How to Line a Gutter with EPDM Rubber
How to Line a Gutter with EPDM Rubber
Box gutters, parapet gutters and old concrete or asphalt valley gutters are among the most persistent leak sources on UK buildings. They sit out of sight, they collect debris, and the traditional repairs — bitumen paint, flashband, a fresh layer of felt — last a couple of winters at best. Lining the gutter with EPDM rubber turns it into a single continuous waterproof channel with no joints along its length. This guide covers when lining is appropriate, how to measure a gutter, and the step-by-step method.
What kind of gutter can be lined?
EPDM lining works on any gutter with a solid, continuous base that can be prepared to take adhesive. That includes timber box gutters and parapet gutters, concrete gutters on older commercial and municipal buildings, asphalt-lined gutters where the asphalt is sound but crazed, metal-lined gutters where the metal has corroded or split, and valley gutters between two pitched roofs.
It does not work on standard uPVC or cast-iron half-round rainwater gutters hanging off a fascia. Those are drainage components, not roof surfaces — if one of those is leaking, replace the section or the joint.
The gutter also has to be structurally sound. Rubber lining is a waterproofing layer, not a repair for rotten timber or a collapsed concrete gutter sole. If the base is failing, rebuild it first.
Why line rather than replace
Replacing a box or parapet gutter usually means stripping back the adjoining roof coverings on both sides, which turns a contained job into a large one. Lining works over the existing profile, needs no hot works, and can be done in a day on a typical domestic run. Because EPDM comes in long sheets, a 10m gutter is lined with a single piece with no joins along the direction of flow — which is the whole reason gutters leak.
Measuring a gutter for lining
The measurement most people get wrong is the girth. You are not measuring the width of the gutter; you are measuring the developed length of the profile — the distance a piece of string would travel if laid across the gutter from the top of one upstand, down the side, along the sole, up the other side and to the top of the other upstand.
The formula
Girth = upstand height + side depth + sole width + side depth + upstand height, plus 100mm allowance
Worked example
A timber box gutter 300mm wide at the sole, 150mm deep on each side, with the membrane taken 100mm up the vertical face at each side:
- 100mm (upstand) + 150mm (side) + 300mm (sole) + 150mm (side) + 100mm (upstand) = 800mm
- Plus 100mm allowance = 900mm girth
For length, measure the full run and add 150mm at each end for the stop end and the outlet detail. A 10m gutter therefore needs a strip 0.9m x 10.3m. Order the width from the girth, never from the gutter’s apparent width. If your gutter changes width along its run, girth the widest point.
Our EPDM gutter lining kit supplies the membrane, adhesive and sealant sized for the run.
What you will need
| Item | Notes |
|---|---|
| EPDM membrane, 1.5mm | Cut to girth x run. 1.5mm is preferred in gutters for its robustness |
| Contact adhesive | Used throughout — the gutter has vertical and sloping faces, so water-based deck adhesive is not suitable |
| Lap sealant | All terminations, cut edges and outlet junctions |
| Termination bar or wall trim | Where the lining terminates against a vertical wall |
| Outlet or drain kit | A bonded flange outlet at each rainwater pipe |
| Corner and stop-end patches | For gutter ends and any change of direction |
Tools: adhesive brush, silicone seam roller, trimming knife, wire brush and scraper for preparation, and a means of safe access. Gutter work is edge work — a proper tower or scaffold, not a ladder leaned against a gutter you are about to remove material from.
Step-by-step
Step 1 — Clear and inspect
Remove all debris, moss, silt and loose material. Then look at what is underneath. Probe timber gutter soles with a screwdriver for softness, check concrete for spalling and check that the existing falls still run to the outlet. Anything structural gets fixed now, because it cannot be reached once the lining is bonded.
Step 2 — Prepare the surface
Scrape off loose bitumen, flaking paint and corrosion. Fill any hole or void so the lining is continuously supported — rubber bridging a void will eventually be pushed into it by standing water and debris. Ease any sharp arris at the junction between the sole and the sides. The surface must end up clean, sound and completely dry before adhesive goes anywhere near it.
Step 3 — Fit the outlets first
Work out where each rainwater outlet sits and prepare its opening. Fitting the outlet flange arrangement before the field membrane means the lining is dressed into a finished detail rather than cut around an obstacle afterwards.
Step 4 — Dry-fit the membrane
Lay the strip into the gutter without adhesive and check it reaches the intended height on both sides along the entire run. Mark the termination line on both walls with a pencil or chalk line. A gutter that is 20mm wider at one end than the other will show up here, while you can still do something about it.
Step 5 — Bond the sole
Fold half the length of the strip back on itself. Brush contact adhesive onto both the gutter sole and the underside of the membrane, allow it to flash off until tacky, then lower the membrane into place, working from the centre of the sole outwards. Roller it down firmly. Repeat for the other half.
Contact adhesive grabs on touch, so alignment must be right before contact. In a narrow gutter you have very little room to correct a misplaced sheet.
Step 6 — Bond the sides and upstands
Working along the run, brush adhesive onto each side face and the corresponding area of membrane, flash off, then dress the material up the side and onto the vertical face to the marked line. Push it firmly into the internal angle where the side meets the sole — this angle is the highest-stress point in the whole lining, and any tunnel here will eventually crack.
Step 7 — Detail the stop ends and outlets
At each end of the run, dress the membrane up the stop end and fold the surplus at the two internal corners rather than cutting it, exactly as you would on a roof corner — see the internal corners guide for the fold technique. Cover each with a corner patch. At each outlet, bond the flange to the lining and seal the perimeter with lap sealant.
Step 8 — Terminate and seal
Fix a termination bar or wall trim along the top edge of the lining where it meets a vertical wall, and seal the top edge. Where the wall is exposed masonry, a cover flashing chased into the mortar course over the termination is the durable detail. Seal every exposed cut edge.
Step 9 — Test
Run water down the gutter from the far end and watch it discharge. Check for ponding, check the outlets take the flow, and check for any weep at a termination or patch. This is a five-minute test that saves a return visit.
Mistakes that cause a lined gutter to fail
Measuring width instead of girth
The most expensive mistake, because it means the material is simply too narrow and has to be reordered. Girth the profile with a tape following the surface, not across it.
Using water-based deck adhesive
Deck adhesive relies on membrane weight holding it in contact while it cures. In a gutter almost every surface is vertical or sloping. Contact adhesive throughout.
Bridging voids and holes
Unsupported membrane over a hole becomes a puncture once grit and standing water sit on it. Fill and support first.
Cutting at stop-end corners
The same rule as roof corners: fold, bond flat and patch. A cut at the end of a gutter sits in the deepest standing water on the whole run.
Terminating too low
A blocked gutter fills up. If the lining terminates 50mm above the sole, the first autumn leaf fall puts water over the top of it. Take terminations as high as the profile allows.
Frequently asked questions
Can I line a plastic or cast-iron half-round gutter with EPDM?
No. Those are hanging rainwater goods rather than roof surfaces, and a leaking one should be repaired or replaced at the joint. EPDM lining is for box, parapet, valley and concrete gutters with a solid continuous base.
What thickness should a gutter lining be?
1.5mm is the sensible choice. Gutters collect grit, take the concentrated flow off the whole roof, and are periodically cleared by hand or with tools, so the heavier sheet is worth having.
Do I need to remove the old asphalt or bitumen first?
Remove everything loose, flaking or delaminated. Sound, well-bonded asphalt can usually be left in place as a substrate once cleaned, but anything moving must come out. Check the adhesives and primers guide for substrate-specific advice.
How long does gutter lining last?
EPDM has a design life in excess of 50 years and is unaffected by UV and ozone. In practice the lining will outlast the terminations and outlets around it, which is why those details deserve care.
Can one piece cover a long gutter run?
Yes — EPDM sheets are long enough that most domestic and many commercial runs are lined in a single piece with no joints in the direction of flow. Where a run is too long for one piece, laps must be formed correctly with the upstream sheet over the downstream one.
Will the lining reduce the gutter capacity?
Negligibly. The membrane is 1.5mm thick and follows the existing profile. If capacity is genuinely marginal, the answer is a larger outlet or an additional one, not a thinner lining.
Can I line a gutter in winter?
Contact adhesive needs the surface dry and ideally above 5°C. Gutters stay damp longer than roofs and are often in shade, so winter lining frequently means waiting for a genuinely dry spell rather than just a dry day.
Shop related products
- EPDM gutter lining kit
- 1.5mm heavy-duty EPDM membrane
- Contact adhesive
- Internal corner patches
- Horizontal drain kit
- Flashing and trims