*by Scott A Orr
Environmental control is an inconceivably important aspect in managing heritage collections for which many guidelines and specifications have been developed. These guidelines should be contextualised by international climate variability and consider the integral contribution of building envelopes in managing heritage environments.
Temperature and relative humidity are two important factors in environmental control that govern changes in physical dimensions and hygroscopic properties. Over the course of the twentieth and twenty-first centuries ideas about ‘ideal’ conditions have changed, but there are a few main principles that have emerged (see CCI ‘Agents of Deterioration’):
- Temperature: upper and lower limits, rates of change, and fluctuations
- Relative humidity: above damp or ‘critical’ levels, above 0%, and fluctuations
Similar aspects are echoed by PAS 198 – a recent collaborative development facilitated by BSI Standards Limited. One crucial feature of these guidelines is the concept that conditions should be allowed to ‘drift’ within a certain range to adjust for external seasonal variability. This principle has been successfully implemented at The National Archives in Kew, resulting in a less-variable environmental condition and significant energy savings.
Many standards and guidelines – as well as cumulative knowledge – on environmental control for collections have emerged from the United Kingdom. These have been accepted formally and informally as international practice. This is evidenced by North American institutions in the early- and mid-twentieth century looking to the “experience of European museums” to establish climatic parameters. It is enshrined in the publications of Plenderlieth and Thomson. These experiences informed, and continue to inform, decision making at an international level.
The UK has a temperate oceanic climate. In general, the climate of the UK is cool and often cloudy, and temperature extremes (outside the range of -5 to 25 ° C) are rare. However, warm ocean currents do bring substantial amounts of humidity to western parts of the islands.
This is rather convenient for collections, as converting external air into internal conditions that are appropriate is simple. By taking external air that is cool and damp (e.g. 5 °C with 80% RH) and raising the temperature to desired levels, relative humidity will end up in the general range of collection conditions. A similar idea can be applied in summer conditions with cooling.
It becomes trickier for regions that have more extreme climates, such as Canada. Many of the urban regions experience very cold winter conditions. At these lower temperatures, the air becomes saturated with water very quickly. For example, the amount of moisture in the air at -20 °C and 50% is the same as 5-10% RH at 10 °C. Increasing the temperature alone will not produce a sufficient environment for many collections. To achieve ideal conditions for collections in a colder climate in winter seasons, additional humidification is usually required. Modern heating, ventilation, and air condition (HVAC) systems can manage these processes with various levels of energy consumption.
HVAC is only one part of what governs the relationship between indoor and outdoor environments – the building envelope is also crucial. The ‘envelope’ refers to physical materials that separate the interior and exterior of a building. In considering these type of environmental interactions, the concept of interfaces become very important.
The interfaces between interior and exterior environments and the envelope can make managing environmental conditions difficult. This is due to the conduction of heat through walls and the creation of microclimates. Specifically, this can cause problems in colder wintertime climates, where a more significant contrast between the external environment and indoor set-points creates greater drive for heat transfer.
The Thomas Fisher Rare Book Library – part of the University of Toronto– is famous for three reasons: for forming part of a complex that undoubtedly resembles a giant avian creature, for being used as exterior shots of the prison setting in Resident Evil: Afterlife, and for constituting the largest collection of publicly accessible rare books and manuscripts in Canada.
|The infamous peacock of the academic complex formed by the John P. Robarts Research Library for the Humanities and Social Sciences, the Claude Bissel Building which houses the Faculty of Information, and the Thomas Fisher Rare Book Library — visible in front beneath the tower.
Robarts Library, University of Toronto; stu_spivack.
|The interior of the Fisher Rare Book Library. One crucial design feature was the placement of shelves for collections abutting the building envelope.|
The library recently garnered national media attention after it was reported that the library’s moisture problem had been solved by first-year engineering students. The library management was told by architecture firms that to address the issues they would need to relocate the collections and shut the library for an extended period. Looking for alternative solutions, they turned to Engineering Strategies & Practice (ESP). ESP is an innovative first year course that matches groups of students to real-world problems as an exercise in problem-solving and working with clients.
In 2014, a student group’s proposed design solution was to apply a foam coating to the exterior of the building. Three years later, this is exactly what is being done.
However, the article incorrectly states that “the aging walls of the 1973 building… were failing, allowing water to get through.” The library has never had a problem of water infiltrating through the walls by seeping through the concrete.
The risk to collections in this scenario is at the interface. The potential issue is caused by the imbalance of temperatures on either side of the walls, which were not designed to sufficiently buffer the Canadian winter. The library environmental set points revolve around 20 °C and 50% RH. At these conditions, the dew point – the temperature at which water droplets begin to condense and dew can form – is about 9 °C. To this end, without sufficient insulation, severe external temperatures can cause the internal surface of the wall to decrease to a level where condensation can occur.
One of the most striking features of the library is the openness of the future-chic design – one that is achieved in part through an open-concept design that abuts shelves for collections against the envelope. This puts items at greater risk of influence from the external environment.
To address this, the retrofit will apply a spray foam insulation to the existing external façade. This will moderate the interior surface temperature, thereby mitigating condensation in the interior. The overcladding is designed as a rainscreen system with an airspace between it and the insulation to enable ventilation. It is being made of a pre-cast concrete, to maintain harmony with the brutalist character of the complex.
The retrofit of the Thomas Fisher library demonstrates that environmental control extends beyond identifying set points and having an appropriate HVAC system. The building envelope plays a crucial in achieving those goals accurately, evenly, and with lower energy consumption. It demonstrates that retrofits can be undertaken without needing to relocate collections or causing significant disruption to institutional activities. It provides insight for how to sensitively adapt brutalist and late-twentieth century heritage – something that is becoming more topical as buildings of this era require modifications and, potentially, acquire stricter protection laws.
Environmental control standards for collections have been developed and improved upon for over a century – and yet, it is equally important to consider appropriate building envelopes as an integral component of sustainable heritage.