Each week we’re bringing you an in-depth look at one of the standard conditions we encounter and document during inspections of buildings and civil structures. 

Part 9: Guano

Guano refers to the excrement of birds and bats. Most of the guano we encounter during building investigations is produced by birds, but both bird and bat guano can be present in interior building spaces. Guano can accumulate on any building material that presents a horizontal or near-horizontal surface.

guano accumulation on marble

The occasional bird dropping is not of concern, but large deposits of guano can produce chemical reactions that break down building materials. The presence of bat and bird droppings in significant quantities can be a health hazard for people accessing the affected areas of a building or structure. Hazardous buildups of guano must be removed following appropriate precautions. Anti-roosting installations are often used to prevent birds from landing and perching on skyward-facing surfaces of buildings and structures.

guano accumulation on granite

Next in this series: Pack Rust

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