Core TradesQuestion 110 of 700

Proper sequencing of roof components requires that water always flows over, not under, the layer below. Therefore drip edge at the eave and underlayment should be arranged so that:

a.Underlayment goes over the drip edge at the eave and under it at the rake
b.Drip edge is installed last on top of shingles
c.No drip edge is needed with underlayment
d.At the eave the drip edge is under the underlayment, and at the rake the drip edge is over the underlayment

Explanation

Correct sequencing puts the eave drip edge beneath the underlayment (so water on the underlayment sheds onto the drip edge and off the roof), while at the rake the drip edge goes over the underlayment. This maintains the shingle-over-lower-layer principle; the other arrangements let water get underneath.

Law Reference: 2025 CA Building Code, Chapter 15 (Roof Assemblies)

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