What are the common causes of excess humidity in your home?

One of the main causes of excess humidity in your home is poor ventilation.  The level of ventilation in your home including how much fresh air is entering the house from outside and how effectively contaminated air is being exhausted from the house can have a major impact of the quality of air in your home.  Humidity occurs in indoor environments due to building related causes. Porous walls, rising damp, and leaks in the home are determinants for structural dampness due to elevated humidity levels. The construction of the building can also lead to humidity and unwanted moisture in the indoor environment. Wet materials, such as lumber stored unprotected outdoors before construction, can lead to increased humidity indoors for up to the second year of occupancy in a new or newly renovated home.