Timber-aluminium composite window

What is a timber-aluminium composite window?

A timber-aluminium composite window combines two materials into a single integrated frame: a timber core that faces the interior and an external aluminium protective casing. The timber, typically FSC- or PEFC-certified pine treated with water-based acrylic or clear lacquer, provides superior thermal insulation and natural aesthetic warmth inside the home. The external aluminium skin, usually fabricated from EN AW-6060 or EN AW-6063 alloy and powder-coated in any RAL colour, shields the timber from direct weather exposure and maintenance.

The two layers are mechanically and thermally bonded, with the timber functioning as a thermal break between interior and exterior environments. Most designs use triple glazing with argon gas between panes to maximise energy performance. The entire assembly is sealed with multi-layered compression gaskets that provide both airtightness and weather resistance, critical properties for passive-house performance and condensation prevention.

How is a timber-aluminium window different from timber-only or aluminium-only windows?

Timber-only windows deliver excellent thermal performance and natural warmth but require regular maintenance: repainting every 5-10 years and careful monitoring for moisture and rot, particularly in Slovakia's humid continental climate. Aluminium-only windows are durable and virtually maintenance-free but transfer heat far more readily; they require thermal breaks (polyamide or polyurethane) within the frame to avoid cold-surface condensation, and they achieve lower thermal performance than timber.

What makes timber-aluminium windows suitable for passive houses?

Passive-house design demands exceptional thermal performance: whole-window U-values of 0.80 W/m2K or lower. Timber-aluminium windows routinely meet and exceed this. A quality timber-aluminium frame paired with triple-glazing (two sealed cavities with argon gas) and a sill detail optimised for thermal continuity can achieve whole-window U-values as low as 0.60-0.64 W/m2K.

The timber core acts as a thermal insulator; the aluminium exterior, though thermally conductive, carries only weather exposure and minimal heat load. Advanced thermal-break design (foam or rubber gaskets between aluminium components) ensures that the exterior metal does not conduct cold into the interior. The result is a frame temperature close to room temperature, eliminating the condensation risk that could trigger mold in a highly sealed, low-ventilation passive house.

In Slovakia, where passive-house design is increasingly adopted for new residential construction and deep energy renovation, timber-aluminium windows from manufacturers like Internorm, KUNAJ, and local joineries have become the standard choice. Their ability to integrate seamlessly with high-performance walls, roofs, and heat-recovery ventilation systems makes them essential to meeting Passive House Institute standards.

How much maintenance do timber-aluminium windows require?

The maintenance demand is exceptionally low. The powder-coated aluminium exterior never needs repainting; periodic cleaning with mild soapy water and occasional lubrication of hinges and locks (twice yearly) is all that is required. Unlike timber-only windows, the aluminium shield protects the timber core from direct UV and rain exposure, eliminating the primary drivers of paint degradation and wood movement.

The timber interior may be refreshed optionally every 15-20 years if aesthetic appearance is the concern, but this is purely cosmetic. The protective coating applied at manufacture remains effective far longer. Modern construction standards, including advanced moisture barriers, drainage systems built into the frame, and precision sealing, have effectively eliminated the historical moisture and rot risks that affected timber windows in Slovakia's humid continental climate with high rainfall in spring and autumn.

What is the typical lifespan of timber-aluminium windows?

Timber-aluminium windows routinely deliver 40-50 years of service or longer. Unlike double-glazed units (whose seals typically degrade after 20-25 years and require replacement), modern timber-aluminium frames are designed for disassembly: the glazing unit can be removed and re-sealed or replaced without replacing the entire frame. With proper care, the frame and hardware can last 60+ years, making them significantly more durable than uPVC windows (typically 25-30 years) and competitive with high-quality all-aluminium systems.

What thermal performance should you expect?

Whole-window thermal transmittance (U-value) depends on the glazing type and frame depth. A typical timber-aluminium window with double glazing and 78 mm frame depth achieves a U-value of around 0.85-0.95 W/m2K. Triple glazing with a thicker frame (85-90 mm) and advanced thermal break design pushes this down to 0.60-0.70 W/m2K, approaching or exceeding Passive House performance targets. The glazing typically comprises two or three sealed panes filled with inert argon gas, which provides superior insulation compared to air alone.

In Slovakia's climate, characterised by cold winters with significant heating demand and warm summers where cooling can become problematic, this level of performance proves decisive. Minimal heat loss through windows during winter heating season is essential for maintaining interior comfort without excessive energy consumption. Conversely, minimal solar heat gain in summer can be managed through external shading strategies such as fixed or operable brise-soleil, external blinds, or deciduous vegetation, which prevents overheating without compromising daylighting.

The airtightness of timber-aluminium windows (typically n50 = 0.3-0.5 air changes per hour at 50 Pa pressure difference) means they contribute effectively to the overall air barrier in well-designed building envelopes. This airtightness is especially important in Slovakia's climate zones where wind speeds can be significant and where air leakage through window frames historically contributed to draughts and thermal discomfort. When specified with high-performance triple glazing and proper installation detail at the window sill and reveal, timber-aluminium windows become a decisive component in achieving Passive House certification.