Why does wind damage flashing more than the shingles?
Flashing is metal that sits at the joints where the wind moves fastest, and it has less overlap to hold it down than the shingles do. Wind can lift the edge and break the seal, and the joint then leaks.
The corners and edges of a chimney or a wall intersection catch the wind and funnel it under the flashing. A flashing that was fixed with a few nails and a sealant strip can lift and bend when the wind gets under it, and it may not return to its original position.
Once a flashing has lifted, rain runs under it instead of over it. The water then reaches the decking and the wall behind it, and the leak can run down a wall cavity for some time before it shows in a room.
Can flashing be sealed rather than replaced?
Sealant can hold a small gap for a while, but it is not a durable repair for flashing that has lifted or corroded. The technician resets or replaces the flashing and uses sealant only where it is the right material.
Sealant on its own does not restore the overlap between the flashing and the shingles. A sealed joint can fail again within a season if the flashing is still lifted, and it can trap water behind it.
A proper repair resets the flashing so the water flows over it, replaces any metal that is corroded or bent, and uses sealant only at the joints where it belongs. The technician states which of the two is needed for the joint.
What should a chimney repair include beyond the flashing?
A chimney repair should include the flashing, the mortar joint, the cap and the crown, since each can let water into the stack. The chimney is checked from the roof and from the attic where it passes through the roof.
Mortar joints in a brick or stone chimney can crack over time, and water gets into the stack through the cracks. The technician checks the joints and notes any that need repointing or sealing. A chimney cap that is missing or damaged lets rain into the flue.
The crown, the concrete top of the chimney, can crack and let water run down the inside of the stack. Crown cracks are recorded, and the homeowner is told which repairs are urgent and which can wait.
How is flashing checked after a storm?
Flashing is checked after any storm that brought wind, starting at the chimney, the walls and the valleys. A check after a storm finds the lifted joints while the damage is still small and before a leak develops.
The storm record shows the wind speed and the warnings that covered the house. A check after a storm with strong gusts looks closely at the flashing, because wind is the most common cause of lifted metal.
The findings are recorded with the storm, and the photographs show the joint before and after the repair. The record is useful for an insurance claim as well as for the next checkup.
Can the homeowner check the flashing from the ground?
Some signs can be seen from the ground, such as a bent edge or a gap at the base of a chimney. Most of the joint, however, is hidden under the shingles, and it is checked from the roof or from the attic.
A visible gap or a bent edge at a chimney or wall is a clear reason to call. The homeowner should photograph it from a safe distance and keep the photograph with the house file.
A safe ground check does not replace the roof check. The joint underneath, the underlayment and the nails can only be seen when the shingles are lifted, and that is done by a technician on the roof.
