NatHERS Certificate FAQ's

• Deemed To Satisfy versus a NatHERS Star Rating

  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.

• How much does a NatHERS Assessment cost?

  To see a guideline of our NatHERS pricing, please click here

   

• What are ways to avoid double glazing?

  One of our most frequent requests from our clients is to reduce or remove the requirements of double glazing on their projects. Double Glazing can cost up to twice the amount of single glazing and on some projects it can tip the feasibility scales. Every year it seems the ever improving Energy Efficiency - Section J of the National Construction Code and the National Thermal Comfort (NatHERS) regulations are making it increasingly difficult to avoid specifying double glazing. However, at Certified Energy we have 5 tried and true tips that will go a long way to avoid specifying double glazing on your next project.

   

  1. Keep your Glass to Floor ratios down

  Perhaps the only, yet most important variable that we as Thermal Comfort Assessors don't have direct control over on this list is the Glass to Floor Ratio on a project. A Glass to Floor (GtF) ratio is the total glazed area added together on a project divided by the total floor area of a project to give an overall percentage. Coming from an Architectural background I can understand that this dynamic glass to floor relationship on a project can be at the heart of the overall aesthetic appeal, but if it is not taken into account at the early design phases of a project an overly high Glass to Floor Ratio can have devastating effects to the heat loss of your project, as heat loss is generally twice high in glazed sections of your project compared to insulated walls.

  From our experience and as a general rule of thumb, here are our recommended glazing types that are required based on a projects overall % of glass to floor area (applying to the majority of climate zones).

  • 0 - 25%     Requires Single Glazed Clear Glass
  • 25 - 35%   Requires Single Low -e Glazed Clear Glass
  • 35 - 45%   Requires Double Glazed Clear Glass.
  • >45%        Requires Double Glazed with Low -e Clear Glass which generally requires improved aluminium Argon gas filled frames.

  To further illustrate this point, a typical project home will have approximately 18-20% of glass to floor ratio, this can be compared to an Architecturally designed 2 story 'glass box' type house which we previously assessed that had an unusually high glass to floor ratio of over 55%.

   

  2. Use higher performing wall insulation

  Standard bulk wall insulation with reflective foil to fit within a 90mm frame for typical Brick Veneer construction has a highest R value of R2.5. It is possible however to use rigid foam insulation which comes in thickness of up to 40mm which can then provide a total Rt of up to R5.6 for Brick Veneer construction. Providing two layers of this rigid insulation product in the 90mm brick veneer frame effectively doubles the insulation in the external walls. This method is often much more cost effective than having to specify double glazing on a project.

   

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• What is a 6 Star Rating?

  The National Construction Code (NCC formally known as the BCA) requires all new residential dwellings in Australia (Except NSW)* to achieve a minimum of a 6 Star Rating using the Nationwide House Energy Rating Scheme (NatHERS), approved software.

  This NatHERS software estimates the internal temperature in each room of a dwelling for each hour of the year based on assumptions about occupant behaviour, information about the structure and specification of the dwelling and standard weather data for the dwelling's location.

  The internal temperature is compared against a comfortable temperature range and occupancy pattern to estimate the annual heating and cooling loads per square metre of floor area to keep the temperature within the comfort range. The loads are adjusted and converted into a star rating between 0 and 10. A 10 star home is unlikely to need any artificial cooling or heating to maintain comfortable internal conditions, whereas a 0 star home would offer virtually no protection from the external temperature.

   

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• How are NatHERS star ratings assessed?

  NatHERS is assessed through a process of thermal modelling where the proposed dwelling is modelled using NatHERS approved software. The construction type, materials, glazing, lighting and insulation are used to assess the overall annual thermal performance of the project. Climate data within the software determines the development’s total heating and cooling load throughout the year, with specific heating and cooling targets outlined by NatHERS that need to be met.

  NatHERS Accredited Software is used to calculate an energy efficiency star rating and is based on expected indoor temperatures. This is assessed by assessing the project’s design, climate and household use. The tool therefore does not take electrical appliances within the dwelling into consideration, other than the air flow from the dwelling’s ceiling fans.

   

  Develop a simulation model

  A NatHERS accredited assessor will enter data into the software which will generate a simulation model of the dwelling. The simulation model will include: sizes and functions of the rooms, sizes and specification of openings, building materials/windows/products, type of construction, dwelling orientation and location.

   

  Determining the temperature of the development

  The simulation model will determine the level of heating or cooling temperature that is needed for occupants to remain comfortable within the dwelling.

   

  Determining the need for heating and cooling systems

  The NatHERS Accredited software model will determine the need for heating and cooling systems when internal temperatures fall outside of a comfortable range. This is based on assuming that occupants will open and close windows, blinds or awnings in an attempt to restore a comfortable temperature level prior to using the heating or cooling system.

   

  Calculating a rating out of 10

  Once the steps above have been completed, the total annual estimated levels of energy efficient heating and cooling are determined by a ranking out of 10 stars.

   

  To read more about NatHERS Certificates, click here

• What are the requirements of a NatHERS certificate?

  For an accredited assessor to assess a project through the NatHERS process, they require the full plans, sections and elevations for the building as well as the building materials and glazing types that are intending to be used so that the building can be simulated accurately.

  Generally, appliances such as, air-conditioners, etc. do not need to be known by the assessor as they do not affect the star rating as NatHERS energy ratings are based on how well designed the dwelling will be. Appliances that are added to the building and are likely to be changed in the future are not taken into consideration.

   

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