Talking About Counter-Flashing

All roofs have to end somewhere. Either they terminate at a wall, parapet, expansion joint, metal edge or a tie-in with another roof. In all cases, where the roof ends, there is a weak link. Walls and parapets require vertical flashings. The flashings are generally attached at the top to keep them from sliding down the wall. The flashing attachment is usually screws, concrete fasteners, nails, or some other fastener fastened through a termination bar — a flat strip of metal with pre-punched holes. Termination bars are supposed to provide attachment along its entire length because it will continuously press against the wall.

Most roof manufacturers understand that this is a weak point in the roof and require a counter-flashing. A counter-flashing is a material, usually metal, that covers the upper edge of the flashing to divert water away from it. If the counter-flashing is not properly installed, water can get behind it and the membrane flashings. The counter-flashing then requires a sealant to be applied at the top.

This problem is just a sample of the considerations that need to be addressed in designing, installing and maintaining a roof. A good understanding of how a roof actually works and knowledge of the strengths and limitations of the different types of roofing systems is essential for the long-term performance of any roof system. The roof system should be designed with the particular building in mind, not just which is cheapest.