NZ Construction News (Apr / May 10) Concrete: A Design for Comfortable Homes

01 Apr 2010

Concrete – A Design for Comfortable Homes
Rob Gaimster – Cement & Concrete Association of New Zealand (CCANZ)
As the cold embrace of winter gradually tightens around us, we inevitably reach for the heat pump remote while blocking out the painful thought of the power bill, or pray that the recently purchased firewood isn’t as wet as we suspect it is. 

Why are New Zealanders apparently doomed to such cold misery in winter? - not to mention oven-like conditions during the height of summer. The answer lies predominately in how we have designed our houses, and the materials we have used to build them.

Escaping an over-crowded Europe, the first New Zealand settlers sought separation from their neighbours. Land was plentiful, and so was timber. With the advent of the motorcar stand-alone houses became even more isolated, as a garage and driveway became almost obligatory.

Exposed to the elements on all sides, our lightweight houses have always been exceptionally difficult to heat, as well as to keep cool in summer.

However, it seems that as a nation we are becoming increasingly concerned with the issue of energy efficient houses. EECA’s EnergyWise initiative has been well received, while at a regulatory level NZS 4218:2009 Thermal Insulation - Housing and Small Buildings has recently been updated, and changes have occurred to the New Zealand Building Code clause H1 Energy Efficiency. 

As designers and consumers begin to understand that the majority of energy in a building is consumed during its operation, the desire to reduce the energy demands of active or mechanical heating and cooling will grow.

The initial incorporation of passive solar design principles is key to achieving a reduction in a home’s energy requirements. A core component of passive solar design is to exploit the mass of heavy building materials, such as exposed concrete or concrete masonry, in conjunction with the sun’s changing elevation angle during the year.

By using concrete’s high mass together with the heat of the sun - or solar energy - more comfortable living conditions can be achieved with reduced reliance on space heating or cooling, and subsequent reduced energy demands.

An exposed, well-insulated concrete element has the capability to absorb, store and later radiate the sun’s heat, off-setting temperature troughs and peaks, to create a moderate living environment.

To optimise concrete’s thermal mass, it must be used in conjunction with appropriate thermal insulation, window placement for good solar gains and natural ventilation as part of an integrated and sustainable passive solar design.

CCANZ first sought to promote the benefits of passive solar design with the publication in 2001 of Designing Comfortable Homes. The book quickly became recognised as an invaluable guide for anyone interested in designing energy efficient homes. 

As well as providing general guidance on design considerations, the book also provided data on expected performance of homes based on three different combinations of glass, mass and insulation. These were defined as 'code minimum', 'better' and 'best'.

As a direct result of the 2001 edition of Designing Comfortable Homes, Standards New Zealand published a specification document (SNZ PAS 4244) in 2003, which used the 'code minimum', ‘better' and 'best' insulation options from Designing Comfortable Homes as its basis. 

Subsequently the Building Code’s minimum requirements for insulation were raised to a level defined as 'better' in the 2001 edition. This, along with the development of improved products and systems making very high-energy efficiency more achievable, prompted CCANZ to create the second edition of Designing Comfortable Homes. 

Addressing the misconception that compliance with the energy efficiency requirements of the Building Code is best practice, the second edition defines two higher levels of insulation: Better Practice and Best Practice, and through computer modelling shows the comfort and energy efficiency benefits these and other improvements can provide. 

With the overall aim of providing readers with an understanding of the basic principles of passive solar design – the key to thermal comfort and reduced energy requirements in New Zealand homes – the second edition of Designing Comfortable Homes will be launched at the New Zealand Sustainable Building Conference (SB10 NZ) to be held in Wellington in late May, after which hardcopies will be available free of charge from CCANZ. 

CCANZ has further met its educational objectives recently with the revision of The Guide to Concrete Construction. The popular New Zealand text covering the constituents of concrete, the manufacturing and supply of concrete, concreting and related site practices, along with concrete properties, specifying, ordering and testing.