Replace or Fix Shingles

• Shingles are one of the weakest spots when it comes to valley leaks. If you have improperly installed shingles, consider replacing them entirely. If the shingles are new but have been improperly cut at sharp angles that allow water to flow into the valley, you may be able to simply access the shingle ends and make a secondary cut, taking off the tip of the shingles where they meet in the valley so the water does not have a path through the valley.
  
  

Additional Felt Paper

• If you need to repair the rooftop and replace materials altogether, consider adding felt paper below the shingles before you start your work. Two strips of felt paper attached to either side of the valley is a common method for preventing leaks, and plastic membranes can be added for more protection. While you may be able to install these on existing rooftops it is usually more practical to start over with new materials.
  
  

Hem Work

• The metal flashing that runs down the center of the valley can be hemmed at the edges, which shingles cover from sight. Left open, these edges provide potential access points for water. With a metal brake, you or your roofer can hem the edges inward, bending them back on the flashing itself and making it more difficult for water to pass through, capturing and redirecting rain instead.
  
  

Replace with Flashings

• Some valleys do not use metal flashings at all. Instead, they are installed with asphalt sheets or interwoven shingles. These options are more susceptible to damage. If you have roofing damage in a valley and no flashings, consider replacing materials with metal flashings running down the valley. The flashings provide a sturdier support for the shingles and better protection against storm damage.