A flat roof drip edge is perimeter edge metal that carries runoff clear of the fascia and locks down the membrane along a low-slope roof, and it works nothing like the drip edge on a shingle roof. On a pitched roof the drip edge slips under or over the shingles. On a flat or low-slope membrane roof, the metal goes down first and the membrane laps over it, so the water path, the fasteners, and the wind rules are all different. Get the lap direction wrong and the edge becomes the first place the roof leaks.
What is a flat roof drip edge?
A flat roof drip edge is an L-shaped or T-shaped metal flange, usually aluminum or galvanized steel, fastened around the perimeter of a low-slope roof to shed water past the fascia and to anchor the membrane edge. It sets the finished edge line, protects the wood fascia and roof deck from rot, and on ballasted or gravel systems it holds the aggregate in place. Roofers also call it edge metal, fascia metal, or a gravel stop, depending on the profile.
The core job is water control. The horizontal flange bonds to or clamps the membrane, the vertical face covers the fascia, and the hemmed lower lip forces water to drip away from the wall instead of running back underneath. Because a low-slope roof drains slowly, the edge sees standing and wind-driven water far longer than a steep roof does, so the detail has to be watertight, not just decorative.
Flat roof drip edge vs shingle drip edge: the key difference
The difference is lap direction and what secures it. On a shingle roof the drip edge is installed over the underlayment at the eave and under it at the rake, and the shingles overhang the metal. On a flat membrane roof the edge metal is set first and the membrane is carried over the top flange and sealed or welded to it, so the waterproofing layer sits above the metal, not below it. Treating the two as the same detail is the most common flat-roof edge mistake.
| Detail | Shingle roof drip edge | Flat roof drip edge (edge metal) |
|---|---|---|
| Governing standard | IRC R905.2.8.5 (drip edge required) | ANSI/SPRI ES-1, via IBC 1504.5 |
| Lap order | Metal at eave under shingles; membrane not lapped over it | Metal first, membrane laps over the top flange |
| What secures the edge | Roofing nails, shingle overhang | Cleats or fasteners plus membrane strip-in or a termination bar |
| Primary failure mode | Fascia rot, ice damming at eave | Wind uplift peel and membrane pull-off at the corner |
| Typical profile | Type C, Type D (hemmed L) | Drip edge, gravel stop, coated (clad) metal |
Types of flat roof edge metal
Flat roof edge metal comes in a few distinct profiles, each matched to the roof system and the surfacing. The right one depends on whether the roof is a single-ply membrane, a built-up or gravel-surfaced roof, and how the perimeter is fastened for wind. A drip edge sheds water, a gravel stop also dams loose aggregate, and coated metal lets a welded membrane bond straight to the flange.
| Profile | What it does | Best for |
|---|---|---|
| Standard drip edge / fascia metal | Hemmed lower lip sheds water past the fascia; covers the edge board | EPDM, TPO, PVC, mod-bit edges without ballast |
| Gravel stop | Raised vertical leg holds back gravel or ballast and stops washout | Built-up (BUR) and gravel-surfaced or ballasted roofs |
| Coated (clad) metal | TPO- or PVC-laminated flange the membrane heat-welds directly onto | Fully welded TPO and PVC systems for a monolithic edge |
| Termination bar plus counterflashing | Bar clamps the wrapped membrane; a drip cap covers the fasteners | EPDM edges, wall transitions, retrofit tie-ins |
| Canted / drip cant | Sloped face at the edge to break the angle and speed drainage | Roofs with parapets or edges prone to ponding |
How the membrane and edge metal fit together, by system
Each flat roof system terminates its edge a specific way, and the membrane manufacturer’s detail is what the warranty is written against. The shared rule is that the membrane must be continuously sealed to or over the metal flange so wind cannot get under it. What changes is whether that seal is welded, taped, or clamped with a bar.
EPDM (rubber)
On EPDM the membrane is wrapped over a formed edge bent to a 1/2-inch minimum radius so the rubber is not stretched thin, then clamped with a drip-edge termination bar. Butyl termination tape seals the rubber to the fascia behind the bar, and a cured cover strip or water block finishes the top. Adhered EPDM edges often set the metal in a bed of bonding adhesive with a 6-inch membrane strip-in over the flange.
TPO and PVC (welded single-ply)
TPO and PVC edges use coated metal, a drip edge with the same membrane laminated to its flange. The field sheet is hot-air welded directly to that coated flange, making a single welded plane from field to edge. This is the strongest single-ply edge because there is no tape or sealant relying on adhesion to hold under uplift.
Built-up and modified bitumen
BUR and gravel roofs use a gravel stop with a raised leg to contain the aggregate. The metal flange is set in flashing cement, nailed on roughly 3-inch centers in a staggered pattern, and stripped in with two plies of felt or a membrane target sheet set in mastic. Modified bitumen edges torch or cold-adhere a cap sheet over the metal flange.
Does code require a flat roof drip edge?
Yes, low-slope roof edge metal is code-regulated, but under a different rule than shingle drip edge. Section 1504.5 of the International Building Code requires perimeter edge systems on low-slope roofs, other than gutters, to be designed and tested to resist wind uplift per ANSI/SPRI/FM 4435/ES-1. That standard sets pull tests for the horizontal flange (RE-1), the fascia (RE-2), and the fastener line, so the edge stays attached in a design wind event.
This matters because the roof edge is where wind uplift is highest. FM Global and NRCA both trace a large share of membrane blow-offs to edge metal that peeled first and then let the wind get under the field. The residential shingle rule, IRC R905.2.8.5, requires drip edge on asphalt shingle roofs but does not govern membrane edge systems, so a low-slope roof answers to ES-1, not the shingle section.
How to install a flat roof drip edge
Installing edge metal on a membrane roof follows a fixed order: prep the edge, set the metal, then lap and seal the membrane over it. The sequence below is the general single-ply method. Always confirm fastener spacing and strip-in width against the membrane manufacturer’s published edge detail, since that is what the warranty requires.
- Prep the edge. Confirm the fascia or nailer is sound, dry, and at least nominal 2-inch lumber for fastener holding. Round or ease sharp edges so the membrane is not cut.
- Snap a line and dry-fit. Set the metal to a chalk line for a straight edge. Lap sections 3 to 4 inches in the direction of drainage and set the joints in sealant.
- Fasten the flange. Nail or screw the horizontal flange on roughly 4-inch centers, or per the ES-1 rated spacing, staggered. Use a continuous cleat on the fascia leg for high-wind edges.
- Lap the membrane over the top. Carry the field membrane over the metal flange. On TPO and PVC, weld the sheet to coated metal. On EPDM, strip in with 6-inch cover tape or wrap and clamp with a termination bar.
- Seal the terminations. Apply lap sealant or water block at cut edges, bar tops, and corners. Prefabricated corner pieces beat field-cut miters for watertightness.
- Check drainage. Confirm the edge does not dam water and that the drip lip throws runoff clear of the fascia toward scuppers, drains, or gutters.
Materials, sizing, and gauge
Flat roof edge metal is specified by material, thickness, and face and flange dimensions. Heavier gauge and a longer roof flange raise wind resistance and are what push an edge into ES-1 compliance. Match the metal to the membrane chemistry and the coastal or wind exposure, not just to price.
| Material | Typical thickness | Notes |
|---|---|---|
| Aluminum | 0.032 to 0.050 in | Light, corrosion resistant, common on residential single-ply |
| Galvanized / Galvalume steel | 24 gauge | Strong, economical, standard for commercial gravel stop |
| Coated (TPO/PVC-clad) metal | 24 or 22 gauge core | Weldable flange for single-ply; buy to match the membrane brand |
| Copper | 16 oz | Premium, long life, used on visible or historic edges |
Face height usually runs 2 to 6 inches to cover the fascia and edge build, and the roof flange runs 3 to 5 inches for fastening and strip-in. Longer flanges and closer fastener spacing are what an ES-1 wind design calls for on tall or exposed buildings.
Cost of flat roof drip edge
Flat roof drip edge material runs about 2 to 9 dollars per linear foot depending on metal and profile, and installed cost typically lands between 4 and 14 dollars per linear foot. Coated metal for welded TPO and PVC and heavier gauge gravel stop sit at the top of that range, while plain aluminum drip edge sits at the bottom. Corners, custom bends, and high-wind ES-1 detailing add labor.
On a retrofit, the bigger cost driver is what the edge ties into. Re-terminating existing membrane, replacing rotted fascia or nailer, and forming new corners can double the linear-foot price versus new construction where the edge goes on clean. Price the edge as part of the drainage and perimeter package, since it works with the scuppers, drains, and gutters, not on its own.
For how the whole perimeter sheds water, see our guides on flat roof drainage design and the parapet wall flashing detail. For the membrane side of the edge, our EPDM roofing installation guide covers termination bars step by step, and you can compare systems in our breakdown of flat roof types. If you have a sloped or shingled roof instead, the rules differ, so read our separate guide to shingle roof drip edge. Start at the Learn About Roofing hub for the full library.
Flat roof drip edge FAQ
Do flat roofs need a drip edge?
Yes. A flat or low-slope roof needs perimeter edge metal to shed water past the fascia and to anchor the membrane against wind uplift. Under IBC Section 1504.5, that edge system must be tested to ANSI/SPRI ES-1. Skipping it exposes the fascia and deck to rot and leaves the membrane edge free to peel in high wind, which is a leading cause of flat roof blow-offs.
What is the difference between a drip edge and a gravel stop?
Both are perimeter edge metal, but a gravel stop has a raised vertical leg that dams loose gravel or ballast so it cannot wash off a built-up roof. A plain drip edge has a hemmed lower lip that sheds water but no raised leg, so it suits smooth single-ply membranes like EPDM, TPO, and PVC that carry no aggregate.
Does the membrane go over or under the drip edge on a flat roof?
Over. On a flat membrane roof the edge metal is fastened first, then the membrane laps over the top flange and is welded, taped, or clamped to it. This is the reverse of a shingle roof at the rake. Lapping the membrane over the metal keeps the waterproofing layer continuous and stops wind from getting under the edge.
What size drip edge do I need for a flat roof?
Face height usually runs 2 to 6 inches to cover the fascia and edge build, and the roof flange runs 3 to 5 inches for fastening. On tall or wind-exposed buildings, the ES-1 wind design may call for a longer flange, closer fastener spacing, and heavier gauge, so size the edge to the calculated uplift, not to a default.
Is flat roof drip edge required by code?
Yes, low-slope roof edge metal is code-regulated. IBC Section 1504.5 requires perimeter edge systems other than gutters to be designed and tested to ANSI/SPRI/FM 4435/ES-1 for wind uplift. This is separate from the residential shingle drip edge rule in IRC R905.2.8.5, which does not govern membrane edges. Local amendments can add requirements, so confirm with your building department.
Can you add a drip edge to an existing flat roof?
Often yes, but it means re-terminating the membrane at the perimeter. A roofer lifts or cuts back the edge membrane, sets new edge metal, and strips or welds the membrane back over the flange. On EPDM, a termination bar retrofit is common. Rotted fascia or nailer usually has to be replaced first, which is what drives the cost of the upgrade.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.