Thermal Resistance

10 July 2006

An increased focus on sustainability and changing building practices prompted the Department of Building and Housing to initiate and sponsor a revision of the Standard for Methods of determining the total thermal resistance of parts of buildings, NZS 4214. The revision updates the interim 2002 edition with new information and now includes a method of dealing with ventilated wall cavities.

The Standard is used to establish insulation properties for building components, which may be made up of several types of material, with different insulation properties. For example, a wall will contain timber framing and insulation material, as well as cladding on the outside and lining on the inside. It is important to be able to determine the insulation properties of the finished wall and this Standard is designed to do just that.

“The revised Standard sets out methods for calculating the total thermal resistance of parts of buildings in steady-state environmental conditions, and includes information to take account of the ventilated cavities now required in many residential designs,” says Martin Greenough who is the Employers and Manufacturers Northern Association representative on the committee.

Martin, who is also Chair of the committee that reviewed the Standard, says, “the Standard helps designers to determine appropriate measures to insulate buildings, by providing a method to calculate thermal resistance of complex building components, along with suggested measurement methods for materials and assemblies.”

Three methods for the determination of thermal resistance are provided:

  • Laboratory measurement
  • Site measurement
  • Calculation

Once a designer has worked out the insulation values for each building component, they can then use NZS 4218:2004 Energy efficiency – Small building envelope, to work out whether the combination of all the building components will meet the minimum energy efficiency required by the NZ Building Code (the Code). If necessary, the designer can increase the insulation material to achieve greater energy efficiency and exceed the Code requirements.

Designers who understand the value to their customers of a warm, comfortable and energy efficient home, aim to not only meet the Code minimums, but to give their customers the choice of even better performance. These designers now have an additional tool – SNZ/PAS 4244:2003 Insulation of lightweightframed and solid-timber houses, which provides not only Code minimum requirements, but also offers ‘better’ and ‘best options’.

With these Standards, designers are now better placed to meet the needs of today’s customers, where sustainability is an important issue for many.

Copies of NZS 4214:2006 Methods of determining the total thermal resistance of parts of buildingsNZS 4218:2004 Energy efficiency – Small building envelope and SNZ/PAS 4244:2003 Insulation of lightweight-framed and solid-timber houses are available for purchase online by clicking on the title or calling 0800 782 632.