This blog about step flashing is part of a 6 part series on roofing underlayment. To access the main page of this series and learn more go to Roofing Underlayment 101: An Overview Of Roofing Underlayment.

Step flashing is a piece of bent metal, usually in an ‘L’ shape, that are installed where the roof meets any vertical surface (e.g. Chimneys). When a step flashing application is necessary it is absolutely crucial to have it installed it correctly. This protects the most vulnerable areas of the roof from leaking. This article will cover most of what you need to know about the topic from its use to its installation process.  

Why Install Step Flashing?

Having it installed protects against leakage. The areas where the shingles on your roof meet a vertical surface are most susceptible to water. A step flashing creates a watertight seal around chimneys and walls. This prevents water from entering into the roof deck or attic. 

By extension, this helps extend the lifespan of your roof and lowers the need for regular maintenance. Otherwise moisture could gain entry and lead to a whole array of issues such as wood rot, algae/mold growth or loss of structural integrity. 

Where is It Most Needed? 

Step flashing should be installed in any area of transition on the roof. This can include the base of the chimney as well as dormers and skylights. In addition, any second or third story section of the house that extends outwards from the roof should also have it installed at the base. 

Step Flashing Installation  

You need a separate piece of step flashing for each individual shingle that makes contact with a vertical surface. One part of the step flashing is butted up to the wall while the other is laid under the shingle, effectively sealing the exposed area.  

Step flashing comes in all shapes, colors, and sizes, commonly aluminum or galvanized steel. Depending on your roofing needs, a professional roofer would be best able to recommend what type of flashing would be best. However, the bare minimum for home installation should be at least 4 inches as a standard. Care has to be taken during installation to ensure no gaps remain between each piece of step flashing. 

For a more detailed look at how to properly install, I found this guide to be very informative on the topic.


A step flashing installation is typically paired with counterflashing. A counterflashing is a continuous strip that is installed and covers over the exposed surface of the step flashing.

Improperly installed step flashings can not only contribute to leakage but themselves might be very expensive to fix. You will need to have the shingles around it and the counterflashing over them removed before repairs can be done, which is quite labor intensive and would require extra materials. Avoid the risk by opting to have your step flashings installed by well-trained hands. For roof installation or other roofing services in Hamilton, look no further than our team of professional roofers at Peak Roofing. For a free estimate or any queries, call 905-746-5792 or email us at  

Published On: April 20th, 2020 / Categories: News / Tags: , , , /

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