Top 6 Reasons a Roof Leaks

April 4, 2017 Laura MacCormac

Roofs will leak for several reasons.  The most common reasons are improper drainage, damaged flashing, granule loss (the top protective layer), damage to the roof membrane, and ventilation issues.

The wear-and-tear caused by weather in every season will affect every roof on every building and the only thing you can do to lessen it is preventative maintenance.  Keep the roof strong because it’s your first line of defense; It covers the whole building. Fall storms with flying debris, snow and ice in winter, heavy rains in spring, hot sun and strong UV rays in summer – all of these are forces you cannot control and they all damage your roof.

Here are the 6 most common roof leak causes that you can control:

1. Improper Drainage

backed up gutter

Gutter Back-Ups

This is an obvious one because it is easy to see the signs of gutter problems.  Is it draining?  Is it on tight or coming loose?  There are a number of things that could be blocking gutter drainage such as ice, leaves, growing weeds, dirt, etc.  Gutters should be checked at least twice a year. The pressure of the built up water will cause a leak at the weakest area around it.

leads to water build up on roof

Clogged Drains

Drains get clogged easily because the water flowing to them brings debris.  The drain screen you see here keeps the water flowing despite the leaves.   However, in time, the build up of debris will clog the drain.  Regular maintenance is the only answer.

2. Damaged Flashing

Damaged flashing

Flashing is used to protect areas of the roof where major parts join, like the roof edge, large vents, chimnies, HVAC units, etc. It diverts water away from the areas where water is most likely to get in.  There are a variety of materials used to make the flashing from metal to liquid membranes.  This example shows damaged metal flashing.

3. Granule Loss and Damaged Shingles

Direct UV rays damage the roof membrane; Granules are used to protect it.  Shingles are coated with granules.  Flat roofs typically have a layer of granules though sometimes stones and other materials are used and the same rule applies. Weather causes degranulation.  It’s important to monitor that protective layer and ensure shingles are in good condition.


If there’s moisture there could be moss issues. Moss retains water in the roof system leading to granule loss and deterioration of the roof system. It can be removed and treated but over time it will start growing back.

november 25, 2015 93505 am pst-resized-320

Broken shingles need to be replaced to keep the roof membrane covered and protected.  Water will seep under the shingle and rot the wood and lead to a leak.


You can see how the membrane is directly exposed in this example.

roof membrane weakens
This is a worn down membrane on a flat roof that hasn’t been properly protected.

4. Deterioration of Roof Membrane

There are many types of roof membranes and all of them experience some kind of wear. If you are getting a roof replacement, avoid cheap roof membranes that claim to cost less.  In the long run, that cheap roof membrane material will cost you more.

roof membrane has holes
Seams can open, membranes can be punctured, they can blister and crack and over time deteriorate.

5. Vents and other Roof Penetrations

There are several types of vents: doghouse, whirlybird, flat, chimney, plumbing, etc.  Other penetrations are skylights, hatches, HVAC units, and more.

Roof vents need to be sealed
All of these need to be thoroughly sealed.  Sealants wear down over time and that leads to water ingress.  They can also rust which leads to holes, another big cause of leaks.  All penetrations need to be looked at regularly to prevent leaks.  In this example there is actually no caulking at this doghouse penetration.

6. Poor Ventilation

Condensation is how a roof can break down from the inside.  The roofing system needs to breath so air can circulate and stay dry.  If the ventilation system is not adequate or gets plugged up it will lead to condensation which will lead to mold growth and rot and water will find it’s way in and make the situation worse.  When that gives way you not only have a leak to deal with but mold and the health issues and high costs of replacing damaged structures.

mold grows if soffits don't work

attic condensation

The attic and soffit vents are important parts of ventilation and need to be maintained.

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