The construction repair shown in the photo has one problem – It will not work.
Applying flashing in a Band-Aid fashion such as this will do little if anything to alleviate a leak. Flashing is the most critical and usually most difficult component in exterior weather enclosure. If it is done improperly, no amount of caulking will stop the infiltration of moisture.
Using this Independence home as an example, here are the issues: 1) There is no means to stop water running down the wall from going behind the flashing; 2) Water is completely free to go under the flashing; 3) The situation is worsened because the gutter above dumps additional water onto the roof.
To keep the rain from pouring into the house at a roof/wall juncture such as this, a specific installation sequence must be followed:
- Framing of walls and roof
- Sheathing of roof and walls
- Roofing felt/tar paper on roof sheathing and turn up the wall 4 inches
- Base flashing along roof/wall joint
- Air moisture barrier wrap such as Tyvek on wall and lip over base flashing
- Finish siding on wall, cut off above the roof deck to separate from shingles
Of course paper, flashing and shingles are installed first at the low point and placed upward. Every step in the process is done with consideration of the simple fact, water flows downhill. Overlaps should face downhill. Proper construction insures that water flows over, not under the barriers.
No doubt the original construction was done improperly and the house leaked. Rather than face the expensive and daunting task of tear out and reconstruction, the flashing was added on top. It may redirect some water, but it cannot keep out the water below.