Passive Solar Down Under, the Te Kauwhata House

The Solarei Architecture firm based in New Zealand, is building sleek, efficient passive solar homes that integrate natural ventilation to help cool and heat the building, while respecting the surrounding environment by building sustainably.

The home from Solarei, based in New Zealand

The Te Kauwhata House designed by Solarei, based in New Zealand

Based out of New Zealand and Bangkok, Thailand, Solarei is a young architecture firm building an impressive portfolio of passive solar homes.

The featured home is situated in New Zealand, located to the south-east of Australia.

Countries located in the southern hemisphere experience the sun in an opposite manner than in the northern hemisphere.  If it is summer in the northern hemisphere, it is winter in the southern hemisphere.  In the northern hemisphere, in order to receive maximum solar gain, the windows (glazing) and active solar must be facing the south.

The northern hemisphere is highlighted in yellow. The southern hemisphere is white.

The northern hemisphere is highlighted in yellow. The southern hemisphere is white.

Because they are located ‘Down-Under’ the equator, in order for a house to receive maximum solar gain in the winter, the home’s large windows face the north.  All other basic aspects of passive solar, including adding thermal mass, building an overhang or solar control to block the summer sun, adding adequate insulation, are the same.


Mercer, New Zealand.Green Living House.

A cross section of the Te Kauwhata house.

Passive solar homes save energy by working with existing natural elements.  They can vary in size, finishes and are being built all around the world.  The Te Kauwhata House is 240 sq. meters, the equivalent of 2583 sq. feet. It has been designed to allow the occupants to appreciate and enjoy the beautiful place the home was built.  Space saving features such as built-in shelves have also been built into the home.

The occupants can also easily enjoy the outside deck area that extends the livable areas of the home.



The angles of the winter and summer sun are specific to their location, but illustrates the general principles of passive solar design.



Back wall with clerestory windows

In addition to the large northern facing windows, the home design has been integrated with thermal mass, within the concrete slab floors and concrete walls to absorb the winter sun’s heat.

In the winter, the mass absorbs the solar heat throughout the day and slowly releases it through the cooler night, allowing the home to be naturally heated in the winter, maximizing its efficiency.




A gleaming concrete floor integrates nicely with the open design of the house.

The floor of the home is a dark, gleaming color to better absorb the winter sun’s heat.


Even with the darker colored floor and back wall, the home feels open and larger than its 2583 square feet.


The passive solar building also leverages basic laws of physics to help cool the home.  Heat always rises.  To facilitate the cooling the home they have created natural air flows by strategically placing windows near the top of the walls.


The clerestory windows, located near the top of the building (sometimes located over the roofline) allow warm air to leave the home. Integrating this type of airflow in a home is also sometimes referred to as an ‘envelope house’.



The placement of windows located higher along the walls facilitate natural ventilation to cool the home.

One of the principals of Solarei, Duncan Firth sums up their passive solar design philosophies:



Duncan Firth

Passive design principles use what is already provided to us by nature. This is abundant free radiant energy from the sun and natural airflow.

Correctly designing for sunlight and airflow reduces dependency on mechanical devices for heating and cooling or can eliminate these altogether. There are opportunities to incorporate passive design principles with mechanical air circulation systems which increase efficiency, suitable in certain climates and regions.

Solarei was founded on the idea that environmental design can smartly, creatively and economically govern how we design houses and buildings given the correct practical application of environmental design and thinking.

blueprintPassive solar and passive cooling design principles maximize the benefits of good orientation to sun and wind in temperate climates.

By designing homes which trap radiant energy (the suns heat) in thermal mass (concrete) we are able to sufficiently heat a house naturally over winter.

During summer we design for natural ventilation and passive cooling. A passive solar home can reduce its energy consumption by up to 40%. This will be higher for clients who really commit to these ideas and could be as high as 70% energy reduction. “


Solarei primarily works in New Zealand and Asia. Is Solarei interested jobs in the States?

Yes, Solarei is interested in and open to projects in the United States.



Design and sustainable materials in the passive solar home.  Click on the image to see a larger version.

Can you tell me more about the systems that collect rainwater for use?

The house has two tanks each with 9500 gallons of water supply which is collected from the roof. Main utility water supply was considered uneconomic given the isolated geographical location of the house. One tank is used for house hold water and the second tank is used for watering gardens. A water pump distributes water throughout the house and a domestic water filter guarantees clean drinking water.


What tools are you using to anticipate solar movement and maximum temps reached during the day?

We used a few different types of analysis as well as were able to gain insight from the clients, who had lived in the area for years.

Sunpath Diagrams from Victoria University of Wellington, New Zealand were used to study and anticipate solar movement through the house for different seasons during the year. Several floor plan designs were considered before selecting one. Further refinements where made to the eaves design, window locations, window sizing to thermal mass ratios, R Value specifications for concrete floors, walls, ceilings and insulation details for foundations.

Sunshine hours from NIWA (National Institute of Water and Atmospheric Research, New Zealand) were considered in analyzing the potential thermal performance (solar gain and heating) of the house relative to the amount of sunshine hours the house might receive at different months during the year.

The clients, having lived in the local district for twenty years, had clear insights and experiences of the prevailing seasonal winds. Strong south westerly winter winds, intensified by the natural surrounding geography of the land (acting like a wind tunnel at times) and moderate to sometimes cold north easterly winds during summer were known considerations. The information was then used to further develop the location and layout of house.  The house is positioned further forward (or north) to reduce the direct impact of the south west wind. Thicker walls with higher R values on the south elevation buffer the wind and help to retain more heat inside the house.

The anticipated temperature range for the house was between 17 degrees Celsius minimum (early morning, 62.6 Fahrenheit) through to 22-24 degrees (afternoon 71.6-75.2 F) mid-winter (June-July). To quantify this, the house has been monitored over several winters with temperature data loggers located through the interior and as well as exterior.

The results fall within the overall anticipated temperatures range of between 17 degrees early morning (5-7 am) and peaking at 24 degrees during the later afternoon (2-4pm) mid- June. External temperature ranged from -1 degree to, 14 degrees, mid-June.

The goal of any passive solar house is to self-heat during winter keeping the occupants naturally warm, comfortable and healthy all year round. It’s likely a passive solar house when designed correctly will cater for 95% of all natural heating requirements; however, some form of back up heating is recommended for times during the year when sunshine hours might be below average, or temperatures and cold chills might be extreme. This can be achieved with portable gas heating, a wood burner, under floor heating or other option.

It’s awesome to have a architecture firm that focuses on passive design principles while combining them with active solar and client desires.

A few other Q & As with Solarei:

What is environmental design?
Environmental design takes into consideration the natural world we live in and human activities related to this. Our job is to interpret this circular process and relate this to the built world. In architecture and design this largely relates to local sun path directions, micro and macro seasonal wind flows, ecology, flora and fauna, materials and technologies, transport, human habitats, cultural environments, local landscapes and, political and media influences.


Diagram showing energy consumption types in New Zealand, and comparing overall energy use in the U.S., New Zealand, Australia and Thailand, from the Solarei website.

How much electricity do you save by using passive design principles?
This depends on living habits and is different for each client. If a house is designed using passive solar, passive cooling principles and with the addition of a passive hot water heating system/ or hot water heat pump we would expect a 40% reduction in the annual energy usage compared to regular houses. However, this will be higher for clients who really commit to these ideas and could be as high as 70% energy reduction.



The view from the kitchen, also featuring the clerestory windows.

Passive hot water heating system or hot water heat pump?
A passive hot water heating system makes use of natural sunlight for heating and a hot water heat pump sucks heat out of the air, so it is always a good idea to use these free resources. Hot water is also responsible for 27% of our total annual power bill so combined with passive design principles will significantly contribute to the overall reduction in annual energy usage for a household.


Kudos and thanks to Duncan Firth and Solarei for helping to make this article possible. They are a firm to follow in the upcoming years.  All images and diagrams courtesy of Solarei.


The government of New Zealand puts out a great passive solar resource. While some of the information is targeted to solar specific information (since solar gain can be fine tuned to a specific location on earth) for New Zealand, it still has relevant and valuable general passive solar information: NZ Passive Solar Guide (46 page pdf, 930 KB)

Solarei Website:

Keya Lea

Keya Lea likes to spend time outside, enjoying the sun.

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4 Responses

  1. emory e says:

    hello my name is Emory and I am a middle schooler at Zebulon middle school and my science teacher is Mrs. Jones. To me I think the article was amazing I even came up with a passive design just like brett gobar. Wish me luck everyone.

  2. brett gobar says:

    great article; i have a passive design and am looking for a builder experienced in SCIPS PANEL residence construction, two stories…there seem to be very few in US , especially Hawaii, where i am. any help or referrals would be appreciated ! brett, maui, hawaii

    • Keya Lea says:

      Hi Brett! Hawaii must be nice this time of year, and probably for most of the year. Although I can’t really complain. I don’t know any builders in Hawaii, however, I bet if you contact any SIPS (did you mean SIPS – structured insulated panels ?) builder, for example, either the one mentioned in the article above, or Brian Knight, a builder who builds with SIPS in North Carolina, either could probably work from afar, but it’s always advantageous to work locally with someone who knows the current building environment. Sorry I can’t help more, but best of luck building!

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