Roofing shingles are excellent at shedding water on a slope, but they cannot seal corners or walls. That is the job of Flashing—thin sheets of impervious material (Aluminum, Steel, or Copper) installed at every intersection.
Data shows that over 90% of roof leaks originate at flashing points, not in the field of the shingles.
1. Step Flashing vs. Continuous Flashing
When a roof meets a sidewall (like a dormer), there are two ways to flash it. One is right, and one is cheap.
✅ Step Flashing (Correct)
Individual L-shaped pieces of metal are interwoven with every single shingle. This ensures that if water gets under one shingle, it hits metal and is directed back out on top of the next shingle.
❌ Continuous/L-Flashing (Wrong)
A single long strip of metal installed along the wall. It relies entirely on caulk/sealant to keep water out. Once the caulk cracks (in 3-5 years), the roof leaks.
2. Kick-Out Flashing (Code Requirement)
IRC Section R903.2.1 requires a “Kick-Out” diverter where a roof eave meets a perpendicular wall. Without this simple piece of plastic or metal, roof runoff is directed inside your siding, rotting the wall framing without you ever seeing a leak inside.
3. Chimney Crickets
If your chimney is wider than 30 inches, code requires a “Cricket”—a small triangular roof structure built behind the chimney. This diverts water around the masonry. Without it, water pools behind the chimney, eventually eating through the flashing and causing massive rot.
The answer should always be NO. Flashing is punctuated by nail holes from the previous roof. Reusing it is a guaranteed recipe for leaks.