45 x 60 mm Aluminium Profile Solutions for Windows and Facades

01What does a water tightness test actually measure?

Not whether water touches the inside face. It measures whether water crosses the inner plane of the assembly while a pressure difference is applied to the outside and water is sprayed at a defined rate. Under ASTM E331 the usual arrangement is a static pressure of 20 percent of the design wind pressure, with a minimum around 300 Pa, a spray rate of about 3.4 litres per minute per square metre, held for 15 minutes.

The distinction matters because a frame can be wet inside and still pass. What the test looks for is water reaching the interior plane, which is a different question from whether water got past the outer seal. That is the whole logic of drained construction: let water in, then lead it out before it reaches the inner line.

02Why is a drain hole not the same as pressure equalisation?

A drain hole lets water out. It does nothing about the pressure difference across the inner seal, and that pressure difference is what pushes water in. If the chamber behind the outer gasket is sealed, water accumulates there and the pressure on both sides of the inner gasket is the same as the outside, so the inner gasket sees the full wind pressure and leaks.

Pressure equalisation is a different arrangement: the chamber behind the outer gasket is vented to the outside, so the pressure in the chamber tracks the outside pressure and the differential across the inner seal falls to nearly zero. The drain then removes whatever water got in, at low pressure, which is a much easier job.

• The vent area should be at least equal to the drain area, and preferably larger. A system with big drains and small vents does not equalise.
• The chamber needs depth, typically 5 mm or more, so it can hold the transient water without bridging to the inner seal.
• The inner seal should be continuous and on the warm side, so it is not the primary barrier against driving rain.
• Drain slots must not be blocked by the gasket when it compresses. Check the compressed gasket section, not the free one.

03How do NSCP wind speeds translate to a test pressure?

Through the velocity pressure, q equals 0.613 times the wind speed in metres per second squared, which gives pascals. For a basic wind speed of 250 kilometres per hour, that is 69.4 metres per second, and q is about 2,950 Pa. That is the velocity pressure, not the design pressure on a facade.

The design pressure applies pressure coefficients: roughly 0.8 outward on a windward wall and up to minus 1.5 at corners and edges, where suction governs. So a facade designed to 2,950 Pa velocity pressure sees a design pressure in the region of 2,300 to 2,400 Pa on the field of the wall, and considerably more at the corners. The water test pressure is then 20 percent of that.

04Is a 45 x 60 T-slot section a window system?

No, and it is worth being direct about that. A proprietary window system has gasket grooves, a thermal break and a drainage chamber built into the extrusion. A 45 x 60 T-slot section is a structural frame: it carries the glass, it takes a separate bead, and the gasket line and drainage path have to be created by the assembly detail.

That is not a criticism of the section. For shopfronts, screens, secondary glazing and facade supports it works well, because those assemblies are usually built with a separate bead and a machined drainage path anyway. What it will not do is replace a purpose-made window profile on a high-rise unitised facade, and a supplier who claims otherwise is selling you a problem.

05What happens at the coast with stainless fixings?

A galvanic couple forms, and the aluminium is the anode. Stainless steel is cathodic to aluminium in a chloride environment, so at every stainless fastener in contact with the frame, the aluminium around the fastener corrodes preferentially. The visible result is a white salt bloom around the fixing and pitting of the frame, and the structural result is a hole that grows.

The fix is isolation, not a different stainless grade. A nylon or EPDM washer under the head, a sleeve in the hole, and a sealant barrier at the interface all break the electrical path. It is cheap at the design stage and awkward to retrofit.

06What five numbers should be on the enquiry?

A facade enquiry is a performance enquiry. Give the performance and the section follows.

Location and wind zone

the NSCP basic wind speed for the site, not the city name

Water test requirement

ASTM E331 or AAMA 501.1, and the pressure to be held

Glass and span

thickness and panel size, because the span check needs both

Coating class

AA20 or AA25 depending on distance from the shore

Assembly type

shopfront, screen, secondary glazing or facade support, because they drain differently

Section

45 x 60 mm at 2.8 kg/m, or 45 x 90 at 4.10 kg/m for taller panels

Related sections and categories

The 45 x 60 is listed under 45 Series Aluminium Profiles, and the 45 x 90 mm six slot section at 4.10 kg/m covers taller panels. For outdoor structures rather than windows, the typhoon-zone frame page covers wind load on freestanding frames.