How to Choose the Right Window Frame Material – the Pros & Cons of Each Option

Aluminium windows

One of aluminium’s greatest advantages is its strength and durability. Because of its innate stability, you can have smaller frames and larger panes of glass when compared to uPVC and timber. “Ultimately, you’re buying windows to look through and let in light rather than to stare at the frames,” says Edward Stobart, technical sales manager at IDSystems. This strength means it can be used for large picture windows, making it a particularly popular choice for modern properties with expansive glazing.

Although popular in contemporary schemes, aluminium needn’t be grey and square – it’s available in an almost infinite array of colours and can be curved to suit your design, making it very versatile. Having said that, it can be difficult to find casement, sash or other more traditional windows in aluminium, as there is less public demand for them.

Like all metals, aluminium is a natural conductor of heat, so the frame technology must counteract this if the windows are to be thermally efficient. This is often achieved through thermal breaking, where an insulating barrier is placed inside the frame to block the colder or hotter outside metal transferring that temperature to the internal aluminium.

Kloeber fitted the aluminium windows and doors for this timber-clad extension and capitalised on the material’s strength to create a large, slim-framed picture window that matches the small sightlines of the patio doors

Aluminium window maintenance

Compared to other frame materials, aluminium is lower maintenance as, apart from keeping the frame and opening mechanisms clean and lubricated, there is no ongoing upkeep needed. Its strength means it has a very long lifespan, too: according to the BRE, you can expect a well-maintained and looked after aluminium-frame window to last roughly 30-45 years.

When it eventually needs replacing, aluminium is fully recyclable and, even though it is carbon heavy to initially manufacture, its carbon footprint will be spread over a larger lifespan compared to uPVC, which has a shorter longevity.

Aluminium window costs

From a price perspective, aluminium is comparable to high-end timber so is at the top end of the market. Although, the cost gap between it and uPVC is narrowing over time. “Ten years ago, aluminium would have been about 50% more expensive, but now uPVC has developed technologically, it is only 15-20% more costly,” says Edward.

Composite alu-clad windows

Alu-clad is an abbreviation of aluminium-clad – a composite product that comprises a timber frame clad externally in aluminium. This is a great option for those who want the traditional visual appeal of timber for their interiors but lower maintenance and more weather-resistant aluminium external frames.

Even though totally timber frames can be very durable, alu-clad could be a more sensible option for those living in exposed or coastal areas where timber would need greater upkeep and repair. “For exposed locations, particularly by the sea, it’s worth looking specifically at the finish and corrosion resistance of the external aluminium rather than just accepting the base material,” says David Johnson, account manager at Internorm.

The alu-clad P31 window from Norrsken has internal sightlines of 44mm and can be made into a whole-window system with a U-value of 0.67 W/m²K

Alu-clad window maintenance

As most of the frame is timber with a layer of aluminium cladding, many of the benefits of alu-clad windows are the same as traditional timber – it naturally conducts heat much more slowly than metal, and – with the right care and maintenance – can be the longest lasting option. This makes it a good choice from both a thermal efficiency and durability perspective. While the strength of fully aluminium windows is often used to create slim frames with expansive glazing, alu-clad has the strength of timber, so cannot be used as well in this capacity.

Alu-clad window costs

Alu-clad tends to be more expensive than standard timber or aluminium as the base price of the timber is combined with the expense of aluminium cladding and the manufacturing involved to integrate the two. However, given that the finished product can last up to 65 years and allow people in exposed locations to have a low-maintenance timber frame option, it can very well be worth the cost.

Case study Farmhouse-style self build in Angus with sleek, high-performance alu-clad glazing

When Neil and Sandra Caul decided to build a multi-generational home, they had only one site in mind. Three fields away from their house at the time, they found a brownfield site with a series of derelict farm buildings on it. A planning application lodged by former owners for a house on the plot had been refused, and the planning authority said they didn’t see a scenario that would change their mind. “But the plot was beautiful with panoramic views, so we were keen to focus on this as the location for our new home,” says Neil. “We then met architect Ann Nisbet at a trade show and liked a house in rural Ayrshire she designed. She took us on and got us through planning successfully.”

Photo: David Barbour

In terms of Neil and Sandra’s brief, they were looking for a new house that was low maintenance, economical to run, had an ecological ethos and would accommodate a mix of family and private spaces for three generations to live comfortably. The overall design, built around the footprint of the original farm sheds, features three buildings formed around a shared courtyard. The main house is comprised of two, one-and-a-half storey buildings arranged as an L-shaped plan. The third structure is a one-bedroom single-storey annexe for Neil’s mother.

Photo: David Barbour

The first view on approach from the road is the south facing facade of the main house, and the three window apertures reflect the form of the cart shed buildings of rural Angus. The house features several stunning, triple-glazed picture windows with slim alu-clad frames. The windows have been designed without mullions to ensure expansive, uninterrupted views over the Perthshire hills, Fife and beyond. Even opening windows and doors are designed to maximise glazing and minimise frames. A mixture of aperture shapes adds playfulness to the overall exterior scheme – large square frames sit next to tall rectangular to add visual intrigue.

The Cauls utilised the east-west facades of the house to maximise solar gain through the windows – a continuous corridor from the east-facing master bedroom to the west-facing lounge with some well-placed windows along the way mean the sun can always enter the home. This, in combination with triple glazing everywhere, maximises the glazing’s potential to heat and illuminate the house.

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Steel windows

Steel and aluminium offer very similar finishes and qualities. Like aluminium, steel is exceptionally strong so is great for thin frames and large panes of glass, perfect for modern houses. It’s primary use historically, however, has been for Art Deco, early-20th century and industrial windows, meaning it is well suited to authentic restoration projects where other materials would feel out of place. If your heritage property is listed or in a conservation area, you may be obliged to replace faulty steel windows like for like – check with your local conservation officer.

Steel window maintenance

If well looked after, steel can be just as durable as aluminium, but it needs higher maintenance of its rust protective coatings to keep it healthy and maximise its longevity. It may therefore not be the most suitable choice for coastal or highly exposed homes. Like aluminium, it needs thermal break technology to ensure good thermal efficiency as, even though steel conducts heat less quickly than aluminium, it can cause heat loss and condensation if not properly insulated.

The Clement EB20 range of steel windows is designed to replicate the appearance of historic designs while improving their thermal efficiency and weather resistance

Steel window costs

Steel can be considerably more expensive as the raw material costs more, is heavier and requires more stages in the manufacturing process to protect it from rust. Many homeowners who want the look of steel without the price tag opt for steel-look aluminium – it’s also lighter and easier to maintain.

uPVC windows

In recent years, uPVC has progressed from the purely affordable option to an aesthetic and effective fit for many projects. “uPVC had a bad rep years ago, but it is a good product now and has a place on newer builds looking for something cost effective,” says Dave from Ventrolla. In the past, uPVC was available in only a limited selection of colours and designs, but now there are some convincing timber-effect ranges on the market that can be shaped to mimic heritage designs like sash or mullioned casement windows. When these styles are combined with historical-effect handles, they can produce a classic overall finish at a better price point.

Although there is greater uPVC design variation these days, the material is not as strong as others so isn’t a good fit for large expanses of glazing. Likewise, the sightlines on the frames cannot be as slim as with aluminium or steel, so it tends not to work on sleek modern frames where they are designed to be as unobtrusive as possible.

These timber-alternative uPVC sliding sash windows from Roseview Windows feature thoughtful details like run-through sash horns and deep cills. They are also available with trickle vents that are invisible from the outside

uPVC window maintenance

If you’re looking for a low maintenance material, uPVC needs little ongoing care apart from keeping all the mechanisms clean and lubricated. If kept in this state, the windows should last between 20-30 years before their performance is affected. Telltale signs that a uPVC window is nearing the end of its life is if the exterior starts to discolour and turn brittle.

uPVC window costs

Despite sitting at the more accessible end of the market, uPVC is prone to greater price fluctuations than other materials. “Plastic-based windows have increased in price quite dramatically recently. Because they are made from oil, prices can vary a lot,” says Dan.

How much does each window frame material cost?

Trickle vents, triple glazing, solar control glass, colour upgrades, heritage glazing bars, super-slim frames and lifting equipment can all change the final cost (keep reading for more on these elements). Installation is additional, and window replacement projects may also involve removal, disposal, making good and repairs to surrounding finishes.

These figures are indicative, supply-only starting points for a good-quality 1,200mm x 1,200mm double-glazed, double-opening casement window meeting current Building Regulations, excluding VAT and installation.