Fibre Reinforced Facade Encyclopedia: Design and detailing
Movement joints are deliberate gaps in a facade that allow the cladding, the substructure and the building frame to change dimension without the panels loading one another or cracking. Every facade moves. The design question is never whether to allow movement, but how much, in which direction, and at which lines the movement is released. This page covers the movement itself and where the joints belong; the detailing of the gap is covered under joint design, and the deviations that eat into it under tolerances.
A 6 metre glass fibre reinforced concrete panel warmed 40 °C grows about 2.4 to 4.8 mm. Ten such panels in a continuous run, restrained at both ends, put 24 to 48 mm of growth into joints that were drawn at 10 mm.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Thermal movement, GRC | 10 to 20 x 10⁻⁶ per °C | About 0.6 to 1.2 mm per 6 m per 10 °C |
| Thermal movement, FRP | 15 to 30 x 10⁻⁶ per °C | Higher than concrete; joints size up accordingly |
| Thermal movement, aluminium | about 23 x 10⁻⁶ per °C | The substructure rails move as well |
| Surface temperature range | minus 5 to 80 °C | Dark panels in Australian sun; confirm against project climate data |
| Moisture movement, GRC | 0.05% to 0.15%, or 0.5 to 1.5 mm per metre | Reversible wet to dry; often larger than thermal movement |
| Structural movement | Slab deflection, creep, shrinkage and settlement | Obtain the figures from the structural engineer |
| Inter-storey drift | Typically height/500 under serviceability wind | Project specific; confirm with the structural engineer |
| Seismic movement | Per AS 1170.4 earthquake design category | Non-structural component provisions apply to cladding |
| Typical panel to panel joint | 10 to 20 mm for GRC and FRP | Nominal width before tolerance is added |
The four movements
- Thermal. The panel, the substructure and the frame all expand and contract with temperature, and at different rates. A dark facade in full sun can run 50 to 60 °C above the shaded winter minimum, and the coefficient of thermal expansion decides what that means in millimetres.
- Moisture. Cementitious materials swell when wet and shrink when dry, reversibly, and shrink once irreversibly as they cure. For glass fibre reinforced concrete, moisture movement is frequently larger than thermal movement and is the one most often forgotten.
- Structural. Slabs deflect under load, concrete creeps and shrinks for years, columns shorten elastically, and foundations settle. All of it happens behind the facade and all of it has to be released somewhere.
- Seismic and wind drift. The frame racks sideways under lateral load. Cladding is a non-structural component and must be able to follow the frame without becoming a structural element in the load path.
The four are not additive in a simple way. Thermal and moisture movement act on the panel and are largely reversible. Structural creep and shrinkage act on the frame, are one-directional, and mostly occur in the first two years. A joint has to survive the worst realistic combination, not the sum of all four maxima.
Sizing the movement
Thermal movement is a three-number calculation: length, coefficient of expansion, and temperature range. A 3 metre glass fibre reinforced concrete panel with a coefficient of 15 x 10⁻⁶ per °C over an 80 °C range moves about 3.6 mm. Do that calculation for the panel and separately for the substructure rail it is fixed to, because an aluminium rail will move further than the panel it carries and the difference has to go somewhere.
Moisture movement is sized from the material data, not from the weather. Take the reversible movement value for the specific mix, apply it over the panel dimension, and add it to the thermal case for cementitious panels. For fibre reinforced polymer the moisture term is negligible and the thermal term is larger. Structural movement is not calculated by the facade designer at all; it is requested from the structural engineer, in writing, as slab deflection, creep, shrinkage and drift at each level.
Where the joints go
In a modern panelised facade almost every panel to panel joint is a movement joint. Panels are not butted and bonded into a continuous plane; each one is an independent element with its own fixed point, and the joint between it and its neighbour absorbs the difference. That is the fundamental difference between panelised cladding and a rendered or tiled wall, where movement joints are occasional and deliberate.
Beyond that, joints are mandatory at a short list of locations. Any structural movement joint in the frame must continue through the facade at the same line, uninterrupted, and no panel may bridge it. A joint is needed at every floor line where the frame allows inter-storey movement, at a change of substrate, at a change of cladding material, at every external and internal corner, and at any point where a continuous substructure rail exceeds the length the system permits. Long horizontal runs of rail need a break even where the panels above do not appear to need one.
Releasing movement at the fixing
A joint only works if the fixing lets the panel move into it. The standard arrangement is one fixed point per panel and sliding or slotted connections everywhere else, so that the panel expands from a known origin in a known direction. Fixing a panel rigidly at four points guarantees that thermal and moisture movement will be resisted by the panel itself, and a thin-section material will crack before a bracket yields.
Stud framed glass fibre reinforced concrete panels handle this with flex anchors: slender rods that carry wind load in tension and compression but bend to let the skin move independently of the steel frame behind, while separate gravity anchors carry dead load at a fixed point. Fibre reinforced polymer panels typically use bonded inserts with slotted brackets. Either way, the principle is the same, and it belongs in the shop drawings rather than being resolved on site. See panel fixing systems and substructure.
What goes wrong
The second most common is sealant beyond its capability. A sealant with plus or minus 25 per cent movement capability in a 10 mm joint accommodates 2.5 mm, which a 6 metre panel will exceed on a hot afternoon. The third is a continuous element crossing a movement line: a coping, a flashing, a rail or a corner panel fixed both sides of a joint that was otherwise correctly designed. The joint is only as good as the least flexible thing crossing it.
Standards and references
- AS/NZS 1170.0 and AS/NZS 1170.2 Structural design actions, general principles and wind actions
- AS 1170.4 Structural design actions: earthquake actions in Australia, including parts and components
- AS 4284 Testing of building facades, including imposed inter-storey movement
- AS 3600 Concrete structures, for creep, shrinkage and deflection of the supporting frame
- GRCA Practical Design Guide for GRC (movement, joint spacing and anchor flexibility)
- ISO 11600 Building construction: jointing products, classification and requirements for sealants
- BS 6093 Design of joints and jointing in building construction
- PCI MNL-122 Architectural Precast Concrete, movement and joint provisions
Related terms
Questions specifiers ask
How much does a facade panel move?
A 6 metre glass fibre reinforced concrete panel over an 80 °C range moves about 5 to 10 mm thermally, plus a moisture term that can be as large again. Fibre reinforced polymer has a higher thermal coefficient and a negligible moisture term.
Is every joint between panels a movement joint?
In a panelised facade, effectively yes. Each panel is an independent element with one fixed point, and the joints around it absorb its movement and its neighbours’. That is different from a rendered or tiled wall, where movement joints are occasional.
Where must a movement joint be located?
At every structural movement joint in the frame, at floor lines where inter-storey movement is allowed, at changes of substrate or cladding material, at corners, and wherever a continuous substructure rail exceeds its permitted length.
What is a fixed point?
The single connection that locates a panel and does not slide. Every other connection on that panel is slotted or sliding, so the panel expands away from the fixed point in a predictable direction rather than being restrained and cracking.
Do moisture and thermal movement add together?
For cementitious panels, treat them as additive for joint sizing. Moisture movement in glass fibre reinforced concrete is often the larger of the two and is the term most frequently omitted from a joint calculation.
Sizing joints for a moulded panel facade? We can supply movement coefficients and anchor arrangements for ShapeShell-RC and ShapeShell-RT at design stage. Talk to our engineering team
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.