Fibre Reinforced Facade Encyclopedia: Properties
Thermal expansion is the dimensional change a material makes when its temperature changes, expressed as a coefficient of linear expansion in units of 10 to the minus six per degree Celsius. On a facade it decides joint width, fixing type and whether a panel cracks, because a panel that is restrained from moving will relieve the stress by cracking instead.
A 3 m GRC panel heated 50 degrees above the temperature at which it was installed grows about 2 to 3 mm. The same panel in FRP grows about 3 to 4.5 mm. Both are more than a nominal 5 mm joint can absorb once building tolerance is added.
At a glance
| Property | Typical value | Note |
|---|---|---|
| GRC | 10 to 20 x 10⁻⁶ per °C | Varies with polymer content and moisture state |
| FRP laminate, glass and polyester | 15 to 30 x 10⁻⁶ per °C | Higher across the fibres than along them |
| GRG, alpha gypsum | about 12 to 18 x 10⁻⁶ per °C | Typical for gypsum composites; interior use |
| Aluminium | 23 to 24 x 10⁻⁶ per °C | Substructure rails and brackets |
| Steel | 11 to 12 x 10⁻⁶ per °C | Stud frames, brackets and building structure |
| Surface temperature range, Australian facade | -5 to 80 °C | Dark colours reach the upper end; alpine sites the lower |
| Movement of a 3 m panel over 50 °C | 1.5 to 4.5 mm depending on material | Before tolerance and moisture movement are added |
| Practical facade joint width | 10 to 15 mm | Movement plus tolerance plus the movement capability of the sealant |
Calculating the movement
The change in length is the coefficient multiplied by the original length multiplied by the temperature change. A 3,000 mm glass fibre reinforced concrete (GRC, GFRC) panel with a coefficient of 15 x 10 to the minus six per degree, heated 50 degrees, moves 2.25 mm. Half of that is taken at each end if the panel is fixed at its centre, so each joint sees about 1.1 mm from this panel and the same again from its neighbour.
The temperature range to use is the surface temperature of the panel, not the air temperature. A dark panel in full sun in Queensland runs far above ambient, and the range that matters is measured from the temperature at which the panel was fixed, which is why installation temperature belongs on the shop drawings.
The materials on a facade do not match
Thermal movement causes trouble at the interfaces. An aluminium rail expands roughly twice as much as the GRC panel bolted to it, a steel stud frame behind a GRC skin moves at a different rate to the skin, and glass in the adjacent curtain wall moves less than either. Wherever two materials with different coefficients are connected over a length, the connection either slides or it absorbs the difference.
That is the reason for the fixing vocabulary used on moulded panels: one fixed gravity anchor carrying the weight, and flexible or slotted restraint anchors everywhere else that hold the panel against wind but let it grow. Bolting a panel rigidly at four corners guarantees a crack. Panel fixing systems and flex anchors cover the hardware; the coefficient is the input that sizes the slots.
Thermal movement is not the only movement
- Moisture movement: GRC swells when wet and shrinks when dry, typically 0.5 to 1.5 mm per metre, the same order as thermal movement and sometimes larger
- Drying shrinkage: an irreversible component in the first months after casting, which is why panels are cured and conditioned before installation
- Creep: sustained load slowly increases deflection, particularly in polymer laminates
- Structural movement: floor deflection, column shortening and inter-storey drift
- Construction tolerance: the gap on site is never the gap on the drawing
Joints are sized for the sum of these, not for thermal movement alone. Moisture movement is the one most often missed on cementitious panels.
Joint width and sealant capability
A sealant is rated by its movement accommodation factor, the percentage of the joint width it can take in extension and compression without failing. A 25 percent rated silicone in a 10 mm joint absorbs 2.5 mm. If the calculated movement plus tolerance exceeds that, the joint is widened or the panel is made smaller, and there is no third option that works.
Open jointed rainscreen construction removes the sealant from the movement path entirely. The panel edge is returned or baffled, the cavity behind takes the water, and the joint can be as wide as the movement and the architecture require. That is one practical reason moulded GRC and FRP panels are so often detailed as open jointed rainscreens.
Where it goes wrong
Two further cases repeat on projects: dark colours on large panels, where the surface temperature range is underestimated and the joints close up on the first hot afternoon, and mixed material assemblies where an aluminium subframe and a cement panel are rigidly fastened on a long run, so the rail drags the panel.
Standards and references
- ASTM E831 Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis
- ASTM D696 Coefficient of Linear Thermal Expansion of Plastics
- ISO 11359-2 Plastics, Thermomechanical analysis, Determination of coefficient of linear thermal expansion
- GRCA Practical Design Guide for Glassfibre Reinforced Concrete, movement and joint design
- AS/NZS 1170.0 Structural design actions, General principles, including imposed deformations
- ISO 11600 Building construction, Jointing products, Classification and requirements for sealants
Related terms
Questions specifiers ask
What is the thermal expansion coefficient of GRC?
Typically 10 to 20 x 10 to the minus six per degree Celsius, similar to concrete. The figure varies with polymer content and with how wet the panel is.
How wide should a facade joint be?
Wide enough for thermal movement, moisture movement, structural movement and construction tolerance combined, within the movement accommodation factor of the sealant. On moulded panels that is usually 10 to 15 mm.
What temperature range should be used?
The panel surface temperature range, not the air temperature, measured from the temperature at installation. Dark surfaces run well above ambient in Australian conditions.
Can thermal movement crack a panel?
Yes, if the panel is restrained. A restrained GRC skin over a 50 degree swing can exceed its limit of proportionality and crack at the fixings.
Sizing joints and fixings for a moulded facade? The ShapeShift facade calculators cover panel movement, weight and fixing layout. Open the facade calculators
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.