If the summer sun has you raring to get that roofing job done, don’t forget about flashing.
Don’t worry, this kind of flashing is legal. It’s the metal stuff that covers the joints between surfaces, and keeps rain from getting under the shingles.
At chimneys, attached sheds, and skylights, your roof slopes along the side of a vertical surface. In these cases you must use step flashing, which comes in small squares bent in half at 90 degrees. Step flashing diverts any water which gets under the shingle to the top of the next shingle down.
Starting at the bottom with your first course of shingles, install the step flashing in the joint, and nail it to the roof. (Make sure it covers the drip edge at the eaves.) Cover it with your first shingle.
After that, start each course of shingles with step flashing. Install it to sit on top of the next shingle down, with the vertical flap overlapping the flashing below. Then cover it with the first shingle of the course.
Don’t attach flashing to the wall, as attached structures often settle independently.
Of course, that means there’s nothing to stop water from creeping down the wall and getting under the flashing. So next step is an overlap. On a frame house, siding does the job. Either remove it beforehand and replace it (tons of fun), or try and slide the flashing underneath the siding as you install it. On a brick wall or a chimney you need to install cap flashing. Starting at the bottom, chisel out the mortar two bricks above step flashing, and insert the flap on the cap flashing in the groove. Seal with fresh mortar and repeat, working up, overlapping previous flashing.