Cladding Framing Systems for Rainscreen Façades

A cladding framing system, also called a rainscreen subframe or support system, is the frame of brackets and rails that holds a façade off the building, and BDF Architectural designs, supplies and installs aluminium and galvanised steel cladding framing systems for rainscreen and other cladding on commercial and residential façades. We install across London and the South East and supply UK-wide, for main contractors, developers and architects.

The framing fixes back to the structure, carries the weight of the panels and the wind load on them, and sets the cavity behind the cladding. Bracket spacing, rail sizes and fixings are engineered to the wind load and to the panel system, so the framing is designed with the cladding rather than chosen from a catalogue.

Cladding framing is not the same as SFS, the light gauge steel framing system used to build infill backing walls between the floor slabs. The SFS wall, with its sheathing board and membrane, forms the backing wall; the cladding framing is fixed through the insulation in front of it, with the brackets normally fixed into the SFS studs or the slab edge rather than into the sheathing board alone.

A typical system has three parts: brackets fixed to the structure or backing wall, vertical or horizontal rails fixed to the brackets, and the clips, rivets or screws that hold the panels to the rails. Helping hand brackets, the L-shaped wall brackets most systems use, adjust in depth so the rails can be set to a true line in front of an uneven wall, taking up the tolerances in the structure. The bracket length also sets the depth of the cavity and the thickness of insulation it can take.

Aluminium framing is light, does not corrode and is easy to adjust on site, which is why it is the usual choice behind aluminium rainscreen panels. Galvanised steel is stiffer and is often used where loads or spans are higher. Where aluminium and steel meet, they are isolated from each other to prevent galvanic corrosion.

Aluminium expands and contracts with temperature more than the building behind it, so rails are not fixed rigidly at every bracket. Each rail has a fixed point that carries its weight, and the other brackets act as sliding points, with slotted holes that let the rail move along its length. Rails are broken with a gap at intervals, usually at each floor, so the movement does not build up along the façade.

Every bracket is a small thermal bridge through the insulation. Thermal isolator pads behind the brackets, or thermally broken brackets, reduce the heat lost through them, and the number and type of brackets are taken into the wall's U-value calculation.

What the brackets fix into matters as much as the brackets themselves. Concrete frames, steel frames and lightweight backing walls each need a different fixing design, so structural information about the backing wall is needed early. Where the specification or the anchor manufacturer calls for it, pull-out tests on the substrate confirm the anchors will carry the design load before the framing goes up, which is particularly important on existing buildings.

The framing is chosen to suit the panel system: aluminium cassettes hang on or fix through the rails, flat sheets are riveted or screwed, and fibre cement, ceramic and other panels each have their own rail and clip arrangement. As part of the external wall, the brackets, isolators and fixings are specified against Approved Document B and the fire strategy with the rest of the wall.

We install framing on new build and refurbishment projects, usually as part of an aluminium rainscreen package with the rails set out to the panel joints, so the brackets, rails and panels are designed, checked and installed by one team. Our guide What is rainscreen cladding? shows where the subframe sits in the wall build-up. To price, send elevations and sections, the cladding system, the backing wall and structure, the target U-value, and programme dates.