When a shingled roof meets a side wall, improper installation of flashing can cause rainwater to leak inside. Keeping this area of the house dry is a tough endeavor so taking extra care to prevent leaking will prevent callbacks and future headaches.
Pieces of flashing are sometimes correctly lapped over each other, but incorrectly lapped over the wall’s housewrap. It often happens when roofers are asked to install the flashing after the building paper is already on the wall. The flaw can direct rain behind the flashing into the structure.
The ideal way to install step flashing is to put the vertical leg of the flashing against the wall sheathing, then seal the flashing to the wall with an applied layer of peel-and-stick flexible membrane. The final step is to lap the housewrap down over this sealed joint.
If the housewrap is already in place and the step flashing has already been applied, here’s a fix: slit the housewrap above the step flashing and slide the peel-and-stick up under the existing housewrap, lapping it down over the existing step flashing. Cut and fit a housewrap patch to cover.