U-value is a measure of heat transfer/loss in a building element. Lower U-values indicate higher levels of insulation.

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What is a U-value?
A U-value is a measure of heat transfer/loss in a building element such as a wall, floor or roof. It can also be referred to as an ‘overall heat transfer co-efficient’ and measures how well parts of a building transfer heat. This means that the higher the U-value the worse the thermal performance of the building envelope.


A low U-value usually indicates high levels of insulation. They are useful as it is a way of predicting the composite behavior of an entire building element rather than relying on the properties of individual materials.

Why use U-values?
U-values are important because they form the basis of any energy or carbon reduction standard. In practice, nearly every external building element has to comply with thermal standards that are expressed as a maximum U-value.


Knowledge of how to simply calculate U-values at an early stage in the design process, avoids expensive re-working later on in a project. It allows the designer to test the feasibility of their project at an early stage to ensure it is fit for purpose and will comply with regulatory frameworks.

Reference source: John Brennan [online] Available: www.architecture.com/RIBA/Aboutus/SustainabilityHub/Designstrategies/Earth (13 November 2014)





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Many people underestimate the role of the window frame in energy efficient home design. Without windows our homes would be dark and uninviting. Windows play a critical role in your home’s comfort and energy consumption. They set the tone of your home by providing daylight, views, ventilation and a sense of spaciousness.

The use of modern performance glass and the thermal break technology in Dowell ThermaLine™ allows the home owner to have large windows while delivering outstanding energy efficiency and comfort. In fact, the most energy efficient windows result from a combination of both an insulated frame and the right glass to achieve superior energy performance.


Dowell ThermaLine™ windows have been rated as the most energy efficient thermally broken aluminium windows on the Australian residential market today, based on a glass to glass comparison*.


Reference source: * Window Energy Rating Scheme [online] Available: www.wers.net.au, based on double glazed thermally broken aluminium windows and doors (13 November 2014).




By analysing the impact of the sun on a site, the designer can take full advantage of passive solar design features and increase the energy efficiency and comfort of the building.

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The simplest way to assess the passage of sun across a site is by observation. A site visit can also help identify site-specific conditions, how obstructions such as adjacent buildings, trees and landforms will impact on the site and the potential design, how the site’s shape, slope and orientation affect solar access.


Sun-path diagrams provide a broader overview of the sun on a site, as they map the path of the sun across the sky at different times during the day throughout the year. They can help establish the position of the sun relative to a site and can be used to determine the effect of shadows cast by buildings, trees and landforms on and around the site.


In the sun-path diagrams, the centre is the point of observation and the arcs represent the sun’s altitude angle at different times of the day throughout the year, using a 24 hour clock (12 hours ahead of GMT), rather than solar time. They are accurate to approximately 1 degree north or south of the allotted latitudes, however it is important to have accurate contour lines when using them.

Altitude and azimuth
The position of the sun with respect to an observer is commonly represented by two angles – altitude and azimuth. Altitude is the angle of the sun’s rays compared with the horizon. At sunrise and sunset, the altitude is zero, and in the southern hemisphere,

the maximum altitude of the sun at any specific location occurs at solar noon on 21/22 December (longest days of the year).

Azimuth (sometimes known as bearing) is the direction of the sun as shown on a compass. Solar or ultraviolet (UV) radiation is the energy from the sun. The amount of solar radiation available on a site depends on the latitude and the sunlight hours received.


Shade is often required in summer, but in most parts of the country, winter sun is desirable. Obstructions on a site may block sunlight access at times when it is required.


When considering sunlight and building design, assess the impact of obstructions in the future as well as the present. For example, a small tree on an adjacent site may grow into a large one that blocks sun, a building may be erected on a currently vacant site or an existing building may be demolished and replaced by a larger one. Alternatively, existing trees may be retained for summer shade.


Calculating the sun-path
Using web based tools to calculate the sun path can easily determine which window configuration would be most suitable on a particular side of the building. Resulting in a clever design combination of Dowell Thermaline™ and Dowell standard double glazed or single glazed windows to achieve maximum cost-energy efficiency building solution.

Reference source: Level, SunCalc and Sunearthtools.com; [online], Available: www.level.org.nz/site-analysis; www.suncalc.net; www.sunearthtools.com (13 November 2014).




The energy performance of buildings is greatly influenced by local conditions. In most climates Dowell ThermaLine™ assists the designer to achieve star rating improvement from 4 to 5 and up to 6 stars or greater.

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Attaining energy efficiency within your home offers a powerful and cost-effective tool for achieving a sustainable energy future. Improvements in energy efficiency can reduce the need for investment in energy infrastructure, cut energy bills, increase comfort and improve ones personal health. Other environmental benefits can also be achieved by the reduction of greenhouse gas emissions and local
air pollution.


With an ever-increasing need to find the most effective ways to design and build more energy efficient homes, choosing a Dowell ThermaLine™ energy efficient window is an easy solution.

Dowell ThermaLine™ superior thermal performance allows you to add more windows or more floor area without compromising home energy ratings, helping create a brighter and more spacious home environment.


Limited ability to change orientation on some building sites requires high performance windows. The design can either increase window size or increase energy rating or a combination of both.

*As verified by the Windows Energy Rating Scheme (WERS). Reference source: WERS [online] Available: www.wers.net.au, based on thermally broken aluminium windows and doors (13 November 2014)




Dowell ThermaLine™

As much as 49% of the heat lost during winter and as much as 87% of the heat gained during summer can come from the windows*.


In Melbourne around 75% of household energy usage is for heating, while around 90% of energy is used for cooling homes in Brisbane. The emphasis on selecting the right product to reduce heat loss in a colder climate and reduce heat gain in a hotter climate should be an important decision to achieve greater comfort and energy efficiency. Choosing the right product and glazing option will help.

The award winning Dowell ThermaLine™ product range with its custom glazing options provides outstanding comfort, noise reduction and energy efficiency, all factors that are highly desired when constructing a new home or renovating an old one.

Reference source: * Australian Window Association [online] Available: www.awa.org.au resources/windows-for-good-energy-efficiency; www.efficientglazing.net; (13 November 2014); Testing based on an average house containing 8% area of glazing in the entire building fabric (windows, walls, floor and roof).

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