Eco Priority Guide: Walls
Eco-Priorities
The following issues relate to both potential positive and
negative issues associated with each product class:
Structural:
Priority Order
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Pbd*
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Timber stud
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Steel stud
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Brick wall*
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Conc
Block wall*
|
AAC wall*
|
Conc. Tilt
panel
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1
|
Resource
|
Resource
|
GHG
Resource
|
GHG
|
GHG
|
GHG
|
GHG
|
2
|
|
Toxics
|
Toxics
|
Resource
|
|
Toxics
|
Resources
|
3
|
|
|
|
|
|
|
|
Example
|
|
|
|
|
|
|
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Facings:
Priority Order
|
Straw*
|
Weather-board solid timber
|
Weather-board Recon. timber
|
Fibre Cement Sheet
|
Steel sandwich panel
|
Alumin. sandwich panel
|
Glass Curtain Wall
|
1
|
Resource
|
Habitat
|
Habitat
|
GHG
|
GHG
|
GHG
|
GHG
|
2
|
|
|
GHG
|
Resource
|
Toxics
|
Resources
|
Toxics
|
3
|
|
|
Toxics
|
|
|
Toxics
|
|
|
|
|
|
|
|
|
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Example
|
Ortech
|
Baltic Pine' w'bd
|
Weather-tex
|
James Hardie/CSR
|
|
|
|
Pbd = plasterboard. AAC = autoclaved aerated concrete
* For wall finishes refer 'Paint', 'Timber', 'Resilient Floors'
(for vinyl wall siding) for internal and external finishes
Overview
The plethora of wall structure and facing systems commonly used
vary enormously in their environmental attributes, production
intensity, life expectancies, and potential for reuse. To take
three examples:
· A timber stud wall with a timber weatherboard cladding and
insulation has an embodied energy of 169 MJ/m2
· A timber stud wall with a clay brick veneer cladding and
insulation has an embodied energy of 561 MJ/m2
· A steel-faced (enamelled) sandwich panel wall has an embodied
energy of 1087 MJ/m2(Lawson 1996).
However each of these has quite different profiles for potential
for habitat, resource, Greenhouse, toxicity and human health
components.
Quick Guide - walls
Plasterboard Lining
|
For:
· 100% recyclable product
· High natural content
·
|
Against:
· Not recycled currently
· Relatively high waste in construction
|
Timber stud (SW)
|
For:
· Relatively low thermal conductivity
· Renewable resource
· Potentially non-toxic (unless preservatives used)
· Readily repaired
· Some low toxicity carrier oils (linseed) being used with
Permethrin (Hyne T2)
|
Against:
· To obtain termite protection for timber treatment is required.
While boron-based paints are available for surface application,
surface treatments commercially available are LOSP (permethrin/
TBTO or soon bifenthrin based - refer 'Timber') formulations,
considered stronger toxins
· Dimensional tolerances can vary
· Increased embodied energy if treated, although figures not
available
· Dust a potential health hazard
· Concern over land & aquatic impacts from some chemicals
used in plantations e.g. atrizine
|
Steel stud
|
For:
· Dimensional tolerances of steel very high
· Steel does not require treatment with preservatives to give
anti-fungal or pesticide properties
· 100% recyclable
· Approx 20% recycled content in Australian steel (most
light-gauge steel is BHPPort Kembla product)
· Potentially superior fixing strength
|
Against:
· A steel stud will conduct 10x as effectively as a timber stud
(EBN 3 (4) p.10) potentially causing heat loss/ gain thermal
bridging and condensation issues
· Steel will expand with heat load
· A US study comparing timber and steel framing found that steel
required for a 185m2 home used 270,000kg of water, while timber
used no municipal supplies. C02 figures were overall comparable,
with total embodied energy requirements of timber about 75% that of
steel (EBN 3 (4) p14).
· Will conduct electricity in event of a short
· Expansion and contraction noise
|
Straw
|
For:
· Natural agricultural by-product
· Extremely insulation
· Passed for bushfire performance subject to proper assembly
(tight packing limits flammability)
· A US study has show straw bale saving 32% on framing timber
(some still required) (EBN Sept 2002 p.6)
· Cost-effective
|
Against:
· Additional space required for bale type construction- average
wall >450mm thick + lining
· Unconventional
|
Compressed Straw with Kraft Paper faces Manufactured
wall system-
|
For:
· Natural agricultural by-product
· Extremely insulation
· Passed for bushfire performance subject to proper assembly
(tight packing limits flammability)
· Recycled paper faces
· Effective integrated walling system self supporting internally
without studs
· Only 75mm thick
· Fire rated
· Ready to paint
· Cost-effective
|
Against:
· Unconventional
|
Brick Wall
|
For:
· Extreme durability and low maintenance
· Excellent thermal mass reservoir if used in appropriate
location and in combination with passive solar design
principles
·
|
Against:
· Recyclability poor with contemporary high-strength portland
cement mortar mixes
· Poor insulator
· Relatively low embodied energy per kg, but used in large
quantities in ordinary use. Fourth largest EE source in domestic
house studied (Commonwealth of Australia 2002) section 3.1
|
Concrete Block wall
|
For:
· Durable and low maintenance
· About half the embodied energy of fired bricks
|
Against:
· Wicks moisture unless sealed
· Thermal bridging unless used in combination with insulation or
cavity
· Required additional steel and concrete reinforcing in most
exposure/load/uplift conditions
|
Tilt Panel
|
For:
· Ease and speed of construction
· Fire resistance
· Strength
|
Against:
· High embodied energy
· but needs to be used in conjunction with other materials to be
effective thermal wall
· Poor R-Value, needs external wall insulation in most
climates
|
AAC Wall
|
For:
· Superior insulation value compared to other masonry walls
· Fire resistance
· Speed of construction
|
Against:
· Requires both skins to be rendered and external skin to be
waterproofed
· Loads need to be spread due to lower structural capacity
· Care needs to be taken with expansion and contraction
design
· Care needs to be taken with render applications
|
Fibre Cement-Weatherboard
|
For:
· Lower Embodied energy compared to Hardboard,
Steel,
· High Durability
· Fire resistance
· No chemicals used in manufacture
|
Against:
· Higher embodied energy compared to natural timber
weatherboards
· Comes pre-primed with water based run-of market
acrylic
· Requiresongoing maintenance by painting
|
Fibre Cement- Sheet
|
For:
· Lower Embodied energy compared to Hardboard,
Steel, & FC Weatherboards
· High Durability
· Fire resistance
· No chemicals used in manufacture
|
Against:
· Higher embodied energy compared to natural timber
weatherboards
· Comes pre-primed with water based run-of market
acrylic
· Requires ongoing maintenance by painting
|
Weatherboard, solid timber
|
For:
· Intrinsic insulation value
· Fire resistance
|
Against:
· Habitat implications, need third party certification to ensure
not from HighConservationValueForest
· Most certified plantation timbers are softwoods that need
preserving treatment
|
Weatherboard, manufactured timber -
|
For:
· Superior insulation value (check)
· Fire resistance
· Uses logging by-waste that would otherwise be chipped
· No chemicals used in manufacture
|
Against:
· High embodied energy
· Comes pre-primed with water based run-of market acrylic
· Requires ongoing maintenance by painting
|
References
Commonwealth of Australia (2002). Your Home. Canberra,
Australian Greenhouse Office.
Lawson, B. (1996). Building Materials, Energy and the Environment.
Sydney, Royal Australian Institute of Architects.
Baggs, D. (1999). Designer's Guide to the Eco-rating of Building
Materials.