Straw-Bale or Hemplime Construction Which is More Appropriate for an Environmentally Responsive Low-Density Housing Development in Suffolk

GSE MSc Architecture: AEES Essay May 2010: Straw-bale or hemp/lime construction: which is more appropriate for an environmentally responsive low-density 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] Page 1 of 37


Table of Contents TABLE OF CONTENTS.............................................................................................. CONTENTS.............................................................................................. 2 INTRODUCTION.......... INTRODUCTION ..................... ..................... ..................... ..................... ..................... ..................... ......................................... ...............................3 CRITICAL ANALYSIS......... ANALYSIS.................... ..................... ..................... ...................... ..................... ............................................ ..................................4 CONCLUSION.......................................................................................................... CONCLUSION .......................................................................................................... 20 GLOSSARY.............................................................................................................. GLOSSARY .............................................................................................................. 22 BIBLIOGRAPHY........... BIBLIOGRAPHY ..................... ..................... ..................... ..................... ..................... ................................................. .......................................23 23 APPENDICES........................................................................................................... APPENDICES ........................................................................................................... 30



Introduction This essay relates to t o several lectures of Module C3, ‘Environmentally ‘Environmentally responsive materials’, particularly the ‘Straw-bale Building’ and ‘Hemp/Lime’ ‘Hemp/Lime’ lectures. The Housing and Regeneration Bill (now enacted) ‘ Supports the delivery of three million new homes by 2020 ’ 2020 ’ (UK Parliament, 2008). The construction of this number of houses could be environmentally devastating devastating as production and transport of construction materials uses 10% of UK energy consumption (EA, 2003). However, However, the bill explicitly states that it ‘provides ‘ provides for the establishment of new settlements like eco-towns and for simplifying the ways in which the Homes and Communities Communities Agency would facilitate delivery of these projects’ 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 Environmental Action Plan (Appendix 1) for 2009-2010, includes the goal ‘ to be an exemplar in tackling climate change’ change ’ and ‘reduce ‘reduce its CO2 emissions by 60% by 2025 ’. ’. Theme 1 of the plan ‘Climate Change’ includes the sub-theme ‘Sustainable ‘Sustainable Construction and Development’ (SCC, 2009). Using environmentally responsive responsive building materials will help achieve these ambitions. This essay will compare hemp/lime to straw-bale construction, particularly embodied embodied and sequestered CO 2, and ascertain which is more suitable for new low-density dwellings in Suffolk.



Critical Analysis Suffolk Suffolk 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, (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 f lat 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 wheat (DEFRA, 2009). Suffolk has the potential to ‘grow-its-own’ ‘grow-its-own’ building materials.

Housing need Suffolk’s population density density is less than half that of England’s, at 188 1 people/km2 offering scope for low-density 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 weight-bearing walls consist of a ‘brickwork ‘ brickwork outer leaf, insulation, 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 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 t his ‘Developer’s ‘ Developer’s vernacular ’ vernacular ’ (2005). Figure 1. Developer’s vernacular vernacular used in Durrant Road, Hadleigh, Hadleigh, Suffolk. Not in keeping with other buildings in the ancient market t own.

Source: Google (2010) Woolley has criticised the weighting placed on the energy-in-use of houses when considering considering ‘green’ credentials, arguing that the embodied CO 2 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 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 load-bearing and infill. With load-bearing 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 Amazonails promote load-bearing straw-bale building, building, stating it is fast and easy for non-professionals non-professionals to follow (Jones, 2009). However, Snell and Callahan argue in



favour of the infill method stating that the load-bearing 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 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. 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 hurds 2 mixed with lime binder 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 f orms 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 Historically Suffolk had a well-established hemp industry (Fordham, M) and the county is home to t he ongoing revival. Hemp Technology, Technology, a hemp processing plant in Halesworth, 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 t o build a 2-bed terrace with 400mm walls (Rhydwen, 2010a). To supply 3,289 properties requires 6,834 hectares 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 National parks or SSSIs.



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

Singleton Birch lime pit North Lincolnshire

Needham chalk pit Suffolk

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 CO 2 emissions than OPC, they are still fairly high and large-scale opencast mines destroy landscapes. Lime is abundant, abundant, but finite and minimising its use is essential (Rhydwen, (Rhydwen, 2010b).



Figure 4. Singleton Birch lime pit in Barnetby, North Lincolnshire Lincolnshire showing damage to the landscape caused by mining. Singleton Birch is the UK's largest independent 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 CO 2. 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 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/m 2) 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 CO 2 sequestration/emissions sequestration/emissions vary more for hemp than for straw st raw because hemp needs processing into hurds whereas straw is a by-product of cereal production. Rhydwen calculates that 1000m 3 of hurds weighing 100kg sequester 127–181kg CO2. Therefore a 400mm thick wall sequesters 50.8–72.4kg CO 2/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 Rhydwen calculates that the net CO 2 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, wall, it contains 16.6-42kg/m2 embodied CO2.

CO2 Sequestration minus Emissions for 1 m 2 wall. This section will attempt to ascertain whether straw-bale or hempcrete walls have a better CO2 balance per m 2. 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 CO 2 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 t he 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 CO 2, Sequestered CO 2 and CO2 balance for straw-bale and hempcrete walls (negative values indicate net sequestration). Embodied (E) Sequestered Net CO2 emissions CO2 (Kg)

(S) CO2 (Kg)

Low E CO2 - S CO2 (Kg)

78.2

High E CO2 - S CO2 (Kg) -61.6

Straw-bale

16.6

plastered one side

to

to

with 35mm lime

42

-36.2

plastered. Straw-bale

33.2

plastered both sides

to

to

with 35mm lime

84

5.8

78.2

-45

plastered. Embodied (E)

Sequestered

Net CO2 emissions

CO2 (Kg)

(S) CO2 (Kg)

Low E CO2 - Low S CO2 (Kg) Low E CO2 - High S CO 2 (Kg) High E CO2 - Low S CO2 (Kg)

400mm Hempcrete

34.7 (25.2+9.5)

50.8

High E CO2 - High S CO 2 (Kg) -16.1 (34.7 - 50.8)

wall plastered on

to

to

-37.7 (34.7 - 72.4)

one side with 20mm

88.8 (64.8+24)

72.4

38 (88.8 - 50.8)

lime (hempcrete +

16.4 (88.8 - 72.4)

plaster) 400mm Hempcrete

44.2 (25.2+19)

50.8

-6.6 (44.2 - 50.8)

wall plastered on

to

to

-28.2 (44.2 - 72.4)

both sides with

112.8 (64.8+48)

72.4

62 (112.8 - 50.8)

20mm lime

40.4 (112.8 - 72.4)

(hempcrete + plaster)

Table 1 shows that when comparing like-for-like values for embodied CO 2 within the lime, straw-bale walls walls sequester more net CO 2 than all hempcrete wall scenarios, and whether the straw-bale walls walls are plastered on one side or both with lime. E.g. Craig Embleton, 0750553, Group 15 (Lucy Cartlidge), C3 Essay [email protected] Page 11 of 37


the best value for straw-bale walls 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 would ever sequester more CO 2 than a straw-bale wall, a range of different thicknesses of hempcrete wall were investigated. (The width of the straw-bale st raw-bale wall wall is fixed). The T he results are presented in graphical format. Figure 5 compares walls 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 CO 2 emissions for lime and high and low values for CO 2 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 CO 2 emissions for lime. 60 y = 35x + 24 40

24 20

27.5 22.1

31 20.2

34.5

18.3

38

16.4

9.5 2 O C g K

0 .0

-3.3 0 .2

0 .3 -9.7

-14.1

0 .4 -16.1

-20 -25.9

-40

14.5

12.6

y = -19 x + 24 3.1 -2.3 0 .1

0

45

41.5

0 .5

0 .6

y = -64 x + 9.5 -22.5 -28.9

-37.7 -36.2

y = -118x + 9.5 -49.5 -60

-61.575 Thickness hempcrete walls m

-80

-61.3

High Embodied CO2 & High Sequestered CO2 High Embodied CO2 & Low Sequestered CO2 Low Embodied CO2 & High Sequestered CO2 Low Embodied CO2 & Low Sequestered CO2 Straw High Embodied Embodied CO2 Lime Plaster Straw 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 CO 2 emissions for lime and high and low values for CO 2 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 CO 2 emissions for lime. Craig Embleton, 0750553, Group 15 (Lucy Cartlidge), C3 Essay [email protected] Page 13 of 37


80

60 48

51.5 46.1

55 44.2

40

2 O C g K

20

58.5

42.3

62

40.4

y = 35x + 48 65.5

6

y = -19x + 48 38.5

36.. 36

19 5.8

12.6 7.2 7.2

6.2 6.2

0 0.0

0.2-4.6

0.1

-0.2 0.3

0.4-6.6

0.6

-13 -13

-16.4

-20 -20

0.5

y = -64x + 19 -19. -28.2 y = -118x + 19

-40 -40

-44.95

-40 -40 Thickness hempcrete walls walls m

-60 -60

High Embodied CO2 & High Sequestered CO2 High Embodied CO2 & Low Sequestered CO2 Low Embodied CO2 & High Sequestered CO2 Low Embodied CO2 & Low Sequestered CO2 Straw High Embodied CO2 Lime Plaster Straw Low Embodied CO2 Lime Plaster

Source: Author’s calculation based on Rhydwen ‘s hemp/lime data (2010b) and Atkinson’s straw data (2008)


-51.


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 CO 2 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 st raw-bale walls 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

High Embodied

Low Embodied

Low Embodied

CO2 & Low

CO2 & Low

CO2 & High

Sequestered CO 2 Sequestered CO 2 Sequestered

Sequestered CO 2

CO2 Plastered outside with 20mm lime and inside with 20mm clay Equation y = -19x + 24 y = 35x + 24 y = -64x + 9.5

y = -118x + 9.5

Width in metres Including 40mm

3. 3.17

-1.72

1.11

0.62

3.21

(unobtainable) -1.68

1.15

0.66

y = -64x + 19 1

y= -118x + 19 0.54

1.04

0.58

plaster (unobtainable) Plastered inside and outside with 20mm lime Equation y = -19x + 48 y = 35x + 48 Width in metres 2. 2.22 -1.21 Including 40mm plaster

2.26

(unobtainable) -1.17 (unobtainable)

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 CO 2 in hempcrete. If the wall were plastered with lime on both sides it would require a thickness of 580mm before it sequestered as much CO 2 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 CO 2 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. wall. The hemp/lime forms f orms a no-cavity wall around the frame. Although the hemp/lime does provide support the house does not rely on this (T hompson, 2010). Load-bearing straw-bale straw-bale walls can withstand loads of 48,826kg/m 2. 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 straw-bales have a U-value between 0.13 and 0.20. W /m 2K (Jones, 2009). However Andersen discovered that the U-value on sections of plastered straw-bale wall 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/strawlime-plaster/strawbale/clay-plaster bale/clay-plaster wall to have a U-value of 0.13W/m 2K (2008). The U-value of Adnams brewery thick hempcrete brick walls are 0.18 W/m 2K. Lime Technology Ltd’s headquarter building building has a calculated U value of 0.14W/m 2K. The walling walling is 500 mm thick Tradical ® Hemcrete (Bevan and Woolley, W oolley, 2008). However the Haverhill houses did not perform as well as the conventional houses houses although heating bills were the same (Rhydwen, 2010b). Indoor air quality Hemp/lime walls 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 ‘did not perform as well as the traditional (brick-andtraditional (brick-andblock) houses’ houses ’ in terms of soundproofing soundproofing (Rhydwen, 2010b). Jones claims that Amazonails has ‘overwhelmi ‘overwhelming ng experiential evidence that straw walls offer far more sound insulation than 20 th Century wall building techniques’ 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 construction is less expensive expensive than standard construction in terms of materials, though labour needs vary. Both techniques are more accessible to selfbuilders than brick-and-block construction. Both hemp and straw are sustainable, renewable products that can be harvested year after year and sequester CO 2 in the process.



Comparing hemp/lime to straw-bale Table 3. Summary of the properties and merits of hemp/lime and straw-bale. Embodied energy and U-value criteria criteria also include lime plaster. Other criteria do not. Environmentally

Hemp/lime

Straw Bale

Total content.

-37.7 to 38 kg CO2/m2 for 400mm

-61.6 to -36.2 kg CO2/m2 for

Negative value

hempcrete wall externally plastered

standard straw-bale wall

indicated

with lime.

externally plastered with

Low for hemp is an annual crop.

lime Nil. Straw is a by-product of

High for lime as it must be mined.

grain production and energy

Processing /

Low. Hurds must be extracted and

is already accounted for. None – already baled

Manufacture

chopped, but done locally.

during grain harvest so

High for lime burning, but less than

energy is already accounted

cement. Low. Low. To and and from from Hale Halesw swor orth th from from

for. Small. Already grown and

the rest of Suffolk. Lime can be

baled locally. May be

produced locally, locally, but is often

transport minor distances.

responsive criteria Embodied Energy

sequestration Extraction

Trans Transpo port rtat atio ion n

trucked in from Lincolnshire. Lincolnshire. Environmental legacy Sustainable

Hemp can be grown organically organically as

Sustainable Sustainable if organic.

production

a break crop. Lime is very

Whilst cereals are grown for

abundant but not finite.

grain, straw is available as

Grow Grown n as a brea break k crop crop,, hemp hemp

a by-product. None. Land already farmed.

Defo Defore rest stat atio ion n

requires no additional land to be cleared of trees. Opencast lime mining strips the Toxic waste

land of vegetation including trees. None with hemp.

None with straw.

Mining can cause heavy metal Pollution

pollution. Some CO2 emissions- see

None. Pollution from

embodied energy.

farming accounted for in

Various water and land pollution

cereal production.



Environmentally

Hemp/lime

Straw Bale

Health issues Waste

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

None if used correctly. None.

End of life

causes spoil. Hemp/lime can be broken up and

Composts.

(recyclability,

burnt to produce lime. Pozzolans

reusability,

may cause issues.

responsive criteria

disposability) Performance in use Ener Energy gy in use use

Vari Variab able le resu result lts. s. Bett Better er and and worse orse

Good due to insulation.

Indoor Indoor air quality quality

than brick-and-block. Excellen Excellentt if correct correct finishes finishes applied. applied.

Better than brick-and-block Excellen Excellentt if correct correct finishes finishes

Structural

Same as a timber-framed brick-

applied. Non-load-bearing same as

performance

and-block.

a timber-framed brick-andblock. Load-bearing walls

Thermal

Thermal performance variable.

up to 48,826kg/m 2. Thermal performance good

performance: U-

U-value 0.14-0.18W/m 2K.

when properly constructed.

values, thermal

(Including plaster.)

U-value 0.13-0.20W/m 2K.

mass

Medium thermal mass.

(Including plaster.)

Poorer than brick-and-block

Low thermal mass. Better than brick-and-block

Acoustics

(source material not Availability of the

Hemp renewable

checked). Straw renewable.

material Ease of construction

Lime abundant. Non-specialist. Non-specialist. No more labour

Non-specialist. Non-specialist. Labour

(Labour intensive)

intensive than brick-and-block.

intensive. Best with a group

Initially longer than brick-and-block

of people. Quick with a group of

for skilled craftsmen. Potential to

people and suits that

on Economics and

be quicker. Hemp production is a good

method. Excellent Excellent second source of

ethical

revenue stream for farmers and

income for cereal farmers

considerations

sequesters CO 2. Lime production is

and sequesters. CO 2.

less damaging than concrete.

Empowers self-builders.

Length of constructi

Empowers self-builders.



Conclusion Summary of the case made Straw 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 economic benefits, are suitable for amateurs and professionals alike and produce structurally sound buildings. buildings. Both types of building have similar air quality properties, but straw-bale buildings buildings may have better soundproofing and thermal performance than hemp/lime, and brick-and-block, but results are inconclusive. inconclusive. Minimising Minimising lime use minimises the environmental destruction caused by mining, and the associated CO2 emissions. Straw-bale buildings buildings used less lime than hemp/lime buildings and usually sequester more CO 2. Only the best-case scenario for a hemp/lime building with very thick walls could match the net CO 2 sequestration of a straw-bale building. Considering Considering all factors, f actors, straw-bale building is more appropriate appropriate than hemp/lime for the construction of low-density dwellings dwellings in Suffolk.

Existing Orthodoxy Brick-and-block is the default housing type in the UK. These materials have highembodied energy. However, 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’. ‘environmentalists’. This essay challenges these assumptions and focuses on the embodied CO 2 of environmental environmental responsive building materials. It investigated whether the superstructure of straw-bale and hemp/lime buildings buildings could be CO 2 sinks by calculating how much CO 2 each technique could sequester. The essay also Craig Embleton, 0750553, Group 15 (Lucy Cartlidge), C3 Essay [email protected] Page 20 of 37


challenges the assumption that building materials must be mined and manufactured by specialists remotely by showing showing that Suffolk could grow and process building materials for its own needs.

Limitations of the essay The 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, dwellings, the use of the materials for constructing internal or party walls, or their use for other purposes such as flooring or loft insulation. insulation. Although the essay looked at a range of estimates f or embodied and sequestered CO2, it did not examine a continuum of values, or consider other GHGs associated with cultivation, such as NO 2. When clay plaster was considered it was assumed to have no associated CO 2 emissions, which may not be valid. The essay concentrated heavily on the embodied/sequestered embodied/sequestered CO 2/m2 within the walls. walls. It touched upon, but did not focus on other properties such as structural performance or performance in use.

Further research An evaluation of the embodied/sequestered embodied/sequestered CO 2 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. 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 CO 2 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 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 Aff airs EA – Environment Agency EU – European Union GHGs – Greenhouse gases LCA – Life Cycle Analysis OPC – Ordinary Portland Cement OPDM – Office of the Deputy Prime Minister Minister SCC – Suffolk County Council SSSI – Site of Special Scientific Interest UK – United Kingdom of Great Britain and Northern Ireland



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Word Count – 2,724



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

Action

Timescale

Responsibility

Local Area Agreement Target or National

Envi En viro ronm nmen entt

Indicator Reduce the

construction working

and Transport

amount of CO2

of buildings in Suffolk

group in Suffolk to look

(Sustainable

emissions for each

and through this reduce

at key plans, policies

Environment/

person in Suffolk

carbon emissions.

and methodologies

Sustainable

NI186.

including local

Development)/R

Make sure

development

esource

adequate plans are

frameworks and the

Management

in place so that

Suffolk Design Guide

(Corporate

Suffolk can adapt

for sustainab sustainable le

Property

and respond to the

construction.

Services)

issue of climate

Resource

change NI188 Reduce the amount

D1. Improve the

Lead a sustainable

environmental attributes

Ong On goi oing ng

D2. In disposing of

Continue to work with

Ongoing

property consideration

partners and

Management

of CO2 emissions

will be given to

developers involved in

(Corporate

for each person in

promoting the highest

the Chilton Woods

Property

Suffolk NI186

environmental

development to

Services)

Make sure

standards.

discuss how this

adequate plans are

development can

in place so that

contribute to creating

Suffolk can adapt

the objectives of

and respond to the

Creating the Greenest

issue of climate

D3. Establish a culture

County. Implement the

End 2009

Resource

change NI188 Reduction in the

of environmental/

council’s BREEAM

for strategy.

Management

county council’s

sustainable excellence

policy by:

Action Plan

(Corporate

CO2 emissions

in the built environment.

maintaining a website

by 2010/11

Property

NI185

BREEAM policy:

resource for staff to

Services)

Reduce the amount

Where the council has

increase awareness of

of CO2 emissions

influence over a design

the council’s BREEAM

for each person in

and build project it will

policy, what BREEAM

Suffolk NI186

expect a standard of

is and how it can be

Make sure

BREEAM ‘excellent’.

implemented;

adequate plans are

Where this is not

implement the

in place so that



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

Action

Timescale

Responsibility

Local Area Agreement Target or National

possible (in

council’s BREEAM

Indicator Suffolk can adapt

circumstances agreed

policy assessment

and respond to the

by the Environmental

system for all

issue of climate

Panel) the council

qualifying building

change NI188

expects a minimum

schemes. To be

Working age

environmental standard

overseen by the

people with access

of BREEAM ‘very good’

Environment Panel;

to employment by

(or equivalent) to be met

develop energy, water

public transport

and will aim for

and environmental

(and other specified

‘excellent’ in particular

minimum standards for

modes)NI176

aspects of BREEAM e.g.

new builds.

energy or biodiversity.

Deliver the Property Strategy for Fire Stations which includes environmental criteria and then develop an action plan to implement the Property Strategy for

D4. Ensure that

Fire Stations. Undertake the

Commence

Children and

Reduction in the

sustainability is a key

procurement for wave

s in 2011.

Young People

county council’s

element in the Building

6 of Building Schools

(Building

CO2 emissions

Schools for the Future

for the Future with the

Schools for the

NI185

programme.

intention of ensuring

Future

Reduce the amount

60% carbon reduction

programme)

of CO2 emissions

on 2002 equivalent

for each person in

builds.

Suffolk NI186

Aim to include 1

Make sure

carbon neutral school

adequate plans are

in wave 6 of Building

in place so that

Schools for the Future.

Suffolk can adapt and respond to the issue of climate change NI188



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

Action

Timescale

Responsibility

Local Area Agreement Target or National Indicator Children traveling to school – mode of travel usually used

Envi En viro ronm nmen entt

NI198 Reduce the amount

against the proposal

and Transport

of CO2 emissions

impacts of

for a second runway at

(Sustainable

for each person in

developments that affect

Stansted Airport.

Development)

Suffolk NI186

Suffolk’s communities communities..

Minimise the

Make sure

environmental impact

adequate plans are

of any future nuclear

in place so that

power station

Suffolk can adapt

development at

and respond to the

Sizewell whilst

issue of climate

maximising community

change NI188

D5. Seek to minimise

Continue to lobby

the environmental

Ong On goi oing ng..

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.

Source: Suffolk County Council, 2009



Appendix 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:

S u m m a r y R a t i n g

C l i m a t e c h a n g e

All building types

W a t e r e x t r a c t i o n

M i n e r a l r e s o u r c e e x t r a c t i o n

S t r a t o s p h e r i c o z o n e d e p l e t i o n

H u m a n t o x i c i t y

E c o t o x i c i t y t o f r e s h w a t e r

N u c l e a r w a s t e ( h i g h e r l e v e l )

E c o t o x i c i t y o f l a n d

W a s t e d i s p o s a l

F o s s i l f u e l d e p l e t i o n

E u t r o p h i c a t i o n

P h o t o c h e m i c a l o z o n e c r e a t i o n

A c i d i f i c a t i o n

T y p i c a l r e p l a c e m e n t i n t e r v a l

E m b o d i e d C O

R e c y c l e d c o n t e 2 n ( k t g ( C k g O ) 2 e q . )

R e c y c l e d c o n t e n t ( % )

R e c y c l e d c u r r e n t l y a t E n d o f L i f e ( % )

Brickwork outer leaf, insulation, aircrete blockwork inner leaf: Cement

A+ A

A+ A+ A+ A

A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ 60 60+

73 0.6

0 83

A+ A

A+ A+ A

A+ A+ A+ A+ A+ A+ A+ A+ A

60+

74 3.5

2 86

A+ A

A+ A+ A+ A

A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ A+ 60 60+

72 0.6

0 83

A+ A

A+ A+ A

A+ A+ A+ A+ A+ A+ A+ A+ A

74 3.5

2 86

mortar, plaster, paint Cement mortar, plasterboard on battens, paint Cement: lime mortar, plaster, paint Cement:

60+

lime mortar, plasterboard on battens, paint Anderson et al (2009).



Appendix Appendix 3 – Summary of studies into embodied energy of UK houses Ten most energy intensive materials in each study.

Build type

Material

Study: Harris, D.J.

Study: Brinkley,

Study: Asif, M. et

(1999) Brick-and-block with

M. (2006) Detached brick-

al. (2007) Scottish three

aluminium window

and-block house

bedroom semidetached EE % Total

frames. EE

% Total

EE

% Total

(kWh)

EE

(kWh) 13,800 1,800

EE 15.2 2.0

800

0.8

47,000 6,348

44.9 6.1

11,300 27,100

12.4 29.8

Concrete Concrete tiles Concrete external works Plastics Bricks Ceramic tiles Timber Steel Cement Mineral wool Clay tiles (roof) Aluminium Lightweight blocks Goods transport Plasterboard Glass Mortar Damp course

24,882

23.8

10,300 8,580 2,433 2,052 1,088

9. 9 .8 8.2 2.3 2.0 1.0

828

0.8

6,500 6,000

5,200 5,000 3,200 2,700

(kWh) 36,336

EE 61.5

8,956 8,334

15.2 14.1

1,631

2.8

1, 1 ,500 1,133 667 525

2.5 1.9 1.1 0.9

7.2 6.6

5.7 5.5 3.5 3.0

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

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

High Embodied High Embodied Low Embodied

Low Embodied

thickness (m)

CO2 & High

CO2 & Low

CO2 & High

CO2 & Low

Sequestered

Sequestered

Sequestered

Sequestered

CO2 24

CO2 24

CO2 9.5

CO2 9.5

0.0



0.1 0.2 0.3 0.4 0.5 0.6

22.1 20.2 18.3 16.4 14.5 12.6

27.5 31 34.5 38 41.5 45

-2.3 -14.1 -25.9 -37.7 -49.5 -61.3

3.1 -3.3 -9.7 -16.1 -22.5 -28.9

Straw-bale

-36.2

-36.2

-61.575

-61.575

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

Low Embodied

CO2 & High

CO2 & Low

CO2 & High

CO2 & Low

Sequestered

Sequestered

Sequestered

Sequestered

0.0 0.1 0.2 0.3 0.4 0.5 0.6

CO2 48 46.1 44.2 42.3 40.4 38.5 36.6

CO2 48 51.5 55 58.5 62 65.5 69

CO2 19 7.2 -4.6 -16.4 -28.2 -40 -51.8

CO2 19 12.6 6.2 -0.2 -6.6 -13 -19.4

Straw

5.8

5.8

-44.95

-44.95

Appendix 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 CO 2. 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 CO 2. 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

-61.57 -61.5755- 9.5

= -64x -64x

-71.075

= -64x

-71. -71.07 075/ 5/-6 -64 4

=x

1.11

=x

Low embodied CO2 and high sequestered CO2. y

= -118x + 9.5

-61.575

= -118x + 9.5

-61.57 -61.5755- 9.5

= -118x -118x

-71.075

= -118x

-71.07 -71.075/-1 5/-118 18 = x 0.60

=x

Hempcrete plastered on both sides with lime plaster. High embodied CO2 and low sequestered CO 2. 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 CO 2. 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. -44.95 95 – 19

= -64x -64x

-63.95

= -64x

-63.95 .95/-6 /-64

=x

1.0

=x

Low embodied CO2 and high sequestered CO2. y

= -118x + 19

-44.95

= -118x + 19

-44. -44.95 95 – 19

= -118 -118x x + 19

-63.95

= -118x

-63. -63.95 95//-11 118 8

=x

0.54

=x


Straw-Bale or Hemplime Construction Which is More Appropriate for an Environmentally Responsive Low-Density Housing Development in Suffolk

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