How and Where to Look for Damaging Moisture

Finding, treating, and managing the sources of damaging moisture requires a systematic approach that takes time, patience, and a thorough examination of all aspects of the problem-including a series of variable conditions.Moisture problems may be a direct result of one of these factors or may be attributable to a combination of interdependent variables.

Factors Contributing to Moisture Problems

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

Debris will impede the normal flow of water from the roof's gutter and downspout system to the ground and result in moisture problems. Photo: NPS files.

• 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.