Dowell ThermaLine™

In the past 100 years the low cost of energy has allowed architects to design buildings that can ignore natural ventilation, daylight and the suns energy, by replacing it with an artificial environment that is air-conditioned, humidified and artificially lit. This approach emerged through the harnessing of energy from fossil fuels, but with the move away from energy dependence this has translated into a fresh approach to housing design.

In Europe housing design has embraced the concept of Zero Energy Building (ZEB) as the response to changing environmental pressures. In general the term ‘future-proofing’ refers to the ability of something to continue to be of value into the distant future; that the item does not become obsolete.

Principles of future-proofing buildings
Some of the principles of future-proofing buildings include; Nil deterioration of existing materials by other structures or materials and products used in building construction, the

encouragement of design flexibility, the building design adaptability in relation to the environment, consideration to the occupant needs, and future technologies.

Building design and features should enable a long service life and increase durability. Provide products with the capacity to meet future requirements and thereby reduce the likelihood of obsolescence. Taking into consideration the long term life-cycle benefits by calculating the future benefits against initial costs.

The term ‘future-proofing’ in relation to sustainable design began to be used in 2007. It has been used more often in sustainable design in relation to energy conservation to minimise the effects of future global temperature rise and/or rising energy costs. In the context of building, the term usually refers to the ability of a structure to withstand impacts from future shortages in energy and resources, increasing world population, and environmental issues, by reducing the amount of energy consumption in the building.

Reference source; Byrd, Hugh (2012) Energy climate buildings: an introduction to designing future-proof buildings in New Zealand and the tropical pacific. Transforming Cities, Auckland, New Zealand.




Window design and performance in Australia has traditionally lagged that of Europe, North America and New Zealand. This has largely been driven by builders designing to price points that have not allowed some of the high performance window and door systems to be adopted in Australia.

In Europe the climate extremes and rising energy costs were pivotal in the adoption of higher standards of fenestration. In North America the oil shocks of the 70’s and subsequent power blackouts saw the rapid adoption of the PVC double glazed windows and doors displacing aluminium systems. The North American window industry subsequently developed thermally broken aluminium products and a large share of the market was regained.

In most economies, regulation has played an important part as it has in Australia and New Zealand. In New Zealand, consumer demand has, however, overtaken regulatory requirements largely driven by the ‘Future-Proof Build’ programs that have seen double glazing dominate the new house window market. More recently, thermally broken systems have become popular, as design and performance have become critical in consumer purchasing and construction thinking.

The global approach to improving building performance has gained traction and these tend to be based on overall U-value for the building. Windows represent a large part of the building envelope area and become an increasingly critical design element to achieving the overall target U-value.




Dowell ThermaLine™

Regulation has been the main driver of change with mandatory requirements established. These have commonly been based on prescriptive codes based on U-values for individual construction elements.

In Australia, the Nationwide House Energy Rating Scheme (NatHERS) supports the efforts of the Australian Governments to reduce the energy and greenhouse gas impact of residential buildings. NatHERS encourages energy efficient building design and construction by providing a reliable way to estimate and rank the potential thermal performance of residential buildings in Australia.

Heating and cooling accounts for the majority of the average Australian household’s energy use, but efficient building design can reduce the reliance on artificial temperature controls. To determine how efficient the design of a home is, it is given a star rating between zero and ten stars. Homeowners can make use of these ratings to determine modifications to existing houses or in planning the designs for a new house.

The star rating is calculated using software accredited for this purpose under NatHERS. The software simulates expected conditions based on climate zones and other known factors about the location, occupancy and dimensions of the house. Allowances are made for different sized houses and different climates to ensure a fair comparison of buildings and consistent ratings across Australia. While the software can be used by

anyone, only an assessor who has received NatHERS accreditation from a relevant organisation can provide a credible rating.

NatHERS tools provide one method of demonstrating compliance with the minimum energy efficiency standards for new residential buildings outlined under the National Construction Code (formerly the Building Code of Australia). Additionally, NatHERS software is a powerful tool for optimising energy efficient house designs for Australian climates. It also highlights the weakest link in the building envelope.

The Australian Window Energy Rating Scheme (WERS) audits and provides the window ratings used in building design and are available on the WERS website.





Dowell ThermaLine™

The main difference between a passive house window and a standard window is that the windows within a passive house play an important role by reducing the heat loss from the house. Passive windows are insulated and trap solar gains within the building. Passive homes require double low-e or triple glazed windows to ensure the correct U-value is achieved. Insulated frames are also used to minimise heat loss and ensure the occupants comfort within the building.

Standard windows don’t have insulated frames and sometimes only have single or double glazing, by using these windows in a passive house the occupants will not be comfortable due to the huge temperature difference between the window and the wall, there might also be problems with thermal transfer and condensation.

The ‘Passive House’ standard requires that the building fulfills the following requirements:

1. The building must be designed to have an annual heating and cooling demand as calculated with the passive house planning package of not more than 15 kWh/m² per year (4746 btu/ft² per year) in heating and 15 kWh/m² per year cooling energy, or to be designed with a peak heat load of 10W/m².

2. Total primary energy (source energy for electricity) consumption (primary energy for heating, hot water and electricity) must not be more than 120 kWh/m² per year (3.79 × 104 btu/ft² per year).

3. The building must not leak more air than 0.6 times
the house volume per hour (n50 ≤ 0.6 / hour) at
50 Pa (N/m²) as tested by a blower door.

Passive solar design can also be used to optimise the free energy from the sun. Depending on the expanse of glazing, orientation and available shading, it is likely that the window specification (glass and frame) required will be Uw 2.0 or below.

Of the three defined, a typical passive house accounts for as much as 50% of the heating and air-conditioning loads, and accounts for most of the discomfort due to draughts or excessive heat gains. A typical Australian home built before 2000 would likely achieve an airtightness test result in the realm of 10 air changes per hour (ACH), measured in a pressurised building (to 50Pa), and in many homes this can be up to 25 ACH.


Passive House: Karuna House, on the hilltops of Yamhill County, Oregon.


Zero Energy Building
A zero-energy building, also known as a zero net energy (ZNE) building, is a building with zero net energy consumption, meaning the total amount of energy used by the building on an annual basis is roughly equal to the amount of renewable energy created on the site. These buildings still produce greenhouse gases because on cloudy (or non-windy) days, or at night when the sun isn’t shining, and on short winter days, conventional grid power is still the main energy source. Because of this, most ZNE buildings still get half or more of their energy from the grid.

Buildings that produce a surplus of energy over the year may be called ‘energy-plus buildings’ and buildings that consume slightly more energy than they produce are called ‘near-zero energy buildings’ or ‘ultra-low energy houses’.

Traditional buildings consume 40% of the total fossil fuel energy in the US and European Union, and are significant contributors of greenhouse gases. The zero-energy goal is becoming more practical as the costs of alternative energy technologies decrease and the costs of traditional fossil fuels increase.

The development of modern ZNE buildings became possible, not only through the progress made in new energy and construction technologies and techniques, but also improved by significant scientific research, which collects precise energy performance data on traditional and experimental buildings and provides performance parameters for advanced computer models to predict the efficacy of engineering designs.

Heating and insulating buildings
Architects need to know how well different materials will insulate the building they design. To help them with this they need to know the U-values of different materials.

A U-value of 1 W/(m2 ºC) means a 1 metre square area of the material with a 1ºC temperature difference across the material will conduct heat at a rate of 1 joule per second.

U-values measure how effective the properties of the insulating materials are. The lower the U-value the better the material is at insulating.

U-values for windows (Uw-values)

Dowell ThermaLine™ windows and doors have been designed to allow building designers to achieve energy efficient designs. They are efficient in terms of Uw-value and also air leakages rates to minimise heating and cooling loads.

Reference source; 1. Building Connection Magazine (Winter 2014 Issue), ‘Building a Passive House’; 2. Passive House Builders [online] Available: (13 November 2014)

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