Building - the energy within
As the Sustainable Housing Exp is happening this Sunday, I thought I might start a topic on building.
I have been a builder myself over many years, building houses for my family, myself and with friends. I have mainly been in the fringe area of low impact materials such as mud, straw bale, recycled timber, roofing ireon, slate etc.
One of my pet hobby horses is that I am very anti-concrete.
Cement as invented by the Romans or perhaps earlier in Middle Eastern culture, is undoubtedly a superb material and it is no wonder builders leap upon its use.
Because of manufacturing techniques, cheap energy and transport, the ready-mix trucks turning up at the building site have become synonymous with building.
One extreme extrapolation of this has been the development of the 'concrete tilt' structure, where panels are cast in concrete, often on site and then raised into position by cranes. Buildings go up very quickly, and I am sure quite inexpensively.
So what is wrong with that?
Every tonne of concrete, can be responsible for 8 tonnes of Carbon Dioxide released to the atmosphere.
Limestone and shale have to be quarried and carted to the cement works.
At the factory, the limestone and shale are burned in large rotating kilns.
The cement produced is then trucked to the concrete batching centres, or sold as cement for brick laying etc. The concrete formed from mixing cement, water and aggragate is then trucked to the building site. All of these steps involve heavy pollution of CO2.
One must be conscious of looking at alternatives when one 'bags' a particular method of building, which becomes accepted as 'best practice'.
No doubt the pricing of carbon will spur more innovation, but in the meantime what is the environmentally responsible to do?
Starting with the ubiquitous slab flooring, perhaps it is time to consider the use of plantation timber as a renewable resource and return to timber flooring. The threat of white ant infestation in wooden structures is a very real problem (not totally defeated by concrete slabs), but without having to resort to chemical treatment of the building footprint, stainless steel mesh barriers can be used effectively.
When considering concrete, which in eco-minded terminology, carries a high embodied energy - roughly translated its combined energy of manufacture and transport to the site of use per unit weight.
Other common building materials carrying high embodied energy are glass and aluminium, but they are not used in the same quantities by weight as concrete is.
Some common building materials and their embodied energy.
Kiln dried sawn softwood 3.4
Kiln dried sawn hardwood 2.0
Air dried sawn hardwood 0.5
Hardboard 24.2
Particleboard 8.0
MDF 11.3
Plywood 10.4
Glue-laminated timber 11.0
Laminated veneer lumber 11.0
Plastics – general 90
PVC 80.0
Synthetic rubber 110.0
Acrylic paint 61.5
Stabilised earth 0.7
Imported dimension granite 13.9
Local dimension granite 5.9
Gypsum plaster 2.9
Plasterboard 4.4
Fibre cement 4.8*
Cement 5.6
Insitu Concrete 1.9
Precast steam-cured concrete 2.0
Precast tilt-up concrete 1.9
Clay bricks 2.5
Concrete blocks 1.5
AAC 3.6
Glass 12.7
Aluminium 170
Copper 100
Galvanised steel 38