Focus Corner

Green walls

February 9th, 2009 by   (View Author Profile)

Building a straw wall, green wall, IrelandA recent email from my friend in New Zealand raised the old question of: What is the best wall for a building in terms of energy efficiency and environmental conservation?

Green Wall Types

Many solutions have been tried and many more are still being tested. People around the world have experimented with natural wall materials ranging from peat, sods, straw bales, logs, vegetation, rammed earth, hand-made bricks of various types (including dung), rubble & lime mortar, etc. Recycled man-made materials have also been used including tyres, bottles (plastic or glass), plastic crates, etc. You get the picture – for every ′solution′ there are dozens, if not hundreds, of variations.

Some Questions

Ask yourself if the material choice is right for your site and your situation, i.e.:

  • How much will it cost to transport and/or process the materials?
  • Will they provide the building life-span you need? (i.e. will they remain stable in terms of load-bearing and weatherproofing qualities, etc?)
  • How do they meet legislative requirements (building regulations, environmental health & planning policy, etc)?

Then ask:

  • Can you devote months of spare time for such a project? Time taken off work will be balanced in part by the low project costs of building your own home, but the bills will still have to be paid somehow.
  • Alternatively, do you know anyone who could work with the materials you want to use? Would you still have to be there every day to give guidance, or can your architect / designer do this for you?

Modern Alternatives

Many people with modern-day commitments are becoming increasingly aware that manufactured materials might well prove to be right for them. Rendered insulating panels over timber-frame for example can be very efficient and the life-cycle carbon costs could be low or very low, depending on the mix, quality and longevity of the materials (remember – carbon = money). Such systems are well suited for off-site fabrication, quality control is easier to manage, ′wet′ trades are minimised and site labour costs are much reduced.

The Right Solution

There is no ′one size fits all′ solution for every project – this is a decision for the individual, but it must be well-informed. A good eco-designer will be able to set up simple computer models for you to compare heat-flow and air-permeability values through different wall types and match these to building costs. A shortlist can then be made and the carbon life-cycle impacts can be evaluated. At the end of such a process, you should be in a position to specify the best energy-efficient, environmentally friendly solution for your site and your circumstances.

Bear in mind that figures for some of the more unusual materials properties might not be as well researched and an ′over-specified′ solution could prove to be the best way forward, but should still be based upon a calculated assessment as a starting point. In any case, don′t be afraid to think ′outside the box′.

(This article discussed walls, but the principles can be applied to the other building components, i.e., roofs, floors, etc.)





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