Energy-efficient construction has become one of the major trends in contemporary architecture. More and more homeowners are paying attention not only to the appearance of the building, but first and foremost to its energy performance.
Properly selected windows play a key role in this – up to 25-30% of heat may be lost through the fenestration. Therefore, choosing the right window system is not only a matter of comfort, but also of real savings in the household budget.
What’s the difference between energy-efficient and passive construction?
An energy-efficient home is one that uses modern technologies to minimize heat loss and energy consumption. A passive house goes further: its heating demand is so low that most of its warmth comes from internal gains (occupants, appliances) or solar heat, requiring only minimal supplemental heating.
In Europe the difference is often defined by the U-factor (thermal transmittance) of a window: the lower the U-value, the better the insulation. For example, in some European rules you might see targets like Uw ≤ 0.9 W/(m²K) for energy-efficient windows, and Uw ≤ 0.8 W/(m²K) for passive construction.
Why invest in high-performance windows?
Modern energy-efficient windows can significantly reduce heating (and sometimes cooling) loads. Replacing older windows with Uw ≈ 1.3–1.5 W/(m²K) with ones meeting Uw ≤ 0.9 W/(m²K) may reduce heat loss by roughly 30%. That can mean savings from hundreds to several thousands of dollars annually – depending on building size, local climate, and heating source.
Alongside lower energy bills, you get improved thermal comfort and acoustics: fewer drafts, no cold spots near the glass, less outside noise intrusion.
To qualify as an energy-efficient window, one should look for:
a triple-pane glazing unit with a glass U-value (Ug) of about 0.5-0.6 W/(m²K) or better,
a “warm edge” spacer to reduce thermal bridging,
a multi-chamber frame with at least three seals,
proper installation in the insulation layer (so-called “warm installation”),
high air-tightness (e.g., equivalent to class 4 under EN 12207 for European products).
For passive houses the requirements are even more stringent: apart from Uw ≤ 0.8 W/(m²K), the frame’s U-value (Uf) may need to be ≤ 1.0 W/(m²K), and the glazing Ug ≤ 0.7 W/(m²K).
Windows from Bertrand for energy-efficient and passive homes
At Bertrand we offer a wide range of window systems that meet – or exceed – the current efficiency requirements for high-performance fenestration.
Some are even designed for passive house construction and carry official certifications from the Passive House Institute (PHI).
| System | Type | Installation depth | Uw value* | Intended use |
|---|---|---|---|---|
| LINEAR | PVC | 74 mm | up to 0.80 W/(m²·K) | Energy-efficient |
| KONTUR | PVC | 82.5 mm | up to 0.70 W/(m²·K) | Energy-efficient |
| MB-104 Passive | Aluminium | 95 mm | from ~0.53 W/(m²·K) | Passive |
| Alutrend Passive | Wood-Alu | 106 mm | from ~0.61 W/(m²·K) | Passive (PHI certified) |
*Uw values are reference values under European metric standards for the specific systems.
Alutrend Passive Classic – certified fenestration for passive buildings
The Alutrend Passive Classic system is designed for the most demanding projects combining top energy performance with premium craftmanship. With a profile depth of 106 mm, triple seals, and glazing unit Ug = 0.5 W/(m²K), the system achieves Uw ≈ 0.78 W/(m²K).It is officially certified by the Passive House Institute (PHI), meaning it can be used safely in passive-house projects across Europe.
The combination of natural interior wood and durable exterior aluminium delivers long-term stability, beauty and high performance.
How to choose windows for an energy-efficient home (US version)
Look at the whole-window U-factor (in the US, this might be labeled simply U-factor rather than Uw). The lower, the better.
Choose a high-performance glazing package: triple-pane, low-E coating, inert-gas fill (argon or krypton).
Ensure the window frame is well insulated and has multiple seals and warm-edge spacers.
Pay close attention to installation quality: a high-performance window improperly installed will not perform.
Consider building orientation: large glazing toward the south can capture solar gains, while north-facing windows benefit from better insulation.
Think about additional shading: exterior roller shades or blinds can reduce unwanted heat gain and improve efficiency.
Is it worth it?
Absolutely. Specifying high-performance windows is an investment in comfort, energy savings, and long-term building value. For homes built in the US that target high performance (e.g., very low-energy or near-passive houses), make sure the selected products are certified by recognized bodies such as the NFRC (National Fenestration Rating Council). Look for published U-factors and solar heat gain coefficients (SHGC) suited to your climate zone and design goals.
With the right specification and installation, you’ll get a durable, comfortable, and efficient building envelope – and long-term savings on energy costs.