AskCodeMan

905.2.8.6 allows for the option of the felt going over or under the drip edge at the eaves but is silent on the rake.
is this option allowed on the rakes or is it strictly over only?

Bungalows wrote:905.2.8.6 allows for the option of the felt going over or under the drip edge at the eaves but is silent on the rake.
is this option allowed on the rakes or is it strictly over only?

You are referring to this in the 2009 IRC:
- R905.2.8.6 Drip edge. Provide drip edge at eaves and gables of shingle roofs. Overlap to be a minimum of 3 inches (76 mm). Eave drip edges shall extend 1/2 inch (13 mm) below sheathing and extend back on the roof a minimum of 2 inches (51 mm). Drip edge at eaves shall be permitted to be installed either over or under the underlayment. If installed over the underlayment, there shall be a minimum 4 inch (51 mm) width of roof cement installed over the drip edge flange. Drip edge shall be mechanically fastened a maximum of 12 inches (305 mm) on center. Where the basic wind speed per Figure R301.2(4) is 110 mph (49 m/s) or greater or the mean roof height exceeds 33 feet (10 058 mm), drip edges shall be mechanically fastened a maximum of 4 inches (102 mm) on center.

You've raised an excellent point: That the new section does not specify how the drip edge on the rake (the gable as the code refers to it) is to be installed. That leaves the installation to be in accordance with the manufacturers installation instructions, all of which I have seen state that the drip on the rakes are to be installed *over* the underlayment.

This is from a typical Owens-Corning asphalt shingle installation instruction:
- 1a Deck Preparation For Standard Slope Decks - 4" in 12" or more
- - Application of underlayment, metal drip edges, and eaves flashing:
- - - (C) Apply metal drip edge over underlayment at rake.
and
- 1b For Low Slope Decks - 2" in 12" to less than 4" in 12"
- - Application of underlayment, metal drip edges, and eaves flashing:
- - - (C) Apply metal drip edge over underlayment at rake.

The reason that the code now states that the underlayment may be installed under the drip edge at the eaves is because to do otherwise (install the underlayment over the drip edge at the eaves) exposes the entire shingle roof to being peeled off during high wind events. In Florida, we figure that out decades ago and, especially in South Florida (where hurricanes are more prevalent) acknowledged that in the codes by *requiring* the drip edge be installed over the underlayment, first placed in a bed of roof cement followed by roof cement applied over the drip edge - then a change which no longer required the bed of roof cement under the drip edge just the roof cement over the drip edge. That has finally been incorporated into the IRC as that same method would be the appropriate method for all areas subject to high wind events and hurricanes.

The drip edge installed along the rake should be on top of the underlayment to help keep water out from underneath the underlayment, and, though not specified in the installation instructions or the code yet, there should be the same 4 inch wide application of roof cement down the rake drip edge to seal the shingles to the drip edge and the underlayment for help with water sealing and to help with keeping the edge of the shingles down during high wind events.

You do not want the underlayment over the drip edge along the rake, the underlayment must be under the drip edge in those locations.