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

Pbd*

Timber stud

Steel stud

Brick wall*

Conc

Block wall*

AAC wall*

Conc. Tilt

panel

1

Resource

Resource

GHG

Resource

GHG

GHG

GHG

GHG

2

 

Toxics

Toxics

Resource

 

Toxics

Resources

3

 

 

 

 

 

 

 

Example

 

 

 

 

 

 

 

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

 

 

 

 

 

 

 

 

 

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.