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Passive House

Learn what a passive house is, how it is achieved and what you can expect from one.

What do we mean when we talk about Passive House?

A Passive House is designed to retain more heat over time meaning less energy is needed to maintain temperature – much like a thermos flask. Careful design & detailing combined with a comprehensive understanding of the Passive House principles means it is possible to construct a house which uses almost no heating and has a fantastic indoor climate.  It is then very easy to create a Net Zero Energy House, because your energy requirements are so low.

In a traditional New Zealand House a substantial amount of heat is lost through the walls, floors and roof, even in what most people would say are well insulated houses. As a result, this heat has to be replaced, meaning a high energy output (and high energy bill). In a Passive House that heat loss is minimal, and, with the use of a combination of passive heating and heat recovery ventilation, almost all of your heating requirements are provided for.

Energy Use in New Zealand Households

Report on the 10 year analysis for the Household Energy Use Project (HEEP). BRANZ Study report No. SR 155 (2006).

How do you achieve that?

A Passive House combines the following primary principles:

  • Very high Levels of Insulation (specific to your climate)
  • Well-insulated window frames and glass (often triple glazed, low-E, with inert gas)
  • Thermal bridge free construction
  • Airtight building envelope
  • Highly efficient heat recovery ventilation 

For more information read The Comfort Equation here.

What does it mean for you?

Comfort and health with minimal on-going costs.

Passive House was created (in Germany in the 1980s) to hit the sweet spot between creating low energy buildings, designed to achieve the World Health Organisation recommended temperatures and levels of humidity, at a cost which most people could afford. 

There are no specified materials or construction methods, and the buildings are designed specific to the climate region. 

This means you will have a known outcome in terms of comfort and energy usage, but the design or method of construction is not dictated. This is why it is applicable throughout the world, and can be adapted to suit any type of design or building.

How much energy does a Passive House consume?

Specific Energy Demand

The Passive House standard has a Specific Energy Demand (heating & cooling) of 15kWh/(m2a). Team Green Architects has a company minimum standard of 50kWh/(m2a).

The table below shows you a three bedroom house in Queenstown (which is above TGA minimum). The site is North Facing, with a lot of solar gain. It shows what energy would be required to keep the same building to 20 degrees for the whole year, based on different construction methods.

Note: Buildings built pre 2007 are not designed to maintain an indoor temperature of 20 degrees at all times, however the current Building Code requirement in H1 does require the building internal environment to be over 20 degrees.

Specific Heat Demand (SHD)

1 - Passive House

SHD less than 15 kWh/m2a

  • European timber triple glazed windows
  • Best practice insulation and Thermal Bridge free design
  • Airtightness of 0.5 air changes per hour at 50 pascals pressure. (Note: PH requirement is 0.6 minimum)

2 - TGA Premium

SHD of 25 kWh/m2a

  • European timber triple glazed windows
  • Insulated well above NZB Code, minimised Thermal Bridges
  • Airtightness of 1.5 air changes per hour at 50 pascals pressure. (Note: this is a minimum requirement in a lot of countries)

3 - TGA Minimum

SHD of 35 kWh/m2a

  • Double glazed, Thermally broken  aluminium windows
  • Insulated well above NZB Code, minimised Thermal Bridges
  • Airtightness of 1.5 air changes per hour at 50 pascals pressure. (Note: this is a minimum requirement in many countries)

4 - NZBC Building Code Minimum

(built after 2007): SHD of 140kWh/m2a

  • Double glazed aluminium windows
  • Insulated to current code minimum for South Island, with lots of Thermal Bridges
  • Airtightness of 4 air changes per hour at 50 pascals pressure

5 - Typ NZ

Typical NZ building in Queenstown built between 1978 and 2007 with a SHD of 285kWh/m2a 

  • Single glazed aluminium windows
  • Poorly insulated thermal envelope
  • No real Airtightness - Air leakage

Primary Energy Use

The Passive House standard has a maximum annual Primary Energy Use of 120kWh/(m2a). This is the total energy of all household appliances, and is achieved by reducing the requirement for grid electricity. This can be done by utilising highly efficient Hot Water Heating, LED for lighting, and the highest Energy Star rated appliances. This will further reduce your overall energy usage and therefore energy bill. You can then look at alternative forms of renewable on-site energy production. This will much more easily allow you to have a Net Zero Energy Building/House bringing your annual energy bill to zero.

How comfortable can I expect to be in a Passive House?

You can expect your building to be comfortable all year round with minimal need for heating. Passive House guidelines suggest you can expect the following:

  • Operative temperatures* in Winter of at least 20°C (throughout the house)
  • Operative temperature* in summer does not exceed 26°C at 60% Relative Humidity (or equivalent) for more than 5% of the time
  • Relative Humidity is in a range of 30-70%
  • Air Velocity is below 0.2m/s
  • No thermal draft
  • Ability to adjust hydrothermal conditions to a degree
  • Frequency of overheating ≤ 10% of the time

* Operative temperature is the mean of the surface temperature and radiant room temperature

Additional Passive House Criteria

  • Maximum Heat Load ≤ 10W/m2
  • Specific Energy Demand (heating & cooling) ≤ 15kWh/(m2a) (Energy required for space heating or cooling)
  • Maximum Annual Primary Energy ≤ 120kWh/(m2a)
  • Airtightness (under pressure of 50 Pascal) n50 ≤ 0.6 per hr 
  • Internal Surface Temperatures ≤ 3°C Below mean ambient Temperature
  • Thermal Bridges ≤ 0.01 W/(mK)
  • Ventilation System ≥ 75% efficient