When a metal roof is installed, it is desirable to have permanent, trouble-free flashings. In some cases, this includes flashing against stone walls or other very uneven surfaces.
SOLUTION
Flashings should be formed out of the same metal as the roofing panels themselves. Appropriate flashing methods should be used where the roof panels join the flashing. This Technical Bulletin does not deal with that issue but instead with the issue of joining the flashing to the uneven wall itself. In some cases, it can be helpful to use dimensional lumber to create a collar around the stone wall or other item. This collar can create a more even surface for the flashing to rest against. After that, it must be determined whether a saw cut can be made into the wall for the purpose of inserting the flashing. This is always preferable to just butting the flashing against the wall. However, underneath the flashing, the roof underlayment should be extended up the wall or dimensional lumber collar and it should be sealed with a long term sealant such as a butyl rubber caulk. By using a compass to trace the uneven texture of the wall onto your flashing metal and then trimming that metal appropriately, the flashing can be cut very accurately to either butt against the wall or be inserted into a saw cut.
