The roofscape of the new library is a lively and playful reinterpretation of the surrounding College’s gabled roofs, not only in terms of form but also materiality. The Cross Laminated Timber (CLT) roof ‘lanterns’ define the exterior and interior of the structure giving the building its unique and bold character.
The CLT roof lanterns are square in plan and are formed by 2 pitched roofs intersecting at right angles to each other. The lanterns are supported in the corners at the bottom of each valley by bespoke steel connectors (image a). This detail was conceived by consulting engineers Smith and Wallwork and further developed and optimized for manufacture and assembly by Eurban. Such collaboration between the consultants at the design phase as well as during the construction phase was key to the success of the project.
The square roof lanterns allow light to penetrate the entire building. The 4 sides of the 12 lanterns are fitted with glazing, so natural light from each orientation filters into the space. The roof lanterns, in combination with light wells connecting the 3 levels, result in a light filled space even at the centre of the library’s relatively deep plan. Shafts of light animate the interiors throughout the day, from sun rise to sun set.
Eurban were responsible for assembling all the structural timber elements. A total of 4 site visits were required for each level of the building and the oak window frames. The first floor glulam beams and CLT floor panels were installed in 1 week in the summer of 2019, then Cocksedge carried on building the brick walls and structural piers. Eurban returned 2 months later to install the second floor which took about 3 weeks. After another month the team returned again to install the 12 roof lanterns. This last installation was the longest and most complex part of the site assembly and took 6 weeks, just before Christmas 2019.
Eurban proposed to use two jigs for the roof lantern construction developing a flying factory delivery model to improve health and safety conditions on site while improving quality and speed of construction.
The project utilised two main sources of timber, with 149m3 of oak and spruce for glulam coming from Switzerland and 180m3 of spruce for CLT coming from Austria. All timber utilised PEFC certification to ensure a sustainable supply of timber. To put this into context, the Swiss forest covers one third of the country’s area, with an overall stock of 422 million m3 of wood standing. The yearly growth is estimated at 10.4 million m3, while only 5.2 million m3 is harvested for timber.
This means the timber from Switzerland used in the project will only take 7.5 minutes to grow back, while it locks in 109 tonnes of CO2 over its lifetime. The Austrian growth rate is similarly vast, with an annual growth of 30.4 million m3, meaning the timber used for the CLT will grow back in just 1 minute on a summer’s day.
Client: Magdalene College Cambridge
Architects: Niall McLauglin Architects
Engineers: Smith and Wallwork
Timber Engineers and Specialist Installers: Eurban
Suppliers (Glulam and Oak window frames: n’H International Ltd
Suppliers (CLT): Stora Enso