When every millimetre matters: specifying a low-profile deck framing system

8 October 2026

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For projects where deck height, durability and access to the substrate all need to be carefully considered, an aluminium framing system can offer a more robust alternative to conventional timber framing.

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On a drawing, the difference between a timber deck frame and an aluminium one can seem relatively minor. In practice, however, the choice of subframe can have a significant effect on the finished level, longevity and even how much space is available for the deck build-up.

For architects and designers working with tight floor-to-deck thresholds, membrane decks or existing slabs, those few millimetres can become particularly important.

This is where Unex’s TreadTech aluminium deck framing system has found its niche. Designed to work in situations where there is limited height available beneath the finished decking, the system can achieve a deck build-up of as little as 50mm including the aluminium frame and pedestal.

“The sweet spot is for use where there’s not much height down to a substrate,” says Unex’s Lincoln Thomas. “One common application is a second-storey membrane deck, where the finished level needs to sit close to the threshold of the internal floor.”

Conventional timber framing can become difficult to work with at these dimensions, particularly when the timber has to be cut down to accommodate a fall.

“When you get that small, the timber doesn’t stay nice and straight,” Thomas says. “Especially in time with the elements, it can buckle and bow.”

Unex' TreadTech system is ideal for projects where deck height and access to the substrate is important.

The same issue can arise when bringing an existing patio or concrete area up to the level of the interior floor. While an aluminium system may not necessarily be the lower-cost option at the outset, its dimensional stability means the finished deck is less likely to develop the movement and unevenness that can occur as timber weathers.

For designers, however, the advantage of working with a low-profile system goes beyond the immediate deck build-up. It can create opportunities to make better use of constrained spaces and simplify the relationship between the deck, building envelope and balustrade.

TreadTech can also be used in conjunction with balustrades that are attached directly to the deck framing, rather than relying solely on fixing back to the building. Thomas says this can be useful where there is limited room around the perimeter of a balcony, such as where an internal gutter or nib restricts the available fixing zone.

There is another consideration on deeper balconies. As the deck falls away from the building, the difference in height between the internal threshold and outer edge can become significant.

That can mean a taller balustrade is required at the perimeter, with increased structural demands.

Reducing the overall build-up of the deck can therefore help designers manage that relationship more efficiently.

The Tread Tech system can take timber, composite and tile decking.

Choosing the finished surface

The aluminium framing system is designed to accommodate several common decking finishes, giving designers flexibility over the appearance and materiality of the completed deck.

Timber is one option, including species such as pine and other timber decking products. Composite or WPC boards can also be used, as can structural pavers designed to span between supports.

The latter can offer a particularly useful alternative to placing large-format tiles directly on individual pedestals. While pedestal systems provide an adjustable solution, Thomas says achieving a consistently stable surface can be difficult, particularly across a sloping membrane.

“With a big square 600 by 600, one only has to be, say, a millimetre too low and it feels rocky,” he says.

An interconnected aluminium frame provides a more stable plane, helping the finished surface resist movement and rocking.

It also addresses an important practical consideration for membrane decks: access. Following changes to deck construction after the leaky homes crisis, the ability to access the membrane beneath the finished surface has become an important part of designing and maintaining these spaces.

With a framed system, decking or pavers can be lifted when access is required, whether to investigate a potential leak or reach a blocked outlet.

“It means you can always lift the decking or lift the tiles off,” says Thomas. “It makes maintenance and serviceability much better.”

That combination of low-profile construction, dimensional stability and access makes aluminium framing worth considering well before the decking finish is selected. For residential balconies, new homes and renovations, as well as apartments, aged-care projects and other shared outdoor spaces, the subframe can be an important part of the design rather than something that simply sits underneath it.

Explore TreadTech from Unex, or browse products, professionals and projects on ArchiPro for your next project.