A dryer vent termination is, from a bird’s perspective, an excellent nest site: elevated, sheltered, warm, and lined with soft material. It is also, from a fire safety perspective, a complete airflow blockage made of dry twigs sitting inside a heated duct.
Why Terminations Attract Nesting
Roof caps are the primary site. They are elevated, protected from weather and predators, and periodically warm. Wall caps at second and third floor level attract nesting too, particularly where the damper flap has seized open. Species vary by region — house sparrows and starlings are the most common in US multifamily — but the behaviour is universal.
A damper that no longer closes is an open invitation. Damper failure is therefore the precursor to nesting, and damper condition is something an annual inspection catches.
The Fire Risk
A nest blocks airflow completely or near-completely. The duct behind it fills with lint at an accelerated rate because nothing is being exhausted. Meanwhile the nest itself — dry grass, twigs, feathers — sits directly in the path of heated exhaust air. Two independent fuels, one heat source, no airflow.
Nests are also frequently found some distance inside the duct, not just at the cap. Removing the visible material at the termination does not clear the run.
How You Find Out
Usually through resident complaints of long dry times, clustered in units on the same stack or the same building elevation. Sometimes through visible nesting material at the cap. Occasionally through the sound of birds in the duct. Rarely through inspection — because most properties do not inspect.
Removal
Nests are removed mechanically during full-run cleaning. Where active nesting is present with eggs or nestlings, timing and legal considerations apply — several common species are protected under the Migratory Bird Treaty Act, and removal of an active nest may be restricted. This is one reason to inspect and clean outside nesting season where practical, and to address damper failures before they become nest sites.
Prevention
Functioning backdraft dampers are the primary defence. A damper that closes when the dryer is off closes the entrance. Damper condition should be checked and documented at every annual inspection.
Correct termination caps. Dryer exhaust terminations should never use screened or meshed caps — screens trap lint and create the very blockage they appear to prevent. Purpose-designed dryer vent caps with a functioning flap are the correct specification. Bird guards designed for dryer exhaust exist and do not restrict airflow the way general-purpose screens do.
Annual inspection. A nest that formed in spring and is found in autumn has restricted a resident’s dryer for six months. A nest found at annual inspection is a maintenance item, not an incident.
What We Document
Every termination is photographed before and after. Nesting, damper failure, screened caps and damage are logged with unit locations in the deficiency report — so the underlying cause gets fixed, not just the nest removed.