+ A+ A+ A+ A+ A 60+ 74 3.5 2 86

Anderson et al (2009).





Appendix 3 – Summary of studies into embodied energy of UK houses

Ten most energy intensive materials in each study.

Study: Harris, D.J.

(1999)

Study: Brinkley,

M. (2006)

Study: Asif, M. et

al. (2007)Build type Brick-and-block with

aluminium window

frames.

Detached brick-

and-block house

Scottish three

bedroom semi-

detachedMaterial EE

(kWh)

% Total

EE

EE

(kWh)

% Total

EE

EE

(kWh)

% Total

EEConcrete 13,800 15.2 36,336 61.5Concrete tiles 1,800 2.0

Concrete external

works

800 0.8

Plastics 47,000 44.9 11,300 12.4Bricks 6,348 6.1 27,100 29.8Ceramic tiles 8,956 15.2Timber 24,882 23.8 8,334 14.1

Steel 10,300 9.8 6,500 7.2Cement 8,580 8.2 6,000 6.6Mineral wool 2,433 2.3Clay tiles (roof) 2,052 2.0Aluminium 1,088 1.0 1,631 2.8Lightweight blocks 5,200 5.7Goods transport 5,000 5.5Plasterboard 3,200 3.5 1,500 2.5Glass 828 0.8 2,700 3.0 1,133 1.9Mortar 667 1.1Damp course 525 0.9

Slate 12 0.0Total 104,727 90,800 59,093Source: Harris (1999), Brinkley (2006) and Asif et al. (2007) in Embleton (2009)

Appendix 4 –CO2 emissions / sequestration of hempcrete wall of various thicknesses plastered on one side with lime. Negative values indicate net CO2 sequestration. Straw-bale wall values shown for comparison.

Hempcrete

thickness (m)

High Embodied

CO2 & High

Sequestered

CO2

High Embodied

CO2 & Low

Sequestered

CO2

Low Embodied

CO2 & High

Sequestered

CO2

Low Embodied

CO2 & Low

Sequestered

CO20.0 24 24 9.5 9.5





0.1 22.1 27.5 -2.3 3.10.2 20.2 31 -14.1 -3.30.3 18.3 34.5 -25.9 -9.70.4 16.4 38 -37.7 -16.10.5 14.5 41.5 -49.5 -22.50.6 12.6 45 -61.3 -28.9

Straw-bale -36.2 -36.2 -61.575 -61.575

Appendix 5 – CO2 emissions / sequestration of hempcrete wall of various thicknesses plastered on both sides with lime. Negative values indicate net CO2 sequestration. Straw-bale wall values shown for comparison.

High Embodied

CO2 & High

Sequestered

CO2

High Embodied

CO2 & Low

Sequestered

CO2

Low Embodied

CO2 & High

Sequestered

CO2

Low Embodied

CO2 & Low

Sequestered

CO20.0 48 48 19 190.1 46.1 51.5 7.2 12.60.2 44.2 55 -4.6 6.20.3 42.3 58.5 -16.4 -0.20.4 40.4 62 -28.2 -6.60.5 38.5 65.5 -40 -130.6 36.6 69 -51.8 -19.4

Straw 5.8 5.8 -44.95 -44.95

Appendix 6 – Thickness of hempcrete wall required to match sequestered carbon of straw-bale-walled house (20mm of lime plaster not added to thickness).

Hempcrete plastered on one side with lime plaster.

High embodied CO2 and low sequestered CO2.

y = 35x + 24

-36.2 = 35x + 24

-36.2 - 24 = -35x

-60.2 = 35x

-60.2/35 = x

-1.72 = x

High embodied CO2 and high sequestered CO2.

y = -19x + 24

-36.2 = -19x + 24





-36.2 - 24 = -19x

-60.2 = -19x

-60.2/-19 = x

3.17 = x

Low embodied CO2 and low sequestered CO2.

y = -64x + 9.5

-61.575 = -64x + 9.5

-61.575- 9.5 = -64x

-71.075 = -64x

-71.075/-64 = x

1.11 = x

Low embodied CO2 and high sequestered CO2.

y = -118x + 9.5

-61.575 = -118x + 9.5

-61.575- 9.5 = -118x

-71.075 = -118x

-71.075/-118 = x

0.60 = x

Hempcrete plastered on both sides with lime plaster.

High embodied CO2 and low sequestered CO2.

y = 35x + 48

5.8 = 35x + 48

5.8 - 48 = 35x

-42.2 = 35x

-42.2/35 = x

-1.21 = x

High embodied CO2 and high sequestered CO2.

y = -19x + 48





5.8 = -19x + 48

5.8 - 48 = -19x

-42.2 = -19x

-42.2/-19 = x

2.22 = x

Low embodied CO2 and low sequestered CO2.

y = -64x + 19

-44.95 = -64x + 19

-44.95 – 19 = -64x

-63.95 = -64x

-63.95/-64 = x

1.0 =x

Low embodied CO2 and high sequestered CO2.

y = -118x + 19

-44.95 = -118x + 19

-44.95 – 19 = -118x + 19

-63.95 = -118x

-63.95/-118 = x

0.54 = x



Straw-Bale or Hemplime Construction Which is More Appropriate for an Environmentally Responsive...

Documents

Transcript of Straw-Bale or Hemplime Construction Which is More Appropriate for an Environmentally Responsive...