Ask the Expert: Material Choice

Which metal is best for balcony construction? A good question and not easy to define without some explanation. Between 1992 and 2009 we specialised in stainless steel and aluminium balustrades. Then from 2009 to 2014 we were using mainly galvanised steel balconies along with our balustrade systems.

Since, we’ve developed our unique hybrid Glide-On™ system which uses all three metals! So, with all this experience we have a good knowledge of their characteristics.

What standards must balcony materials meet?

• must be non-combustible which is a class A rating. All three metals meet this condition.
• most are looking for a 60-year design life which is often a requirement of warranty providers. Aluminium and stainless steel meet this condition, but mild steel will always need a coating.

What material should soffits be made from?

• They will often perform a drainage function and are subject to prolonged water contact so a non-corroding material would seem sensible. Stainless steel is heavier and more expensive than aluminium, so the favourite for this item is aluminium.

Is aluminium or steel better in a fire?

• Neither metal burns – both are class A1.
• Following testing we carried out, we found that an aluminium soffit will keep the area above cooler during the first 30 minutes of a fire source from below due to its capacity to ‘heat-sink’ rather than reflect heat. This is particularly important as this initial period is essential for escape. While steel has a higher melting point, the amount of energy needed to melt it is nearly identical to aluminium. By the time temperatures become high enough for aluminium to melt (660.3⁰), any possibility of escape via the balcony has long since passed.
• Finally, an external fire will not reach such high temperatures as it would in an enclosed space. Either will be suitable but aluminium is preferred in an escape scenario.

Should I choose the metal based on strength or lightweight properties? What about the number of connections?

• Choose both. Anchors, stubs and arms can be made using a combination of stainless steel and galvanised steel.
• Choosing a lightweight balcony structure (e.g. aluminium) combined with stronger anchors minimises the number of penetrations required for connections. This leads to thermal improvements along with direct cost savings as there will be fewer fire stops, waterproofing interruptions and façade trims. You will also have a material that does not rely on a coating for its longevity.
• The lighter the balcony the fewer connections required and aluminium balcony frames weigh less than half of steel. Using aluminium frame, decking, soffits and vertical bars would mean a total weight of around 500-700kg whereas a steel version with WPC decking would be at least 1500kg

Which material has the most design flexibility?

• Steel, aluminium and stainless are all easy to profile and fold and all can be welded too.
• Aluminium is easy and cheap to extrude meaning bespoke designs can be easily created. Stainless and steel are not easily extruded meaning bespoke shapes are difficult and expensive.
• Steel must be corrosion treated before an aesthetic coating. Stainless and aluminium coat well and don’t need a prior protective coating. Aluminium can also be anodised or brushed anodised to create stainless steel appearances cost effectively.

Does my material choice affect my balcony deflection?

• Strength comes primarily from the anchors, the lighter the balcony and stronger the anchors, the fewer you need.
• Bolt-on balconies often rely on the strength of steel to stop flex in the balcony back member. Glide-On means moment forces are transferred to the slab edge, the best place to resist it.

Which material minimises corrosion risk?

• Steel can rust so all parts need to be galvanised or coated with a corrosion resistant finish, any defect, imperfection or damage to the coating may cause rust spots or rust weeping.
• Stainless steel does not corrode as steel does but the use of 316, or marine, grade is important in areas which will be visible. 304 grade can contract impurities if not regularly rain-washed, and develop surface imperfections.
• Aluminium does not rust and works well with stainless steel fixings.

Recommend me an approach….

We recommend you use a Hybrid of three materials,

• Stainless steel brackets, (best thermally and corrosion resistance and great strength)
• Galvanised steel stubs and arms (with stronger anchor designs these are best suited to transfer moment forces to slab edge and resist deflection)
• Aluminium Cassette frames, soffits and decking (lighter weight, ultimate corrosion resistance, cost effective, more sustainable, better suited for custom shapes, requires fewer connections)

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