High-performance glass is only part of a high-performance skylight.

When discussing the thermal performance of windows and skylights, most of the attention naturally goes to the glass.

But there is another important path for heat to travel through: the frame.

Aluminium is strong, durable and well suited to architectural roof glazing, but aluminium is also a very good conductor of heat. Without an effective thermal break, heat can move readily through the frame from one side of the building envelope to the other.

A thermal break separates the internal and external aluminium sections using a material with much lower thermal conductivity.

This reduces the direct path for heat transfer through the frame and improves the thermal performance of the roof window as a complete assembly.

That distinction matters because building code requirements consider the performance of both the glazing and the frame when establishing a skylight’s construction R-value.

Thermal bridging can also influence internal surface temperatures. Improving the thermal separation within the frame can help keep internal surfaces warmer during cold conditions, reducing one of the factors that can contribute to condensation.

Harmony Roof Windows use large polyamide thermal breaks to thermally separate the internal and external aluminium components of the frame.

Combined with Low-E double or triple glazing, this allows the complete roof window to be considered as a thermal system rather than simply a piece of high-performance glass sitting inside an aluminium frame.

When comparing roof windows, the question therefore shouldn’t only be:

“What glass does it have?”

It should also be:

“How well is the frame thermally isolated?”