Authors:
Anri Doda, MSc CEng FCIBSE MSFE – Patrick Ryan Associates
Patrick Ryan, BSc PhD MIStructE FSFE – Patrick Ryan Associates
Introduction
Our Grosvenor Waterside journey began early in 2021, prior to the implementation of the Building Safety Act (BSA), with the appointment of a professional team following the identification of unsafe cladding material by the building owner. Nearly 3 years later, Caro Point, the building featured in this article, has achieved practical completion in September 2023.
According to figures released by the Government, at the end of July 2024 there were 4,630 residential buildings of 11 metres and over, identified as having unsafe cladding. The scope of this reporting changed at the beginning of the previous year (in 2023) and figures now include all buildings which come under the five Government schemes:
- ACM remediation scheme - Buildings over 18 metres high with ACM cladding unlikely to meet building regulations
- Building Safety Fund (BSF) - Buildings over 18 metres with unsafe non-ACM cladding
- Cladding Safety Scheme (CSS) – Buildings 11-18 metres with unsafe cladding
- Developer – Led Remediation
- Social Housing sector
The figures are shown graphically below.
As mentioned above, the figures in the rectangle show that that 4630 buildings have been designated as having flammable materials in their cladding so far. The obvious question here is, how many more are there? These will come to light only as building owners investigate further.
Overall, 3,280 buildings (71%) have either started or completed remediation works. Of these, 1,350 buildings (29%) have achieved practical completion. But this still leaves 2331, around 50%, of buildings which presumably still need to start construction. A worryingly high figure which the new Labour government has now pledged to reduce.
Grosvenor Waterside – Caro Point - Case Study
Since 2021, Patrick Ryan Associates along with a team of professional organisations including DMWR Architects, project managers Carter Jonas, fire engineering consultants Tri-Fire and structural engineers Mason Navarro Pledge, have been involved in the recladding of the two main buildings at the development known as Grosvenor Waterside, located in the Chelsea area of South-West London. Our work covered RIBA Stage 3 – 5.
The first of these buildings, namely Caro Point, is the focus of this case study which looks at a typical fire recladding project to give context to the future of façade remediation. This article introduces some of the challenges we are facing, the environmental vs cost considerations, the role of the Building Safety Act (BSA) and their impact in moving forward as an industry.
Grosvenor Waterside is a prestigious and well-established development of quiet, waterside residences in one of London’s most sought-after districts.
The original development started in 2000 when planning permission was granted to turn the dock site into high end housing in Chelsea, West London.
In 2020, following identification of unsafe cladding, these being the existing High-Pressure Laminate (HPL), flammable insulation and missing cavity barriers to the stone cladding, the building was registered under the Building Safety Fund programme and a professional team was appointed to undertake the remedial works. The timeline of events is as follows:
RIBA Stages 3 to 5
The project began at RIBA Stage 3, with the investigation of the existing cladding and the identification of flammable materials. This was followed by discussions with the fire engineering consultant, building structural engineer, and client on the items that needed replacement.
At RIBA Stage 4, we produced the detailed façade concept design including fire strategy elevations, structural and thermal calculations, drawings and façade details for tender as well as the façade specification for a traditional contract. This stage also included closing out all the items in the building control tracker so that a letter of compliance from the Building Control Officer could be issued.
RIBA stage 5 included construction drawings as well as the answering of the “Requests For Information” (RFI’s) throughout the construction period and the guidance of the contractor throughout the construction process. There were also regular site visits to inspect contractors work with reports back to the project manager and client as well as a CWCT hose test on the finished cladding. A final snagging took place at practical completion.
Project Challenges and design solutions
There were many challenges to us, as façade engineering consultants on this project which had an approximate cladding and stonework package value of £15,000,000. Some of these challenges were:
- As this was an existing building with complicated site conditions, it required individual solutions for structural, fire, thermal, and other aspects of the cladding and stone design, resulting in a very high number of RFI’s (150 in total), from the contractor.
- With the building having been constructed over 20 years ago, very little of the original design information existed. PRA needed to devise a recladding solution based on the necessarily limited investigations carried out at commencement of the project. As more cladding was exposed during the construction phase, the problems became clearer, and design solutions were adapted.
- An EWS1 assessment, which demands an A1 rating, was requested by the client. This meant that all flammable materials present in the façade needed to be removed, including the insulation and sheathing board behind the stone. This meant removal of all the stone cladding.
- The thermal, condensation and acoustic performance was required to be as good as, or better than what was in place originally. This required careful design to provide sufficient insulation, to eliminate cold bridging and provide the necessary acoustic performance. Condensation performance could not be improved, without major works to the inside skin, but the resulting performance matched the original construction.
- All works needed to be completed whilst the residents remained in situ. This meant that construction had to happen without the removal of windows or doors for safety. Serious consideration had to be given to the removal of cladding and insulation in colder months, speed of replacement and control of noise.
With all the above challenges, a series of integrated design solutions were devised, achieved through:
- Working closely with the Building Structural Engineer, for example to provide strengthening to the existing SFS support frame. Workmanship defects and corrosion due to water ingress were identified and remediated.
- Liaising with the Fire Engineering Consultant to produce acceptable fire safe solutions
- Working with the Architect and Principal Designer with regards to planning requirements and CDM compliance
- Liaising with the Building Control Officer to ensure full compliance and approval
- Discussions with the client’s representative and cost consultant to ensure fire safety
- Working with the sub-contractor to retain or recycle the stone cladding
We maintain that a robust tender package is essential for a re-cladding scheme that involves of removal of flammable materials to make a building safe. Design solutions must comply with all aspects of the Building Regulations. On this project this required the following remedial actions:
- All the Trespa Meteon HPL and stone cladding needed to be removed to extract flammable insulation, flammable cement particle board and introduce cavity barriers as necessary.
- Design details of the cladding and stone systems were produced (which included at a later stage the construction issue and as-built drawings). The design included all the secondary support system up to the bracket fixings to the SFS. An assessment of the existing support wall was undertaken by a qualified building structural engineer.
- Structural design was produced for the new aluminium cladding, stone cladding including associated finite element analysis to define the stiffeners of the panels under critical loadings.
- Thermal and condensation analysis was carried out for the whole of the exterior wall to improve performance. The existing U-value for a typical wall build up was reduced from the anticipated 0.37W/(m2*K) to 0.28 W/(m2*K), a significant improvement reducing fuel bills and improving the operational carbon emissions.
- To satisfy the EWS1 A1 rating required, materials were sought which would achieve a European fire classification of A2,s1-d0 or A1. The design required membrane to be of European fire classification B-s3, d0 or better. These membranes needed to be flexible enough to accommodate the necessary building movements, something which is not easy to achieve with the modern fabric type membranes.
- Actions were taken within the design to achieve minimal disruption to the residents and to avoid as much as possible, light reduction due to scaffolding during the construction phase. This included understanding how the windows were supported whilst keeping them in place during construction and devising details which minimised drilling into the existing structure. The integrity of the internal SFS and interior plaster board lining was also maintained.
Environment vs Cost
It seems a sometimes almost impossible balance needs to be struck between meeting environmental targets and economic considerations on fire façade remediation projects.
One of our biggest challenges on this particular scheme was whether we could reuse the existing stone cladding or whether indeed it needed to be replaced, partially or in its entirety. Investigations were carried out into the nature of the fixings and how easy it would be to dismantle the stone, transport to storage, store, transport back to site and reinstall. Working closely with our specialist stone sub-contractor, it was concluded that approximately 35%-40% of the existing stone cladding was re-usable. The client then had to consider the questions of cost, visual appearances of reused stone and warranties, resulting in a decision to replace the stone in its entirety. Whilst this was not a win for the environment, we do understand the reasons behind the decision and encouragement was given to the contractor to recycle the stone for other uses as a minimum.
On a broader front, it’s worth mentioning some of the main ways in which embodied carbon emissions can be reduced on these projects, including:
- Specification and selection of products that are low energy in the manufacturing process.
- Choosing local suppliers and manufacturers.
- Replacing as little of the original construction as possible, consistent with fire safety.
- Repurposing materials and systems (for example, aluminium secondary support systems for support of cladding, flashings, outer brickwork)
- Reducing waste on site and recycling of any materials removed from the building or waste materials. This is a matter very much in the hands of the contractor, but much can be achieved by specification.
Keeping costs down, whilst maintaining environmental integrity is often a challenge on legacy projects such as this which fulfil the duty to the leaseholder but produce no profit for the developer/contractor. However, it is a challenge we think is achievable, if these suggested practices are employed.
Introduction of the Building Safety Act
As mentioned at the beginning of this article, the work was started and completed before the implementation of the Building Safety Act. However, since April of this year, the act has come into force and all construction work on high-risk buildings comes under the scrutiny of the new Building Safety Regulator.
All design work pertaining to the recladding of an HRB needs to be fully compliant with the requirements of the BSA, as well as other statutory requirements, for example CDM and the Building Regulations. Of particular importance within the BSA are the three Gateways. Most significantly for design of recladding projects on HRBs, no works can commence on site without the design work passing Gateway 2. The assessment process undertaken by the Building Safety Regulator may take up to 12 weeks.
The competence of the team to carry out such design work on HRBs is also part of the assessment and the HSE website has guidance on this. Those façade engineering consultants engaging in the recladding of HRBs will require a design team with the right competence to meet their legal duties. This can be using existing staff or teams or third parties, so long as they are sufficiently competent or trained to carry out the necessary work. Management of the team is key to a successful conclusion. The HSE website also adds:
“ Those managing HRBs (or those appointed to do so) should have sufficient working knowledge to make informed decisions, ask intelligent questions, understand when to bring in any expert help and understand how to co-ordinate action based on this expert advice. “
The Building Safety Act is a new and necessary advance in building safety and in our opinion, there’s nothing within it or its outworkings, that is beyond the capabilities of the very excellent professionals we have within façade consultancy here in the UK.