One of the most common questions we hear is:
"I'd love a skylight, but won't it make the room unbearably hot in summer?"
The short answer is it depends on the type of skylight and the glazing used.
Older skylights could certainly contribute to heat gain. Many homeowners still remember large acrylic dome skylights or single-glazed roof windows that allowed both sunlight and heat to pour into the room.
Modern skylights, however, are very different. Advances in glazing technology now allow abundant natural daylight while significantly reducing unwanted solar heat gain.
Understanding the difference helps explain why today's skylights perform so much better than those installed decades ago.
Why did older skylights get hot?
Years ago, most skylights used either:
- acrylic domes
- twin-wall polycarbonate sheets
- single-pane glass
These materials were practical and economical for their time, but they offered limited control over solar heat.
While acrylic and polycarbonate naturally filter a significant amount of harmful UV radiation, they do very little to reflect the sun's infrared energy—the part responsible for heating your home.
Similarly, older single-glazed glass without modern Low-E coatings allowed large amounts of solar heat to pass straight through.
As a result, rooms beneath these skylights could become noticeably warmer during summer.
Heat and UV are not the same thing
Many people assume that if a skylight blocks UV, it also blocks heat.
These are two different things.
Ultraviolet (UV) radiation is responsible for fading fabrics, carpets and furniture.
Infrared (IR) radiation carries most of the sun's heat.
A skylight may provide excellent UV protection while still allowing significant solar heat into the room.
This is why the type of glazing is so important.
Tubular skylights behave differently
Not all skylights transfer heat in the same way.
Traditional skylights and roof windows allow sunlight to enter directly through the glazing and into the room. The light warms the surfaces it strikes—floors, walls, furniture and benchtops—which then release that heat into the living space.
Tubular skylights work differently.
They capture daylight at roof level and transport it through a highly reflective tube or flexible shaft to a diffuser mounted in the ceiling. While the room receives excellent natural daylight, much of the heat remains within the roof collector and tube assembly rather than being transferred directly into the occupied space.
This is one reason tubular skylights are often an excellent choice for hallways, walk-in robes, laundries and bathrooms.
Modern glazing has changed everything
One of the biggest advances in skylight technology has been the development of high-performance insulated glazing.
Many premium roof windows now use insulated glass units consisting of:
toughened outer safety glass
argon-filled insulating cavity
laminated Low-E inner safety glass
Compared with older glazing systems, modern insulated glass provides:
- significantly lower solar heat gain
- excellent natural daylight
- outstanding UV protection
- improved winter insulation
- enhanced occupant comfort
Perhaps surprisingly, these high-performance glazing units have also become far more affordable than they once were.
Advances in manufacturing, standardisation and global supply now allow premium insulated glass to be used in many standard-sized skylights without the substantial price premium that existed years ago.
Understanding Low-E glass
One of the biggest advances in modern skylights has been the development of Low-E (Low Emissivity) glass coatings.
These microscopically thin metallic coatings are almost invisible, yet they significantly improve the thermal performance of the glass. Their primary purpose is to reduce unwanted heat transfer while still allowing abundant natural daylight into the home.
There are many different Low-E glass products available. Manufacturers use various coating technologies and often market them under proprietary names such as Low-E, Low-E 360, Triple Low-E and many others.
While these brand names can be useful, they do not necessarily indicate how the glazing will perform in your home.
When comparing skylights, it is more important to look at the published performance of the complete glazing unit, particularly its:
- SHGC (Solar Heat Gain Coefficient) – how much of the sun's heat passes through the glazing.
- U-value – how effectively the glazing insulates against heat transfer.
These figures provide a far more meaningful comparison than marketing terminology alone.
What is SHGC?
If you're concerned about summer heat, SHGC is one of the most important numbers to understand.
The Solar Heat Gain Coefficient (SHGC) measures how much of the sun's heat passes through the glazing.
- A high SHGC allows more solar heat into the room.
- A low SHGC reduces unwanted summer heat.
For most Australian homes, SHGC has a greater influence on summer comfort than the number of glass panes.
What about double glazing?
Many people assume that double glazing keeps the heat out during summer.
That's not quite correct.
The primary purpose of double glazing is to improve insulation, reducing the transfer of heat through the glass. This is measured by the U-value.
A lower U-value means the glazing is better at keeping warmth inside during winter and reducing conductive heat transfer between indoors and outdoors throughout the year.
While this certainly contributes to comfort, controlling solar heat gain is mainly the role of the Low-E coating and the SHGC of the complete glazing unit.
Roof orientation still matters
Even the best glazing cannot change the path of the sun.
A large west-facing skylight in Perth will receive very different solar exposure from a south-facing skylight in Melbourne.
When selecting a skylight, it's important to consider:
- roof orientation
- roof pitch
- room size
- glazing specification
- ventilation
- whether blinds are required
Choosing the right skylight is about selecting the right combination for your home—not simply the biggest opening.
Opening roof windows can improve summer comfort
Heat naturally rises.
An opening roof window allows warm air to escape from the highest point of the room, encouraging cooler air to enter through lower windows.
This natural ventilation can significantly improve comfort during summer and is one of the reasons opening roof windows are popular in kitchens, bathrooms and rooms with cathedral ceilings.
The bottom line
Modern skylights are very different from those installed decades ago. Older acrylic domes and single-glazed skylights often allowed considerable solar heat into the home.
Today's premium skylights use advanced glazing technologies that can significantly reduce solar heat gain while still providing abundant natural daylight.
When comparing skylights, don't focus on marketing names alone.
Instead, compare the performance of the complete glazing unit—particularly its SHGC and U-value—and choose a product suited to your home's orientation, climate and intended use.
