Skylights and Roof Windows: Thermal Pros and Cons
Skylights bring light but also heat. Here is how to enjoy the daylight without wrecking your energy rating.
Skylights and roof windows transform a dark room with beautiful natural light. They can also be a thermal liability if chosen and placed carelessly, because the roof is where the sun is strongest. Here is how to get the light without the heat penalty.
The trade-off
A skylight is glass on the hottest surface of the home. In summer it can pour heat into the room below, and at night in winter it can leak warmth back out. The daylight benefit is real, but so is the thermal cost, so the details matter.
How to do skylights well
- Size sensibly. A modest skylight lights a room without flooding it with heat.
- Choose performance glazing. Better glass dramatically reduces the heat penalty.
- Place thoughtfully. South-facing roof planes catch less harsh direct sun.
- Consider shaft design. A splayed shaft spreads light while a tubular skylight can light a space with less glass area.
- Add controls. Blinds or openable units help manage heat and ventilation.
Tubular skylights as a low-impact option
| Type | Light | Thermal impact |
|---|---|---|
| Large fixed skylight | High | Higher, needs good glazing |
| Openable roof window | High, plus ventilation | Moderate with controls |
| Tubular skylight | Good for small spaces | Low |
The bottom line
Skylights are not the enemy. A well-chosen, well-placed unit with good glazing adds daylight while keeping the thermal cost in check. The trouble comes from oversized, single-glazed skylights on a sun-baked north or west roof.
Frequently asked questions
Will a skylight ruin my rating? Not if it is sized and specified well. We can model the impact before you commit.
Are tubular skylights better? For small spaces they deliver light with a low thermal cost, which makes them an easy choice.
Thinking about skylights? Let us model the impact so you get the light without the heat.
BASIX & NatHERS specialists, a division of Contrive Consultants. We help NSW homeowners and builders achieve energy-efficient, compliant homes.