The two main methods used are :
1. Deemed To Satisfy - Elemental Provisions
This method is often referred to as “Deemed To Satisfy” or DTS.
This method assesses each of individual element in your build to ensure that they satisfy the Energy Efficiency provisions in the NCC. This includes the Total R-Value (or thermal resistance value) of the roof, the walls and in some cases the floors, as well as ensuring that your glazing and ventilation comply with the provisions.
This is a quick and simple method for assessing compliance for your build. The advantages are that the assessment is usually cheaper to obtain, and sometimes will result in less expensive building materials being required (for example, R1.5 in your walls, rather than a higher value). This method is the best method to use for alterations and additions, as in most cases only the new elements will need to be assessed and achieve compliance.
The disadvantage with this method is that every element needs to comply with the miniumum standard, and so there is not the flexibility to consider the whole house and 'trade-off' better performing elements against lower performing elements as with the Energy Rating Method.
2. “Deemed to Satisfy – Energy Rating”
This method is referred to as NatHERS Star Rating or a NatHERS Assessment.
With the Energy Rating method, every element of the build is entered into energy-use modelling software approved by the National House Energy Rating Scheme (NatHERS). The software models the energy required to heat or cool every habitable room in the home to a comfortable temperature across every hour of every day in the year. It takes into account many other factors such as the climate, the orientation, the breezes, the building materials, the colour of the roof, and so on. The result is an area-adjusted figure of how much energy your particular design will use across a year in heating and cooling. This figure is then converted to a Star Rating out of ten. Currently, the NCC requires a 6 Star Rating in most situations, although credits are given for some additional elements such as qualifying outdoor living areas in warmer climates.
The Star Rating Method is a much more accurate and informative method for predicting energy-use in heating a home. Much more flexibility is given to home builders to compensate for specific design choices. For example, in hotter climates, lighter coloured roofs are recommeded to achieve a better Energy Rating, (as they absorb less Solar Heat than a darker colour). However, if a client wanted a dark colour roof, the Energy Consultant could model this and compensate for it by increasing the insulation required in the walls or improving the quality of the glazing required, so that the house used the same amount of energy to heat and cool as if it had the lighter roof. With the Software, it is possible to easily change particular elements to see the effect they have on the Energy Rating. For clients who are wishing to achieve an Energy-efficient home with a high Energy Rating and low running costs, this is usually the best method to use.
Wondering which method would be best suitable for your project? Ask us the question, we will be happy to assist.
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