Drip Edge and Eave Detailing on a Metal Roof
The eave is where wind uplift starts, where ice dams form, and where every drop of water on the roof eventually goes. The detail there does more work than any other.
If you want to know whether a metal roof was installed by someone who understands the system, look at the eave. It is the most heavily loaded detail on the roof: the highest wind uplift, the place ice dams form, the termination point for the deck, the underlayment and the panels, and the handoff to the eavestrough. It is also the detail most often reduced to a piece of bent metal and a row of screws.
What the Eave Detail Has to Do
Four things at once. It has to carry water off the deck and clear of the fascia so it lands in the trough rather than running down the face of the house. It has to terminate and protect the edge of the underlayment and the sheathing. It has to anchor the bottom of the panel against uplift, which is where wind loads are highest. And it has to do all of that while letting the panel slide as it expands and contracts.
Eave Trim and the Cleat
There are two common arrangements. The simpler one uses a one-piece eave trim with a hemmed lower edge that acts as a drip kick, and a vertical leg on the roof side that the panel hooks over. The better one uses a separate continuous cleat: a strip of formed metal fastened to the deck along the eave, with the eave trim installed and then the panel end hemmed and locked over the cleat.
The cleat approach is worth the extra step. A continuous cleat holds the entire length of the panel edge rather than resisting uplift at discrete fastener points, and the hooked hem lets the panel slide along the cleat as it moves. It also puts no fastener through the panel face at the most weather-exposed line on the roof.
The Panel Hem
The lower end of a standing seam panel is bent back on itself — a hem of roughly three-quarters of an inch to an inch — and hooked over the cleat, then closed with a hand seamer. Two things happen. Mechanically, the panel is locked down along its full width, so wind cannot get under the edge and peel it. Hydraulically, the hem breaks capillary action: without it, surface tension can draw water back around a raw panel edge and onto the fascia, which is how you get staining and rot on a roof that never actually leaked.
- ✓Hem allowance has to be added when panels are cut to length. Forgetting it produces panels that are short at the eave and there is no fixing that.
- ✓The cleat is fastened at close centres — tighter than you might expect, and tighter again in high-exposure locations. It is doing structural work.
- ✓Trim laps run around one to two inches with butyl in the lap, and the fastening should not show on the exposed face.
- ✓Use trim of the same gauge and finish as the panel. Thin, flimsy edge metal flutters in wind and telegraphs every fastener.
- ✓The trim should project past the fascia far enough that drips land inside the eavestrough — commonly an inch or so — but not so far that it becomes a lever for wind.
Underlayment Sequence
The traditional convention is that at the eave the drip edge goes down on the deck first and the ice barrier membrane laps over its roof-side flange, so water reaching the membrane drains out over the metal. At the rake it reverses: membrane first, trim over. Metal panel systems frequently use a variation on this, with the eave trim or cleat set over a self-adhered membrane and bedded into it. Follow the panel manufacturer's eave detail, and sanity-check it against the principle: at every layer, water moving downhill should end up on top of the layer below, never behind it.
Wind failures on roofs start at the edges. Uplift pressure is highest along the eaves and rakes and highest of all at the corners, because that is where airflow separates from the building. A field of the roof that is properly clipped means nothing if the eave is held down by a few widely spaced screws through the panel face. This is the detail to spend attention on.
Ice, Snow and the Eavestrough
Two Ontario-specific issues meet at the eave. The first is ice damming: heat loss melts snow on the warm part of the roof, the meltwater refreezes over the cold overhang, and water backs up behind the ridge of ice. That is why self-adhered membrane runs from the roof edge well past the interior face of the exterior wall, and why the eave metal must lap correctly over it.
The second is snow shedding. A metal roof sheds snow, sometimes in one large release, and the eavestrough is directly in the path. Hanger spacing needs to be tighter than a shingle roof would require, hangers should be screwed into solid fascia, and on roofs above walkways, entrances or driveways, snow retention should be part of the conversation from the start rather than added after someone's eavestrough ends up in the garden.
Common Eave Mistakes
Panels face-screwed at the eave instead of hemmed, which pins a panel that has to move and puts fasteners in the wettest line on the roof. No hem at all, so the panel edge flutters and capillary action wets the fascia. Trim projecting too short, so water runs behind the eavestrough. Reused old drip edge, which is nearly always the wrong profile and the wrong material for a metal system. Membrane run under the drip edge instead of over it, so water reaching the membrane drains behind the fascia. And an eavestrough hung the way it would be on a shingle roof, with no allowance for a slab of snow arriving on it in March.
Frequently Asked Questions
Does a metal roof need drip edge if it has eave trim?
Eave trim on a metal roof is the drip edge — it is a purpose-formed piece that does the same job plus anchoring the panel. What matters is that the edge metal is present, correctly lapped with the membrane, and detailed to hook the panel rather than just cover the deck edge.
Can the existing drip edge be reused when switching to metal?
In practice, no. Shingle drip edge has the wrong profile for a metal eave detail, it will be the wrong gauge and colour, and it has already been nailed through repeatedly. It comes off with the old roof.
Will the eavestrough survive snow sliding off a metal roof?
It survives if it is hung for it — closer hanger spacing, screwed fasteners into sound fascia, and consideration of snow retention where the shed path is over an entry or a driveway. It does not survive if it is hung to shingle-roof standards and the roof lets go all at once during a February thaw.
Should the panel be hemmed over a cleat, or is face-fastening acceptable?
Hemmed over a cleat, on any standing seam roof. Face-fastening at the eave defeats the concealed-fastener principle of the system, pins the panel against thermal movement, and puts exposed fasteners at the highest uplift and wettest location on the roof.
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