How to specify aluminium curtain wall profiles — a buyer's checklist

First decide the system, not the profile

Stick systems arrive as bars and are assembled on site: mullions go up, transoms go in between, glass is glazed from outside. They are cheaper to ship, tolerate site dimension changes, and need more labour and more scaffolding time on the façade.

Unitised systems are assembled and glazed in a factory into storey-height frames, then hung on the building. Installation is fast and quality is repeatable, but the profiles are more complex, tolerances tighter, and any error is expensive because it is already glazed.

This choice comes first because it changes everything downstream — the section geometry, the gasket layout, the machining, even how the extrusions are packed. Telling a supplier "curtain wall profile" without saying stick or unitised is the single most common reason a quotation is meaningless.

What actually sizes the mullion

Buyers often ask for a profile by weight per metre. That is backwards — weight is the outcome, not the input. What sizes a mullion is the wind load at that building's height and exposure, the floor-to-floor span it has to bridge, and the weight of the glass unit it carries.

Give a supplier those three and the section can be checked. Give only a weight target and you will get a profile that hits the weight and may not hit the deflection limit — which is the number that actually matters on a façade.

If the façade engineer has already run the calculation and issued a section drawing, send the drawing. Extruding to a proven die is faster, cheaper and lower-risk than redesigning a section from scratch.

Thermal break: when you actually need it

A thermal break is a low-conductivity strip — usually polyamide — mechanically locked between the inner and outer aluminium sections so heat cannot bridge straight through the metal. It turns one profile into two thermally separate halves.

It is not automatic. In a hot dry climate with no heating season and no condensation risk, a plain profile may be entirely adequate and considerably cheaper. In any project with a real heating or cooling load, a condensation requirement, or an energy code to satisfy, the break is not optional.

The decision belongs to the project, not the supplier. What we need from you is simply which one the specification calls for — retrofitting a thermal break into a section after tooling is made is not a small change.

Alloy, temper and tolerance

6063 in T5 temper is the workhorse of architectural extrusion: it extrudes into complex thin-walled sections cleanly and finishes beautifully. Where a member carries more load than 6063 comfortably allows, 6082 in T6 offers higher strength at the cost of a more difficult extrusion and a less forgiving surface.

Dimensional tolerance is where curtain wall differs from ordinary profile work. We extrude to EN 12020, and for façade sections the tolerances that matter most are usually straightness and twist over the full bar length, not just cross-section dimensions — a mullion that is dimensionally perfect but bowed will fight you on site.

Ask for the dimensional inspection report. It is part of our standard QC and costs you nothing to request.

Finish — and why the façade case is different

For façades the finish is not cosmetic; it is the corrosion protection on a surface that will never be re-coated. Both anodizing and powder coating perform well, and the honest comparison between them is a longer discussion — we wrote it up separately.

What is specific to curtain wall: coastal and high-UV sites deserve a deliberate conversation about coating grade and pre-treatment rather than a default. And on a large façade, batch-to-batch colour consistency is visible in a way it never is on a window — if the elevation is one continuous colour, say so in the enquiry, because it affects how the order is batched through the finishing line.

Coating thickness and salt-spray testing are part of our standard quality checks, and the reports are available on request.

The six things to send with an enquiry

1. System type — stick or unitised. 2. Section drawings, or the wind load, span and glass weight if the section is not yet designed. 3. Thermal break: required or not. 4. Alloy and temper if the specification fixes them. 5. Finish — anodized shade or RAL number, plus the site environment. 6. Quantity in tonnes or metres, and the delivery window.

With those six, a quotation is a real number you can build a budget on. Without them, any figure you receive is a guess dressed up as a price — which helps nobody.