Roof Variations

Monopitch Roof

• For monopitch and other roofs where there is no restraint to the ridge purlin via apex ties some equivalent anchor must be used.
• This may take the form of a simple tie to a substantial ridge beam or alternatively by a combination of struts and diagonal bracing between the top two purlins.
• Restraints should be used at mid-span for purlin spans greater than 3.5m and at one third and two thirds of span for purlin spans greater than 7.5m.
• For long roof slopes additional diagonal bracing may be required.

Tiled/Mansard Roof

• These types of roof covering may cause bending about both axes of the roof purlins due to their weight. In order to provide adequate restraint rigid struts should be used in lieu of anti sag ties.
• The ridge purlins should be tied using a rigid apex strut.
• Diagonal bracing wires are required between the top two purlins.
• Additional diagonal bracing will be required for every 6m length of roof slope.
• The struts should be arranged such that the maximum unrestrained purlin length is restricted to 2m.
• The timber rafters should be joined across the apex or be fixed to a ridge board.

Non-restraining Cladding to Roof

• Many modern cladding systems do not provide adequate lateral restraint to the top flange of the purlins. In this situation it is necessary to replace the standard anti-sag ties with angle strut braces.
• The struts should be arranged such that the maximum unrestrained purlin length is restricted to 2m.

Steep Roof

• For roof pitches greater than 25° diagonal bracing should always be provided.
• These diagonal wires used in conjunction with angle strut sag bars allow for bending about both axes of the purlin.
• Rigid apex ties are also required.