Discussions on the requirements of building energy codes and regulations often prompt a similar set of questions. In South Africa energy requirements for buildings are provided for in SANS 10400XA Ed2. Common questions and views on 10400XA include: Why is this so complicated? How can double glazing and cavity wall technology be required? Do contractors know how to build cavity walls and install newer more efficient technologies? What about Innovative and Alternative Building Technologies (IBTs, and ABTs)? Can indigenous construction materials that use earth and thatch be compliant with 10400XA?  Here are some responses.

Why is this so complicated?

Achieving minimum energy efficiency standards for technology, such as air conditioning systems and lighting can be very simple – and in 10400XA they are. 10400XA defines minimum Coefficients of Performance that can be specified for heat pumps and HVAC systems. It also provides for minimum lighting power densities (the wattage of lighting/area) that can be easily calculated.

It becomes more complicated when you address occupant comfort and the thermal dynamics of a building envelope over a full climate year. This is where the thermal performance of roofs, walls, glazing and shading requirements come in –  and calculations are required. However, if you follow the basics of good passive design, including orientation, building form, glazing-to-wall ratios, shading, thermal mass and insulation and draw on some of the excellent calculators that are available, it should not be difficult to demonstrate compliance using the Prescriptive Method of 10400XA. An alternative is to use the Rational Design Route, where energy modelling is carried out to demonstrate compliance – more about this next.

How can double glazing and cavity wall technology be required?

The building sector has to make its contribution to achieving carbon emission reduction targets. The design of buildings can support this by having thermally effective building envelopes that minimise the requirement for heating and cooling. In some regions of South Africa (set out in the map above) meeting the prescriptive requirements of 10400XA means having cavity walls and double glazing. However, double glazing and cavity walls may not always be necessary.

Well-designed passive buildings with highly insulated roofs, single clear glazing, solid walls and efficient hot water systems and lighting, may achieve better energy performance than poorly designed buildings that have cavity walls and double glazing. This can be shown through energy modelling – and is provided for in SANS 10400XA. In 10400XA, the Rational Design Route based on energy modelling using accredited software and following defined protocols is used to develop a rational design report. This report is then submitted as an alternative to following the prescriptive requirements. The advantages of this approach are that very energy-efficient buildings can be designed and significant savings can be achieved in building fabric, glazing and systems. These savings usually far outweigh the cost of the rational design process.

Do contractors know how to build cavity walls and install newer more efficient technologies?

Increasingly contractors are getting used to building cavity walls and installing more efficient technologies. Industry bodies, such as the Clay Brick Association and manufacturers are also providing guidance and products that make this easier.

What about Innovative and Alternative Building Technologies (IBTs, and ABTs)?

IBTs and ABTs often have Agrement certificates that provide details on their thermal performance. Data from tests and modelling associated with certification can be used in the Prescriptive or Rational Design routes to achieve compliance with 10400XA.

Can indigenous construction materials such as earth and thatch be compliant with 10400XA? 

R-values of indigenous materials like thatch and earth-based materials are available and can be used in wall and roof calculations and in energy modelling to meet 10400XA requirements. A good source of information on the thermal performance of indigenous materials are technical bodies that support the particular type of construction, such as the Thatchers Association of South Africa. Care should be taken to ensure that the thickness of the material is reflected correctly in the calculations and modelling as thatch roofs and earth-based walls are often more substantial than conventional equivalents.