(See also Guidelines for Assessing and Choosing Materials, below)
Buildings are large entities and, as such, they impact upon the environment in various ways. Present-day designs clearly consume large quantities of physical resources such as materials, energy and money in their construction, maintenance and use; but they also can result in effects such as loss of amenity and biodiversity which are much more difficult to assess.
If we are going to build in ecologically-sustainable manner, or even substantially reduce the environmental impacts of current building approaches and practices, it will be necessary to consider the impact of a building over its full life-cycle, sometimes described as a 'cradle-to-grave' analysis. ('Cradle-to-reincarnation' may be more appropriate, as it more clearly raises the issues of re-use and recycling of materials.)
The life-cycle of a building material can be considered to have five stages:
For most building materials, the major environmental impacts occur during the first two stages but as waste-disposal problems increase, we are also being made increasingly aware of the impacts associated with the demolition stage. It is apparent that the energy used to produce the building material (its embodied energy) is only an approximate indicator of its environmental impact.
An Australian system, BMAS (Building Material Assessment System), based on life-cycle analysis, has been developed to compare the relative ecological impacts of various types of wall, floor and roof assemblies. Some indicative results are as follows (NB: High numbers indicate greater environmental impact; lower numbers indicate lesser impact):
|Timber Frame, Plasterboard||7.2|
|Steel Frame, Plasterboard||7.4|
|AAC Blocks - rendered||20.6|
|Clay Bricks - rendered||49.1|
|Timber, Brick Piers, Footings||41.9|
|Concrete Raft Slab||74.4|
|Timber Frame, Corrugated Steel||5.2|
|Timber Frame, Terracotta Tile||20.6|
One thing suggested by these figures is that relatively small quantities of materials that have high impact (eg, steel), may be preferable to large quantities of materials that have lower impact (eg terracotta tile).
As always, designers, builders and building owners have to seek a balance between often conflicting considerations, appearance, comfort, ease of construction, maintenance costs, capital costs etc. Now, environmental impact is an added variable. However, it has been shown that if environmental considerations are included early in the design process, it is possible to incorporate them without incurring additional costs.
The twentieth century has been one of incredible technological and social change, yet as a general rule, the theme current in the Modern movement in architecture at the beginning of this century remains valid today, albeit for different reasons...
Methods for assessing and choosing materials are based on the following guidelines:
1. Environmental factors
2. Local materials and transport needs (savings)
3. Needs of occupants of dwellings
4. Need for appropriate building design for marketing
5. Need for financial viability/affordability
6. Need to make best use of current technology, through the Building Material Assessment System (see above).
Each material is assessed at five stages of its life:
The assessment is covered by 14 different parameters:
a) The damage to the environment during mining or harvesting of the basic material.
b) How much damage in relation to the quantity of materials (what else is disturbed or damaged?).
c) The source, size, or renewability of the basic material.
d) The recycle content.
e) Waste residue, solid or liquid, in production.
f) The air pollution due to manufacture and production.
g) The embodied energy
h) The energy consumed during transportation to site of usage.
i) The energy consumed on-site for erection or assembling.
j) The on-site waste and packaging.
k) The maintenance required during the life-cycle.
l) The environmental impact during the life-cycle (ie, toxic emissions).
m) The energy and effects associated with demolition/disposal at the end of the life-cycle.
n) The recyclability of the demolished/dissembled material.
NB: Each parameter is assigned a weighting between 1 and 5, and all the weightings must total 42. This method allows users to stipulate any personal priorities. The weightings can be altered according to the philosophies of the client.