When Architype Architects director Jonathan Hines presented the design for a new library in Ledbury to members of the town council, he did so in its chambers in the striking 17th century half-timbered market house.
Built in 1653 by John “the king’s carpenter” Abel, the market house is a classic example of its type – a ‘ground floor’ entirely open to the elements, contained within massive oak beams supporting a timber frame structure above. Not only is it a thing of beauty and craftsmanship, it also shouts timber’s durability as a building material from its rooftop.
So when a councillor queried the proposed extensive use of timber in the construction of the £2.9m library on the grounds that he wasn’t sure “how long timber would last”, an expansive gesture by the architect indicating the structure around them was sufficiently convincing.
The market house provided Architype with more than just a compelling argument for using timber – it also provided inspiration for the design of the new library, which is to occupy an even more historically significant site.
The brief was to construct a library within the two-acre St Katherine’s Hospital site, which comprises St Katherine’s Hall, Chapel and Almshouses, the Master’s House and a 17th century timber-framed barn. Together they form an extremely rare example of a medieval hospital complex, founded in 1232 to provide care for the elderly, the sick and infirm and travellers.
The task was to come up with a design that was in keeping with the existing buildings, but that also showcased them, and to create a “civic heart” for the town, complete with a small public square. The library was to contain not just shelves of books, but exhibition spaces, a children’s activity area, a café, ICT facilities and study areas.
The second phase for the development will focus on the restoration of the Master’s House, which will provide a hub for Tourist Information Services, Register Office, Citizens Advice Bureau and community rooms.
“This was one of those projects where you really had to think about how to respond to the brief – in addition to the normal meetings and consultations you’d expect to have,” said Hines. The response that won the contract for Hereford- and London-based Architype, following a stiffly contested design competition, embraced the local architectural vernacular.
“Ledbury is a very interesting market town with strong traditional architecture and very little modern intervention,” said Hines. “It has many classic black and white medieval half-timbered buildings, many of which feature repeated gables.
“We created a modern interpretation of that so that the building will feel strongly rooted in Ledbury, but not be a pastiche. We sought to design a building that was visibly timber frame and to express the structure and echo the market house, so it will have an almost completely glazed ground floor – giving the idea of the open market building – and a more ‘solid’ upper floor.
The main structural elements of the 750m2 library will be 200mm square two-storey height glulam beams (ground floor to ceiling is 3m, while ground to ridge is 11m) and this will be enclosed with wall panels comprising I-beams.
The library will be built to Passivhaus standards so the panels will be highly insulated with Warmcell. The
I-beams provide a thicker wall with less timber, providing more space for insulation and reducing thermal bridging. In order to achieve some thermal mass, the interior face of the wall panels will be lined with Fermacell, which is denser than ordinary plasterboard. “If we use two layers we can get up to about 35mm thickness, which gives you enough mass for night cooling,” said Hines.
Lack of thermal mass in lightweight construction is often used by the brick and block fraternity as an argument for not using timber frame, but Hines disagrees, maintaining that only “enough” mass is required. “We’ve carried out a lot of modelling and found that, if you have too much mass in a heavily insulated building, when it warms up you can’t get rid of it,” he said. “It’s much better to get the balance right in the first place.”
The roof features the repeated gables of the surrounding Ledbury architecture and will probably be constructed with lightweight scissor trusses – which will remain exposed to view – supporting insulated roof cassettes. Welsh slate will top the lot.
As well as echoing the medieval style, the repeated gables also work with the orientation of the building. “The series of repeated roofs provides the opportunity to get good daylight onto the building and contribute to controlled passive solar gain,” said Hines.
Most of Architype’s work over the past 20 years has been in timber, and sustainability has been at its heart. For example, it achieved a BREEAM Excellent rating for its RIBA Award-winning St Luke’s Primary School in Wolverhampton (see p51). So this focus on design detailing rather than add-on technologies to improve the building’s energy performance is no surprise.
The target is for walls, roof and floors to achieve a U-value of 0.15, while the triple-glazed windows – timber or timber/aluminium – should achieve 0.6. Combined with rigorous airtightness standards, the resulting building will be the first Passivhaus building in Ledbury and, as far as it is known, the first Passivhaus library in the UK.
Architype uses timber “holistically”, so its aesthetic applications are just as important as its structural and sustainable ones. The upper storey will be clad in Douglas fir, but constructed as a slightly ‘transparent’ screen, with spaced vertical cladding held off the façade with horizontal support battens.
“Some windows will open through the cladding, while others will have the cladding continuing in front of them and will just provide a glow of light at night,” said Hines. “The idea is that at daytime it [the elevation] is quite blank, but that at night-time it comes to life.” The windows are more about framing views than allowing light in, he added, as roof lights will fulfil that function.
Timber will abound internally, too. Along with the roof trusses, the glulam beams will be left exposed, the walls will be wood clad and shelves and furniture will be timber.
Oak and ash will predominate and, like the Douglas fir exterior cladding, will be sourced locally. Architype is a champion of local sourcing, a fact demonstrated at its Herefordshire site – a converted barn in the middle of rolling hills and farmland – which features chestnut harvested from woodland a few hundred metres away.
It’s hoped that construction of the library will start next spring and it is expected to take around a year. Once complete, the restoration of the Master’s House will begin, bringing a project that works “at a functional level, a civic level, an environmental level and an historic level” to fruition.
| The Master's House masterplan |
The £2.9m of funding raised for the library construction includes £350,000 of enabling work to be carried out on the Master’s House, prior to its restoration, which itself is subject to negotiations with English Heritage and another £1-2m being raised.
Dendrochronology has shown that the Master’s House is built from oak felled in 1487. It was used green and the house would have been erected in either the same or the following year.
It’s been added to and adapted over the centuries, to the point where its original timber structure has been completely obscured and even removed in parts. However, Architype has been working with medieval timber frame specialist Butler Hegarty Architects on the building and initial survey work has revealed that a lot more of the original timber frame exists than had originally been thought.
“We’ve carried out a very extensive and detailed fabric analysis of the building,” said Gary Butler of Butler Hegarty. “We had some work by an archaeological company given to us – measurements of the principal medieval timbers that could be seen – and we carried out some thermographic surveys.”
 Many hours were spent crawling among the spiders in the roof space looking for patterns. “Timber frame buildings of this period have a fairly coherent typology so we looked for details that would suggest other features,” said Butler.
“For example, two peg holes in the ridge beam are in the right position for a pegged louvre at the ridge, suggesting the Master’s House may have had a central fire at some point,” he said, although he cautions that this extrapolation of the evidence is always “best guess”.
Little remains of the original timber frame at ground level – in fact Butler describes it as a building that’s been “chopped off at the knees leaving a medieval halled house ‘floating’ above some 18th and 20th century work”. However, he estimates that 75% of the medieval timber remains in the main hall and two cross wings and, he said, it’s in “wonderful condition – absolutely superb. Most of the timber is very high quality, slow-grown and it was all swivel sawn”.
In terms of its structural integrity, while it’s not likely to fall down tomorrow, the building clearly needs a major overhaul. “It [the medieval timber frame] is propped, but the problem is that the top is now trying to adjust to its chopped condition. We need to reorganise the way the structure works.”
Decisions regarding the precise nature of the remedial work – how much of the frame is disassembled, how much new oak is spliced in and where seasoned oak might be used instead of green oak – will have to be made when the restoration begins in earnest, but Butler’s vision is that 21st century visitors will be welcomed into a two-storey medieval hall, with all its 500-year-old timber on view, much the same way as 15th century visitors seeking alms or accommodation would have done.
“It’s a very poetic resonance about travellers, arrival and location,” he said and it’s a sentiment with which the architect behind the newest addition to St Katherine’s complex, agrees.
“As the medieval timber frame is revealed it will create a strong relationship between it and the exposed timber structure of the new building,” said Jonathan Hines. “The link between the past and the future will be very powerful.” |
|
The new structure is also a modern interpretation of Ledbury's timber-framed market hall |
|
Energy consumption will be so low that a biomass boiler is deemed 'overkill' and winter heating will be provided by a conventional domestic gas boiler |
