3 EVALUATION OF THE BUILDINGS

The thermal and vapor characteristics of the building must be determined, for they will determine the environmental conditions that can be maintained inside the structure. Materials used to construct the building are important, since wood, stone, and brick all have different thermal and vapor characteristics. For example, horsehair and plaster walls will retard moisture penetration to a greater extent than will modern drywall. Thermal and vapor qualities of a building are also greatly affected by its construction, i.e. post-and-beam, wood frame, laid stone. It would be dangerous to introduce additional humidity into an uninsulated wood frame building during cold winter months. However, a brick or stone building with plaster interior walls may safely support a calculated level of additional humidity.

The first step of the building evaluation process is to monitor the inside temperature and humidity to determine the building's thermal and vapor characteristics and evaluate its response to the outside environment during each season of the year. Several monitors are required for each building since most structures have several distinct climate areas, such as attic, basement, and various levels. Since it was not feasible to monitor all 33 collection buildings at Shelburne Museum, Landmark Facilities Group, the engineering firm that conducted our environmental assessment, categorized the buildings based on construction characteristics and selected seven representative buildings for extensive monitoring.

After a full year of monitoring and recording temperature and relative humidity levels, and interpreting large amounts of raw data, six distinct building categories were established, each capable of supporting a different level of climate control (Conrad 1989). Each of the museum's 33 collection buildings was assigned to one of the following six categories:

1. Open structures (sawmill and bridge). No climate control is possible in such structures, even though they often shelter collection artifacts.
2. Sheathed post-and-beam structures (barns and sheds). These buildings have limited climate-control potential. Building exhaust ventilation should be used to reduce interior heat and moisture accumulation in the summer.
3. Structures with framed and sided walls and single-glazed windows (rough frame houses) or uninsulated masonry structures. A higher level of climate control is possible in such buildings. Low-level heating and humidistatic heating should be used for RH control in cool seasons and building exhaust ventilation should be used to reduce interior heat and moisture accumulation in the summer.
4. Structures with heavy masonry or composite walls with plaster, tight construction with storm windows (finished houses). Modified conventional climate control can be used in these structures. Such measures include low-level ducted heating and cooling, with low-level humidification in the winter and cooling with reheating for summer dehumidification.
5. Insulated structures with vapor barriers, double-glazed windows (formal exhibition galleries and storage area, usually new construction). These structures can support conventional climate-control systems that use ducted heating and cooling with complete humidification and dehumidification capabilities.
6. Double-wall construction, interior rooms with sealed walls and controlled occupancy (storage rooms, vaults, exhibition cases). In these areas, precisely controlled heating, cooling, and humidification systems can be installed to protect very sensitive artifacts that require extremely stable conditions.

This building classification system is an example of the environmental control continuum discussed earlier. It must be emphasized that buildings were assigned to these categories only after many months of temperature and humidity monitoring in representative museum buildings. The monitoring, data interpretation, and physical examination of the buildings required for classification should be carried out by qualified personnel.