Builder & Contractors (Nov 09) A Concrete Foundation (or Wall) For Energy Efficient Houses

01 Nov 2009

A Concrete Foundation (or Wall) For Energy Efficient Houses

Rob Gaimster – Cement & Concrete Association of New Zealand (CCANZ)

It seems that the issue of energy efficient housing is currently generating a lot of headlines in the trade as well as the mainstream media – and rightly so.

New Zealand’s over reliance on lightweight construction materials for residential properties has for decades meant occupants have had to tolerate an interior living environment that is generally too cold in winter and too hot in summer.

Awareness of this issue has also been raised recently with the release of NZS 4218:2009 Thermal Insulation - Housing and Small Buildings, and the changes to the Building Code clause H1 Energy Efficiency.

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

This reduction in a building’s energy use can be achieved through the incorporation of passive solar design principles in the building’s preliminary design stage.

A key component of passive solar design is to exploit the mass of heavy building materials, such as concrete and concrete masonry, in conjunction with the difference in altitude angle of the sun in the sky between summer and winter.

By harnessing the natural advantage of 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.

Exposed concrete slab foundations, and concrete or concrete masonry walls, have the capability to absorb, store and later radiate the sun’s heat. Exposed concrete can absorb heat during the daytime, reducing temperatures by 3° to 4°C, and delaying peaks in temperature by up to six hours. During the night, natural ventilation is used to cool the concrete, priming it for the next day.

Employing the thermal mass of concrete can help to reduce or even eradicate the need for energy-intensive heating and cooling devices, while maintaining a comfortable temperature for occupants.

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.

The benefits afforded by integrating concrete’s thermal mass into an overall passive design are clearly evident in the Beacon Waitakere NOW Home®. After two years of occupancy results are extremely encouraging, with a comfortable interior living environment being achieved while reducing energy use.

In addition to its thermal performance, the use of concrete as a foundation slab or wall element offers a range of other benefits, including durability, fire resistance, acoustic separation and flood resilience, that render it ideal for residential construction. The huge variety of colours and decorative finishes now available in New Zealand also enable any concrete surface to be tailored for a particular aesthetic taste.

As temperatures are set to rise over the coming decades, achieving reduced energy use in our housing stock, while at the same time ensuring a comfortable living environment, can be assisted through the incorporation of concrete’s thermal mass as part of an integrated passive solar design.

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