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Common roofing terms

Apex roof with purlins


Cladding is the covering of the building, it can be asbestos, fibre-cement, plastic, steel, or any other manufactured sheets exposed to the external environment. Cladding is not designed to take weight or stress other than that of nature, such as snow or wind.


The profile of a building is the shape of the cross-section of the cladding.  There are four main types of profile:

  • Sinusoidal (more commonly known as corrugated).
  • Trapezoidal (more commonly known as box profile).
  • Ribbed trapezoidal.
  • Grecia (more commonly known as a small box profile).


The term roofing generally refers to cladding.


The substrate is the base material of the cladding, although sometimes it can be the structure, often plywood or chipboard over which cladding is laid.

SWG (Standard Wire Gauge)

SWG is the thickness of the substrate in metal cladding (+ or - 10%). It is now normal to use millimetres to describe this thickness.

Standard wire gauge Thickness (mm)
18 SWG 1.2
20 SWG 0.9
22 SWG 0.7
23 SWG 0.6
24 SWG 0.55
25 SWG 0.5
26 SWG 0.45
27 SWG 0.4

Twin Wall

A twin wall is a structure where two walls are joined together by internal supports.

Triple Wall

As above, but three walls are joined.