Thermal-break vs non-thermal frames
Aluminium conducts heat, which is its virtue in a heat sink and its problem in a window frame. A thermal break puts a non-conductive bridge between the outer profile and the inner profile, so the two do not conduct into each other; a non-thermal frame is one extrusion of aluminium from inside to outside, and it is the cheapest way to hold glass. The choice is set by the climate and the energy code, not by preference — a cold or a code-driven market needs the break, a warm interior partition does not.
What the break does
The thermal break is a strip of non-conductive material — polyamide or a glass-fibre-reinforced nylon — that separates the inner and outer aluminium extrusions. The two halves are mechanically crimped or rolled together with the strip between them, so the frame is as strong as before but the heat path is cut. Without it, the aluminium is a continuous bridge from the warm face to the cold face, and in a cold climate that shows up as condensation on the inner frame and a higher U-value for the whole unit.
Where non-thermal is still right
Inside, a non-thermal frame is honest: an internal partition, a screen frame, a shopfront in a warm market where the energy code does not reach. It is cheaper, lighter and simpler, and there is no cold face for it to conduct to. The mistake is to use it on an external opening in a code-driven market, where the condensation and the energy rating both fail.
How it reads in the numbers
The break is what lets the frame carry a low U-value, because the frame is part of the rated assembly. A non-thermal frame drags the whole-unit U-value up whatever the glass does, which is why the energy code effectively forces the break in a heating or cooling climate. The frame value (Uf) is quoted alongside the glass (Ug) and the spacer for the whole-unit number, and the break is the frame part of that sum.
What to put on the schedule
- Whether the position is external and in a code-driven market, which sets whether the break is required.
- The frame U-value the assembly needs, alongside the glass and the spacer.
- The break material and the joint, because a break that is not properly crimped does not perform.
- Non-thermal only on internal or non-code positions, stated as such so it is not substituted on an external wall.
Questions
No — the two extrusions are joined through the strip by crimping or rolling, so the frame keeps its structural strength while the heat path is cut.