View source for 25-32 Chancery Lane, London

==Article in [https://www.newsteelconstruction.com/wp/wp-content/uploads/digi/NSC_Feb16_digi/pubData/source/NSC_Feb16_digi.pdf#page=12 NSC February 2016]==
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'''Retaining a City streetscape'''<br>
A modern [[Continuous_frames|steel-framed]] [[Multi-storey_office_buildings#Mixed use commercial buildings|office and retail scheme]] in the City of London is being constructed behind two [[Facades_and_interfaces#Facade retention in building renovation|retained façades]].<br> 

Set in the heart of the City of London’s legal quarter, a new 9,300m<sup>2</sup> development in Chancery Lane will provide nine floors of modern [[Multi-storey_office_buildings#Mixed use commercial buildings|office and retail accommodation]] behind two [[Facades_and_interfaces#Facade retention in building renovation|retained façades]].

The four-storey façades of the previous building - Lonsdale Chambers - have been retained along the entire Chancery Lane elevation and a portion along the Breams Buildings thoroughfare. Originally built in the 1870s, keeping these masonry walls and windows will add continuity to the surrounding streetscape. “[[Facades_and_interfaces#Facade retention in building renovation|Retaining the façades]] was one of the planning stipulations,” explains Scott
Brownrigg Assocaite Ian Wood. “They help make our new building less obtrusive, while also maintaining the look of the street.”

“Above the façades the new [[Continuous_frames|steel-framed]] floors are set-back which reduces the impact from street level along Chancery Lane.”

Overall the new development comprises a basement, ground floor and seven upper storeys housed in a long span, [[Continuous_frames|steel-framed]] building with [[Floor_systems#Composite slabs|concrete floor slabs]] cast on [[Steel_construction_products#Decking for floors|metal decking]]. In order to maximise the floor-to-ceiling heights, the [[Service_integration|services]] have been incorporated into the structural steelwork zone by using Fabsec [[Long-span_beams#Cellular composite beams|cellular beams]] throughout the frame.

The building’s [[Concept_design#Concrete or steel cores|steel-framed core]] is offset and disconnected from the building floor plate due to vertical service risers. The building’s [[Concept_design#Structural options for stability|stability]] is consequently provided by the structure acting as a [[Continuous_frames|sway frame]] to remove the need to install [[Braced_frames#Vertical bracing|cross bracing]] and compromise the architectural scheme.

A centrally positioned [[Steel-supported_glazed_facades_and_roofs#Atrium Roofs and Sky lights|atrium]] extends upwards from basement to roof level, where it will be topped with glazing that will allow natural light to penetrate the inner areas of the building.
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The basement of the building will accommodate some retail space towards the Chancery Lane end, with plant areas located to the rear in a deeper part of the floor zone. The ground floor will house more retail space, the main office entrance lobby and storage areas for the office tenants, such as bike sheds.

From the first floor upwards the new building will consist entirely of office space, with the first three levels (first, second and third) eventually tied into the [[#Retention systems|retained facades]].

The fourth floor will feature a new mansard design (again mimicking the surrounding buildings) while above this the building steps back to accommodate a large fifth floor roof terrace and smaller terraces above. Because of these outdoor areas, the topmost office floors (5, 6 and 7) have significantly smaller floorplates than the lower floors. “The set-back upper levels don’t disturb the existing streetscape and they also create outdoor usable space for the new development,” adds Mr Wood.

McLaren Construction began work on this project in August 2014 with the demolition of Lonsdale Chambers. Early works included the demolition and stripping out of the original structure and installing associated [[Construction#Temporary works|temporary works]] to support the existing façades, basement retaining walls, pavement vaults and party walls of the adjacent properties. Once the piling of the site, which required approximately 600 piles installed up to a depth of 22m, was completed the steelwork programme was able to begin.
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Steelwork for the new frame begins at basement level and most of the 2,000t of steelwork Severfield has [[Construction#Steel erection|erected]] for this project was lifted into place using the site’s two [[Construction#Tower cranes|tower cranes]]. “The only exceptions were a couple of 20t beams installed at ground and first floor levels which were too heavy for the [[Construction#Tower cranes|tower cranes]],” says McLaren Construction Project. Manager Gavin Turnbull.

“As there is no room for a [[Construction#Mobile cranes|mobile crane]] we had to split one beam into three sections so the [[Construction#Tower cranes|tower crane]] could lift the pieces, while the ground floor beam was installed using a forklift and a block and tackle.” These heavy beams form cantilevers; at ground floor where the frame has to avoid a subterranean obstruction and at first floor where a longer span is needed to accommodate the entrance.

Getting steel or any construction material to a site in central London is always a logistical challenge. On this project there is no space to store any material as the footprint of the site is taken up completely by the new building. Steel was delivered on a just-in-time basis with at least two deliveries every working day. “We had two offloading areas for the [[Fabrication#Handling and transportation|steel deliveries]], one on Chancery Lane and the other within the site boundary adjacent to Breams Buildings, with each area serviced by one of the two [[Construction#Tower cranes|tower cranes]],” explains Severfield Project Manager Richard Grey.

“For the [[Construction#Steel erection|erection]] we split the frame in half, with each of the two areas supplied by one of the offloading areas and with its own dedicated [[Construction#Steel erection|erection]] gang.”

The steel frame is based around a fairly regular [[Concept_design#Floor grids|grid pattern]] offering column-free spans of up to 12m, all the way around the central [[Steel-supported_glazed_facades_and_roofs#Atrium Roofs and Sky lights|atrium]]. Aside from the first three levels of steelwork, the frame was [[Construction#Steel erection|erected]] two floors at a time, with Severfield also responsible for [[Construction#Installation of metal decking|installing the metal decking]] which followed on behind.

Putting the finishing touches to the building, the cladding systems include [[Steel-supported_glazed_facades_and_roofs|fully glazed façades]] above the retained elements, while the remaining façade on Breams Building (excluding the retained portion) features [[Facades_and_interfaces#Curtain walling|curtain walling]] incorporating glazing and terracotta elements of blue, orange and white.

External works to the site include repaving footpaths to Breams Building and Little Whites Alley and high level soft and hard landscaping to the roof terraces from the fifth storey upwards.

25-32 Chancery Lane is scheduled to be completed in November 2016.

==Retention systems==
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The steelwork [[Construction#Steel erection|erection]]  was one of the key elements in keeping the project on schedule as a number of other vital trades and programmes were dependent on the steel completing on time.

The [[Facades_and_interfaces#Facade retention in building renovation|retained façades]] are supported by temporary propping systems around which the new steel frame was [[Construction#Steel erection|erected]] (pictured right). Once the [[Floor_systems#Composite slabs|floor slabs]] up to level four were cast and cured the façades were then tied into the new steel frame via a series of angles. After this the propping was removed as the façades were then supported by the steelwork.

Further down the building each corner of the site was temporarily propped, while the groundworks and then steelwork programme was progressing. Only after the ground floor slab was cast could the basement [[Construction#Temporary works|temporary works]] be removed.

{|class="wikitable" width="400"
|-
|'''Architect'''||Scott Brownrigg
|-
|'''Structural Engineer'''||Campbell Reith
|-
|'''Steelwork Contractor'''||Severfield
|-
|'''Main Contractor'''||McLaren Construction
|-
|'''Main Client'''||Viridis Real Estate
|}

[[Category:Case studies - Multi-storey office buildings]]