Reference · intermediate · 3 min read
Thermal breaks in roof glazing
A thermal break is an insulating barrier within a metal frame that separates inner and outer aluminium sections, reducing heat loss and cold bridging. Thermally broken frames are standard for roof lights over heated rooms.
Aluminium is strong, light and corrosion-resistant — which is why it dominates framed roof light construction. It is also an excellent heat conductor. Without intervention, a continuous aluminium frame lets warmth escape from the room and chills the internal profile, undermining glazing performance and encouraging condensation.
A thermal break solves that by inserting a low-conductivity barrier between the inner and outer metal sections. For roof lights over habitable rooms, thermally broken framing is the baseline specification — not an optional upgrade.
Definition
Thermal break — An insulating structural element within a metal frame that separates interior and exterior aluminium sections, interrupting heat flow through the frame and reducing thermal bridging at the glazing perimeter.
How heat bypasses non-broken frames
Imagine heat leaving a warm room in winter. It crosses the inner pane, travels through the spacer, and reaches the frame. In a non-thermally broken profile, the aluminium leg is one continuous piece from inside to outside. Heat conducts straight through — a thermal bridge. The inner surface stays cold; the declared whole-unit U-value suffers.
Thermally efficient insulating glass cannot compensate alone because the frame forms part of the declared area in CE thermal testing.
How a thermal break works
Manufacturers extrude two aluminium sections — one facing the room, one facing the weather. A polyamide strip (often reinforced with glass fibre) is rolled or cast between them under pressure. The polyamide has far lower thermal conductivity than aluminium, so heat must travel a tortuous path through the insulator rather than a direct metal bridge.
The assembled profile is then machined, powder-coated and built into the roof light frame with gaskets, drainage channels and fixing lugs. The break is invisible in the finished installation but measurable in U-value and surface-temperature tests.
Performance benefits
Specifying a thermally broken framed roof light delivers:
- Lower whole-unit U-value — frame losses shrink, improving the figure used in SAP and SBEM.
- Warmer internal frame faces — reduced risk of internal condensation at corners and gaskets.
- Improved occupant comfort — fewer cold draughts radiating from perimeter metal.
- Regulatory headroom — easier to meet Part L notional benchmarks when roof glazing area is generous.
The glazing itself still needs a suitable IGU — low-E coatings, gas fill and warm-edge spacer — because the break does not replace glass insulation.
Frameless vs framed approaches
Framed roof lights integrate the thermal break in the perimeter frame — a proven route for weathering and thermal rating on flat roofs.
Frameless designs reduce visible metal; performance depends on the glazing edge seal, upstand insulation and any supporting structure. Always compare declared whole-unit U-values for the specific product and size rather than assuming one aesthetic is thermally superior.
What to verify on datasheets
When reviewing manufacturer data:
- Whole-unit U-value for your ordered dimensions.
- CE/UKCA thermal transmittance declaration to BS EN 14351-1.
- Temperature factor or condensation risk data where published.
- Evidence that the frame system includes a genuine thermal break, not merely a thin painted gap.
At Vant Glass thermal framed roof lights, thermally broken aluminium frames are paired with made-to-measure insulating glass for orders where heated rooms sit below the opening.
Related terms
Every Vant Glass roof light is made to order in Britain, backed by a 20-year guarantee and free UK mainland delivery. Configure frameless or framed sizes in the online calculators or call 03330 902 592.
Frequently asked questions
What is a thermal break made of?
Most aluminium roof light frames use a structural polyamide strip — often glass-fibre reinforced — rolled or injected between separate inner and outer aluminium extrusions. The strip is mechanically locked to both sections to maintain structural strength.
Are frameless roof lights thermally broken?
Frameless units minimise visible metal; thermal performance relies on the glazing edge and any supporting kerb or structural silicone detail. Framed systems integrate the break in the perimeter frame — compare whole-unit declared U-values for each approach.
Is a thermal break the same as double glazing?
No. Double glazing is an insulating glass unit. A thermal break insulates the frame. Both are needed for strong overall performance on a framed roof light over a heated space.
Do thermal breaks weaken the frame?
Properly engineered polyamide breaks are structurally bonded and tested with the frame system. Reputable manufacturers CE-mark the complete roof light assembly for load and weather resistance — not the metal profile alone.
When is a thermal break essential?
For any roof light separating a heated interior from cold external air — especially bedrooms, kitchens and living areas. Non-thermally broken frames are generally limited to unheated spaces or internal applications.
Related articles
- Thermal Performance
Condensation on roof lights
Condensation on roof lights forms when warm, moist indoor air meets a surface below the dew point — often at cold frame sections or poorly ventilated cavities. Thermally efficient units and correct detailing reduce risk.
- Thermal Performance
Part L and roof light thermal performance
Approved Document L sets energy efficiency requirements for buildings in England. Roof lights must meet applicable U-value limits and are modelled as part of the whole building envelope in SAP and SBEM.
- Thermal Performance
BS EN 1279 and insulating glass units
BS EN 1279 governs insulating glass units (IGUs) — sealed multi-pane assemblies with gas fill and spacer systems. It defines durability, moisture control and conformity assessment for glazing used in roof lights.
- Thermal Performance
Reducing heat loss through roof lights
Heat escapes through roof glazing via conduction, radiation and air leakage. Lower U-values, thermally broken frames, quality IGUs and careful installation all reduce losses over heated rooms.
- Thermal Performance
What is a U-value for roof lights?
A U-value measures how readily heat passes through a building element. For roof lights, the declared value usually covers the whole unit — glazing, frame and spacer — and lower numbers mean better insulation.
- Thermal Performance
Light transmission through roof glass
Light transmission describes how much visible daylight passes through glazing. For roof lights, it affects room brightness, colour rendering and whether solar-control or privacy coatings are needed.
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