Corrosion and service life
What corrosion needs
Section titled “What corrosion needs”Moisture and oxygen. Steel does not corrode in a dry environment — and the zinc coating still protects it when moisture reaches it occasionally.
So the question is not “does steel rust” but can persistent moisture get into the structure.
Where the moisture comes from
Section titled “Where the moisture comes from”From outside, through leaks
Section titled “From outside, through leaks”Faulty rainwater drainage, damaged facade, poor detailing. This is a risk with every structure, not specific to LGS.
From inside, as vapour
Section titled “From inside, as vapour”This is the bigger risk. Internal vapour diffuses into the wall, cools and can condense. If the vapour control layer is continuous this does not happen — if it is punctured, moisture collects at exactly that point. Vapour control.
Condensation at thermal bridges
Section titled “Condensation at thermal bridges”Where the structure is colder, vapour condenses sooner. Steel conducts heat well, so a thermal bridge here is directly a corrosion risk too. Thermal bridging in steel.
Moisture built in
Section titled “Moisture built in”If wet material goes into a closed structure — soaked insulation, or timber installed damp — it is hard to dry out later. In a light gauge steel wall moisture cannot “get lost” the way it can in a thick masonry wall: whatever is built in stays there for the life of the structure.
How we protect against it
Section titled “How we protect against it”- The right coating for the environment. Zinc coating.
- Continuous vapour control, with an undamaged membrane — which is why cables do not run inside the profiles. Service cavity.
- Thermal-bridge-free junctions, so there is no cold surface in the structure.
- A dry connection to the foundation: damp-proofing under the bottom track.
- No organic, absorbent materials in the external wall.
Service life
Section titled “Service life”In a properly designed and built dry structure, the service life of a galvanised steel frame is comparable to the design life of the building. In practice the risk almost always comes from a construction defect, not from the material.
What can be checked
Section titled “What can be checked”A covered structure cannot be inspected later. So the continuity of the vapour control layer, the junctions and the damp-proofing have to be checked and documented before lining. The construction log.
The point
Section titled “The point”Corrosion is not a material question but a moisture question. As long as the structure stays dry, there is nothing for it to corrode from.