Thermal Movement Allowance in Long Metal Runs

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Long metal runs expand and contract with temperature, so the design must include a planned thermal movement allowance such as expansion joints, sliding fixings or staggered sections. Without it, stress builds up at fixings and welds, causing distortion, noise or cracking. We calculate the allowance together with the design engineer based on material, run length and temperature range.

Why long metal runs move

Metal changes length as its temperature changes. A long run of steel, aluminum or stainless steel that is fixed rigidly at both ends has nowhere to go when it expands in summer sun, so the force goes into the fixings and the structure around them. Aluminum expands more than steel, so the same run length behaves differently depending on the material chosen.

The sun can heat an exposed face far more than the shaded side, which adds differential movement that is easy to overlook at the design stage.

Information we need from the design team

To plan the allowance properly we ask for the following before production starts:

Material and finish of each element
Total run length and the length of each section
Orientation of the façade and the expected temperature range
Support points, anchor type and the substrate
Any glazing or stone that the metal is fixed to

Planning joints and sliding fixings

There are several common ways to accommodate movement. Expansion joints divide a long run into shorter sections with a designed gap. Sliding or slotted fixings allow one end of a section to travel while the other end stays fixed. Staggered sections can also distribute movement across several connections.

The right solution depends on the appearance you want. A visible joint can be a design feature, while a concealed joint keeps the line continuous.

Measurement on site and drawing approval

Our team measures on site and records the actual dimensions, levels and substrate conditions. We then prepare a drawing and a written specification that shows joint positions, gap sizes and fixing types. Nothing goes into production until you and the engineer approve these documents.

Checking the drawing against the building's real conditions prevents costly changes after the metal is already made.

Production and finishing considerations

In the factory we cut and fabricate each section to the approved drawing, leaving the designed gaps and preparing slotted holes or sliding brackets. Welding is planned so that joints do not lock the sections against each other. Finishes such as hot-dip galvanizing or powder coating are applied after fabrication, so coating thickness is considered in the gap and fit.

Installation and checking movement

During installation the sections are set to the drawing, and the sliding fixings are tightened to the correct position rather than fully locked. Installers check that every joint is open to the specified gap before finishing. We recommend a visual inspection after the first hot season to confirm the joints are moving freely.

Exact values for gaps and fixings are confirmed with the engineer for each project, and railings should also be checked against the Israeli standard SI 1142 in general terms.

Frequently asked questions

Do all long metal runs need an expansion joint?

Not always, but any long run fixed rigidly at both ends should be assessed for movement. The need depends on material, length, temperature exposure and how the run is fixed.

Is aluminum more affected by thermal movement than steel?

Yes, aluminum expands more than steel for the same temperature change, so it usually needs more planning for joints and fixings.

Can the movement gap be hidden?

Yes, concealed joints can keep a continuous look, but they must still be designed to allow the movement without binding.

Who decides the allowance for a project?

The design engineer makes the final decision, and we prepare the drawings and production details based on that approved allowance.

Common mistakes to avoid

A common mistake is fixing a long run rigidly at every point, which traps the expansion and leads to distortion or cracked fixings. Another is welding joints that were meant to slide, which locks the movement completely.

Our recommendation

Share the run length, material and façade orientation early so the joint layout is set in the drawing rather than added on site. Ask for the movement gap to be marked on the approved drawing and checked during installation.

Summary

Thermal movement allowance protects long metal runs from stress and distortion when temperatures change. Planning it early with the engineer, using the right joints and sliding fixings, gives a durable and clean result.

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