What is an Anti Ponding Strip?

What is an anti ponding strip? When a tile roof is being installed, the eave detail is critical.

This is a photo of a roofing job being installed on a home in Auburn California in 2001. This roof design had zero gutters on the building at all, but had a fascia and 4×6 exposed rafter tails. When a tile is being installed the roofers use an eave riser on the first course made of wood or metal. The metal sometimes is referred to as a bird stop on Spanish style tile. In this example, the wood fascia is used as an eave riser setting up about an inch and a half. This allows the first course to be the same angle with the rest of the tiles.

The problem with this is, the underlayment is normally installed from the eave to the ridge and covered by a metal eave riser at the eave, which can dam up the debris and water even with weep holes. Wood eave risers need the underlayment to be installed on top of it. Without supports of some kind, it droops down into the void and causes problems with water that gets to the felt. No matter what anybody says. I believe water gets under the tule and on this felt or underlayment. I have seen years of results from tile roofs with poor felt applications like what I have described. The best fix for this not to occur is using an anti ponding strip that fills the void and supports the felt or underlayment. The anti ponding strip I like to use is 3 feet long about a 1.5 inches high and 6 inches wide and is made from styrofoam. By placing it on the roof deck prior to installing underlayment it gives the first course of underlayment support as shown by this application, tapering up to the top of the riser and allowing any water on the felt to spill over and off the roof.

Notice the copper caps on all the beams exposed. Over the life cycle of the first roof, the beams experienced some weathering, some needing replacement. This customer wanted copper to cover the upper side which he got on every rafter tail on this roof.

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