Flashing

The best way to think about flashing is to think like water.  What we so often see is what we call "face flashing". This occurs after the initial roof has deteriorated and the next roofing contractor does not or will not open up the trim details to carry and finish his or her roof to the roof penetrations such as posts and or bell cradles.

Flashing, like water, is designed to flow downhill, and face flashing does just the opposite.  It faces up and water gets behind it regardless of the caulking applied and most often because the caulking creates a wonderful shelf for water to hit and hide behind eventually rotting the posts it was designed to protect.

Any flashing must go to the frame of the structure.  It cannot be effective if placed in front of sheathing or trim.  Flashing always has two components.  The base flash: that which rises from the roof plane up the post or any penetration in the roof.  The counter flash: that flashing that goes over the base flash and follows the flow of water.  Sheathing can be an effective counter flashing.  Trim can be an effective counter flashing.  Banding, caulking, glue and other materials like this do not provide adequate counter flashing.

In every case regardless of the materials used for the base flashing; copper, rubber, asphalt, the base flashing must be applied to the innermost vertical element.  In the case of a belfry or spire, it will be the belfry posts and spire rafters.  

Base flashing and counter flashing are easy to do if you do it right.  It requires some carpentry skill generally which many roofers admittedly do not possess.  It is important on historic structures to understand how the trim and sheathing can act as counter flashing. Start above the roof plane and remove enough of it when redoing the roof to make the counter flashing effective.  Some churches are clad in clapboard and or wood shingles.  It is very easy to remove these cladding materials and flash behind them. Some church exteriors are created with tongue and groove boards horizontally laid up.  It takes time to wiggle the joint apart but it is essential to get the base flashing installed behind the tongue and groove boards.  In vertical trim applications it is often wise to cut an angled bevel joint in the vertical material high enough up the trim detail to install base flashing.  You must be accurate with this surgical cut in the trim, but you would have saved the building from water penetration and you will have also done a good job for the next preservation of the steeple.  

Common Sense and thinking like water will guide your carpentry decision.  Tar, caulk and inattention are your nemesis.