Watertight properties and fixing

Most sheet roof products remain adequately watertight down to a pitch of 5º. Some, particularly the decking profiles, remain watertight on pitches that are nearly flat at 1º. Generally speaking, all sheet roofs should have a waterproof sarking immediately under the roof sheets.

The manufacturers of roof sheets generally produce good quality technical information for their products. They also give extensive information on fixings for high wind areas. In some instances special profiles are produced for use in extreme climatic conditions.

The manufacturers' details include:

  • how many fasteners to use per sheet
  • the location of the fasteners
  • the minimum length of fasteners for steel or timber supports
  • the side lap fastener spacing.

For example, the 'normal' type of corrugation requires three fasteners per sheet at the internal supports and five fasteners per sheet at the end lap supports.

Photo of a house with metal roof sheeting.