Minimum 1x3 counter battens are run vertical and centered over existing rafters. A moisture membrane of felt Tri Flex or ice and water shield is placed horizontally with proper lap to allow the membrane to loop over the counter battens. The main framing and details are then continued. Care must be taken to protect the membrane from penetrations. All cuts and penetrations should be sealed with tape. In a situation where you work from the top down or where there is a back set fascia you will need to telescope the lowest course under the next full course of tiles. In order to hold the panels in plain, you will need to install a filler strip to support the back of the first course in lieu of the batten, usually a 1 inch wide board will suffice.