Brian Newell explains the key points of a new international porcelain cladding standard – and how it should improve build quality.
Porcelain is a lightweight, exceptionally hard, and impervious material, which makes it an ideal choice for building facades. It provides both design flexibility and an extended low-maintenance service life with excellent resistance to staining and weathering.
The new ISO TS 17870-3 standard has been published by the International Standards Organisation (ISO) and BSI following international consultation with stakeholders from across the facade industry. It applies to mechanically fixed porcelain cladding systems.
Engineering out risk with installation-ready panels
One of the key risk factors in any facade installation is the potential for site errors, and this risk is increased if the facade panels require onsite fabrication. While facade installers are skilled specialists, they are not experts in every system. Moreover, site conditions are very different from an ISO 9001-certified factory environment, where all processes are quality assured, all equipment is checked and maintained, and contaminants cannot compromise drilled apertures for undercut anchors or connections for fixings.
To prevent the risk of poor fabrication practices and onsite fabrication issues, the ISO TS 17870-3 standard requires that all porcelain facade systems are supplied as installation-ready panels, with no drilling or fitting of undercut anchors or attached bracketry onsite. Ideally, onsite cutting should also be avoided or minimised.
This stipulation will avoid the potential for reduced undercut anchor pull-out values due to ill-fitting anchors or contamination, for example, which could result in latent fracturing of the porcelain or affect wind load resistance.
Meshing and combustibility
It is common best practice for facade manufacturers to apply an anti-fragmentation mesh to the rear face of porcelain cladding panels. While the standard does not make safety meshing mandatory, it does stipulate that any meshing used should be A1 or A2-s1 d0 compliant to BS 13501-1. As porcelain is usually A1 rated for non-combustibility, this ensures that all ISO TS 17870-3-compliant porcelain facade systems are suitable for residential buildings taller than 18m.
Fixings
Where a system has been specified with apertures formed through the body of the panel to receive mechanical end fixing devices for attachment to the facade substructure, the ISO TS 17870-3 standard stipulates that the fixings should be fitted to allow for anticipated thermal expansion and contraction to help prevent stresses from developing within the facade system that could result in damage and hazards.
For edge-slotted systems, the standard allows for flexibility in the thickness of the facade panel, but recommends that the remaining front and rear edges of the slot walls should be a minimum of 5mm thick. It also recommends that this type of fixing should be avoided for very large porcelain facade panels, as the spans between perimeter fixing points may be too large to achieve adequate restraint against negative wind loading.
Visible overlapping clip systems, where the clips overlap the porcelain façade panel around its perimeter and fix to the facade support structure are also not considered appropriate for very large panel formats. The standard advises that minimum panel thickness for this type of system should be determined by the span between clips without deflection or deformation of the panel, under maximum wind loading, along with the facade system manufacturer’s advice.
Durability and impact resistance
Large-format porcelain cladding panels should be proven to resist hard and soft body impact testing. The vulnerability of large format cladding panels varies depending on the location of the building and the location on the building. More significant and frequent impact is likely at lower levels where the building is more vulnerable to pedestrians, traffic and thrown objects and this should be a consideration when deciding on the thickness of the porcelain panel specified.
All fixing components should have a high level of corrosion resistance, enabling them to retain their properties with little or no maintenance during the lifespan of the facade.
Due diligence
It is not possible to itemise every point set out in the new standard in a single article, which is why it is important to scrutinise ISO TS 17870-3 in full. While cladding manufacturers have a responsibility to ensure that their facade systems comply with all relevant regulations and standards, specification, procurement and installation best practice have a vital role to play in facade integrity and building safety.
The new standard has been developed to reduce the margin for error – from specification through to finished facade – and raise build quality standards. It provides a valuable opportunity for contractors to benefit from the collaboration and expertise involved in developing the document.
Brian Newell MBE is founder and chief executive of British facade manufacturer Shackerley, and the technical lead for the new international porcelain cladding standard published by BSI – ISO TS 17870-3:2023.
