How Thermal Expansion Gaps Affect Long Aluminum Facade Runs

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Aluminum expands and contracts noticeably with temperature swings, so long facade runs need expansion gaps or movement joints to absorb the change. Without them, stress builds up at fixings, mullions and sealants, causing bowing, distortion or joint failure.

Why aluminum moves more than most facade materials

Aluminum has a relatively high coefficient of thermal expansion, roughly twice that of steel. On a building facade exposed to sun on one side and shade on the other, surface temperatures can differ widely across a single day, and a long run of extrusions will grow and shrink with those changes.

The total movement depends on three things: the length of the run, the temperature range it sees, and the temperature at the time of installation. A run fixed tightly on a cold morning will want to lengthen in the afternoon, and that demand has to go somewhere.

What happens when expansion is not accommodated

When movement is restrained, the material cannot relax and the forces transfer into the structure. Common results include:

Bowing or waviness in long mullions and rails
Stress concentrating at anchor points and brackets
Cracked or debonded sealant at perimeter joints
Distorted glazing rebates and loosened gaskets

These problems often appear slowly, so they may only be noticed years after completion.

Designing the expansion gap

Expansion gaps are usually placed at intervals along the run, at changes of plane, and where the facade meets other materials. The gap width is calculated from the run length, the temperature range and the expected material movement, then checked against the joint system selected. The joint should be designed as a deliberate, sealed and visible detail rather than an afterthought.

Exact spacing and gap sizes depend on the specific project, so these values should be calculated by the structural or facade engineer for each building.

Fixing strategy: fixed and sliding points

A common approach is to fix a long run at one point, often near its centre, and allow it to slide at the other supports. This lets movement radiate outward from the fixed point rather than building up at a single location. Slotted holes or sliding clips at non-fixed supports make this possible.

Fixings should be selected to suit both the load and the movement, and the sliding points must be kept free of debris, paint build-up and fasteners that could lock them.

Sealants, cover plates and the envelope

Expansion joints need sealants rated for the expected joint movement, with a correctly sized backer rod and a proper bond-breaker so the sealant stretches rather than tearing. Cover plates or sliding profiles can keep the joint weathertight while still allowing movement. Continuity of the air and water barrier through the joint should be considered from the start.

Coordinating with the fabricator and installer

Good results depend on clear information passing between architect, engineer, fabricator and installer. Drawings should show joint locations, gap dimensions, fixed and sliding points, and the installation temperature assumed. Site installers should understand that an aluminum run must be set with the planned gaps intact, not closed up for appearance.

Frequently asked questions

How often should expansion gaps be placed on a long aluminum facade?

Spacing depends on the run length, expected temperature range and the system used. The engineer should set the interval for each project rather than relying on a general rule.

Can I avoid expansion gaps by using a stiffer profile?

A stiffer profile reduces bowing but does not stop the material from expanding. Movement still needs an accommodating detail, or stress will transfer into the fixings and joints.

Why does installation temperature matter?

A run installed on a hot day has less room to expand later and more to contract in cooler weather. The installation temperature should be recorded and used in the movement calculation.

What is the most common mistake with sealed expansion joints?

Sealant is often applied with the wrong width-to-depth ratio or without a backer rod, so it cannot stretch and fails early.

Common mistakes to avoid

Closing expansion gaps for a neater look or fixing a long run rigidly at every bracket are the most frequent errors. Both transfer thermal stress into the structure and joints.

Our recommendation

Calculate movement for the actual temperature range and run length, define fixed and sliding points on the drawings, and specify sealants rated for the joint movement. Check these details on site before the joints are closed.

Summary

Aluminum facade runs expand and contract with temperature, so expansion gaps, sliding fixings and correctly rated sealants are essential to prevent bowing, stress and joint failure.

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