Fig. 2
Fig. 2
Fig. 1
Fig. 1

Q: Our crews are having some trouble installing a rubberized asphalt flashing. Pushing the membrane tight into the corner between the horizontal and vertical legs of the flashing at the lap joints is difficult. In many cases, a small gap forms in this location. The membrane can be pushed in tight temporarily, but before the brick is put in, some tenting occurs in many of the locations.

How can we avoid this problem?

A: Even with considerable care, it can be difficult to maintain full contact between two adjacent sections of flashing at a 90-deg bend. Tenting often occurs at the transition between the horizontal and vertical legs (Fig. 1). In some cases, it is possible to use a triangular piece of rigid insulation to form a cant, similar to that used in some roofing membranes. A 45-deg angle cant greatly simplifies this transition and makes it much easier to get a tight fill at splice joints.

No matter what method is used, mastic should be troweled onto the edge of the rubberized asphalt at flashing splices after the splices have been thoroughly rolled in order to form a good seal (Fig. 2). This step is necessary because there are often little imperfections at the splice joint, especially at this back corner. Troweling mastic over the edge of the membrane at the flashing splice eliminates leakage.

A Principal at Wiss, Janney, Elstner Associates Inc., Northbrook, Ill.