Timber Jack Rafters Fixed Directly To UltraZED Purlins
The abnormal forces imposed upon roof Purlins by this method of Tiled Roof Construction requires special consideration and demands that adequate restraining methods are employed.
ALL ROOF SLOPES TIMBER JACK RAFTERS
RAFTER CONDITIONS AT ROOF APEX
Timber Jack Rafters must be securely fastened together over the Roof Apex so that any propensity for loaded rafters to pull apart at the apex is resisted.
APEX CONNECTION FOR PURLINS
Purlins must be tied together over the apex using an Apex Strut as shown in Fig.1. and positioned so that the top Purlins are no more than 600mm from the apex.
CLEATS
Stiffened Rafter Cleats should be used on all roof slopes over 30º. For slopes under 30º Standard/Heavy Duty Cleats should be checked for suitability of use.
ROOF SLOPES < = 30º - TIMBER JACK RAFTERS EAVES CONDITION
1.STRUCTURAL EAVES MEMBER (NOT COLD ROLLED SECTION) At the bottom of the roof slope a Heavy Duty Eaves Brace as detailed in Fig. 2. should be fitted between the structural eaves member and the first Purlin.
2.COLD ROLLED EAVES BEAM At the bottom of the roof slope the Eaves Beam must be connected to the first Purlin by an Eaves Brace. Between the first and second rows of Purlins, Diagonal Purlin Brace Assemblies should be incorporated in conjunction with SRS Type Struts.
3.NO EAVES MEMBER At the bottom of the roof slope between the first and second row of Purlins, Diagonal Purlin Brace Assemblies should be fitted in conjunction with SRS Type Struts.
ADDITIONAL BRACING REQUIREMENTS
On long roof slopes in all of the proceeding cases 1 to 3, additional Diagonal Purlin Brace Assemblies are required so that the distance between bracing methods does not exceed 6 metres.
STRUT TYPES
In addition to the proceeding requirements SRS Type Struts are required between Purlins at maximum Strut length of 2000mm.
PURLIN DESIGN
Purlin selection should be made using UltraPRO. Design Software or alternatively by consultation with our technical department.
Providing the maximum length of unrestrained Purlin between Struts does not exceed 2 metres the published load tables may be used. It is recommended that deflection is checked to ensure that it does not exceed span/300 under maximum design load.
ROOF SLOPES > 30º AND MANSARD/MONO-PITCH - TIMBER JACK RAFTERS
EAVES CONDITION
1. STRUCTURAL EAVES MEMBER (NOT COLD ROLLED SECTION) At the bottom of the roof slope a Heavy Duty Eaves Brace, as shown in Fig.2. or similar (by others), should be fitted between the structural Eaves Member and the first Purlin.
2. NO EAVES MEMBER
At the bottom of the roof slope between the first and second row of Purlins Heavy Duty Diagonal Tie Bar (HD-DTB) assemblies and Heavy Duty Type Struts (HDS) should be fitted.
ADDITIONAL BRACING REQUIREMENTS
On long roof slopes in the proceeding cases 1 and 2, additional Heavy Duty Tie Bar (HD-DTB) assemblies are required so that the distance between bracing methods does not exceed 3.6 metres.
STRUT TYPES
When used in conjunction with Heavy Duty Diagonal Tie Bar assemblies
- Heavy Duty Type Struts must be used. The SRS Type Strut may be utilised throughout the remainder of the roof construction. Maximum length of Strut for roof slopes over 30º is 1800mm.
PURLIN DESIGN
In most cases of tiled roof design the Purlin section is subjected to high down slope loads causing bi-axial loading to the section.
Purlin selection should be made using UltraPRO. Design Software or by consultation with our technical department.