Project: Annexe Building, West Smithfield
Main Contractor: McLaughlin & Harvey
JDC Scaffolding have been involved continuously with the overall Smithfield project since 1Q 2017, a collection of iconic buildings which the main parts have been called the last ruin in London. The buildings have been abandoned for many years and were in an extremely bad state of repair or nearing collapse. The works have involved shoring, protection and general access in the building which ultimately is being transformed into the new Museum of London when it moves from its current location at Barbican. Final scheme completion is due to be in 2026.
The Annexe Building was built between 1886 and 1899 and comprises of two main buildings. The Red House which was one of the first cold stores in the world (Currently internally supported by JDC Scaffolding under another project) and the Fish Market. The Fish Market is triangular on plan made up of three clear walkways, Buyers Walk, Clock Arcade and Bridge Arcade with a central office area.
The whole building is constructed over a network of tunnels and basements, including two main Thameslink rail lines.
The external structure is constructed of tuck-pointed brickwork built off stone pediments. The inside structure and the extensive roof is of timber construction with decorative dormers and a number of historic stone features at roof level.
The buildings were vacated in 1983 and were under threat of demolition until 2005. A number of areas of the existing building had been supported with heavy duty RMD type supports.
We first got involved in the building in 2019 when, under a PAYE Stonework contract, we were asked to design some supports for various areas of the building. The main 1st and 2nd floors were collapsing and there were concerns about some of the existing timber trusses over the main arcades. We designed and installed a propping system to the timber floors ensuring each individual room was supported. We also designed, alongside the client and the Heritage Architects a system to temporarily support the trusses, without damaging the structures further.
Around this time, we were asked to look at the possibility of providing a temporary roof over the whole building. We drew up some preliminary designs but these were shelved for a period.
We were approached by McLaughlin & Harvey to look at a package of works at the Annexe. They were on a City of London Framework agreement and were pricing a scheme to work within the Annexe Building to make the building safe, clean the external masonry, replace internal timbers, replace the roof coverings and alter the internal layouts. The enquiry, as with all of the Smithfield works, included a raft of specific design requirements from the Clients engineer, AKT-2.
We had not previously worked with McLaughlin & Harvey but we worked alongside their procurement team to develop a scheme of works which ultimately was let to them.
Design – General
The works are extremely design intensive and the design itself is based on a very specific set of guidelines which has been produced by AKT 11. A suite of documents sets out the allowable parameters in the design with respect to acceptable loadings on the ground floor slab and permissible forces against the external walls.
The original scaffold design was carried out, in house, by JDC Scaffolding with supporting calculations and Design Statement by RDG Engineering. McLaughlin and Harvey are acting as Temporary Works co-ordinator with Alan White Design as their Third-Party Cat 3 checking engineer. All completed collaborative designs would finally be presented to AKT 11 for final sign off. The design process has been challenging due to the ongoing Covid restrictions. All parties have been communicating via email, telephone etc. with regular Teams meetings. These by nature have not been ideal due to connection problems etc.
During the life of the design programme meetings also had to be held with representatives of the City of London Highways department and Network Rail prior to commencement. Some design meetings were also overseen by the Contract Administrator, Buro 4.
A separate contract below both the Annexe Building and the adjacent Meat Market is being carried out by Keltbray. The works involved will ultimately join the two buildings underground. Due to delays in design sign off by all interested parties the interface with the Keltbray scheme has meant that a re-support of a major part of the internal scaffold had to take place to enable a new core to be cast. (See Drawing 5335/18-01)
The original designed scaffolding works comprise generally of the following:-
- External independent scaffold to the main building and the adjacent Red House.
- Temporary roof coverage to the whole building area – comprising five separate temporary roofs of different & complex constructions.
- Supports at ground floor slab and externally.
- Bridged birdcages to the existing arcades.
- Full-length access to the existing roof lanterns to allow timber repairs and glazing replacement.
- Temporary bracing and supports to the existing trusses during remedial works.
The scaffold had to be designed to provide both access to the main elevations for cleaning and to give access for Masons replacing the tuck pointing. The scaffolds also had to give support for the temporary roofs above. (See Challenge No. 2 & 3)
The building is generally triangular on plan and is made up of many differing roof levels. We had to provide coverage to ensure the existing building was protected from weather during the roof replacement works. (See Challenge No. 4)
Below the whole building footprint is a series of existing tunnels and basements. Under a large part of the structure runs two mainline railways which were covered with very fragile tunnel lids.
Below another part of the structure was the existing Salt Store where salt was kept for preserving meat in the adjacent Meat Market.
The railway lines also passed under a large area where our external access scaffold had to be based.
The external perimeter of the building also had a series of vaults and tunnels to consider. (See Challenge No. 2)
Bridged Birdcages to Arcades
Through the existing arcades we had to design and construct bridged birdcages which would both allow access for following trades to access the building with men and materials. The birdcages had to incorporate our previous propping systems and also be sufficient to support further propping to the existing timber roof members.
The birdcages would also support further access scaffold for the roofers and glazers to access the high-level lanterns for repairs and replacement.
Access to Lanterns
Scaffold was design for the access requirement to repair and replace existing roof timbers, dependent on the state of the timber itself.
All scaffolding had to be self-supporting and not to impose any load or allow any fixings into the existing timberwork.
Bracing to Trusses
We further developed our previous design (installed during the early works programme, to give various support options to the existing truss members, dependent on the current condition of the timber and where (if at all) the trusses had degraded. The supports could be at the truss ends (in various configurations), centrally to the main truss or at the mid points picking up both the horizontal and vertical members. (See Challenge No. 6)
SKILLS AND EXPERTISE
The project highlights our design capabilities and the depth of our engineering knowledge, the design development has been an intense process and carried out in difficult communication circumstances during a Pandemic with a very large design team – often with many different ideas.
We have listened, have been patient and have offered alternative design solutions to some seemingly impossible challenges.
The parameters with regards to both vertical and horizontal loadings, set out in many areas looked unachievable, but with time, thought and with the tacit knowledge of our management team we have solved most issues.
We have always suggested practical, workable and cost-effective solutions to all areas of the works. Our workforce has adapted well to changing working practices and processes and the end product on site is well constructed and aesthetically pleasing.
We have erected some extremely complex scaffolds on this project and have nearly always met McLaughlin & Harvey’s programme requirements.
We have ensured that our site team, supervision and visiting management have been constant to ensure continuity throughout the life of the project build.
Our Senior Management Team have been regularly on site to review progress, provide advice, explore options and implement solutions, despite how uncongenial they may be to the client.
We have had the agility to respond to challenges soon after their discovery which has been vital for McLaughlin & Harvey in maintaining progress and achieving their programme.
We have had to be receptive to change on this challenging scheme and have facilitated the development of designs in particular with regard to the specific loading constraints. There was a hugely protracted design lead in which meant that adjacent construction works overtook project milestones. We have had to redesign scaffolds in many areas. This has enabled McLaughlin and Harvey to continually develop their construction strategy in several locations resulting in welcome programme savings.
We have worked closely with the McLaughlin and Harvey team and have built trust and strong relationships which have enabled us to collaborate successfully on the project.
We pride ourselves at all times on our attention to detail in both our design drawings and final delivery on site. The completed scaffold on this project is testament to both these attributes.
Challenge 1 – Covid 19
As with the tender process and the design development, much of the on-site works were carried out under the rules and regulations of the Covid 19 Pandemic. Our operatives and management have worked to the strict site rules and updated policies implemented by McLaughlin and Harvey with regards to Social Distancing, breaks, welfare use, face coverings, testing etc. as well as adhering to the JDC Scaffolding SSOW and Covid 19 rules.
We have also had to deal with meeting programme milestone dates when we were challenged as many of our workforce tested Covid positive during the main installation works and had to self-isolate for the required period.
Challenge 2 – External Scaffold – Ground Bearing
One of the main areas of access scaffolding is on Snow Hill. The scaffold was designed to both give access to the external façade and to support the temporary roofs above.
The supporting calculation pack was produced on the information that was available and was then checked by McLaughlin & Harvey. When the design was checked by the City of London highways team it was then highlighted to all parties that there were actually hidden vaults under 41.00m of the 62.00m long scaffold. We managed to acceptably spread our loads, simply, at low level with the introduction of four lines of 750 Apollo X beams.
It was also pointed out that there was also a hidden tunnel for a further 23.00m of the length of the scaffold and it was decided that this would not take the imposed loads of the temporary roof.
To meet this challenge, we had to design a heavy-duty goalpost support internally to accept the roof loads and the outside elevation would be accessed by a light duty scaffold which would not connect to any of the temporary roof elements above. (See Drawing 5335/001-05)
Challenge 3 – External Scaffold – Tie Forces
When we first designed the scaffold, we set out the ties generally on a 16.00m3 grid, as standard, however, we made sure that the tie pattern was sympathetic with the surrounding structure.
AKT 11 later rejected this pattern and, very late in the design process, stated that the building was in a very fragile nature and that the external fabric would not accept the imposed loadings suggested.
Our design team together with RDG Engineering and Alan White Design developed an intricate tie system with four different types of ties:-
- Standard Excalibur anchors
- Light tie arrangement
- Medium tie arrangement
- Heavy tie arrangement
These details would be situated in very specific locations with differing amounts of actual drilled ties, plan bracing and check fittings
Challenge 4 – Temporary Roofs
Three main challenges we had to overcome with the temporary roofs were the shape of the building, the differing heights of the existing roofs and the lack of external scaffold to support the roofs.
It was decided that the main part of the building would be covered with a Hakitek 750 rolling roof which we have successfully installed on many projects in the past. To support full side of the roof seemed fairly achievable as we had a full length, full height access scaffold below (Note Challenge 2)
For the rest of this roof, it was not possible to achieve a full ground founded support scaffold.
For the other main support, we had to design a 45.00m long spine beam which was only supported internally via three slim 24.00m high towers. These towers had to be positioned in very specific areas so that the roof would only be penetrated in areas of future roof lights.
The use of a standard Haki tie chord system, tube and fittings or a beamed arrangement could not be utilised in this location due to the existing roof projections – chimneys and the like. To achieve the tie chord JDC have designed a system of wire bonds connected with shackles, jaws, thimbles and rigging screws.
To enable us to load out our materials, to construct and roll out the Haki roof and to weather the gable ends we also had to design three further spine beams, each 21.00m long. In total to support this roof we installed region 500.00m of Apollo X Beams
Due to the shape of the remaining roof area it was decided that the roofs would be covered in a traditional ci sheeted solution. A further four roofs were designed two of which took support from the main external independent scaffold. The remaining two roofs were supported from a number of bespoke scaffolds inclusive of a further 30.00m spine beam supported from some existing concrete fins.
All five roofs interconnected and we ensured that the water was managed successfully.
Challenge 5 – Internal Timber Supports/Repairs
The roof of the Annexe Building is made up of 32 arches with a glazed lantern at the top. The existing timber had to be inspected by Heritage Architects, and in some locations structurally tested. It was then decided what would happen with each location.
We had previously installed scaffold supports to 13 No. arches during an earlier contract and had to adapt our new scheme to encompass the original scaffolds.
We were asked to provide a bridged birdcage through each of the arcades with hop ups to enable both the investigative works to take place and any necessary supports to the trussed arches as they were repaired. The scaffold also gave continuous access within the roof lantern to enable the necessary repairs.
Challenge 6 – Resupport to Existing Support Scaffolds
During a previous enabling phase, we had provided propping to all the external shop units to the perimeter of the building. We were based at ground floor and propped to First Floor with Screw Jacks. We then continued the propping at First Floor to the underside of the external roof timbers.
During the new phase of works the First Floor timbers had to be replaced prior to the roof repairs taking place. We developed our existing design to re-support the higher-level scaffold, with new, introducing new standards and ladder beams where necessary.
During the re-support works we were also asked to provide restraint to a perimeter steel beam at First Floor Level which we did with tubular materials, bracing, restraint tubes and check fittings.
Challenge 7 – Budget
The continually developing design has raised a number of budgetary challenges. We have worked closely with the McLaughlin & Harvey commercial team to ensure transparency and best value at all times.
We have also strived to ensure that any items of variance are priced, where possible, in a timely manner to enable works to be agreed early with the client team wherever possible.
- Levels of interface with the client
JDC interfaced well with MCLH from Pre-Construction stage right through to the present. They were always on hand to attend site meetings to discuss issues and overcome obstacles which presented themselves in a historic dilapidated building.
Their onsite Team has been a great asset to the job from the start, a hardworking, problem solving team, which was well needed on a project of this scale.
- Assistance with difficulties – levels of solutions
During our Pre-Construction phase a big issue was uncovered with a piped subway located beneath the footpath where we were to base a support tower for a substantial temporary Haki Roof structure. JDCs engineers working collaboratively with our own Temporary Works Engineer (Alan White Design) quickly came up with a solution to mitigate any delays.
At the outset of the project, there was a vast amount of existing scaffold & temporary propping of the existing roof structures. JDC came up with workable solutions to adapt the existing temporary works & providing safe working access for removal & replacement of the existing throughout the site.
- Levels of interface with the design team
JDC in house Design always made themselves available for weekly Design Team meetings with our Temporary works engineer and client-side Structural Engineers (AKT11)
With the project located over an entire basement area and partially over the Main Thameslink underground network, scaffolding design was subject to a rigorous approval process, JDC where on hand to attend to overcome these obstacles, providing temporary works solutions which required Network Rail, Col Structures and MCLH approval prior to commencement.
- Reducing risk and hazard at the design stage
JDC provided a Temporary roof covering over an obscure site plan, providing us with a water tight temporary roof structure, to enable replacement and refurbishment of the existing roofs, at the same time providing access to internal & external facades to carry out refurbishment works safely.
- Safety elements
JDCs own safety officer attended site weekly followed up with a detailed report using SMART scaffolder which was quick to flag up any relevant safety issues which could be addressed promptly.
- Innovative product development
JDC have used an innovative Haki roof system on this project, which is one of the most impressive temporary roof structures the industry has to offer.
- Aesthetic qualities – neatness and tidiness
JDC have provided us with a very neat and tidy scaffold built to a high standard and quality.
- Adherence and commitment to budget
JDC are keen to adhere to budgets and have generated cost + design options which benefit all parties.
Lee Wasson – Project Manager – McLaughlin & Harvey
JDC has demonstrated excellent standards of safety performance throughout their time on the COL Annexe project to date. On what is an extremely intricate site, they have designed, constructed and maintained complex scaffolding systems with H&S at the forefront.
I have found JDC to be very proactive in their approach to the safety of its workforce and others utilising their scaffolds on site. They have been cooperative throughout and able to provide innovative solutions for safe access to what are often restricted works areas.
Their designs allowed work to be carried out under a scaffold canopy that protected both the listed building and the operatives carrying out the restoration.
Sam Sufferin – SHEQ Advisor – McLaughlin & Harvey
JDC Scaffolding were shortlisted for the 2022 NASC Award for Project of the Year (Medium) and picked up the award.
The NASC said: “The project highlighted JDC’s design capabilities and the depth of its engineering knowledge. The design development was an intense process and carried out in difficult communication circumstances during a pandemic.”