The problem you are having in finding information about Z purlins is probably because they are not used much in the US except in preengineered metal buildings, and the PEMB people are parochial about their design information. If you google, most of the information you will get (at least what I get) is Australian information by Bluescope Steel and Stramit. We use light gauge purlins and girts extensively in engineered (as opposed to preengineered) buildings, and use the manufacturers' well researched and presented design tables. But that is not much help to you if you are indeed in the US and need the data yourself rather than trusting in PEMB companies.
Are you looking for just section properties or actual design information? I know that some old AISC books and bethleham steel books have Z sections in them.
I have a reference manual "Light Gage Structural Steel Framing System Design Handbook" put out by the Light Gage Structural Institute that has all types of information on different shapes (Zees included)Don't know if they are even still around, the manual is copyrighted 1990. The address given is P.O. Box 9052 Dallas, Texas 75209. The Phone number shown is 214-520-2341 and the fax is 214-520-1979. At the time I bought it, the price was $5.00
The manual offers information on different shapes, design formulas, lap information, section properties,sample calculations, load tables etc. It might be outdated but the principles are still valid. You might try the number above or google the name.
