Introduction

Uncontrolled moisture is the most prevalent cause of deterioration in older and historic buildings. It leads to erosion, corrosion, rot, and ultimately the destruction of materials, finishes, and eventually structural components. Ever-present in our environment, moisture can be controlled to provide the differing levels of moisture necessary for human comfort as well as the longevity of historic building materials, furnishings, and museum collections. The challenge to building owners and preservation professionals alike is to understand the patterns of moisture movement in order to better manage it-not to try to eliminate it. There is never a single answer to a moisture problem. Diagnosis and treatment will always differ depending on where the building is located, climatic and soil conditions, ground water effects, and local traditions in building construction.

Remedial Actions within an Historic Preservation Context

In this Brief, advice about controlling the sources of unwanted moisture is provided within a preservation context based on philosophical principles contained in the Secretary of the Interior's Standards for the Treatment of Historic Properties. Following the Standards means significant materials and features that contribute to the historic character of the building should be preserved, not damaged during remedial treatment.

Applying a waterproof coating to an above-ground masonry wall can trap moisture underneath, causing further damage to the historic material. Photo: NPS files.

The Brief encourages a systematic approach for evaluating moisture problems which, in some cases, can be undertaken by a building owner. Because the source of moisture can be elusive, it may be necessary to consult with historic preservation professionals prior to starting work that would affect historic materials. Architects, engineers, conservators, preservation contractors, and staff of State Historic Preservation Offices (SHPOs) can provide such advice. Regardless of who does the work, however, these are the principles that should guide treatment decisions:

• Avoid remedial treatments without prior careful diagnosis.
• Undertake treatments that protect the historical significance of the resource.
• Address issues of ground-related moisture and rain run-off thoroughly.
• Manage existing moisture conditions before introducing humidified/dehumidified mechanical systems.
• Implement a program of ongoing monitoring and maintenance once moisture is controlled or managed.
• Be aware of significant landscape and archeological resources in areas to be excavated.

Finally, mitigating the effects of catastrophic moisture, such as floods, requires a different approach and will not be addressed in this Brief.