roof sheeting

huangyhg

roof sheeting
what are the pros and cons of standing seam and clip seal profiled roof sheeting products against through fix systems? i understand that there are lightening protection requirements that mean a 0.5mm sheet must be used otherwise a system of tapes must be provided which would require through fixing, thereby negating some of the adavntage of a standing seam system.
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i believe that some standing seam roof systems don't provide lateral restraint to the purlins (unless there is an adequately fixed liner sheet).
you can get over this by discussion with technical department of the purlin manufacturer you propose to use, and usually requires additional bracings and diagonal tie wires be provided.
i have used the corus kalzip system, and this has minimum flange widths for purlins also, which is sometimes greater than that required for structural purposes.
water resistance and longevity of such is the primary reason for going with standing seam systems vs. exposed fasteners. as valleyboy noted, the lateral restraint can also be different in different systems.
the gasketing washers used in exposed fastener systems harden with time and allow water intrusion.   
thanks for the info valleyboy and ron. i believe the pitch of the roof is of course an important factor in the choice of fixing method. any comments re. lightning protection?