Lstiburek, J. and Carmody, J.
1991
ORNL/Sub/89-SD350/1. Oak Ridge, TN: Martin Marietta Energy Systems, Inc., Oak Ridge National Laboratory.
| Learn strategies for controlling moisture in building envelopes in order to minimize the risk of moisture problems in your building.
Preface
This handbook is a product of the U.S. Department of Energy Building Envelope Systems and Materials (BTESM) Research Program centered at Oak Ridge National Laboratory. The major objective of the research effort in building moisture control is to provide information to designers, builders, and building owners that will lead to the construction of energy-efficient walls, roofs, and foundations. This handbook is another in a series of design tools produced through the BTESM Program aimed at providing the most current design information. Moisture control is a key component in designing energy-efficient, healthy buildings. The presence of uncontrolled moisture in a building envelope will rapidly degrade structural materials and insulation. Moreover, it can lead to mold, mildew, odors, and pathogens. While the energy use impact of uncontrolled building moisture is not easy to quantify, it is obvious that the overall impact in terms of lost time, productivity, and expensive reconstruction is quite large. By analyzing moisture transport mechanisms in building envelopes and systematically describing control strategies for each, the building designer is provided with information needed to minimize the risk of moisture problems in energy-efficient buildings. This handbook also illustrates that energy-efficient, tight envelope design is clearly part of the solution to healthy buildings when interior relative humidity, temperature, and pressure are controlled simultane ously.
DOE formed a review panel of moisture experts to provide guidance for this effort (listed on the title page). This group reviewed the outline as well as several drafts of the handbook, and through this process strengthened the document. Although most of the committee supports the major underlying concepts, it was clear that there are many unresolved issues in this emerging Moisture Control Handbook field. There are two schools of thought among building designers. Historically, the predominant envelope design strategy used in low-rise residential buildings was to keep out all moisture at all times. The concept of acceptable moisture levels discussed in the handbook, however, recognizes envelopes can get wet or occasionally start out wet. Therefore, a design could recognize this and encourage periodic drying. The construction details shown for heating, mixed, and cooling climates are based on moisture transport principles. However, much work remains to be performed in order to determine the wetting and drying patterns of both conventional and novel envelope systems. Some building researchers believe no moisture, internal to the envelope, is acceptable at any time and that once wet, envelopes are unlikely to dry out. On the other hand, some designers beli eve it is too costly or too risky to completely control moisture entry. In fact, some believe that building envelope materials will frequently have high initial moisture levels, and that degradation of siding, sheathing, sealants, caulking, and flashings can all contribute significantly to the moisture load. Thus, their approach is to keep moisture levels low by providing a path for moisture to escape. A design strategy that assumes building envelopes may get wet and permits them to dry, presents a more forgiving and perhaps less costly alternative. Reliably quantifying the impact of these approaches, particularly wetting and drying within construction assemblies, remains to be accomplished in future editions of the Moisture Control Handbook. This handbook is a first step in helping designers and builders to understand and utilize moisture control strate gies.
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