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Room-Within-A-Room Storage Improvement
Copyright 1997, Marc A. Williams

For many years, ideal storage conditions for historic collections generally have been accepted as 70 degrees Fahrenheit and 50% relative humidity, with the absence of light, dirt and insect pests. For the majority of smaller and medium-sized museums, these levels are not achievable. Far too often, they control temperature only, with resulting wide fluctuations in relative humidity that can range from 5%-100%. Since the deteriorative effect of relative humidity variation is far greater than the effect of temperature, an extensive amount of damage occurs in a misguided attempt at preservation.

Alternatively, many of these museums have no environmental control in storage areas, and the interior levels reflect ambient outdoor levels of both temperature and relative humidity. Surprisingly to lay persons, objects in these totally uncontrolled environments are in better condition than those in environments that are heated only. Nevertheless, long-term preservation can be enhanced greatly by relatively simple storage improvements. These include: installation of insulation; reduction of air infiltration; installation of an effective vapor barrier on the inside of the storage area; blockage of windows and extraneous doors; and inclusion of a moisture-absorbing material in the interior of the storage area.

Unfortunately, retrofitting a storage area to include these improvements has its own set of concerns. These include installation costs, potential damage to the building required for implementing improvements, aesthetic incompatibility with historic structures, and potential long-term deterioration of the building caused by the use of these improvements. These potential problems limit the practicality of storage improvement in many smaller museums.

A solution that provides great improvements on environmental control, yet reduces the potential for negative impacts, is the use of a "room-within-a-room." A free-standing room that incorporates tight construction, heavy insulation, vapor barriers, no windows, and a moisture-absorbing material on the interior walls is constructed inside an existing room. The walls, floor and ceiling generally are constructed with 2x6's on 24" centers and insulated with a minimum of 6 inches of fiberglass insulation. A vapor barrier (6 or 8 mil polyethylene sheeting) is placed on all interior surfaces, including the ceiling and floor. A single door of sufficient size provides access to the space. The door is well insulated and well weather-stripped. The walls and ceiling can be left covered with plastic, or can be covered with drywall for greater protection of the plastic. Plywood for the floor should be exterior grade (not containing urea formaldehyde adhesives) and must be sealed on all surfaces and edges with at least three coats of white pigmented shellac (Bin brand is acceptable) to prevent off-gassing of harmful components from the plywood. The room is built so that it does not touch the walls or ceiling, which allows air circulation around it. Therefore, no damage is done to the architectural character of the original room.

While conditions outside the room will still vary on a daily basis, inside the room, very little change will occur. Seasonally, there will be a gradual temperature shift, but the relative humidity should remain within a fairly narrow range, provided that the space containing the room-within-a-room is not heated. This is accomplished without the use of any mechanical systems. Obviously, proper HVAC system design and installation can improve further upon the passive control methods.

Since the room-within-a room concept functions best in a building without heat, it is perfectly suited for attics, outbuildings and other unheated spaces commonly used for storage at most historical societies and historic house museums. By using this simple technique, preservation of collections can be enhanced greatly. 

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