Fibre Reinforced Facade Encyclopedia: Materials
Facade panels are large-format prefabricated elements that form the visible outer face of a building envelope, engineered together with the substructure, fixings and joints that hold them there. A facade panel is only half a product. The other half is the system that carries it, lets it move and keeps water out, and that half is where facades succeed or fail. For choosing the panel material in the first place, see cladding panels.
A 3 by 1.5 metre GRC panel in a Sydney facade grows and shrinks by roughly 2 to 3 mm over a year from temperature and moisture alone. The joint has to absorb that movement plus the erection tolerance plus the frame’s own deflection.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Typical panel size | 1.2 by 2.4 m up to 3 by 6 m | Material, transport and crane dependent |
| Substructure depth | 60 to 250 mm | Cavity plus bracket plus rail |
| Ventilated cavity | 25 to 50 mm clear | Rainscreen drainage and drying |
| Joint width | 10 to 20 mm typical | Sized for movement plus tolerance, not for looks |
| Panel erection tolerance | plus or minus 3 to 5 mm | Against a frame tolerance often three times that |
| Thermal movement, GRC | 10 to 20 x 10⁻⁶ per °C | Plus reversible moisture movement |
| Thermal movement, FRP | 15 to 30 x 10⁻⁶ per °C | Larger joints or sliding fixings required |
| Design wind pressure | 0.5 to 3.0 kPa | AS/NZS 1170.2; sets fixing count and panel span |
| Facade test suite | AS 4284 serviceability, water, structural, proof | Full-size specimen in a test rig |
| Sealant service life | 10 to 20 years | Shorter than the panel; design for reglazing access |
The five parts of a panelised wall
Every panelised facade resolves into the same five parts. The panel carries wind load in bending and its own weight in plane. The fixings transfer both back to the structure and allow differential movement. The substructure, whether a bracket and rail system, a steel stud frame or cast-in anchors alone, spans between panel and building frame. The joint closes the gap between panels while allowing movement. The cavity behind drains and ventilates.
Specifying the panel without the other four is the most common gap in a facade worksection. A supplier quotes a panel; only a facade engineer confirms that the system carries the load, accommodates the movement and sheds the water.
Substructure and fixing
Fixings are grouped by what they do rather than what they look like. Gravity fixings carry the panel’s dead load and are few, often two per panel, located and detailed to allow no vertical slip. Restraint fixings resist wind load in and out and are slotted or flexible so that the panel can expand without loading the bracket. A panel hung on four rigid fixings will crack itself, and so on a GRC panel the standard arrangement is gravity anchors at the bottom and flex anchors above.
Three substructure types dominate: cast-in sockets and angles, where the panel fixes to a slab edge or column directly; bracket and rail systems, where a bracket carries a rail that the panel hooks or bolts to; and steel stud frames, where the panel is built onto its own frame in the factory and the frame is what gets lifted. Rail systems give the most adjustment and the easiest single panel replacement. Stud frames give the fastest erection and the largest units.
Joints and movement
The joint has to absorb four things at once: reversible thermal and moisture movement in the panel, irreversible shrinkage or creep in the panel and in the building frame, the erection tolerance that was needed to get the panel on the wall, and inter-storey drift under wind and, in some buildings, earthquake. Adding those up honestly is what produces the 15 to 20 mm joint that architects usually want to reduce, and reducing it is what produces the cracked panel corners three summers later.
Two strategies are in use. A sealed joint uses a gun-grade sealant over a backer rod, sized so it works within its movement accommodation factor of 25 or 50 percent. It is simple, and it is a maintenance item, because the sealant needs replacement long before the panel does. An open joint, used in a rainscreen, is left unsealed and relies on a drained and ventilated cavity with a continuous weather barrier behind it. Open joints shed the maintenance liability but demand a properly detailed cavity and a robust membrane.
Movement joints in the building structure must pass through the facade, not be bridged by it. Every panel layout should be set out from the structural movement joints first and the grid rationalised afterwards.
Tolerance, and why it decides the joint
Panels are made to factory tolerance and installed against a building built to site tolerance, and the two are not in the same order of magnitude. A GRC or FRP panel is typically produced to plus or minus 3 mm on overall dimension and plus or minus 3 mm on bow. An in-situ concrete frame is commonly out by 15 to 25 mm over a floor, and cumulative deviation over several floors can be larger again.
The system absorbs the difference in three places: bracket adjustment, usually 20 to 40 mm in three axes; packing behind the bracket; and joint width. When bracket adjustment runs out the installer packs, and when packing runs out the joint takes it, which is why a nominal 15 mm joint becomes 8 mm in one bay and 22 mm in the next. Survey the frame before the panel schedule is released and build the measured deviation into the setting out.
Water, air and weathering
A panelised wall is not waterproof at the panel face and is not designed to be. It is designed to control water, either as a face-sealed wall where the panel and sealant are the line of defence, or, far more commonly now, as a rainscreen where the panel is a screen, the cavity drains and ventilates, and a continuous membrane on the backing wall is the actual weather barrier. Pressure equalisation in a compartmented cavity reduces the driving force that pushes water through joints in the first place.
Weathering is the visible consequence of how water leaves the wall. Runoff concentrating at a sill or projection streaks the panel below, and on cementitious panels it mobilises efflorescence. Drips, throats and recessed joints are the means by which a facade ages evenly rather than in stripes.
Proving the assembly
Above a modest scale the facade is tested as an assembly before it goes on the building. AS 4284 sets the sequence on a full-size specimen in a rig: serviceability air infiltration and water penetration, a static structural test at design pressure, a dynamic water test and a proof test above design pressure. The specimen is the worst case bay, with a horizontal joint, a vertical joint and at least one movement joint.
A visual mock-up runs alongside and settles what the rig cannot: finish, colour consistency, joint shadow. Both should be signed off before the production moulds are committed.
Standards and references
- AS 4284 Testing of building facades
- AS/NZS 1170.2 Wind actions; AS/NZS 1170.0 general principles for serviceability limits
- AS 3600 and AS 3610 (concrete and formed finishes); AS 4100 (steel substructure)
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products (anchor and frame guidance)
- ASTM E283, E331 and E330 (air, water and structural performance of curtain walls, US equivalents)
- NCC 2022 Volume One, Part F3 (weatherproofing of external walls) and Specification 7 (check the edition adopted in your jurisdiction)
- NATSPEC worksections for rainscreen and panel cladding
Where this matters on a ShapeShift project
One Sydney Harbour, Barangaroo: A high rise residential tower, and a clear illustration of why a facade panel is designed as a system rather than as a sheet. Panel format, fixing type, joint width and movement allowance are resolved against one another before any panel is made.
Related terms
Questions specifiers ask
What is the difference between facade panels and cladding panels?
Cladding panel is the broader material term, covering any prefabricated outer sheet or unit. Facade panel usually means a large-format element engineered as a system, with its own substructure, fixings and joint design. The distinction is one of scale and engineering rather than of material.
How wide should the joint between facade panels be?
Wide enough to absorb thermal and moisture movement, frame movement, inter-storey drift and erection tolerance together. On a 3 metre panel that is usually 15 to 20 mm. Setting the joint from the elevation drawing rather than from a movement calculation is the most common cause of edge cracking.
Are facade panels fixed with two fixings or four?
Both, doing different jobs. Two gravity fixings carry the dead load; the remaining restraint fixings resist wind and are slotted or flexible so the panel can move. Four rigid fixings will restrain the panel against its own expansion and crack it.
Do facade panels need a waterproof joint?
Not in a rainscreen. The joint is left open, the cavity is drained and ventilated, and a continuous membrane on the backing wall is the weather barrier. In a face-sealed wall the joint sealant is the barrier and becomes a maintenance item on a 10 to 20 year cycle.
What testing is required for a panelised facade in Australia?
AS 4284 on a full-size specimen covering air infiltration, water penetration under static and dynamic conditions, structural performance at design wind pressure and a proof test above it. A visual mock-up is run alongside for finish and joint appearance.
How much adjustment should a fixing system have?
Enough to absorb the difference between factory tolerance of a few millimetres and site tolerance of 15 to 25 mm per floor. Bracket systems typically offer 20 to 40 mm of adjustment in three axes, plus packing. Survey the frame before releasing the panel schedule.
Bring the fixing and joint design into the panel design early. ShapeShell supplies moulded GRC and FRP panels engineered with their substructure and anchors as one package. Talk to the facade team
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.