On October 29, 2012 this question was asked on Green Building Advisor. The answers are useful to anyone who is building to make sure you meet all the guidelines and code requirements.
Question
“I'm about to enter the WRB stage of my house. I've avoided the use of a WRB on my roof, and would like to go without on my walls. Covering an entire house with a WRB seems excessive in a rainscreen system. Capillary water seems to be the only enemy of a rainscreen wall. Impermeable furring strips, or an impermeable strip at the furring strip layer would appear adequate at preventing capillary moisture from migrating into the wall from wet siding. Asphalt felt, or plastic housewraps do not seem ideal for this task.”
For Answers visit this link: http://www.greenbuildingadvisor.com/community/forum/green-building-techniques/25829/wrb-necessary-rainscreen