The vent is the part of the drain system that carries no water, and for that reason it is the part most often forgotten until something goes wrong with it. It lets air into the pipes behind draining water so that traps are not siphoned, and it lets sewer gas out above the roof. When it is blocked, every fixture drains slowly and gurgles; when it is broken inside a wall, sewer gas enters the house; when a branch vent was cut during a renovation, one bathroom behaves strangely and nobody knows why. An inspection camera on a thin rod entered from the roof sees the inside of the stack from the terminal down to the drain, and finds most of what goes wrong with it.
Quick answer: from the roof, a small-head camera on a thin rod inspects the vent terminal, the stack and the branch vent connections. The common findings are a bird or squirrel nest, a cap of leaves and debris, a dead animal, a frost cap of ice in winter, a collapsed or corroded section in an old cast iron stack, a branch vent that ends in darkness because it was cut, and a vent that is full of water because it connects to a drain lower than it should. A vent that was never installed or is undersized cannot be seen from inside; that is a plumber’s trace.
Symptoms that point at the vent
All drains slow with a clear lateral. Gurgling at one fixture when a neighbour drains, with normal drain speed. Traps that lose their seal and let gas through, especially after a nearby fixture is used. A sewer smell near the roof or in the attic. Symptoms that come and go with wind, cold or season. And any drainage problem that started after a renovation touched a wall with plumbing in it. The gurgling guide separates vent symptoms from blockage symptoms.
Entering from the roof
The vent terminal is a pipe end on the roof, usually 2 to 4 in, sometimes with a cap or a screen. Remove the cap. Feed a small-head camera on a 5 mm rod down the stack; a 17 or 18 mm head fits any vent and a 23 mm head fits most. The rod drops with gravity and needs feeding rather than pushing. Watch for the branch vent openings in the side wall and the point where the stack becomes a drain. A long stack in a two-storey house can be 30 ft; 66 ft of cable is plenty. Entering from a roof vent covers the technique and the safety, which starts with the ladder.
What the camera finds
Nests and debris. Birds, squirrels and wasps nest in vent terminals, and leaves collect on top of the nest. The camera meets a plug of twigs, grass or leaves a short way down. Dead animals. A squirrel or a bird that went in and could not get out. Ice. In cold climates the moist air rising through the vent freezes at the terminal and closes it. Corrosion and collapse. An old cast iron stack corrodes at the joints and at the base, and the camera shows scale, holes and sometimes a collapsed section. Cut branch vents. A branch vent opening that leads into darkness and ends at a cap, a wall or nothing, which is a vent that was disconnected during a renovation. Water. A vent that holds water is connected to a drain below the flood level of a fixture, which is a design fault. The stack inspection guide covers the old cast iron case.
What the camera cannot find
A vent that was never installed. A vent that is undersized for the fixtures it serves. A trap arm that is too long for its size and siphons regardless of the vent. An air admittance valve that has failed shut inside a cabinet. A vent that terminates in an attic rather than through the roof, which the camera might find by following it, but often cannot. For these the camera has done its job by showing the stack is clear, and a plumber traces the vent system by hand. What a sewer camera cannot detect lists them.
Fixing what is found
A nest or debris is pulled out from the top with a hook or pushed through with a rod and flushed. Ice is melted with warm water or waited out, and a larger or insulated terminal prevents it. A corroded cast iron section is cut out and replaced in plastic. A cut branch vent is reconnected, which usually means opening the wall where the camera showed it ending. A screen on the terminal keeps the animals out. Inspection in cold climates covers the frost case.
What to record
The depth from the terminal of every finding, which branch vent openings were seen and whether each led somewhere, the condition of the stack wall, and whether water was present. A plumber opening a wall to reconnect a vent wants to know how far down the stack the branch opening is, and the camera’s depth reading is that number.
Common questions
Can a sewer camera inspect a vent pipe?
A small-head camera on a thin rod from the roof, yes. It finds blockages, corrosion and disconnected branches.
Why does my vent get blocked every winter?
Frost from the moist air rising through it. A larger or insulated terminal reduces it.
Can the camera tell if a vent is missing?
No. It can show the stack is clear, which sends the plumber to look for a vent that was never built.
Related guides
See trap arms and vents, finding a sewer smell with a camera, and the best 17 mm sewer cameras.