Thermal Expansion Allowances in Long Metal Cladding Runs

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Long metal cladding expands and contracts with temperature, so each run needs planned movement joints and fixings that allow sliding in one direction. The allowance depends on the metal, the run length, the colour and surface exposure, and the temperature range the facade will see. Confirm the final values with your structural or facade engineer before issuing the drawings.

Why long metal runs move more than you expect

Metal expands noticeably when it heats up, and a long panel or rail can grow by a measurable amount across a single facade bay. In sunny climates the surface of dark or exposed metal can get far hotter than the air, so the movement is larger than a simple air-temperature estimate suggests. Aluminum moves more per degree than steel, and stainless steel sits in between, so the metal you choose changes the detail.

The key point is that movement is cumulative. A small amount per panel becomes a large total along a long run, and if nothing accommodates it the metal buckles, pulls fixings out, or cracks adjacent materials.

Setting the movement joints

Plan joints at intervals along the run so that each length of metal can move independently. The spacing depends on the material, the colour, and the temperature swing, so there is no single universal number to copy from one project to another. Place joints where they are least visible, such as at changes of plane, behind reveals, or along architectural lines.

Locate joints at structural breaks and corners where possible
Keep joint gaps wide enough to close and open without binding
Use a sealant rated for the expected movement range

Fixing details that allow sliding

Fixings should hold the panel in place while letting it slide along one axis. Use slotted or oversized holes at sliding points and fixed points only where you want the panel to stay put. A common approach is to fix the panel firmly at one central point and allow the rest to float outward from it, so movement radiates in both directions without stressing the attachments.

Avoid rigid connections at every fixing, because they lock the metal and force it to deform. Make sure the sliding clips and washers are detailed so that they do not seize with dirt or paint build-up over time.

Choosing finishes that reduce the load

Surface colour and finish affect how hot the metal gets. Light, reflective finishes run cooler than dark coatings, which lowers the temperature swing and reduces the movement you must accommodate. Powder coating and hot-dip galvanizing behave differently in heat and should be specified with the coating system in mind.

Shaded or ventilated back faces also help, because a panel exposed on one side only will expand unevenly and can bow. Think about orientation early, since a west-facing run in a sunny climate faces a much harder thermal cycle than a north-facing one.

Coordinating with the drawings and the site

Show the movement joints, sliding fixings and fixed points clearly on your details, with the intended gap sizes written in. Our process runs from an inquiry with photos, through on-site measurement, to a drawing and written specification that you review and approve before production. This lets the allowances be checked against the actual wall, the substrate and the sun exposure.

Installers need the same information, so make sure the specification states which points are fixed, which slide, and what gap to leave at installation temperature. Installing on a hot day versus a cool morning changes the starting gap, and this should be noted.

Checking the design before fabrication

Before fabrication, review the run length, the metal, the coating, the orientation and the expected temperature range with your engineer. The exact allowance values, and the calculation behind them, should come from that review rather than from a rule of thumb. For railing elements, the Israeli standard SI 1142 is a general reference, and the specific values are confirmed with the engineer on your project.

Once the allowances are agreed, we produce the work in our factory at 37 Rival Street, Tel Aviv, and finish it before installation so the joints and fixings are built as drawn.

Frequently asked questions

How big should the expansion gap be on a long metal run?

The gap depends on the metal, the run length, the temperature swing and the colour, so it has to be calculated for each project. Confirm the final value with your structural or facade engineer.

Does aluminum need more allowance than steel?

Generally yes, because aluminum expands more per degree of temperature change than steel. The difference should be reflected in your joint spacing and fixing details.

Should every fixing be sliding?

No, a few fixed points are usually needed to locate the panel, with the remaining fixings allowed to slide. Fixing everything rigidly prevents the metal from moving and causes stress.

Does the colour of the finish matter?

Yes, darker finishes absorb more heat and reach higher temperatures, which increases movement. Lighter finishes can reduce the thermal load on the run.

Common mistakes to avoid

The most common error is treating a long run as one rigid piece with no joints, and fixing every point tightly. Another is ignoring sun exposure and colour when the allowance is calculated.

Our recommendation

Mark the fixed point on every run in your drawings, allow sliding at all other points, and get the gap values checked by your engineer against the orientation and finish before issuing details.

Summary

Plan joints, sliding fixings and a clear fixed point, and confirm the allowance values with your engineer for the specific climate and finish.

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