TL;DR: For a four-storey New York brownstone with flat roof how should the dividing parapet wall be covered/sealed?
The brownstone has a rubber-like membrane on the roof that is connected to brick parapet walls. The parapet walls have flags of stone on top of them. These stones aren’t in good condition and parts are flaking off in places. I think it is likely water is getting past the stone and going behind the membrane. In some places I see blisters in the membrane beneath these stones. One of these blisters recently cracked and caused a leak which I fixed with flashing cement and roofing fabric.
My neighbors’ roofs have different treatments.
- Some have this wall covered in cement and painted
- Some have clay coping tiles that look like they are designed for this application
- Some have a sheet metal covering
- Some have cuboid blocks similar to mine but they appear to be concrete instead of stone
My questions are:
- Should be worried about the way my parapet wall has been capped?
- Is the condition of the capping stones the likely cause of the blistering? If not, is there something else I should be looking at?
- How should the parapet wall be capped?
- To keep water off the place where the membrane joins the wall I am thinking of adding inverted U-shaped aluminum flashing over the stones held in place with flashing cement. Is this a sensible solution?