8 vertical extensions you should know about

Author: Charles Gillott

Date published

18 May 2021

Price
Free
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8 vertical extensions you should know about

Blog
Author

Charles Gillott

Date published

18 May 2021

Author

Charles Gillott

Price

Free

The vertical extension of buildings offers a significant opportunity to create new useable floor space, and contribute towards the circular economy through reduced material consumption and waste generation. This article collates some of the author’s favourite vertical extensions from across the UK and Ireland to act as inspiration of the potential offered by this construction technique.

1. Southbank Tower

As part of a wider refurbishment and residential conversion, 11 storeys were added to this 1970’s office block. The building’s existing concrete core was extended, and a new steel-frame cantilevered from this to generate 191 new apartments. Minimal additional structural intervention was required, with the loads experienced by the structures piled foundations being permissibly increased by up to 25% as a result of years of consolidation of the founding clay.

  • Original height: 31 storeys
  • Storeys added: 11 storeys
  • Original structural form: Concrete frame
  • Extension structural form: Steel frame (concrete cores)
  • Fomer use type: Office
  • New use type: Residential
  • Location: Southwark, London
  • Structural Engineer: AKT II
  • Architect: Kohn Pedersen Fox (KPF)
  • More information

 

2. 1 Triton Square

Retaining as much of the existing structure as possible was a primary aim for this 1990’s office building. This lead to the extension of its existing cores and the construction of 3 new storeys above the original roof level. The 3,500 m2 façade was also removed, refurbished and reinstalled as part of this project, further increasing the project’s circularity. Combined, these strategies resulted in a build waste diversion rate of 99.95% and a carbon saving of over 40,000 tonnes compared with demolition and reconstruction of a comparable building.

  • Original height: 5 storeys
  • Storeys added: 3 storeys
  • Original structural form: Concrete frame
  • Extension structural form: Steel frame
  • Use type: Mixed (including office, retail and gym)
  • Location: London
  • Structural Engineer: Arup
  • More information

 

Image: Visual Lab

3. Clerys Department Store

This former department store is being extended vertically as part of a wider refurbishment being completed in the generation of a new Clerys Quarter in Dublin. Previous modifications made in the 1940’s and 1970’s are being removed to make way for a new 2-storey extension that will remain structurally independent from the existing structure. This has meant that, although following the existing structural grid at lower levels, the new steel frame can provide adaptable office spaces through a more suitable structural grid.

  • Original height: 4 storeys
  • Storeys added: 2 storeys
  • Original structural form: Concrete frame
  • Extension structural form: Steel frame
  • Use type: Mixed (including retail, office and restaurant)
  • Location: Clerys Quarter, Dublin
  • Structural Engineer: Waterman Moylan
  • More information

 

4. The Standard Hotel

Three storeys were added to this former council office building as part of its wider refurbishment and conversion to a 266 room hotel in 2019. The brutalist 1970’s concrete structure was largely retained, with additional 3 steel columns being introduced to transfer loads from the extended portion to the first floor transfer slab. In order to provide access to the upper storeys a distinctive ‘red pill’ elevator was also introduced to the exterior of the structure.

  • Original height: 8 storeys
  • Storeys added: 3 storeys
  • Original structural form: Concrete frame
  • Extension structural form: Steel frame
  • Former use type: Office
  • New use type: Hotel
  • Location: Kings Cross, London
  • Structural Engineer: Heyne Tillett Steel
  • More information
 

5. Gatehouse School

Following failed attempts to purchase adjacent land, Gatehouse School was extended vertically by 3 storeys; generating 9 new classrooms to meet growing pupil numbers. The school remained fully operational throughout construction with no structural remediation being required. This was because previous bomb damage meant that the Victorian building and its foundations already possessed sufficient reserve strucutral capacity.

  • Original height: 1 storey
  • Storeys added: 3 storeys
  • Original structural form: Masonry
  • Extension structural form: Steel frame
  • Use type: School
  • Location: Bethnal Green, London
  • Architect: Child Graddon Lewis
  • More information

 


Image: Allsop

6. ARNOLD (formerly Arnold House)

In order to bring the rental value of Arnold House in line with demand in Shoreditch, 3 storeys were added to this office building. This was part of a wider retrofit that included M&E upgrades, a lateral extension, façade replacement and re-glazing. Originally constructed in 1960 and converted to offices in the 1990’s, the extended property is now used as office space, with retail at the ground floor and a roof garden above the seventh floor.

  • Original height: 4 storeys
  • Storeys added: 3 storeys
  • Original structural form: Concrete frame
  • Use type: Mixed (office and retail)
  • Location: Shoreditch, London
  • Structural Engineer: Simpson Associates
  • More information

 


Image: IF_DO

7. Hastings Observer Building

Built in 1924 and originally extended in the 1960's, approval for the demolition of the former Hastings Observer building was already in place when it was bought by developers in 2019. In order to avoid this, plans to remove the original extension (whilst retaining structural steelwork) as part of a wider renovation have now been approved. This will result in a mixed use development comprising leisure, business, and event space as well as low-cost work space, multi-use community spaces, and 16 ‘living rent’ flats.

  • Original height: 4 storeys
  • Storeys added: 1-2 storeys
  • Original structural form: Concrete frame
  • Extension structural form: Steel frame
  • Former use type: Office/ print works
  • New use type: Mixed (including leisure, offices and residential)
  • Location: Hastings
  • Structural Engineer: Webb Yates
  • More information

 


Image: RG Group

8. Crown House

This former office building was extended and converted into residential accommodation as part of a wider development that now provides 355 students flats to both of Sheffield’s universities. The existing upper floor was removed and replaced with 3 new storeys, requiring the existing steel frame to be strengthened. Steel framing was also opted for the extended portion of Crown House, with modular bathroom and kitchen units being used to reduce the project timeline and minimise disruption to nearby buildings and transport links.

  • Original height: 6 storeys
  • Storeys added: 3 storeys
  • Original structural form: Steel frame
  • Extension structural form: Steel frame
  • Former use type: Office
  • New use type: Residential
  • Location: Sheffield
  • Structural Engineer: Tier Consult
  • More information


In addition to the vast carbon savings made in these adaptive reuse projects when compared with comparable new builds or demolition and reconstruction, the above cases show a number of the context-specific opportunities offered by vertical extensions. These include:

  • The potential for extension without increasing the load on the existing structure
  • The capacity to add up to 1/3 the original height to some buildings
  • And the ability of this technique in increasing property value to generate funds for wider refurbishments

The suitability of vertical extension in instances where traditional alternatives are not viable has also been shown, along with its ability to save historic buildings and potential disruption/ programme benefits.

 

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