Can you install drip edge after the shingles are already on?
Short answer. Yes. A roofer can retrofit drip edge on an existing shingle roof by carefully lifting the edge shingles, sliding the metal flange underneath and nailing it where the shingles cover the nails. It works well along the rakes, but at the eaves the metal usually ends up on top of the underlayment instead of under it, so it is a reasonable fix rather than a match for a new installation.
How a retrofit is done
- Work on a mild day, when shingles are flexible enough to lift without cracking but not so soft that they tear.
- Break the sealant strip on the first course or two along the edge with a flat bar.
- Slide the drip edge flange under the shingles and, along the rakes, over the underlayment, which is the same order a new roof uses.
- Nail the flange about every 12 inches, close enough to its inner edge that the shingles above cover the nails.
- Press the shingles back down and hand-seal any that will not reseal in the next warm spell.
The eave compromise
On a new roof, eave drip edge goes on the bare deck first and the underlayment laps over it, so water running down the underlayment lands on the metal and drips clear. On a retrofit the underlayment is already nailed down, so the new flange usually slides in above it, and water that gets under the shingles can still run behind the metal. Some roofers slit the underlayment and tuck it over the flange, which helps if the underlayment is still in good shape.
When to wait
- The fascia or the deck edge is soft or rotted. That repair needs the edge opened up anyway.
- The shingles are brittle, curled or near the end of their life. You will break more than you save.
- A full replacement is coming within a few years. New drip edge goes in the right way then, and code calls for it at eaves and rakes.
For what drip edge does and why codes require it, see drip edge explained; if the fascia already shows water damage, start with common roof leak causes.