105 MINORIES
Can we extend an existing seven storey building to double its height?
Location: City of London
Status: Tender
Client: HUB Residential
Architect: Morris & Company
Structural Design Brief
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Existing seven storey building with basement to be retained
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Six storey vertical extension to maximise site’s potential
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Flying freehold within the existing building to be circumnavigated by load paths
Introduction
The City of London has identified the need to create a mixed use environment, to give a seven day week to the square mile. To do this we need to look at opportunities to repurpose tired buildings stock, to invigorate the business district with a dynamic arrangement of diverse living spaces, alongside cultural, entertainment and amenity offerings. The delivery of 278 short term apartment lets plus substantial amenity space will contribute to the City of London’s Pla, crucially without demolition the existing built fabric to do it.
Building Knowledge & Solution
The project brief has always been to retain the existing seven storey (plus basement) building whilst maximising the number of homes being delivered. Structural capacity assessments were key to unlocking the site’s potential for vertical and horizontal extensions to achieve this.
We worked with the team to coordinate a new proposal, threading steel columns through the existing structure to support a vertical extension of up to six storeys- with the new columns aligning with the risers in party walls between apartments- areas that were being demolished anyway. This avoided reliance on the existing structure and the related uncertainty.
There is a flying freehold from the adjacent building to the south of the site. This could not be loaded but the new building extends over the top of it. A deep cantilever steel beam has been designed to hang the floors above the flying freehold whilst achieving required façade deflection limits. The structures depth is hidden with the Level 10 roof planter, and will be concrete encasement for durability.
The new internal columns land on a mixture of existing pad footings and made ground. Given the constrained basement, it has been proposed to join the existing footings to form a strip footing to distribute the increased load to the founding strata at a depth of circa 2-3 m below the basement. There is also a rear horizontal extension including a new stability core to replace the demolished one. This is to be constructed with blue sky above, so will be piled.
This project is an example of the extent of retention that is possible, as well as how buildings can be extended, when the Client and Design Team commit. A prime case of the potential for urban densification!
