Roof flashing and terminations: coping, base vs counterflashing, vents

One-line orientation

Terminations are where roofs leak, so coping caps the wall and a two-part flashing system (base flashing turned up, counterflashing lapped over it) keeps the parapet joint watertight and serviceable.

Key points

• Coping:
  • Caps a parapet/exterior wall to prevent water infiltration into the wall.
  • Sloped for drainage and given a drip edge so water sheds off the face.
  • Common materials: stone, metal, precast concrete.
• Base flashing: the roof membrane (or matching material) turned up the vertical face of a parapet, curb, or wall — the up-stand that continues the waterproofing onto the wall.
• Counterflashing:
  • Sits over the top of the base flashing and laps down its face to protect it.
  • Lets the roof membrane be replaced because it overlaps (rather than seals to) the base flashing.
  • Sheds weather off the base flashing and accommodates building movement while staying watertight.
• Cant strip: an angled filler used with bituminous and similar roof membranes to ease the turn at a vertical surface. Many single-ply membranes can turn the corner without one.
• Roof vents (attic/roof ventilation):
  • Ridge — continuous airflow at the peak.
  • Box — static exhaust vents.
  • Turbine — wind-powered.
  • Power — electric/active air removal.

Confusions / comparison

Element	What it is	Job
Coping	Cap on top of a wall/parapet	Keeps water out of the wall; sloped + drip edge
Base flashing	Membrane turned up the wall	Continues waterproofing from roof onto the vertical
Counterflashing	Metal lapped over base flashing	Protects base flashing + lets membrane be replaced
Cant strip	45° angled filler at the corner	Eases membrane transition; avoids a sharp 90° crack

Related

→ Roof slope and drainage (this topic): scuppers and drains at terminations · Low-slope roof membranes (this topic): the membrane that turns up as base flashing · Steep-slope coverings (this topic): step flashing at a sloped-roof-to-wall joint.