An innovative internal hybrid CLT and steel frame solution has been used to transform a derelict 1855 Post Office on Islington’s Essex Road. The Old Sorting House, by Ben Adams Architects for Martin’s Properties, has achieved BREEAM Excellent and is a standard bearer for sustainable preservation.
The scheme is formed of three original buildings which have been refurbished to create a new ‘in-between’ building that provides a large, airy office floorplate over four floors. The roof of the original post office has been raised to achieve a new top floor which includes a spectacular mezzanine.
Working with an existing building in a conservation area meant there were strict height limitations relating to the raising of the roof, and the slimmest possible structural build was needed to achieve the required quantity of accommodation. Everything above the existing basement and ground floor level was removed to incorporate the extra storey and using a hybrid cross laminated timber (CLT) and steel frame structure enabled the reduction of floor depth by between 50 and 75%.
Structurally, the CLT slots into the sectional zone of the steelwork which achieves this efficient floor plate. Combining the two materials has made better use of the building fabric as the steel helps restrain the exterior walls of the building, effectively enabling the floor plates to be pulled inward.
A triple height void has been created along each end of the major floor plates which visually connects the basement, ground and first floors while also allowing light into the basement.
“Specification of CLT was the obvious solution in many ways.” Explains Nick Jewell, Senior Consultant and Head of Research at Ben Adams Architects. “Access to the site was particularly constrained and complex because we were retaining the existing facades of the building and incorporating the new CLT and steel structure into it quickly. Using CLT meant we could make everything offsite, which really helped to cut down time in terms of creating new floors and a framework to get the building weather-tight.” Hybrid construction specialist B&K Structures installed the hybrid frame in just 19 weeks.
Internally, the CLT is left exposed throughout and has been treated with a spread of flame treatment which achieves a Class A fire rating, and gives the material a white opaque appearance while still allowing the grain and quality of the wood to be clearly visible.
“Internal comfort was a key consideration. Bringing light into the right places is a key factor and creating an environment that feels warm and pleasing is very important when working within the constraints of existing buildings,” adds Nick.
“I can’t over emphasise the constrained ceiling heights. So making sure we have something that is a natural material, is pale in hue and allows reflected light to be bounced within the environment really helps increase the sense of wellness in the space and the lightness of the environment for the office users.”
Harvey Walker, Stora Enso’s Sales Manager for Building Solutions in the UK and Ireland, says: “We’re increasingly seeing CLT used in the adaptation and re-use of historic and disused buildings and looking at Old Sorting House it’s easy to see why. By embracing the structural and design benefits of CLT, Ben Adams Architects and Martin’s Properties have created a spacious, welcoming space that will extend the life of this wonderful old building for many years to come.”
