TecTopics: How to Stop Popping Corners Before They Become a Warranty Claim

It is one of the smallest details on a roof and one of the most common places for a warranty repair to begin. When corner flashing pops open, the material itself is not always the problem. More often, the failure can be traced to the installation.

Outside corners at curbs, walls, and other angle changes are especially demanding. If the flashing is stretched too tightly while being formed, it can remain under tension and later pull loose or split. Because popped corners usually begin with installation, they are also preventable.

Why Outside Corners Pop
Outside corners are high-movement points. As temperatures change and the roof assembly expands and contracts, stress concentrates at the angle change. Flashing that is forced tightly into place may not have enough slack to move with the roof.

The corner may look acceptable at final inspection, but repeated movement can eventually cause it to pop open. The result may be a Repair for Warranty item, a reinspection, and a return trip to an otherwise clean project. Although corners make up only a small portion of the roof, proper installation can prevent a lot of avoidable repair work.

Installation Factors That Lead to Popping
A durable corner requires correctly oriented and formed flashing, suitable material, and primer that creates a reliable bond.

First, avoid overstretching. Pressing uncured flashing hard into the angle, especially by concentrating force with a thumb, can leave the material under tension. A properly formed corner should look worked into place, not stretched into place.

Material selection and preparation also matter. When installing uncured EPDM, orient the material so the diamond pattern stretches lengthwise. Do not use old material and be sure to use a hot-air gun to help form the flashing, especially in cold weather.

Finally, apply primer evenly and allow it to flash off properly. Too much primer that hasn’t flashed off properly can interfere with the bond, while too little primer can leave areas without adequate adhesion.

Corner Flashing Installation Checklist

• Use material that is within its usable shelf life and in suitable condition.
• For uncured EPDM, orient the material so the diamond pattern stretches lengthwise.
• Use a hot-air gun to help form the flashing, especially in cold weather.
• Apply the correct amount of primer and allow it to flash off properly before completing the bond.
• Always follow the current Carlisle detail and specification for the membrane system being installed. Requirements can differ by application.

---

Don’t Guess: Look It Up in RADIUS™
Even experienced crews can have corner problems when they rely on memory instead of confirming the detail for the exact condition in front of them. Use Carlisle’s RADIUS app before cutting or forming the flashing to confirm the current corner detail, fastening pattern, and other system requirements. A quick check can prevent the material, forming, and primer mistakes that lead to popping. The right detail takes seconds to find, but a popped corner takes a return trip to repair.

RADIUS for iPhone   RADIUS for Android 

---

The Bottom Line
Preventing popped corners requires more than avoiding overstretching. Use suitable material, orient uncured EPDM correctly, add heat when conditions require it, apply primer evenly, and let it flash off before bonding. Most importantly, follow the current detail for the system and condition. A few extra seconds during installation can prevent a future warranty repair.

---

Additional Resources:

Detail video: EPDM Outside Corner with Pre-Cut Pressure-Sensitive Flashing (black)
Detail video: EPDM Pressure-Sensitive Inside/Outside Corners
Complete Detail Video Library