There are both incoming and outgoing plumbing pipes in any dwelling, and either type can be subject to damage. Incoming pipes that deliver water to sinks, toilets and showers can gradually break down over time and develop leaks. Freeze-thaw cycles, foundation shifts or damage during construction or renovation can all potentially create leaks. If there is a pipe leak above your ceiling, mold could be growing and causing the odor. Mold in the home is hazardous, as it can cause respiratory illnesses. Pipes that remove liquid and solid waste are connected to vent pipes that remove sewer gases out above the roof. An improperly installed or damaged vent pipe can trap sewer gases and cause an offensive smell.
Animals such as squirrels, bats, birds and raccoons frequently live in attics. Their activity can be the source of smells in the ceiling below the attic. To enter the space, animals often damage the roofing or soffit materials. The holes they create can allow rain to enter and damage the insulation and wood. If these materials remain damp, mold will grow and cause odors. Excessive droppings and urine from the animals can leak through the ceiling material and cause odors. Mold can also grow and spread around these droppings and be a further cause of offensive smells. Raccoons and other animals that scavenge garbage can bring food back to the attic, where it can rot and smell.
Some construction materials can produce strange or offensive odors. Thousands of products release chemicals known as volatile organic compounds (VOCs) that can remain indoors for long periods. This off-gassing can come from paint, insulation, carpeting and many other building materials, as well as from furniture and electronic equipment. A recent renovation, however small, can explain a strange odor in the home.
Most building codes require ventilation for attics, but every home needs some proper ventilation, not just in the attic. Moist areas throughout the home, especially bathrooms and basements, need air movement to prevent the buildup of mold. You usually smell mold before you see it, as it has a very strong odor and can hide behind walls and ceilings. A persistent and unexplained odor from the ceiling requires investigation and proper remediation, as it could have a serious impact on the building or the health of its residents.