Drip Edge Flashing Installation & Retrofits in Airdrie

The Problem It Solves

Water does not fall cleanly off the edge of a shingle. Surface tension pulls it around the lower edge and back along the underside. On a roof with no drip edge, that water creeps back onto the exposed edge of the roof deck and runs down the face of the fascia board. A surprising share of it ends up behind the eavestrough instead of inside it, which is why an eavestrough can be the right size, perfectly pitched and freshly cleaned, and still leave a dark wet stripe running down the fascia under every rainfall.

That misdirected water does steady damage. The raw edge of the plywood or OSB roof deck soaks it up, swells and starts to delaminate, and a soft deck edge gives the first course of shingles nothing firm to sit on, so the shingles along the eave begin to droop and curl. The top of the fascia stays wet and starts to rot, hanger screws loosen, and water that slips behind the trough drips onto the soffit, stains the siding and lands right at the foundation.

Winter makes the problem sharper. On a Chinook thaw day, snowmelt runs down to the eave and then refreezes when the temperature drops again overnight. With no flashing to carry it out past the fascia, that ice forms against the face of the board and up under the shingle edge, and the next thaw sends meltwater around and behind the ice onto the deck edge. On the gable ends, the rake edge has its own weakness: wind-driven rain and snow blowing sideways across the roof can lift into the gap under the shingles where there is no rake flashing to close it.

How It Works

Drip edge is a length of metal flashing, L-shaped or T-shaped in profile, that runs along the edge of the roof. Its top flange lies flat on the roof deck under the roofing, and its face turns down over the edge and kicks slightly outward. That small offset is what breaks the surface tension: water leaving the shingle follows the metal past the fascia and drops off the lower edge, into the eavestrough, instead of curling back. It also bridges the gap between deck and fascia and supports the shingle edge.

The order of layers is different at the eaves and the rakes, and getting it wrong defeats the purpose. At the eaves, common practice and most shingle manufacturers’ instructions put the drip edge down first on the deck, with the eave protection membrane lapped over its flange, so any water that ever gets under the shingles flows over the metal and out rather than behind it. On the rakes, the order flips: the underlayment goes down first and the drip edge goes over it, so wind-driven water on the gable can’t get under the flashing. Where the two meet at a roof corner, the rake piece laps over the eave piece.

On a house that is already roofed, we retrofit. The first course of shingles is carefully released and the drip edge flange is slid in under it, then the shingles are pressed back down and resealed. Where an eave protection membrane is already adhered to the deck, we don’t tear it up to reach underneath, so a retrofit cannot always recreate the exact layering of a brand-new roof, and we say so. What it does reliably is stop the wicking: water leaves the shingles, follows the flashing and lands inside the gutter channel instead of running down the fascia behind it, which is what prevents rot in the fascia backing and the deck edge.

What Decides the Specification

Profile and reach come first. An L-shaped drip edge is the simple angle; a T-shaped profile adds a small outward kick at the bottom that throws water a little farther from the fascia. The face has to be long enough to cover the top edge of the fascia, or the top leg of any fascia capping, and to land water inside the eavestrough, so the overhang of the shingles past the deck and the height of the trough both matter. The flange has to be wide enough to sit securely under the first shingle course on a retrofit. Prefinished aluminum keeps the edge from rusting and lets the colour match the fascia and eavestrough so the flashing disappears into the trim line.

The condition of the existing roof decides how the job is done, and sometimes whether it should be done now at all. Shingle age and flexibility determine how safely the first course can be lifted. The number of roofing layers, the presence and position of an eave protection membrane, and whether the deck edge is solid or swollen all change the retrofit. If the eavestroughs are being replaced or rehung at the same time, the trough height can be set to suit the new drip edge exactly, which gives the cleanest result of all.

Around Airdrie

Hillcrest has some of Airdrie’s older housing, with homes built through the 1970s to the 1990s, and roofs of that age have commonly been replaced once or twice since. It is common on roofs of that age to find no drip edge at all, a short strip that no longer reaches the fascia after later roofing layers, or rake edges left unflashed. The signs show from the sidewalk: dark streaks down the fascia and sagging first-course shingles. Retrofitting drip edge there, alongside new or rehung eavestroughs, stops that cycle before it reaches the rafter tails.

Midtown is a much newer neighbourhood, 2010s onward, and roofs of that era generally went on with drip edge. The problem there is more often the relationship between the flashing and the eavestrough: troughs hung with their back edge below or outside the drip face, so water still dribbles behind them, or rake-to-eave corners where the laps run the wrong way. The fix is usually adjustment rather than a full retrofit. We do the same work in Crossfield, where older homes in town and newer builds on its edges show both versions of the problem.