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Citi Homes Windows

Aluminium vs timber windows. When to choose which for a London property?

Aluminium and timber are the two materials that dominate serious window specifications in London. uPVC rarely features in projects of any real value, or where planning conditions apply. The choice between aluminium and timber is a genuinely complex one – the right answer depends on the property, the planning context and what the owner needs from the windows over the next several decades.

Thermal performance. What the materials do?

Timber is a naturally poor conductor of heat, which means a timber frame contributes positively to the overall thermal performance of a window without requiring any additional technology. Aluminium conducts heat readily, around a thousand times more so than timber, which is why every aluminium window made for residential use incorporates a thermal break: a polymer strip bonded within the frame profile that separates the two aluminium sections and interrupts heat transfer. The quality and depth of that thermal break varies considerably between systems and manufacturers.

In practice, both materials can meet current UK Building Regulations comfortably with a standard double-glazed unit. The performance gap between a well-specified timber window and an aluminium window with a good thermal break is smaller than is generally assumed. The glazing unit itself, the gas fill, glass coating, and spacer bar type typically have more bearing on the whole-window U-value than the frame material alone.

Maintenance. The full picture

Maintenance is where the two materials diverge most clearly, and it is frequently what drives the decision for homeowners without planning constraints. Aluminium asks very little of the owner; occasional cleaning is about all that is required. The powder coat finish resists fading and does not need repainting. A well-made aluminium window from a reputable manufacturer can realistically last 40 years or more, with seals and hardware needing periodic attention but the frames themselves remaining largely trouble-free.

Timber requires ongoing care. Externally, frames should be inspected annually and repainted roughly every five years, with north-facing or exposed elevations needing more frequent attention. The base of the frame and the cill are the areas most susceptible to water damage and the most costly to put right if maintenance has been deferred. Well-maintained timber windows last as long as aluminium; there are original timber windows in Victorian and Edwardian properties across London still performing after well over a century. The difference is that aluminium demands far less of the owner throughout its life.

For owners who want to retain the internal character of timber without any external painting commitment, alu-clad timber is worth considering. It is the most expensive option in the market, but it eliminates external maintenance while preserving the internal appearance that matters to many period property owners.

Cost. Upfront and over time

Aluminium is typically 15-25% cheaper than high-specification timber at the point of purchase. For a full window replacement on a typical London semi-detached house, aluminium costs in the region of £8,000-£18,000 supplied and installed, depending on the number and size of openings and the system specified. Timber runs from roughly £12,000-£25,000 for a comparable scope, while top-end alu-clad timber can reach £30,000 or more for a whole-house replacement. Over 30 years, factoring in maintenance costs, aluminium and well-maintained timber come out broadly comparable – the gap only widens if the timber is neglected.

When timber is the right choice

In conservation areas, timber is often a requirement rather than a preference. The majority of London’s local planning authorities specify timber as the preferred or required material for like-for-like window replacement in conservation areas, on the basis that it most closely matches the original fabric. Some boroughs have become more flexible – a number now accept slim aluminium or alu-clad windows where the face width, mouldings and glazing bar arrangement closely replicate the original – but this varies considerably between London’s 33 boroughs and should always be confirmed with the local planning authority before specifying.

For listed buildings, the position is stricter: listed building consent almost always requires timber on primary elevations, and secondary glazing within a timber frame is typically the accepted route to improved thermal performance without altering the external appearance. Beyond planning, where period character matters, and the detailing needs to match the original construction, timber remains the appropriate material. It can be moulded, rebated and profiled to match the section and proportions of original Victorian, Edwardian and Georgian window sections in a way that aluminium extrusion cannot easily replicate.

When aluminium is the right choice

For contemporary rear extensions, new builds and projects where slim sightlines and a modern aesthetic are central to the brief, aluminium is the natural specification. Its profile dimensions suit large-format glazing, floor-to-ceiling windows and the minimal framing typical of modern London residential architecture. Anthracite grey, black and off-white are the dominant finishes on this type of work, and systems from manufacturers such as Schueco, Reynaers and Cortizo are specified by architects by name for exactly these projects.

For large spans – bifold and sliding doors over 3m, curtain walling and corner glazing – aluminium is the practical engineering choice. Timber at that scale becomes heavy and expensive to fabricate and handle. For main contractors managing multi-unit schemes, aluminium’s combination of consistent performance, low maintenance and cost efficiency at volume makes it the dominant material on London residential developments.

The planning position in London conservation areas

The assumption that aluminium is automatically refused in London conservation areas is not well founded in current planning policy. Decisions are based on whether the proposed change affects the character and appearance of the area – not on material alone. A well-specified aluminium system with an appropriate profile and finish can be accepted in a conservation area where the result closely matches the original. The practical advice is to confirm the position with the local planning authority before specifying anything. A brief conversation at that stage takes considerably less time and effort than resolving a planning issue after an order has been placed.

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