What kind of house will you get if you build to the New Zealand Building Code minimum?

15 August 2018

What kind of house will you get if you build to the New Zealand Building Code minimum?

The New Zealand Building Code (NZBC) is a document that provides the minimum standards of construction, to ensure your building lasts for 50 years, and is a safe environment in which to live (hopefully).

Unfortunately many people see the NZBC as the standard to be reached for everything to be ok, when it is in fact a minimum standard that you cannot go below without breaking the law.

Professionals working in the industry are aware that more often than not, this relatively low standard is not even being reached in many areas, due to lack of knowledge in the industry. 

A design team who are designing to achieve ‘Code Minimum’ standards will mean that it is only possible for you to have a warm comfortable house if you are prepared to pay extremely high and ever growing energy bills each year. This is because the NZ Building Code for Energy Efficiency (H1) assumes that everywhere in vast areas of New Zealand (i.e. the whole South Island) have the same climate. Clearly this is not the case.

For example, the following table illustrates energy modelling of specific heating energy demand in the Wakatipu region to bring a house to 20°C throughout. 

 

Wakatipu Region

Specific Heat Energy Demand

Cost for a 150sqm house per year to heat based on 0.29cents/kW

Older Housing Stock

200 kWh/m2/annum (or higher)

$8,700 p/a +

NZ Building Code Minimum

150 kWh/m2/annum

$6,525 p/a

Typical NZ house with better insulation

100 kWh/m2/annum

$4,350 p/a

Energy Efficient House (TGA Minimum design)

50 kWh/m2/annum

$2,175 p/a

Passive House Standard

15 kWh/m2/annum

$652.50 p/a

 

Note 1: A study on energy usage by the International Energy Agency indicated that space heating accounts for over 50% of the total energy use of a residential building. In New Zealand the average percentage for space heating of a residential building is 34%. A 2010 paper by BRANZ based on the HEEP (Household Energy End Use Study) indicated that this was due to persistent under heating - living spaces in the South Island were shown to have a mean winter temperature of 14.7°C.

Note 2. The Asthma Foundation recommends a minimum of 17 °C. internal temperature and New Zealand has the second highest Asthma rate per capita in the world. Consider what your family’s health & medical costs if this is not achieved.

 

The NZ Building Code cannot be used as a guide to achieve any form of energy efficiency, comfort or health.

You have the option to make some simple choices at the design stage, which can alter your heat energy bill by up to 90% as indicated in table 1.

Whilst dropping your heating energy bill you are also improving your quality of life, health and comfort. At TGA we have a company minimum standard of energy efficiency. Your homes Specific Heat Energy Demand will be designed to not exceed 50kWh/m2/annum whilst allowing for 20°C everywhere throughout the year. As a client your brief and your budget will determine how much you will want to improve on this minimum standard to bring you closer to the Passive House Standard. An energy model is a tangible way to provide you with the information you need to make informed choices. It will also give you a clear understanding of the point of difference between your house and your neighbours, either for your own piece of mind or to provide information for that future buyer.

 

Back to the blog