Aluminum is one of the most thermally conductive metals in common use. Its thermal conductivity is approximately 160 W/(m·K) — meaning it transfers heat 2,000 times faster than uPVC. An aluminum window without a thermal break is essentially a perfect conductor of cold from the outside to the inside of your home. If you've ever touched the frame of an aluminum window in winter and found it ice-cold, this is why.
Schüco's thermal break technology solves this problem — and does it well enough to achieve Passive House certification in some systems. Here's how it works.
In This Article
1. What Is a Cold Bridge?
A thermal bridge (often called a cold bridge) is a path of high thermal conductivity that bypasses the insulation layer in a building envelope. In windows, the most significant thermal bridge is the window frame itself — particularly in aluminum systems where the metal profile conducts heat directly between inside and outside.
The consequence of a thermal bridge is twofold:
- Energy loss: Heat flows toward cold. In winter, thermal bridges draw warm interior heat toward the cold exterior faster than the rest of the wall, increasing heating demand.
- Surface temperature reduction: The interior face of a thermally bridging frame is significantly colder than the room air temperature. This cold surface can fall below the dew point of room air, causing condensation to form on the frame.
2. The Condensation Problem
Condensation on window frames is not just an aesthetic issue — it's a structural one. Persistent moisture at the window frame leads to:
- Mold growth at the frame-to-wall junction (a health concern and a building defect)
- Paint and plaster deterioration adjacent to the window reveal
- Timber damage in wood-framed reveals and sills
- Sealant degradation at the perimeter joint
In cold US climates — Connecticut winters with -10°F nights, Colorado mountain temperatures reaching -25°F — an aluminum window without an adequate thermal break will condense heavily on the interior frame surface, and in extreme cases, ice can form on the interior face of a non-thermally-broken aluminum window.
3. The Polyamide Thermal Break
Schüco's solution is elegant: instead of one continuous aluminum extrusion running from outside to inside, the frame is made of two separate aluminum sections connected by strips of polyamide (nylon 6.6 with glass fibre reinforcement).
Polyamide has a thermal conductivity of approximately 0.3 W/(m·K) — 500 times lower than aluminum. By inserting a continuous polyamide strip between the interior and exterior aluminum sections, Schüco interrupts the thermal conduction path completely. Heat can no longer flow freely through the frame from inside to outside.
The polyamide strip is poured into matching grooves machined into the aluminum extrusions and then mechanically crimped — a process called the "pour-and-debridge" method. The result is a single structural profile that behaves as a continuous frame mechanically while behaving as two separate profiles thermally.
4. Schüco Systems: MB-70, MB-86N, MB-104 Passive
Our three Schüco systems use progressively wider thermal breaks to achieve progressively better U-values:
Schüco Thermal Break Specifications
| System | Profile Depth | Thermal Break Width | Uw W/m²K |
|---|---|---|---|
| Schüco MB-70 | 70mm | 18mm polyamide | ~1.1 |
| Schüco MB-86N | 86mm | 26mm polyamide | ~0.98 |
| Schüco MB-104 Passive | 104mm | 34mm polyamide (triple-layer) | 0.78 ✅ PHI |
The MB-104 Passive achieves Passive House certification through a triple-layer polyamide strip system — three separate polyamide elements in sequence, creating two air gaps between the polyamide layers. This additional air resistance drives the thermal break's effective conductance down to a level that enables a whole-window U-value below 0.80 W/m²K in aluminum.
5. Thermal Break vs. No Thermal Break: The Numbers
To illustrate the impact, compare three aluminum window scenarios for a US home at -10°F (-23°C) outside, 70°F (21°C) inside:
- Aluminum without thermal break: Interior frame surface temperature approximately 32°F (0°C). Condensation and frost form readily. Uw approximately 4.0–5.0 W/m²K.
- Schüco MB-70 (thermally broken): Interior frame surface approximately 55°F (13°C). No condensation risk. Uw approximately 1.1 W/m²K.
- Schüco MB-104 Passive (advanced thermal break): Interior frame surface approximately 62°F (17°C). Well above dew point, no condensation under any US weather condition. Uw 0.78 W/m²K.
The difference between an aluminum window without a thermal break and a Schüco MB-70 is approximately 75% less heat loss through the frame. The MB-104 Passive takes this further to approximately 85% less heat loss vs. a non-broken aluminum frame.
6. Installation and Thermal Bridge-Free Detailing
Even a perfectly specified thermally broken window can be undermined by poor installation detailing. The window-to-wall junction is a thermal bridge risk zone — if the aluminum frame contacts the concrete or masonry structure directly, cold is conducted around the frame and into the interior.
For all our Schüco aluminum window installations, we provide detailed junction drawings showing the correct insulation continuity around the frame perimeter. Key principles:
- The window frame should sit in the insulation plane of the wall, not at the interior face
- Insulation should return around the reveal to the frame edge, eliminating the cold-bridge path
- The installation bracket or fixing should use thermal isolator clips to prevent direct metal-to-metal contact with the structure
We supply all required installation documentation with every order. For Passive House projects, our technical team provides project-specific junction details for review by the certifier.
