What is the best glazing for my home? – Part 2

Ken Courtney

Technical and Product Development Manager

In Part 1, I talked about how the glass in your home is measured for performance and what makes glazing efficient for windows and doors in Perth homes.

In Part 2, I’ll cover the difference between low-e glass and double glazing.

What is low-e glass?

Low-e glass is ordinary glass that has a microscopic layer of metals applied to its surface. This special performance enhancing coating can be either ‘soft’ or ‘hard’. Hard coated low-e glass is created by baking the metals into the glass pane whilst it is still hot. Soft coated low-glass is created by vacuum depositing the layer directly to the set glass surface. A hard coated low-e glass can withstand a harsh environment, while a soft coated low-e glass is only used between double glazing as it would otherwise deteriorate.

The ‘e’ in low-e glass stands for emissivity which is the amount of radiant energy emitted in the form of visible light, UV rays, and infrared rays (heat).

So, ‘low’-e glass reduces emissivity. As a WA homeowner, you won’t feel that intense summer heat, or notice those strong UV rays fading your furniture. It makes sense then, that the SHGC of low-e glass is closer to zero, as it reflects direct sunlight thereby reducing heat transmission. Low-e glass performs exceptionally well with UV rays, blocking out up to 99%.

Benefits of low-e glass

1.  Improves solar and thermal control

2. Reduces summer heat gain and winter heat loss (depending on how the coating is applied and utilised)

3. Can filter out over 99% of UV rays. This means your furniture, curtains and carpet won’t fade

4. Soft-coated low-e glass used between double glazing creates a superior performance for standard double glazed windows. It can also reduce condensation in double glazing

5. For windows where the sun directly hits the window and external shade cannot be created, low-e glass performs well as it rejects a considerable amount of radiant energy

Things to consider with low-e glass

1.  Low-e glass reduces solar gain in winter as well as summer. This means you may have to turn up the heater in winter, which may create inefficiencies. In Perth, we are lucky to have mainly mild weather, however there are still some cold days where heat entering the home would be beneficial.

2. Hard coated low-e glass requires special cleaning and can be tricky to clean for homeowners.

3. Low-e glass has a lower visible transmission, or natural light entering through the window. As advancements are made with the technology this is improving, however the coating can result in a slightly ‘hazy’ look

What is double glazing?

Double glazing is two panes of glass bonded to a spacer to create one unit, also known as an IGU or insulated glazing unit.

Double glazing works by reducing a window’s ability to conduct heat. Even though glass is a good conductor of heat, double glazing inserts a small air gap between the two panes of glass which significantly reduces heat conductivity. The air gap is often filled with inert gas (e.g. argon) which reduces heat flow even more.

For the homeowner, these insulating qualities means heat is kept inside the home in winter and during summer heat flow coming into the home is reduced. As double glazing allows some heat in, the SHGC value is slightly higher than that of low-e glass. Clear glass panes in double glazing allows for high visible transmission, or plenty of natural light entering the home.

Benefits of double glazing

1.  Insulation of the unit creates excellent thermal control, keeping the home comfortable all year round with reduced need for manual heating or cooling

2. Allows for controlled heat to enter in the home in cooler months, when you need it most

3. Has high visible transmission, meaning your home enjoys plentiful natural light

4. Reduces the need for manual heating or cooling systems, thereby reducing greenhouse gas emission

5. Double glazed windows are locally available and supplied by window manufacturers in Perth

Things to consider with double glazing

1.  Upfront costs are typically high to install in your home

2. Condensation can sometimes appear between the panes due to poor installation

3. Whilst double glazing filters out a considerable 50% – 75% of UV rays, it is no match for the near 99% filtered out by low-e glass

So, which is better? Low e-glass or double glazing? All will be revealed in Part 3.

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