CONVERSATIONS WITH THE DESIGNERS - Windows: What you MUST consider when choosing windows for your renovation or new build.
May 07, 2021
A crucial component of any new build or renovations success is in choosing the right glazing. The right glazing can boost your home's energy efficiency and slash your energy bills.
Gone are the days of choosing a window based purely on its simple function or its size, what view will be gained from it or its ventilation benefits. There are many other properties that need highlighting as they can have a significant impact on your home’s thermal performance and energy efficiency.
Did you know that up to 40 per cent of a home’s heating energy can be lost, and up to 87 per cent of its heat gained, through windows. Therefore choosing the right windows can not only make your home more comfortable naturally, but can make a big difference to your energy bills too.
Windows lose more heat in winter and gain more heat in summer than any other surface in the home. Quality glazing can help do this by improving the efficiency of glass windows and doors. Good glazing reduces heat gain and loss, thereby helping to minimise the use of artificial heating and cooling in a building.
This next section is where we discuss the science and math behind glazing, it may be on the technical side however is great to have a basic understanding of, as you can then have the discussion with your Architect / Designer and Builder about the efficiency of the windows you intend to build with.
SOLAR RADIATION TRANSFER & MEASURING HEAT
U-value: Conduction is measured with a U-value. U-value is the measure of how much heat is transferred through glass. A lower U-value indicates better insulation properties, which means reduced heat gain in summer and heat loss in winter.
Solar heat gain coefficient (SHGC): SHGC is the measure of how much heat from direct sunlight (solar radiation) passes through the window. A greater amount of solar radiation can pass through windows with a higher SHGC, enabling solar heating for the home. A window with a lower SHGC allows less solar heat to pass through. Glass selection has a big impact on the SHGC measure of a window or door.
TYPES OF GLAZING
Double and triple glazing
Double- and triple-glazed windows have at least two sheets of glass with an inert gas such as argon (typically cheaper) or krypton between them. The gas, which is a poor thermal conductor, slows the passage of heat through the glass. The entire unit is sealed in the frame for lower heat exchange rates. These types of windows can also feature soundproofing qualities to reduce the impact of outside noise, as well as UV protection to prevent harmful rays from fading your furniture and finishes.
Double-glazed windows can reduce heat loss or heat gain by almost 30 per cent in comparison with single-pane aluminium windows. Triple glazing performs even better and is ideal for colder environments. The extra pane of glass, however, does make them thicker, heavier and more expensive.
Low-E (low emissivity) glass has a transparent coating – an invisible layer of metallic oxide – that minimises the amount of heat that passes through the glass while still allowing light to flow through. Low-E coatings add to the cost of a window, but they can cut your energy costs.
Optimise your glazing
High-performance glazing costs more than single-pane windows. If you’re building or renovating on a budget, work out which rooms of your home are worth spending the money on and where you might use a cheaper alternative.
Ideally energy-efficient glazing should be used in every part of the home. But rather than taking a ‘one-type-fits-all’ approach, you can optimise thermal performance and keep the budget under control by choosing different glazing types based on a rooms use, orientation and climate.
It makes sense to up-spec and spend money on the glazing in the most frequented spaces of your home such as living rooms and family spaces.
Bedrooms that are used less frequently during the day can have glazing that is lower on the efficiency scale, in saying that be mindful if the bedrooms are located at the front of the home and are exposed to street noise, you may want to consider the acoustic performance of the window.
Less-used areas, such as laundries and bathrooms, have less need for high-performance glass, however, they still contribute to the overall efficiency of a house, in which case low-E may be an appropriate choice.
Before signing off on your floor plans, sit down and spend time going over each individual space on the floor plans and analysis the windows shown.
Take into consideration the use of the space and it's orientation to the sun. Ask your Architect or Designer to run through the window schedule with you. Ask how the windows operate, are they fixed or opening, how much sun are they exposed to, what way are they orientated to the sun. Then assess with their guidance and expertise which windows need further glazing consideration.