Factors Contributing to Moisture Problems in historic buildings

Sharon C. Park, AIA

A variety of simultaneously existing conditions contribute to moisture problems in old buildings. For recurring moisture problems, it may be necessary for the owner or preservation professional to address many, if not all, of the following variables:

Types of building materials and construction systems

Type and condition of roof and site drainage systems and their rates of discharge

Type of soil, moisture content, and surface /subsurface water flow adjacent to building

Building usage and moisture generated by occupancy

Condition and absorption rates of materials

Type, operation, and condition of heating, ventilating, cooling, humidification/ dehumidification, and plumbing systems

Daily and seasonal changes in sun, prevailing winds, rain, temperature, and relative humidity (inside and outside), as well as seasonal or tidal variations in groundwater levels

Unusual site conditions or irregularities of construction

Conditions in affected wall cavities, temperature and relative humidity, and dewpoints

Amount of air infiltration present in a building

Adjacent landscape and planting materials

Diagnosing and treating the cause of moisture problems requires looking at both the localized decay, as well as understanding the performance of the entire building and site. Moisture is notorious for traveling far from the source, and moisture movement within concealed areas of the building construction make accurate diagnosis of the source and path difficult. Obvious deficiencies, such as broken pipes, clogged gutters, or cracked walls that contribute to moisture damage, should always be corrected promptly. For more complicated problems, it may take several months or up to four seasons of monitoring and evaluation to complete a full diagnosis. Rushing to a solution without adequate documentation can often result in the unnecessary removal of historic materials-and worse-the creation of long-term problems associated with an increase, rather than a decrease, in the unwanted moisture.

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