Aluminium Subframes for Australian Windows

Why Use a Subframe?

The junction between a window and a wall needs to accommodate installation tolerances, drainage and, in some buildings, structural movement. A subframe helps deal with these requirements.

For example, a sub-sill provides a base for positioning the window and a path for water to drain outside. A suitably designed sub-head allows clearance above the frame for movement, such as deflection of the floor slab overhead.

Not every aluminium window needs a subframe. Other systems use timber reveals or fixing lugs. The choice comes down to the window system and wall construction, not simply the material the window is made from.

Sub-head, Sub-sill and Sub-jamb

These names describe where each section sits:

Sub-head

Across the top of the window. It receives the main frame’s head and can accommodate movement where the system is designed to do so.

Sub-sill

Beneath the window. It receives the main sill and forms part of the drainage arrangement. Its ends need to be correctly closed and sealed so water does not escape into the wall.

Sub-jamb

Along either side of the window. It receives the main frame’s vertical edges, sometimes with a matching clip or cover.

These sections must suit the selected window system. Profiles from different systems should not be assumed to fit or perform together.

Is a Subframe the Same as a Timber Reveal?

No. A timber reveal lines the opening between the window frame and the internal wall face. In a reveal-fixed installation, it also provides a connection to the building’s timber framing.

An aluminium subframe is a metal receiving system around the main window frame. Specifying one does not automatically resolve the internal reveal or wall finish; those details still need to be agreed.

What to Check Before Ordering

Make sure the drawings distinguish the main window frame size, overall subframe size and building opening size. A quoted window dimension should not be assumed to include the subframe or installation clearance.

Confirm which sections, seals, clips and end caps are included in the supply, along with the finish and installation responsibilities.