New Zealand covers a wide range of latitudes with climates ranging from mild winters and near tropical summers up in Northland to solid German level winters in Central Otago. Designing building so that they are warm, comfortable, healthy, durable and economic to heat/cool requires using an accurate climate that actually represents where the building is located.
Our building code climate regions are strictly for legal compliance and the idea that you would use them for design of a building is almost ludicrous. Just one look at the map of NZBC climate regions and realizing that sunny Nelson is in the same region as wintery Cromwell makes that clear. Unfortunately unless you have an especially enlightened client or designer/architect they tend to build the cheapest prettiest house they legally can; and this means using those legal NZBC climate zones. Borderline insane but that is what happens.
Our advice is the most cost effective strategy when designing a building is to use an appropriate climate & run an energy model to achieve the performance you want. Warm healthy homes and durable buildings sometimes happen by luck but do you want your home to depend on luck? We are often called in to try and fix new buildings that are built well above code but are overheating mercilessly or having condensation issues. To date these ‘problem buildings’ have had no performance modeling done other than to show they met the building code minimum requirements. Having to put a whole new roof on a building or air condition your home most of the year is much more costly than designing it right the first time.