I have been a Homestar Assessor and Practitioner since 2012 and have watched New Zealand Green Building Council’s Homestar Rating scheme grow in acceptance as an objective and standardised process for assessing and rating the sustainability of homes within their environment. Homestar received a substantial boost when the Draft Auckland Unitary Plan gave planning and financial credits to developers constructing multi-dwelling projects. Since then Christchurch, Wellington and some other local authorities have also given concessions to developers in return for their meeting certain conditions, including achieving particular Homestar Rating levels.

The ANZ Bank’s incentive approach is directed towards the purchaser of a dwelling, rather than the developer or builder. Even so, all parties involved with the creation and sale of a property up until the sale is made can benefit from the additional feature of it having a Homestar rating.

A six-star Homestar Rating is not difficult to obtain for houses as they are now being built. Beyond the standard New Zealand Building Code requirements needed for a building consent there are some mandatory minimum standards required to be met for a six-star rating. These relate to thermal comfort, space heating, ventilation, internal moisture, and maximum water-flows for showers and WCs. To reach seven-star, and then eight-stars and beyond, the thermal and moisture levels are more onerous. Of course, the final rating is subject to sufficient points being collected from all available categories.

Aside from the Energy/Health/Comfort category there are seven others; each of which has credits to which particular points can be awarded. The star rating is determined by the total of these points and allocated in bands of 10 points for each Homestar ‘star’, e.g. 67 points gives a 6-star rating, and the maximum of a 10-star rating is achieved with a minimum of 100 points. Homestar is one of several rating schemes run by the New Zealand Green Building Council who audit the assessor’s assessment and issue the formal Built Homestar Rating Certificate.

Assessments are compiled by trained assessors using the standardised Homestar Rating Tool which ensures the ratings are consistent and comparable. During the design process for a house, the potential rating can be estimated by an assessor and advice given as to where points can be gained. While a Homestar Rating is not required to obtain a building consent, it may be a territorial authority requirement under the Resource Management Act, or necessary for a developer to gain concessions. In these cases, there is available an assessed Design Rating which can be used to demonstrate anticipated compliance. This 'Design Rating' is not the formal 'Built Rating'.

A Built Rating can only be assessed after completion of the building plus all its associated features for which points were claimed at the Design Rating stage. This acknowledges the wisdom of the ancient proverb, “many a slip twixt the cup and the lip.” The rating applies to the completed physical dwelling and its environment, not to a proposed project which may need to be simplified, e.g. when the tenders are received.

While a dwelling may achieve a points total which allows a rating above seven-stars it will only be able to be awarded up to a maximum of seven stars if the thermal performance is assessed using the simplified process included in the Homestar Tool. To gain 8, 9 or 10 stars then the heating and cooling demand of the building being assessed needs to be calculated by approved thermal modelling software, or certified by the Passive House Institute of Germany. The thermal simulation software I use, as brought to New Zealand in the late 2000s by EECA for government’s then Home Energy Rating Scheme, is accepted for this thermal modelling analysis.

Over the years my thermal simulation analyses, for NZBC-H1 compliance by the Modelling Method, have shown that apartments and medium-density housing developments can quite easily reach high levels of heating/cooling thermal performance when care is taken with the construction and fenestration detailing. For further explanation, I can be contacted at [email protected]

Specific details of the ANZ Bank’s offers will need to be obtained from the ANZ Bank itself.