Conwy Archive Service - Built Environment and passive storage

Built Environment & passive storage

Conwy Archive Service

In 2015, Conwy Archive Service (CAS) began the process of securing funding for a new archive building. At the time, the service was housed in a draughty Victorian school building in Llandudno with a leaking roof, which posed a threat to the archive collections and offered no space for new additions. A move had become critical.

A decision was made early on that the archives would relocate to Conwy and be housed within a larger centre, which would include a new library, community space, and café. Archive staff visited several recently opened archive buildings for inspiration, including the new Passivhaus-certified building housing Herefordshire Archives. Although they were impressed by the environmental benefits of the Passivhaus approach, Conwy’s limited budget made this option unaffordable. However, Conwy Council aimed to achieve a certified ‘excellent’ BREEAM rating for the new building.

Initial designs for the archive strong room involved traditional mechanical methods to maintain appropriate environmental conditions. As the building design evolved, it became clear that the only place to locate the new strong room would be underground, leading to the idea of a passive strong room. Chris Woods of the National Conservation Service suggested placing the strong room underground, where stable temperatures could be maintained with minimal mechanical intervention. An airtight room would stabilise relative humidity once established at an appropriate level.

The concrete used for the walls, floor, and ceiling needed to dry out, a process that can take several years. Initially, it was recommended that the collections should not be moved until 18 months after the concrete was poured, but delays and the need to relocate the collections led to the decision to move them in February 2020, only 15 months after the concrete was poured. The RH was reduced to 60%, maintained by industrial dehumidifiers and the onsite back-up air handling unit (AHU).

The onset of the COVID-19 pandemic coincided with the move, complicating the usual snagging process for the AHU, with some issues not discovered until 2022. Despite these challenges, the strong room is performing well, with minimal energy costs. However, long-term performance is still being evaluated due to the concrete’s drying time and the pandemic-related delays in resolving AHU issues.

What initial conclusions we can draw about maintaining suitable temperature conditions in the strong room?

The temperature is very stable within the strong room and is typically about 18-18.5 oC and so conforms to BS4971 on a day-to-day basis. However, we do have concerns that the annual average temperature will exceed the requirement to be lower than 18 oC. We expected that the strong room temperature would drop slightly during the winter months and that would bring the annual average temperature was less than 18 oC as required. However, the ground floor of the building is heated by an underfloor heating system seems to be preventing the strong room from experiencing the desired winter drop in temperature. This is an issue that we are still trying to tackle.

What initial conclusions can we draw about maintaining suitable relative humidity (RH) conditions in the strong room?

It was fully expected that during the early years of the strong room active dehumidification would be needed to keep the RH within the acceptable range because of the length of time required for the concrete to dry. In our case getting the humidity well below the maximum acceptable level of 60% has been more difficult than it should have been due to limitations on visiting the building during lockdown and due to initial and on-going issues with the AHU system (see below). That being said we have not required dehumidification constantly. After a concerted effort using just one portable dehumidifier for 6 months we stopped all intervention at the end of August 2023 with the RH at ~48% and have been carefully observing what has been happening since. The RH is very slowly increasing, suggesting there is still some residual drying of the concrete going on, but we do not expect to have to intervene again for some months to come and are hopeful that, in time, we will be able to maintain a suitable RH for several years at a time with no intervention.

What other lessons might be learnt from our experience?

Our overall preliminary conclusion is that our passive strong room is doing a good job for our collections, is saving the council a lot of money in energy bills and is reducing our impact on the environment. That being said I think we have learnt some valuable lessons which are worth sharing especially about the design and construction of our new building.

1. A strong room (whether passive or requiring mechanical intervention) has requirements which are unusual and may well have not been encountered by the building contractors before. Communicating what the requirements of this space are and how crucial it is to get them right is important and not easy. This communication is made harder by the use of multiple subcontractors on a project like ours. Our feeling was that the main contractor came to understand our very specific needs but this understanding never filtered down effectively to the subcontractors and has caused immediate and on-going problems.

2. Unwillingness to listen to the very specific and unusual needs of the strong room led to our conservation consultant (who designed the strong room) being overruled on certain critical decisions. This is most obvious in our case is the AHU system that we have which has proved barely adequate to maintain RH at close to 60%. The situation is exacerbated by the continuing insistence that the AHU should be controlled by the building management system under the supervision of facilities staff rather than being under the direct manual control of the archive staff who actually understand the strong room needs.

3. Because the new archive facilities were to form just part of a larger centre incorporating a library, community space and cafe, the needs of the strong room, were probably less of a consideration within the overall building design and build than they would have been in a single purpose archive building. For example, the consultation consultant was concerned about the potential impact of the underfloor heating system on the environment in the strong room but as the UFH system was a critical part of the overall eco-design of the building the needs of the strong room were seen as secondary. Again this is now the cause of on-going issues.

4. The archive staff had very little direct input to the building design or construction process. A greater, regular presence in project meetings might have helped in communicating the very specific needs of the strong room design. How helpful this could be would depend on the knowledge base of the archive staff involved. Maybe there is a need for specific training for archive staff to enable them to better advocate for their building needs during the design and build process?