Recent studies demonstrate that high-performance timber windows achieve U-values as low as 0.8 W/m²K, while timber doors can achieve whole product U-values of 1.4 W/m²K and under. Wood also has a smaller carbon footprint than building materials such as steel, aluminium and concrete. Over a 50-year building lifecycle, these thermal performance advantages translate to measurable energy savings that compound the material's initial carbon storage benefits.
As carbon accounting becomes mandatory and net-zero targets tighten, it’s imperative to understand the environmental impact of choosing aluminium over timber windows and doors.
Aluminium production devastates ecosystems through bauxite mining. Operations have contributed to approximately 8,500 hectares of forest loss since 2018, with Brazilian Amazon mining causing 1.2 million hectares of deforestation between 2005-2015, representing nine percent of total forest loss.
Aluminium smelting requires 15.37 MWh of electricity per tonne, resulting in a CO2 footprint of 8.24 kg per kg of aluminium. This accounts for two percent of global carbon emissions, making fenestration choices significant contributors to building embodied carbon.
Timber represents the only genuinely sustainable material for window and door manufacturing. For every dry tonne of timber produced, 1.8 tonnes of carbon dioxide is taken from the atmosphere and remains locked up for the life of the wood product. Carbon dioxide is absorbed by trees and continues to be stored for the life of wood products, even timber products in landfill are still storing carbon. This means timber windows don't just have lower embodied carbon; they represent active carbon storage that continues throughout the building's life.
Responsibly harvested timber comes from managed forests where selective cutting promotes biodiversity and forest health. Modern forestry practices ensure harvest rates don't exceed growth rates, creating genuinely renewable material cycles. Certified schemes like FSC and PEFC provide verification that timber sourcing supports rather than undermines forest ecosystems.
The thermal performance difference between materials is stark. Aluminium’s thermal conductivity measures 237 W/mK, while timber has naturally low thermal conductivity that significantly reduces heat transfer across window frames. This natural insulation property translates into superior energy efficiency, with high-performance timber windows achieving U-values as low as 0.8 W/m²K, exceeding current legislation requirements of 1.6 W/m²K for new homes.
Recent studies by the Passive House Institute demonstrate that even thermally broken aluminium systems struggle to reach 1.2 W/m²K. Over a 50-year building lifecycle, this difference translates to measurable carbon savings that compound the material's initial advantages.
Modern timber windows achieve service lives that far exceed any aluminium systems. Aluminium faces degradation issues including thermal expansion stress, seal failure, and galvanic corrosion, particularly in coastal environments.
As embodied carbon regulations strengthen, continued aluminium specification becomes difficult to justify. Timber windows offer superior thermal performance, genuine sustainability, and support forest-based economies rather than extractive industries. In an industry responsible for 40% of global carbon emissions, every specification matters.
Image Credits:
Architecture: Downie North Architects
Build: Heuvel Construction
Photography: Tom Ferguson
Location: Queens Park, Sydney NSW
