Z-Purlin Lap Detail

[AlohaBob]

It makes sense to ensure lapped purlins have the same width flange, but is that necessarily so? And only the purlin thicknesses can vary along a premanufactured building?

I seem to recall a certain ease for stripping a flange if it were necessary.

Even if the flange widths match, the member thickness itself will cause interference at the lap.

 

[ajh1]

A number of manufacturers make a Z purlin with unequal flange widths (1/4" difference or so). The idea is that at the lap the wider flange nests over the narrower flange. It does require flipping alternate spans over so that you can make the joint. For lip angles steeper than about 60 degrees equal flanges won't nest.

 

[AlohaBob]

I spoke with a detailer for a Prefab building manufacturer. This one prefers to keep the flange widths the same along a line of laps. They confirm you must squish the purlins a bit since the thickness does interfere.

I drew the picture of the varied flangewidth. This manuf provides the varied width and same width purlins. I see they nest better and may be rotated along the line for that advantage. That's the key to the cleanest lap joint.