Drip Edge Goes Over the Underlayment?

[jar546]

As controversial as this may seem, I am not sure why drip edge would NOT be in shingle fashion and OVER the underlayment, even if a peel & stick, self-adhering membrane. Let's look at some codes. I'll start with Florida which says (specific to asphalt shingles):

R905.2.8.5 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 shall be installed over the underlayment. Self-adhering ASTM D1970 underlayment may be installed over a primed drip edge flange. There shall be a minimum 4 inch (51 mm) width of roof cement installed over the drip edge flange or the self-adhering underlayment. Drip edge shall be mechanically fastened a maximum of 12 inches (305 mm) on center. Where the Vasd as determined in accordance with Section R301.2.1.3 is 110 mph (177 km/h) 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.


Then there is the 2021 IRC which says:

R905.2.8.5 Drip edge.​

A drip edge shall be provided at eaves and rake edges of shingle roofs. Adjacent segments of drip edge shall be overlapped not less than 2 inches (51 mm). Drip edges shall extend not less than 1/4 inch (6.4 mm) below the roof sheathing and extend up back onto the roof deck not less than 2 inches (51 mm). Drip edges shall be mechanically fastened to the roof deck at not more than 12 inches (305 mm) o.c. with fasteners as specified in Section R905.2.5. Underlayment shall be installed over the drip edge along eaves and under the drip edge along rake edges.

This verbiage of underlayment goes OVER the drip edge and goes back to the 2012 IRC.

When you get to the 2009 IRC, there is no section for drip edge at all. The section for underlayment, however, states it must be installed in a shingle-like fashion which I would interpret to be OVER the drip edge where the drip edge is used.

As a contractor, I put the drip edge on first then started my underlayment, including ice and water shield that would go OVER the drip edge.

Owens Corning, for example, does show the underlayment OVER the drip edge.

So the question is; why does Florida want the drip edge over the underlayment for an asphalt shingle roof?

 

[steveray]

At the edge, I don't think it matters much...At the eave, in snow country, I have heard of ice dams in the gutters backing up and lifting the DE (and the I&W) and water entering that way...Some of the "better" roofers are trying to bring the I&W down onto the fascia....But then it would be under the DE unless you did 2 layers or something weird like that...

 

[jar546]

At the edge, I don't think it matters much...At the eave, in snow country, I have heard of ice dams in the gutters backing up and lifting the DE (and the I&W) and water entering that way...Some of the "better" roofers are trying to bring the I&W down onto the fascia....But then it would be under the DE unless you did 2 layers or something weird like that...

I've even seen the I&W wrapped over the drip edge and down to the fascia with it being hidden by the gutter.

 

[Paul Sweet]

I wonder if it's to help hold down the edges of the underlayment in a hurricane.

 

[ICE]

I wonder if it's to help hold down the edges of the underlayment in a hurricane.

Hurricanes are a factor in just about everything in Florida.

 

[SCBO1]

We have always seen it done like the 2021 code state. I tell the novice: "Think like a ducks feathers, water needs to run over not under. The last sentence is how it's been done here. One issue is the re-roofing does allow the I&WS to remain so that's not typically removed.

Might want to look at Table R905.1.1 (3), cuz your a bit windy!