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Ecological materials

In principle

The concept of an environmentally damage free material presupposes that:-
  • no extractive processes are required to secure the base materials
  • the material is renewable
  • the material is applied to building construction with low energy demands
  • the completed building system has good comfort and aesthetic performance
  • at the end of the building's life the material can be returned to the environment without residual damage, or can be recycled to be used again in another new building development.

In the real world

Working in the real world within existing available building systems, materials choices may be made where very few of the above attributes are secured directly, or other pragmatic priorities possibly with environmental consequences might be added to the list.
Whether these are realistic priorities, or rationalisations, each reviewer will have to decide for themselves.

This practice uses a substantial amount of steel in some projects, including this architect's own home.
Normally such a material derived from extractive mining, with high energy inputs to form the material and further form useable products from the material and its fabrication requirements would be judged environment unfriendly.

    However the driving priorities favouring steel in a pro-environment context included:-
  • that the building could be substantially pre-fabricated and erected on-site initially with only hand tools,
  • erected on-site from within the final building 'footprint' with minimal damage to the surrounding site
  • erected with minimal support machinery until the renewable energy system is operating on the building which then powers the support machinery rather a generator.
Such materials are readily available, well understood by industry and regulatory authorities; and approvals are achievable; although advocacy is needed for these less usual applications of materials made by this practice (notably the use of light industrial steel sections for residential structures).

Assumed to be 'environmental'

The practice also uses materials usually asociated with favourable environmental performance: recycled timbers, stone salvaged from on-site, stabilised rammed earth using site excavated material to bench the building, mud brick and aerated autoclave concrete.

Some regulatory authorities have little experience with some of these, and it is not unusual for advocacy to be needed on individual concerns raised by such regulators.
These concerns include: the structural capacity of recycled or handmade materials, waterproofing of surfaces and materials, guarantees as to definition of colour of surfaces of material embodying natural materials in the completed building.

None of these concerns has a real basis in real world experience; it is usually only the unfamiliarity with the material and its applications by the outside observer.

Fully renewable material

An example of an emergent ecological material is straw bale construction.
There are few local examples of this construction; expertise, prior examples, draft building codes and so on are all sourced from overseas.
As a result local building industry and authorities are perplexed by proposals embodying these materials. Approvals are obtainable by energetic advocacy including the ESD merits and the local application of precedent, technology and experience from elsewhere.

Why devote effort to such building construction?

    This building system embodies most of the desirable ecological material priority characteristics:-
  • the material is sourced from waste in the normal agricultural process, being the remnant stalk usually burnt or turned into the soil
  • new material is generated in the farm cycle each year
  • the material is biological, with no extraction processes needed
  • the material achieves R6 insulation characteristics
  • at the end of the building life, the material is returned to the environment by mulching

    Technology, existing buildings, and draft building codes information is centred in the US.

    The most commonly asked questions about straw bale construction material relate to :-

    1. 'three little pigs'
    2. fire
    3. vermin
    4. moisture

    1. - is a children's fable; and none of the purported characteristics
    of any of the building materials claimed are found in the real world.
    2. - The complete building system includes the straw in a pressed
    and bound bale with fire retardent applied as for cellulose insulation,
    (boric acid) and an external fire resistant render skin.
    The building system as a whole does not support combustion.
    3. - Vermin find the hollow cellulose structure of the straw bale
    unpalatable due to the low cellulose density and regular air pockets
    in the matrix of the material. Vermin is also excluded by damp proof
    course and render envelope which are part of the building system.
    4. - The rendered envelope and damp proof membranes built in as for
    other masonry systems means that the system is not subject to water
    ingress or logging.

    Similar to other masonry systems, the material can be erected as infill to a framed building, or as load bearing masonry.
    In either system the system is internally reinforced with pins between bale layers, and externally reinforced with mesh in the render envelope.

    There is substantial local experience with 'Dri-bond' walls where loose stacked hollow concrete blocks form the core and a glass reinforced render envelope provides structural rigidity.
    In load bearing construction for straw bale, the external reinforcing and render fulfills the same role; additionally full height tie rods and a wall plate bond beam is integral to the straw bale system of construction as for autoclave concrete walls.

    Thus all of the characteristics of straw bale construction are as found in other conventional masonry systems.
    There is some settlement in wall height during construction of load bearing straw walls, and the tiedown and bond beam design allows for this.

    There is nothing alien or technically difficult in the building system.
    Successful application depends on design understanding the system features, and construction practice allowing for these issues.

    Traditional construction systems, notably kiln fired masonry situated on reactive soil sites, have a long history of problems in use;
    including substantial cracking prejudicing structural integrity, but this hasn't stopped their use.

    End of section