Why is flashing the first place roofers look for a leak?
Because joints concentrate water and depend on metal and sealant that age faster than shingles. On a roof with intact shingles, a leak is far more likely to come from a chimney, valley, wall joint or vent than from the open field. Checking them first saves time and money.
A roofer will often find that the stain on a ceiling lines up with a joint above it, a few feet uphill. That is not coincidence. Water runs along the roof and hits the first break it finds.
Ask the roofer to show you photos of what they find. Flashing is out of sight from the ground, and seeing the rust or gap is the best way to understand the repair.
Is roofing cement or caulk a real fix for flashing?
Usually only a stopgap. Sealant dries, shrinks and cracks within a few seasons, and it hides the problem without fixing the overlap that carries water away. A good repair rebuilds the flashing so it works with gravity. Sealant can finish a joint, but it should not be the whole joint.
You will see black roofing cement smeared in layers on many older roofs around the valley. Each layer was someone's attempt to stop a leak. They can make a repair harder, because the roofer has to remove them to see the metal.
If a patch has been applied, tell the roofer. It helps them understand how long the leak has been running.
What about copper flashing and zinc moss treatment?
Oregon State University Extension advises against using zinc moss treatments on roofs with copper gutters or flashing. Zinc runoff can attack copper. If your house has copper details, tell the roofer before any moss treatment is applied and ask about alternatives.
Older houses sometimes have copper valleys or chimney flashing that is still serviceable. Replace it only if needed, and keep any zinc product away from it. The page on roof moss removal and prevention covers the options.
Can flashing be repaired in the rain?
Not well. Sealants and metal need dry surfaces, and working on a wet roof is unsafe. A roofer may place a temporary cover over a failed joint in bad weather and return for the lasting repair when it dries. Ask what is planned and how long the temporary measure should hold.
Because the wet season runs from late October to March, repairs done before it starts last longer. If a leak is already running, see roof leak repair for the steps to take first.
What should a flashing quote spell out?
Which joints are being replaced, what metal is used, whether counter-flashing is set into masonry, what happens to the shingles around each joint, and what is allowed for rotten sheathing. A quote that only says repair flashing leaves too much open. Ask for each location to be listed.
Walk the roofer around the house and ask them to point out each joint on the quote: the chimney sides, the back cricket, the wall step flashing, each vent. The list should match what you saw.
Photographs before and after are reasonable to ask for. Flashing is hidden once the shingles are back, and a photo record is the only way to confirm the work was done as described.
