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Roof Flashings Done Right

March 18, 2016

Step flashing, chimney flashing, and pipe flashings keep water out of the roof, but only if installed well

John DeRosa of IKO Roofing talks about the right way to install flashings. Improper flashing techniques are susceptible to leaking. And nobody wants to see that on a new roof. So, here's what you need to do to help ensure this doesn't happen to you.


Step Flashings

Roof planes that butt against vertical walls at the end of the shingle course are protected by metal step flashing at least 5” high and 5” wide.  When applying the new shingles, each shingle course will be covered by a step flashing.

There are two simple rules to follow:
  1. Each flashing should overlap the one below by at least 3” but not be visible below the shingle top lap
  2. Embed each piece of step flashing in a 3” wide application of asphaltic plastic cement and nail in place.  

Then the end of each shingle overlapping a step flashing must also be well embedded in plastic cement.


The metal step flashing shingles are rectangular in shape and style, approximately 10” long, and at least 2” wider than the face of the shingle being used. For instance, when using metal flashing shingles with a typical 5 - 5/8” exposure, the size of the flashing will be 10” x 8”.

The 10” length is bent in half so that 5” will reach up the wall surface and the other 5” will extend onto the roof deck.

Note: Other step flashing sizes are also acceptable.


To install the flashing shingle on the first course:

  • Place it over the end of the starter strip.Step-flashing-nail-into-roof
  • Place it so that the tab of the end shingle covers it completely.
  • Secure the horizontal flange to the roof deck using two nails. Do not fasten the flashing shingle to the vertical wall. This will allow the flashing shingle to move with any expansion and contraction that may occur with the roof deck.  
  • Place the second step flashing shingle over the end shingle in the first course by positioning it 5-5/8” above the bottom edge of the exposed asphalt shingle. Make sure that the tab on the shingle in the second course will cover it completely.  
  • Secure the horizontal flange to the roof.  
  • The second and succeeding courses will follow with the end shingles flashed as in preceding courses.  


Other common roof flashings

Chimney flashings are secured to the roof over the top of the shingles, and counter or cap flashings are secured to the chimney, providing a waterproof seal.  


Pipe flashings around soil stacks: 

  • Shingle up to the bottom of the stack.  
  • Apply plastic cement around the edges, and then slide the new flashing over the soil pipe and into place.  
  • Nails used to secure flashings to the roof should be used sparingly, not driven close to the pipe, and placed where recommended by the manufacturer.
  • Continue shingling and cutting to fit around the stack. 
  • Each cut shingle should be laid in a bead of cement.  
  • A dab of plastic cement over the exposed nails is recommended to avoid leakage.

As we can see, the measurements and application of products used when installing roof flashing are critical to creating the protection that is sturdy but also flexible enough to adapt to changing conditions of the home or structure, right down to the shingles used for flashings.

Note: This video was filmed in an indoor studio on a prefabricated deck; all safety guidelines outlined by Government Safety and Fall Protection standards must be followed at all times.


—This video is provided by IKO Roofing, a worldwide leader in roofing and waterproofing. 


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