Upper-Roof Downspout Drops That Stop Shingle Wear on Airdrie Lower Roofs

The Problem It Solves

Look up at the roof over the garage on many two-storey Airdrie homes and you will see it: a darker stripe running down the shingles from the spot where an upper downspout ends a few centimetres above the lower roof. That stripe is where the stream of water from the whole upper roof hits the same few shingles in every rain and every thaw. The force of that concentrated flow washes the ceramic granules off the shingle surface, exposing the asphalt underneath to sunlight. Once the granules are gone, the shingles in that stripe dry out, curl and crack well ahead of the rest of the roof. That shingle erosion is premature roof wear in one concentrated line, and it can shorten the life of a lower roof that is otherwise sound.

The water doesn't stop doing damage once it has hit the shingles. A strong stream running straight down a short lower roof picks up speed and shoots over the front lip of the lower eavestrough, so the water that was collected so carefully up top lands on the driveway, the front step or against the garage wall anyway. Where the upper drop lands near a valley or a wall, the flow can push water sideways under the edges of shingles or into the step flashing where the lower roof meets the siding. Loose granules then wash into the lower gutter and build up as grit in its downspout.

Winter is where this detail causes the most trouble. On a sunny Chinook afternoon, snow on the upper roof melts and pours down the upper downspout onto a lower roof that may still be shaded and frozen. The water spreads over cold shingles and refreezes, building a sheet of ice that grows every thaw. That ice sits at the lower eave, blocks the lower eavestrough and can back meltwater up under the shingles, with heavy icicles hanging over the garage door. The bonus room or living space above the garage often adds heat loss to the mix, which makes the lower roof even more prone to melting and refreezing.

How It Works

The simplest fix is a splash shoe: a formed diverter fastened at the bottom of the upper downspout that catches the falling water, slows it and turns it down the slope of the lower roof instead of letting it hammer one spot. A splash shoe spreads the flow over a wider area, which reduces granule loss, and it points the water in the direction of the lower eavestrough. It suits short lower roofs, gentle flows and homes where the upper drop lands a short distance above the lower eave. It is not enough on its own where the lower roof is long, the upper roof area is large, or ice keeps forming in that path.

For those cases, we extend the downspout itself. An extension pipe continues from the upper drop down the lower roof and ends inside or just above the lower eavestrough, so the water never touches the shingles at all. Where the geometry suits it better, we carry the pipe across the lower roof to the end of the lower gutter, next to its downspout, so the combined flow goes straight down to the ground. The pipe is secured with straps and brackets placed to avoid driving fasteners through the shingle field wherever the layout allows, and it is kept clear of valleys and step flashing.

Sometimes the right answer is to take the upper roof water off the lower roof entirely. If there is a clear wall beside the garage or porch, the upper downspout can run down that wall to grade and finish at its own extension, bypassing the lower roof and the lower gutter completely. Whichever option we choose, we check the lower eavestrough before finishing, because it has to handle its own roof plus whatever the upper roof now sends into it. If the lower gutter is undersized or its outlet is too small for the combined flow, we tell you and correct it rather than moving the overflow down a level.

What Decides the Specification

The choice between a splash shoe and an extension pipe comes down to three things: how much upper roof drains to that downspout, how far the water has to travel down the lower roof and what happens to that lower roof in winter. A small upper roof dropping onto a short, sunny lower slope may only need a splash shoe to spread and turn the flow. A large upper roof, a long lower slope or a north-facing lower roof that stays shaded and frozen calls for piping the water all the way to the lower eavestrough so it never spreads across cold shingles. On a steep upper roof the flow arrives faster, which pushes the decision toward an extension.

The lower eavestrough is the other half of the specification. Once upper roof water is delivered into it, that gutter and its downspout carry two roofs' worth of water. We check that the lower trough is sized and pitched for it and that its outlet and downspout aren't a bottleneck, since a flow that the lower gutter can't swallow simply overflows at the point where the extension pipe ends. Where the lower system is undersized, upgrading that eavestrough or its downspout is part of doing the job properly, and a note about it belongs in our recommendation.

Around Airdrie

Kings Heights, largely 2010s-onward growth, is typical of the housing style that creates this problem: two-storey homes that commonly have a bonus room built over an attached front garage, set beneath a larger upper roof. To keep the front elevation clean, upper downspouts on houses like these are often dropped onto the garage roof rather than run down a wall, so a big share of the upper roof water lands on a short lower slope right above the garage door and driveway. After enough summer storms and winter thaws, the granule stripe and the ice at the lower eave above the garage door are easy to spot from the street.

Newer two-storey homes in Ravenswood commonly share the same layout, often with more complex upper roofs that feed several planes toward a single drop. On those homes the garage roof is also frequently shaded by the upper storey for part of the day, which is exactly the condition that turns Chinook meltwater into lower-roof ice. The fix there usually means a full extension pipe into the lower eavestrough, a check that the lower gutter and downspout can carry the extra water, and sometimes rerouting an upper drop down the side wall so the front garage roof carries only its own snow and rain.