How to Fit Edge Trims on an EPDM Rubber Roof
How to Fit Edge Trims on an EPDM Rubber Roof
Edge trims are the last parts fitted to a rubber roof and the first thing anyone sees of it. They do two jobs at once: they mechanically secure the membrane at every edge, and they decide where the rainwater goes — into the gutter on one edge, kept on the roof at all the others. This guide covers the difference between drip trim and kerb trim, which edge gets which, how to cut and fix the lengths, and how the moulded corner pieces tie it all together.
Two trims, two different jobs
Drip trim (also called gutter trim) goes on the edge the roof falls towards — the gutter edge. Its profile carries the membrane over the roof edge and kicks the water outwards, so it drops into the middle of the gutter instead of tracking back down the fascia. A roof normally has exactly one drip edge.
Kerb trim (also called check kerb or raised edge trim) goes on every other exposed edge. It caps the edge with a raised lip that stops wind getting under the membrane and stops water spilling over sides that have no gutter, steering it towards the drip edge instead.
Where the roof meets a wall rather than open air, neither trim is used — that junction is finished with wall flashing trim and cover flashing, which the flashing and detailing guide covers in full.
Before the first trim goes on
- The membrane must be finished first. Fully bonded, rolled, and dressed over every edge with the perimeter adhesive cured. Trims lock the membrane in its final position — fit them over rubber that is still loose or tensioned wrong and you lock the fault in too.
- Count your corners before you order. Every place two trim lengths meet at 90° needs a moulded corner piece — external corners where the roof edge turns away from you, internal corners where it turns in. Walk the roof edge and count both types for each trim profile.
- Tools: a fine-tooth saw or hacksaw for cutting, a drill driver, and 13–20mm screws or polytop pins. Cut ends should be deburred with a light pass of sandpaper so joints sit tight.
Fitting drip trim, step by step
Step 1 — Dress the membrane over the gutter edge
The rubber should already be bonded down the edge and hang slightly into the gutter line. Trim any excess so the membrane finishes inside the gutter — the trim covers and traps it, but the rubber itself must reach past the timber so no wood is ever exposed to the water path.
Step 2 — Start from a corner piece
If the drip edge turns a corner, fit the moulded corner piece first and work the straight lengths into it — it is far easier to cut a straight length to meet a fixed corner than to steer a corner onto two fixed lengths.
Step 3 — Fix through the face at 250mm centres
Offer the trim up over the dressed membrane, sit its top edge level, and screw through the face into the roof edge timber roughly every 250mm. Snug the screws down flat — overdriving dimples the trim face and shows in low sun.
Step 4 — Butt the next length with a small expansion gap
uPVC moves with temperature. Butt each new length up to the last with a 3mm gap rather than jammed tight, keeping the top lines flush. Jointed tight in summer, the trim has nowhere to go except a buckle; gapped correctly, the joints stay invisible from the ground all year.
Fitting kerb trim, step by step
Step 1 — Check the membrane wraps the kerb fully
On raised edges the rubber should be dressed up, over and down the outside face of the kerb. The trim caps this — it never substitutes for it. If bare timber shows on the outside face, dress the membrane further before any trim goes on.
Step 2 — Corners first, then lengths
Exactly as with drip trim: fit the moulded internal and external kerb corners first, then cut the straight lengths to run between them with a 3mm expansion gap at each meeting point.
Step 3 — Fix through the outside face
Screw through the outer face of the trim into the kerb timber at 250mm centres. The raised lip should sit level along the whole run — check it by eye from the gutter edge, because this lip is the line the whole roof is judged by.
Step 4 — Meet the drip trim cleanly
Where a kerb edge runs into the gutter edge, the kerb trim finishes against the back of the drip trim corner (or a moulded piece that turns one profile into the other, where the system includes one). The junction should leave the water a clear path off the kerb edge and out through the drip edge.
How the two edges work — in section
Mistakes that spoil trim work
Kerb trim on the gutter edge
The classic. The raised lip dams the very edge the roof is trying to drain over, water ponds along the gutter line, and in winter it sits there frozen. The edge the falls point at gets drip trim — no exceptions.
Trims fitted before the membrane is finished
Trims are the final trap for the membrane edge. Fitted over rubber that has not been fully bonded and dressed, they hold wrinkles and tension in place permanently — and hide the evidence until the edge fails.
No expansion gap between lengths
uPVC trims grow measurably along a 2m length between a frosty morning and a sunny afternoon. Lengths butted dead tight buckle outwards at the joint; a 3mm gap absorbs the movement invisibly.
Mitred corners instead of moulded pieces
A hand-cut mitre in uPVC trim is an open joint on day one and a gaping one after a winter of movement. Moulded corner pieces exist because they seal the turn properly — count them into the order.
Screws too sparse, or overdriven
Fixings at 400mm+ centres let the trim rattle and flex in wind until the joints open. Overdriven screws dimple the face. 250mm centres, driven snug and flat.
Bare timber left above the membrane line
If the rubber stops short of the edge and the trim bridges bare wood, every drop that gets behind the trim lands on timber. The membrane must cover the full water path first — the trim is armour, not waterproofing.
Frequently asked questions
What is the difference between drip trim and kerb trim?
Drip trim goes on the gutter edge and carries water off the roof, kicking it clear of the fascia into the gutter. Kerb trim goes on every other edge and has a raised lip that keeps water on the roof and stops wind lifting the membrane edge.
Which edge of the roof gets the drip trim?
The edge the falls run towards — the one with the gutter under it. Everything else gets kerb trim, and wall junctions get wall flashing trim instead.
How are EPDM roof trims fixed?
Screwed through the face into the roof edge timber at roughly 250mm centres, over the fully dressed membrane. No adhesive is needed on the trims themselves.
Do I cut the membrane before or after fitting trims?
Dress and bond the membrane over every edge first, trim the excess to its final line, then fit the trims over it. The rubber must cover the whole water path before any trim goes on.
Do I need the moulded corner pieces?
Yes — one for every 90° turn in each trim run, internal and external. Hand-mitred corners open up with thermal movement; the moulded pieces are shaped to seal the turn and they make the straight runs easier to fit too.
Can I cut edge trims with normal tools?
Yes. A fine-tooth hacksaw cuts uPVC trim cleanly — cut on the slow stroke, support the trim near the cut, and lightly sand the burr off the cut end so the joint closes neatly.
Does the calculator include the right trims and corners?
Yes. Our roof kit calculator asks what each edge of your roof does, then puts the correct trim on each edge with the matching corner pieces and fixings in the kit.
Shop related products
- EPDM drip / gutter edge trim — 2m
- EPDM kerb edge trim — 2m
- Drip trim external corner and internal corner
- Kerb trim external corner and internal corner
- All flashings and trims
- Price a complete kit with the right trims — roof kit calculator