Jack Costello, Garland UK Technical Manager

GARLAND UK Technical Manager Jack Costello shares his expert insights on retrofitting unsafe cladding and facade projects, best practices for assessing their replacement and the key considerations for specification.

Assessing Cladding Replacement

Before determining a cladding replacement option, it is crucial to determine whether the replacement is necessary. A comprehensive approach is essential to assess whether a building’s cladding is unsafe and requires replacement, encompassing visual inspections, documentation reviews, and potentially specialised testing.

The initial step involves reviewing the As-Built drawings to identify the cladding build-up used in the construction. Subsequently, a comparison is made between the identified cladding and current building regulations to ensure compliance.

If the As-Built drawings are not available or unclear, a cladding expert can visually identify the cladding. They can help identify the type of cladding used and look for signs of wear, damage, and deterioration. If the cladding expert flags a potential issue, a qualified fire safety surveyor should be appointed if potential combustible materials are identified. They will then conduct a full survey and produce an EWS1 form with an outcome of either Option A or Option B.

Option A is for buildings with an external wall system unlikely to support combustion. Option B signifies that combustible materials are in the facade, and the fire engineer must proceed to conduct a risk assessment. From here, the assessment will categorise the fire risk as negligible or necessitating remedial works. A compliant specification must be written to replace the cladding if remedial works are advised.

Sub-Structure Analysis

The first step in creating this specification is undertaking a structural analysis of the existing building. The analysis should focus on two areas: the load-bearing capacity of the existing structure to determine whether it can support the proposed cladding system, and the assessment of the building’s foundation to ensure it can handle additional loads. This is specifically important when changing from lightweight metal cladding to a masonry/stone facade system.

The type of materials used for the substructure of the existing facade will depend on the building’s age and location. This is important as the proposed materials must be compatible with the existing structure so that they will not cause issues like corrosion or degradation.

Another essential aspect of compatibility with the existing structure is the materials’ thermal expansion and contraction. It needs to be ensured that there are no imbalances and that the necessary precautions are taken to allow this expansion to manifest without risk to the facade.

A common issue with retrofitting facades onto masonry is that there is unlikely to be a sufficient fixing point to suit the new system’s structural and windloading requirements. In this case, a ‘Slab to Slab’ system, a bulked-up version of a helping hand and rail system, can be used. With this method, the helping hand brackets are fixed into the structural floor slabs, and the rails span between the two, removing the need for a fixing point in the masonry or other lightweight secondary structure. This has other benefits, such as removing labour costs and the number of brackets required.

A bespoke sub-frame specification should also be established to fix the new facade system at this stage. Whether it is integrating an existing Steel Framing System (SFS) or utilising a ‘Slab to Slab’ system, the subsequent consideration is determining the size of the void to house the new insulation. For this, an architect or surveyor might have a specific thermal U-value in mind. Alternatively, without a specified U-value, Building Regulations Part L should be used to get the appropriate thermal efficiency for the facade.

Considerations For Specification

R-MER Shield

When aiming for a specific U-value target, it’s essential to consider the selection of insulation type and thickness and evaluate the effects of the subframe on thermal bridging throughout the facade.

The thermal conductivity (Lambda-Value), vapour permeability, hydrophobic properties, density and compression, durability, acoustics, and, most importantly, fire safety must be considered when picking insulation for a retrofit project.

After selecting the appropriate insulation with a specific lambda value (ƛ), most facade sub-frame providers can suggest a suitable bracket height and layout to accommodate wind loadings, meet the required U value, and allow for the necessary ventilation gap.

In comparison, one bracket may seem more expensive than another as an individual item. However, some brackets exhibit superior resistance to thermal bridging, allowing the decrease of insulation depth to achieve the same U-value. Therefore, evaluating the market comprehensively and considering the entire facade cost is crucial rather than relying solely on an individual bracket cost comparison.

The ventilation gap in contemporary facade systems plays a crucial role in the building’s moisture management and temperature regulation. Its design should adhere to the manufacturer’s guidance, contingent on whether the panel joint is open or closed. While the ventilation gap offers significant advantages, it also poses a vulnerability regarding fire safety. As highlighted earlier, incorrect compartmentation within the ventilation gap can serve as a direct pathway for fire to spread throughout the building.

For more information, visit the Garland website.

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