The short answer
An edge trim, also called a drip, is a profile fixed along the perimeter of a flat roof. It pins the covering down at the perimeter and sends runoff off the roof and into the gutter instead of down the fascia. When a trim cracks, lifts or rusts, water runs behind it, soaks the deck edge and fascia and can show as a leak inside. Renewing the edge normally means lifting the covering back and fitting a new trim.
What an edge trim and a drip actually do
A flat roof covering does not simply stop at the edge of the deck. If it did, water would run off the lip, curl underneath and soak whatever it touched. An edge trim solves that with a small shaped profile, usually aluminium, galvanised steel or plastic, fixed to the deck edge with the covering tucked into or over it.
It does two jobs. First, it clamps or protects the end of the membrane so wind and water cannot get under it and peel it back. Second, it forms a drip: a lip, set slightly proud of the fascia, that makes water fall free of the board and into the gutter instead of tracking back along the underside.
The profile differs by system. An EPDM sheet is often finished with a metal drip edge, a GRP roof with a pre-formed edge trim bedded in resin, and a felt roof with a metal drip or a welted edge. The detail is different, but the purpose is the same.
What goes wrong at a failed edge
Edges fail because they take the harshest of everything. They sit at the lowest point of the roof, where water leaves, and at the highest point for wind and sun. Typical faults include:
- Trims cracked by sun and frost, or bent by a ladder leaning against them.
- Fixings that have rusted or worked loose, so the trim lifts.
- Sealant at the joints that has shrunk and split.
- A drip lip that is too short or missing, so water runs back under the board.
- Covering that has pulled back from the trim and left a gap.
None of these leaks on day one. Water gets behind the trim in small amounts, soaks into the edge of the deck, then moves on to the fascia and soffit. The first sign may be flaking paint, a damp patch on the ceiling just inside the wall, or a gutter that is overflowing for no obvious reason. By then the damage is under the surface.
Fascia rot, and why the edge is worth a close look
A timber fascia that is regularly wetted at the top edge will soften and eventually rot. On many flat roofs the deck rests on a rafter or joist end that sits behind the fascia, so water that gets past the trim can reach structural timber and not just a painted board.
MyBuilder's 2026 guide to gutters, fascias and soffits puts fascia at about £80 to £150 per metre, soffit at £100 to £180 per metre and guttering at £30 to £70 per metre, with scaffold extra. Those are UK-wide guide figures, not Supreme prices. They are a useful reminder that a failed edge detail can turn into a bigger job, because rot in the fascia means replacing board and re-hanging the gutter.
It also explains why we check the fascia when we inspect a trim. A trim that has failed for a while often has a fascia behind it that needs attention.
How an edge is renewed
Renewing an edge is not a case of fixing a new trim over the old one. The sequence on a typical roof is as follows.
The old trim is removed and the covering is lifted back far enough to expose the deck edge. Any wet or soft timber is cut out and replaced, which includes the fascia where needed. The deck edge is checked for fall, so water runs towards the gutter and not away from it. A new trim is fixed at the right height and with fixings that suit the material, so the drip stands clear of the fascia. The covering is then dressed into or over the trim and sealed. Joints in the trim are lapped or joined to keep water out.
On a roof being re-covered anyway, the edge is simply part of the job and the trim is renewed with everything else. Where the rest of the roof is sound, a section of edge can sometimes be repaired alone, though that depends on the covering. We explain which in the written quote, which also covers the edge.
Thicker insulation raises the roof edge and may need a deeper trim, an effect we describe in insulating when you replace a flat roof.
Edges on extensions and dormers
Edges behave differently depending on where the roof sits. An extension roof usually has an edge on three sides and a wall abutment on the fourth. Our guide to flat roofs on Stroud extensions covers how those details fit together. A dormer top has short edges, a tight space to work and a pitched roof or wall hard against it, which we discuss in replacing a dormer flat roof.
Wherever the roof is, the edge deserves a look from the ground once a year. Check the line of the trim for gaps, look at the paint on the fascia and see whether the gutter is overflowing at one point. A flat roof should always drain towards the gutter, and the fall and edge trim have to work together.
For the full range of coverings and repairs, start from our flat roofing page. The survey records the edge with photographs, and work we do on the edge sits under our written 10-year guarantee.