Aluminum cladding changes dimension with temperature. If its joints and fixings prevent the intended movement, the assembly can develop stress or visible distortion. If connections are simply loosened to create movement, restraint and safety can be compromised. The task is to design controlled movement, not to choose between “tight” and “loose” installation.
Establish the movement inputs before setting a joint
Record the material’s expansion coefficient, effective length and design temperature range. Use panel surface temperatures appropriate to the location, finish and orientation; ambient air temperature alone may not represent a sun-exposed face. Identify the installation temperature because it determines the remaining allowance for expansion and contraction from the installed position.
The supporting structure also moves. Consider its material, attachment pattern and relevant building movement. A panel moving relative to its rail is a different coordination problem from an entire rail moving relative to the building.
Worked example: free expansion of a 3 m aluminum length
Formula: ΔL = α × L × ΔT.
Assume, for this example, α = 23 × 10−6/°C, L = 3,000 mm and a temperature increase of 60°C.
ΔL = 23 × 10−6 × 3,000 × 60 = 4.14 mm.
This is a free-expansion illustration using an assumed coefficient, not a Lianhui alloy specification or a recommended joint width. Obtain the coefficient for the actual material and the project temperature assumptions before design. A 6 m length under the same assumptions changes by 8.28 mm, showing why the effective length matters.
If that idealized 3 m member is located at its centre and otherwise free to expand symmetrically, each end moves about 2.07 mm relative to the centre for the stated increase. If located at one end, the far end moves 4.14 mm relative to that point. Real panel attachments and subframes require their own movement model; a centre fixing cannot be assumed from the panel’s appearance.
Coordinate fixed and movement-accommodating connections
The design must establish where the panel is located and how movement is accommodated elsewhere. Where sliding connections are specified, show their direction and travel, together with fasteners, washers and the clamping detail. A slot can cease to function if the fastener is installed at the wrong end or clamps the moving component in an unintended way.
Do not enlarge holes, reduce tightening or omit fasteners on site to solve a mismatch. These changes can alter the load path. Resolve the connection with the responsible designer and issue the revised detail before installation continues.
A nominal joint width needs a movement schedule
| Input | Why it matters |
|---|---|
| Panel and support movement | Determines relative displacement, not only expansion of one isolated sheet |
| Installation condition | Establishes the starting gap and remaining travel in each direction |
| Fabrication and setting-out tolerances | Can reduce the usable gap before temperature changes occur |
| Joint system | Open joints, gaskets and sealant joints have different geometry and weathering details |
| Building interfaces | Corners, windows and movement joints can concentrate incompatible restraints |
For sealant joints, select a compatible product and follow its joint-design, adhesion and preparation requirements. Backing and bond-breaker arrangements control where the sealant adheres; unwanted three-sided adhesion can restrict movement. Obtain the required adhesion and compatibility checks on the actual finish. Do not derive sealant width solely by adding a convenient margin to the free-expansion example.
Inspect movement details before they are concealed
- Confirm the fixed-point and sliding-point pattern against the current drawing.
- Check slot orientation, fastener position and specified washers or spacers.
- Measure representative joint widths and note installation conditions.
- Check that sealant, insulation, trims or adjacent panels do not bridge intended movement gaps.
- Photograph critical connections before closing the next panel.
What to include in a cladding enquiry
Send panel dimensions, material requirements, support drawings, project location, temperature assumptions and the proposed joint strategy. Include corners and interfaces rather than only a typical flat bay. Use the shop-drawing checklist to coordinate datums and revisions, then upload the drawing package. Final movement and connection design belongs to the coordinated project engineering.
