Dimensional stability and moisture
What steel does not do
Section titled “What steel does not do”It does not take up moisture from the air. It follows that it:
- does not swell or shrink with humidity,
- does not warp,
- does not crack while drying,
- does not “work” with the seasons.
This means the structural geometry is constant. The accuracy that comes from machine production is therefore not only valid on the day of installation — it stays.
What this means on the finished building
Section titled “What this means on the finished building”Crack-free junctions
Section titled “Crack-free junctions”A large share of the hairline cracks at the junctions of finishes comes from movement in the structure. If the frame does not move, that source of defects disappears.
Doors and windows
Section titled “Doors and windows”Window and door frames connect to the structure. With stable geometry the adjustment stays.
Floors and finishes
Section titled “Floors and finishes”A stiff, stable floor structure also improves the life of the finishes — especially where a rigid finish such as ceramic tiling goes on top.
What does need watching
Section titled “What does need watching”Moisture built in
Section titled “Moisture built in”If moisture gets into the structure and stays there, the problem will not be the steel but the other materials — and the fact that it leaves a closed structure slowly. In a light gauge steel wall moisture cannot “get lost” the way it can in a thick masonry wall.
This is why absorbent organic materials do not go into the external wall, and why dry installation matters.
Movement of the other materials
Section titled “Movement of the other materials”Steel is stable, but the rest of the build-up may not be: gypsum-based boards, timber and bonded layers move. Junctions therefore have to be detailed to follow movement.
Thermal movement
Section titled “Thermal movement”Steel expands with temperature — a different phenomenon from the response to moisture. How steel behaves with temperature.
By comparison
Section titled “By comparison”A timber frame responds to moisture: the timber takes up and gives off vapour, and moves with it. This is manageable — timber framing has its own technology for it — but it has to be allowed for in design. With a steel frame the question does not arise. Steel and timber framing.
The point
Section titled “The point”Dimensional stability is not a detail: the life of the finishes, the windows and the build-up depends on it. A structure that does not move produces fewer defects.