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:

Giải thích

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.