An archive facility in Kent, where strict environmental conditions are demanded to keep the county’s historic records in one piece, presented unique challenges to design-and-build contractor Warings. Jan-Carlos Kucharek reports.
The new £12m Kent History & Library Centre cuts an imposing figure in the town of Maidstone. The new archive facility, complete with underground repositories, draws together more than 14km of archive material from locations across the county, and includes a public library that amalgamates the town’s dispersed collection on one site. But thanks to an ingenious example of cross-subsidy, two large eight-storey residential towers, one for social rented flats and the other for assisted living accommodation, are perched on top of the lot.
Two eight-storey residential blocks rise above Kent’s new archive facility
Set on higher ground to the west of the old city centre, the new building is citadel-like; a fitting look for a building designed to securely hold almost all of this historic county’s regional archive. Apart from historic records dating back as early as the 7th century, the archive also contains letters from Jane Austen and Lord Nelson.
Warings, part of the Bouygues group, acted as both contractor and developer on the whole £26m D&B scheme: to make the scheme commercially viable, it brought on board Housing 21 Assisted Care for one block and West Kent Housing Association for the other.
An additional project partner was The National Archives, which provided partial funding for the archive element of the scheme, had an early design consultancy role, and ensured that the storage facilities met its strict environmental conditions for cultural artefacts.
From a services perspective, Warings and services consultant Frankham therefore had to accommodate distinct approaches for the three spaces, with all plant and equipment centralised in the heart of the building. Throughout the design coordination and construction phase, their job was to ensure that the archive was conditioned and secure, the library light yet comfortable, and the housing warm.
Concrete forms the structural framework for the building’s various functions. Lower ground and basement zones act as the primary repository spaces, while the ground floor area is the “public” face of the building, housing the lending library, archive reading room and access to one of the housing blocks. Additionally, a significant area of the ground floor, situated beneath the social rented housing tower, is wholly devoted to services provision and it’s from this “energy centre” that the integrated M&E systems feed the building’s three areas.
“Besides everything else, the biggest challenge for this project was in meeting the conditions of BS5454, which set the environmental conditions for the archival storage,” says contractor Warings design manager Richard Matthews. “It required not only looking at the air handling of the repository, but the manner in which we constructed it.”
He is referring to the decision to use concrete, based on the waterproofing demands of the below-ground archive space, as The National Archives was adamant that there be absolutely no ingress of ground water into the storage facility.
Matthews explains that concrete was an obvious choice for the archive, and that for the tower structure, it seemed only natural to continue the strategy. “Whilst below ground it is acting as the primary line of defence between the archive and the external environment, it served a dual purpose here. In the towers the concrete’s working well as a means of allowing thermal cooling and heating, which minimises the use of mechanical servicing where possible.”
Warings has been bold with its below-ground waterproofing approach — no double wall and interstitial drained cavity here. Instead, everything is predicated on a 300mm thick wall of waterproof Caltite concrete to create the Grade 3 basement required. “The manufacturer has provided guarantees on its suitability and performance in this scenario,” Matthews adds. He notes that the concrete also provides the requisite fire ratings — two hours throughout, except for the part of the archive that interfaces with the residential, where the concrete is thickened to beef it up to four hours.
To ensure that the finished structure would meet The National Archives’ guidance on moisture content, Warings agreed to monitor the internal environment as the concrete was drying. “We had to produce a drying out report, which meant installing a temporary BMS system with heat and humidity sensors,” says Matthews. “Data was compiled weekly to prove that these figures were changing to meet the desired targets. Three reports were compiled over nine months during the construction phase.”
Beyond limiting any moisture ingress through the repository’s structure, the air handling strategy adopted here acts as an innovative final line of defence against mould growth. BS5454 stipulates very strict air tightness criteria of 0.5m3/(h.m2), or as National Archives programme manager Dr Melinda Haunton puts it: “Less than two air changes per day. Absolutely stabilised internal conditions are needed, with air virtually static, but with enough residual movement to ensure no pockets of
dead air, encouraging micro climates.”
A suitable strategy is often found in supplying air from the side and venting it out through the centre, adds Haunton. Here, Warings has adopted this, but went one step further, with supply ducts running around the perimeter creating a curtain of conditioned air down its concrete walls, immediately evaporating any moisture or condensation that might occur on the surface. In this way, relative humidity is held at between 45% and 60% at an ideal temperature of 20oC.
Haunton, who was consulted all the way through the specification process, is a convert. ‘‘Wall washing with supply air is a relatively innovative strategy but we think it could become standard good practice,” she says.
The prevention of mould growth has also had implications on the design of the whole archive complex, resulting in the creation of conditioned “accession” and treatment rooms between the delivery area and the main repository. These not only allow fragile items to acclimatise to their new, highly-tuned storage conditions, but allow spore-contaminated items to be identified and isolated.
High-performance glass, mitigating heat loss and solar gain, gives the building a dark and reflective glazed elevation
The double-height space of the public library gives users a light and airy feel
The archive repository uses an innovative approach of supplying air down the building perimeter wall, and drawing it from the centre
The archive’s air-handling system is fed by air source heat pumps sitting on the roof of the adjacent library block — an installation strategy driven by planning restrictions. Warings’ Matthews points out that the planners were keen to ensure that the housing was exposed to sedum on the roof, rather than plant. “It did all have cost implications, as we had to effectively split up the air handling,” he says. “We would have wanted it all on the roof, but in the end, it was only the repository AHUs that made it on.”
The AHUs for less demanding library areas were mounted on a dedicated wall at ground level, behind layers of sound-attenuating material, out of residents’ view and earshot. Being air-source heating and cooling, the decision obviated the need to install chillers, which also helped reduce on-site noise generation.
Meanwhile, a central boiler system feeds three independent heating circuits serving the three areas. With planning restrictions on rooftop solar thermal provision, and not enough site area to adopt an effective ground-source heating solution, thoughts turned to biomass. “The on-site provision of pellet storage would have proved too onerous space-wise, so we opted for bio-diesel,” says Frankham’s Francisco Pelegrin — although this still requires 5,000 litres of on-site tank storage. The B100 boiler runs at a 300kW output, supplemented by a 200kW gas condensing boiler. Interface units — heat exchangers that take this centrally generated heating water and transfer it into a local, flat-based hot water circuit — are installed in each flat.
Within the double-height library space, Pelegrin explains that the demand for conditioned air is assisted by high performance “low e” glazing units, with a deep tint to ensure low heat gain and loss, with the client particularly concerned about mitigating heat gain. With no need for fire rating on the single-storey structure, the exposed steel columns and ceiling soffits did not require an intumescent coating, giving the space an airy and light feel. Kitted out with seminar spaces for visiting school parties, and interfacing with the public archive search space and reading room, the library blends leisure use with serious academic study.
The National Archives’ Haunton, having seen the project through almost from the start, is especially pleased with the outcome. “It’s an exciting national archive and regional library tie-up and should increase footfall and awareness of the archive,” she says. “Hopefully it’ll encourage the public to explore it more — it really is an amazing collection.”
The entrance to the social housing block is raised above the central plant room
“If things are lost, they are lost forever”
Why archive space demands such a high specification
Dr Melinda Haunton of The National Archives emphasises the highly risk-averse nature of design guidance for archives. “Basically, if things are lost, they are lost forever, which is why archives’ specification is so high,” she says.
Currently, one main standard — BS5454 — guides archive specification and this deals with the key issues of light, security, moisture, infestation and microbial contamination. But new guidance — PAS198 — has just been published, which sheds new light on all of these concerns. “It’s more about a risk-based approach to environmental management, and deals more with sustainability in traditionally high-energy scenarios,” says Haunton.
Unlike BS5454, which is more prescriptive guidance, PAS198 challenges designers to look at situations on a case-by-case basis and make risk-based decisions bearing in mind that sustainability considerations must now be prioritised.
The new standard was developed in response to a statement issued by the UK National Museum Director’s Conference that “museums need to approach long-term collection care in a way that does not require excessive use of energy, while recognising their duty of care to collections”.
Haunton acknowledges that designing state-of-the-art archive facilities is ultimately a thwarted endeavour: “Archive materials are organic things and all these things ultimately degrade. It is about creating the conditions that optimise their longevity whilst ensuring that you do not encourage microbial growth,” she says.
“The general rule is keeping temperatures under 20oC and under 60% relative humidity, but now it’s also about reducing the building’s energy use given these constraints.”
The National Archives’ role at the Kent History Centre is regulatory, as materials are being held here on the nation’s behalf. It therefore needed to ensure that best practice was adhered to and it did that by bringing its experience to costs, facilities and technical specification. It was involved from the early stages working on the spatial programming of the building.