Put that raincoat away! We’re talking about the sheet material (metal, vinyl, etc.) covering joints on the outside of your house to keep moisture from getting in.
Here’s a quick rundown on what to use where.
Vents: Wherever vents protrude from your roof, you need flashing to seal out water. The flashing is flat with a hole, so you can slide it over the pipe, capped by a metal cone which sheds water. Install as you would a shingle, tucking it under the shingles above it, and lapping over the shingles below it. Seal the cone or cap to the pipe with roofing cement.
Windows and doors: Where a door or window meets a wall, there is usually some sort of crack where water can get in. Prehung units usually come with a flashing system, but older doors and windows or custom units may need special treatment. Z-flashing slides under the siding, caps door or window trim, and laps over the outer edge of the trim.
Roof valleys: For shingle roofs, use valley flashing: a continuous length of metal flashing bent to fit in the valley. Install the shingles over the flashing, applying roofing cement on their edges and leaving a gap between them which widens by 1/8″ per foot as you descend. For wood shingles, use W-flashing, which has a ridge to prevent water from on one side ofthe valley from crossing over and running under the shingles on the other side.
More next time.