How much should drip edge overlap?
Short answer. Adjacent pieces of drip edge must overlap at least 2 inches under the International Residential Code, and some roofers lap a little more for extra protection. On rakes, the upslope piece goes over the downslope piece so water runs across the joint instead of into it, and at the eaves the laps simply need to be tight, fastened and covered by the underlayment.
The code requirements
- Overlap between adjacent pieces: at least 2 inches.
- Extend at least a quarter inch below the roof sheathing.
- Extend at least 2 inches back onto the roof deck.
- Fasten to the deck at no more than 12 inches on center.
- At eaves, underlayment goes over the drip edge; at rakes, the drip edge goes over the underlayment.
Local amendments and shingle manufacturer instructions can be stricter, so follow whichever is more demanding.
Which piece goes on top
- Rakes. Start at the eave and work up toward the ridge, so each higher piece laps over the one below. Water running down the rake then flows over the joint instead of into it.
- Eaves. Water runs down the roof into the gutter rather than along the edge, but wind and gutter splash still find seams. Keep each lap tight and fastened, and run the underlayment over the metal so water landing on the joint flows into the gutter.
Making clean overlaps
Snip the vertical leg of the overlapping piece back about an inch so the roof flanges nest flat, rather than letting the face legs bunch up. Some installers add a dab of compatible sealant in the lap. At outside corners where eave meets rake, the rake drip edge laps over the eave piece, with the eave piece notched and folded so no raw gap is left at the corner.
Why it matters
Gaps at drip edge joints let water reach the fascia and the edge of the decking, and leave a path for insects and wind-driven rain. See drip edge explained and roof flashing explained.