Using Metal Flashing with Asphalt Shingles

Insufficient Drip Edge on Asphalt Shingle Roof: © Valiant Exteriors

Some eavestroughs fail to do their job properly because water drips down from the roof behind them. This causes soffits to rot, and mould to grow inside a house. Capillary action is behind this. Did you know water is sticky and it can even defy gravity?

Capillary action is essential for tree trunks to draw moisture up from their roots. However it can be real pain with gently-sloping roofs. If asphalt shingles or other roofing materials don’t extend sufficiently over eavestroughs, then rain and melt water sucks back on the drip edge, until gravity causes it to fall behind the gutter.


Several Ways to Solve this Frustrating Problem


In theory, we could simply extend the overhang of the lowest row of asphalt shingles. In reality, these are laid down first and are full size so this ‘solution’ is impractical.

Therefore – short of redoing the roof – the solution lies in positioning a strip of curved metal flashing under the drip edge, so as to lead the water down under the gutter and safely away as we show in the illustration.

We did this on an old house we were renovating externally. The photos also illustrate how a home can deteriorate when the consequences of short overhangs are left to fester.

A Roof Is a Complex Water-Handling Structure


Roofs’ prime purpose is to keep the rooms below dry, although they have become decorative features too. However. they still need to do their primary job of catching rain and melt water, and depositing it in eavestroughs.

Achieving this can be quite complex in extended houses with hips, valleys, and step walls. This is why homeowners often prefer eavestrough specialists to attend to roof leaks.


Several More Uses for Metal Flashing on Asphalt Shingle Roofs


Asphalt shingles are designed to shed water, not seal against step walls, valleys, chimneys and drip edges. They may shed water wonderfully, however they are no use at all at these interface points.

This is where metal flashing comes into its own. We can tuck it under shingles and bend it to flow the water away while resisting capillary action. This is particularly important where drip edges overhang gutters as in our illustrations.

A experienced contractor in roofing and eavestroughing knows how to get these interfaces right. If they know as much as we do about water-damaged soffits, then they could tackle these for you too.

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