Guides
Aluminium and Steel Windows: A Buyer's Comparison
Steel and aluminium windows are both metal, both slim and both sold as durable, and that is where the similarity stops. One rusts and one oxidises, one is welded and one is mechanically jointed, and the two fail in different places after a decade outside. This comparison takes the points a buyer actually has to weigh, in the order they change a decision.
Two metals, two failure modes
A steel window fails by corrosion. Rust starts where the coating is broken, spreads behind the paint film and eventually pushes it off, so the frame thins from inside the section. An aluminium window fails at its seals and hardware first, because the metal forms a protective oxide and holds its section. That difference decides which one rewards maintenance and which one punishes neglect on a coastal site.
Stiffness, wall and the size of the light
Steel is stiffer for the same thickness, which is why a steel window can carry a large light on a slim sight line. Aluminium gets its stiffness from depth and from the chamber layout: the 118 casement runs 118 mm across six chambers and a 2.0 mm wall, while the 112 casement, on the same wall, uses five chambers with a flush line. A light a steel section spans easily can still be built in aluminium, with a deeper frame as the trade.
Coating, repair and the second decade
Steel needs a protective system and a repaint cycle, and every repaint is a site operation on a scaffold. Aluminium takes anodising, a powder coat or fluorocarbon, with RAL matching and two-tone faces on request, and a damaged area can be recoated without stripping the frame. Neither coating is permanent. The difference is what a repair costs in access and disruption, and that is a building decision before it is a product one.
Wind load, weight and the fixing
A steel frame is heavy, and the weight goes into the fixing and into the lintel. An aluminium frame is lighter, so a large module is easier to handle and to fix into a thin wall, and the load path runs through the mullion rather than the whole frame. At height the question becomes deflection across the module, and deeper sections with heavier walls answer it in aluminium as a heavier steel section does.
Maintenance and how to compare the two
Steel asks for inspection of the coating, touching in of chips, and a repaint before rust takes hold. Aluminium asks for a wash, a check of the gaskets and a clear drainage path. Compare the two on one opening schedule with the same glass and the same finish requirement, then read the replies against the same drawing set. A frame needing scaffolding every few years is a different proposition from one needing a hose.
FAQ
Frequently asked
Which is cheaper, aluminium or steel windows?
It depends on the section, the finish and the size of the order rather than on the metal alone, so a like-for-like figure only comes from a quotation against your own schedule. Steel often starts lower on a small standard opening, and loses that position once a protective coating and a repaint cycle are counted over the years. Send the schedule through WhatsApp and compare delivered scope, not the headline.
Does aluminium rust?
No. It oxidises, and the oxide layer stays on the surface and slows further attack, which is why an unpainted aluminium section outlasts a bare steel one outside. What does fail is the finish at a cut edge and the hardware at a fixing. A coastal frame still needs the right coating and the right track material.
Is a steel window stronger?
It is stiffer for the same thickness, which is not the same as stronger in every case. A steel section carries a wide light on a slim line, and an aluminium frame reaches the same result with more depth and a chambered wall. Strength at the fixing and stiffness across the light are separate questions, and both are answered on the drawing.
Which needs more maintenance?
Steel, over a long life, because the coating has to be inspected and renewed and access is part of the cost. Aluminium needs washing, a gasket check and clear drainage. Neither is maintenance free, and a coastal site shortens the interval for both. Ask what a repaint involves before choosing a steel frame for a high elevation.
Can the two be mixed on one building?
They can, and the risk is a colour and joint mismatch rather than a structural one. Two metals in contact need a separation detail to avoid galvanic corrosion, and the finishes have to be matched on samples rather than on screens. Where a facade mixes both, fix the colour across the two systems at the sample stage.
Send your opening schedule
Series, glazing and finish come back as one quotation, with the full dimensional pack on PDF and CAD on request.