Purlin Ties
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Purlin Ties (anti-sag bars) perform two functions:-
1. To control rotation of the Purlin during wind uplift conditions.
2. To provide a stable working platform for cladding large spans and particularly where deep/heavy/composite cladding is used to achieve satisafaction of current and proposed building regulation requirements.
In response to changes resulting from Part L of Building Regulations and future possible changes, maintaining the accuracy of purlin spacing is of paramount importance. Sealing cladding joints to eliminate air leakage, allied to the increasing depth of insulation necessary to acheive the ‘U’ value performance requirements of Part L means it is critical that purlin twist is minimised and straightness as well as purlin spacing is accurately and consistently maintained.
The inclusion of Purlin Ties will assist in this, particularly when an ‘in-situ’ cladding construction is utilised. Our Purlin and Apex Ties are manufactured from cold roll formed pre- galvanised Steel Channel fitted with corrosion resistant retaining springs combining positive location with ease of use.
Purlin Tie orientation is dependent upon the method of cladding attachment. See drawing.
Purlin Wind Uplift Capacity is determined by the number of Purlin Ties used per span and the ultimate load capacities are as shown in the published load tables or defined by our computer software. However, the tables below give guidance to the inclusion of Purlin Ties whatever the wind uplift condition.
Alternatively, or in addition to the following, it may be that temporary propping/spacing of Purlins is required during the sheeting of the roof.
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FOR PURLIN WIND UPLIFT CAPACITIES USE UltraPRO. DESIGN SOFTWARE.
PURLIN / APEX TIE ORIENTATION - Screw fixed Cladding
NB:-Purlin Tie orientation illustrated is for screw fixed cladding.
Reverse Purlin/Apex Tie orientation for Hook Bolt Fixed Cladding.
TO FACILITATE TEMPORARY SUPPORT OF PURLINS DURING CLADDING IT IS RECOMMENDED THAT ALL PURLINS ARE PUNCHED TO ACCOMMODATE PURLIN TIES EVEN WHEN THEIR USE IS NOT INTENDED.
NB:-On roof slopes >20º (included angle < 140º) Apex Tie is cranked threaded rod.
1.Eaves Brace or SRS type Strut should always be included at eaves or valley area of roof.
2.Apex Ties or Apex Struts should always be included at roof apex- even when Purlin Ties are not utilised.
GUIDANCE ON PURLIN TIE INCLUSION >3º - <=20º SCREW FIXED METAL SINGLE SKIN AND “IN-SITU” BUILT-UP LINER/INSULATION/OUTER SHEET SYSTEMS.
The notes below relating to the inclusion of purlin ties are for general guidance only. Omission of purlin ties should take into account some or all of the following factors together with any others that may affect the roof construction:
1. Cladding type and composition, roof slope and structure .
2. The specific needs and requirements of the sheeting contractor - see table 3 below.
3. Purlin span and system - see tables 1 and 2 below.
For COMPOSITE PANEL ROOF sheeting the inclusion of Purlin Ties is advised on spans > 6.1m For Fibre Cement sheeting the inclusion of Purlin Ties is advised on spans > 5m
TO FACILITATE TEMPORARY SUPPORT OF PURLINS DURING CLADDING IT IS RECOMMENDED THAT ALL PURLINS ARE PUNCHED TO ACCOMMODATE PURLIN TIES EVEN WHEN THEIR USE IS NOT INTENDED.
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Sec Ref.
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Table 1
Sleeved, Heavy End Bay, Double Spanning,
Non-continuous & UltraLAP End Bay
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Table 2.
UltraLAP
Inner bay
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Table 3.
All purlin systems for close tolerance construction i.e: To assist in achieving part 'L' (& better) building regulations
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Max recommended
span without purlin
ties
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Max recommended span without purlin ties
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Max recommended
span without purlin
ties
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145
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6.1 metres |
6.5 metres
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5.5 metres
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170
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6.2 metres
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6.5 metres
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5.8 metres
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200
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6.8 metres
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7.1 metres
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6.1 metres
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225
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7.1 metres
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7.6 metres |
6.5 metres |
255-285
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7.6 metres
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7.6 metres
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6.8 metres
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(> 10m SRS)
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(> 10m SRS) |
(> 10m SRS) |