Comment: Metal gutters fit for the future

Carlton Jones of the Metal Gutter Manufacturers Association (MGMA) explains the improvements brought by a new standard for metal guttering in the context of climate change.

Extreme weather is now an all-year-round likely occurrence in the UK, ranging from flash floods one day to heat waves the next. Average wind speeds are rising faster than predicted and, according to the latest reports from the Meteorological Office, the UK could soon see a repeat of the sort of flooding that has hit in recent years. Forecasters have said that there is a one-in-three chance that a new record will be set for monthly rainfall during coming winters.

Climate change is one of the key drivers for improving roof drainage and water management; developing new standards, regulations and testing methods to ensure products and solutions align with worst-case climate model scenarios is essential.

Rainwater systems are integral to protecting our buildings, and channelling water from roof to ground. Therefore gutters, outlets and downpipes must be able to demonstrate in situ strength and structural capability when handling increasing volumes of rainfall and wind loadings.

The recently published BSi standard is BS 9101:2017 – ‘Steel and Aluminium rainwater systems. Specification’. It specifies the requirements for the design and manufacture of metal gutters on industrial, commercial and residential buildings. This includes the materials, tolerances, mechanical properties and surface conditions, coatings, laminated surfaces, jointing methods and fixings for rainwater systems, including fittings and accessories for assembly or support.

BS 9101:2017 puts particular emphasis on the design strength of the metal gutter. This is determined by loading capabilities in the form of downward rain, wind uplift and snow. Products require either Finite Element Analysis (FEA) or physical testing to ensure they meet the new standard. FEA is a computer based method of analysing the behaviour of engineering structures and components under certain conditions. It is an advanced engineering tool that is used in design and to augment or replace experimental testing.

Before BS 9101:2017, standards such as BS 8530:2010 were developed to establish the requirements of traditional cast systems. However, the standard for pressed and extruded gutters was still open to interpretation.

The industry had referenced BS 612 for pressed gutters, cover- ing ‘Eaves gutters and rainwater down-pipes of metal sheet’, as it was the only standard that came close. In 2005 this was updated and defined as ‘Eaves gutters with bead stiffened fronts and rainwater pipes with seamed joints made of metal sheet’. A bead- stiffened front is defined as a rolled section rather than a pressed sheet. As such, pressed sheet gutters are covered under the new standard (BS 9101:2017).

With regards to extruded gutters, the industry used to reference BS 1474 – ‘Specification for wrought aluminium and aluminium alloys for general engineering purposes: bars, extruded round tubes and sections’ – this standard was withdrawn in 1987 and replaced by EN Standards, which apply to the material and not in-situ structural strength. As a result, the new BS 9101:2017 standard is far more comprehensive and detailed to meet specific metal sheet and extruded gutters, and has been developed to cover gutters that are excluded from the previous BS 8530.

Setting new British Standards is a time consuming and detailed process. The BSi depends on expert advice from leading UK manufacturers with regards to design parameters, loadings and specifications. A diverse group, representing all parts of the metal gutter industry, as well as consultants, was drawn together by the Metal Gutter Manufacturers Association (MGMA) to work in partnership with BSi to review current standards for rainwater products, and advise on new developments and technologies for the benefit of the industry. Developing new standards also helps eliminate bad practices among manufacturers producing inferior or unsafe products.

The new BS 9101:2017 standard raises the bar for metal rainwater specifications and will prove invaluable to metal gutter manufacturers. But often new standards are complex and the implications on project designs are not always clear.

Many architects, specifiers, design engineers or installers may not be aware of the latest developments or the significance to their projects. Members of the MGMA can offer the relevant support and technical advice to their specifier and installer customers so that metal rainwater gutter systems are correctly specified across all projects. At a time when the demands put on our buildings by major factors such as climate change are increasing, it is essential that they benefit from the best solutions to protect them for the future.

Carlton Jones is director at the Metal Gutter Association.Detailed advice on the specification of metal rainwater systems from the Metal Gutter Manufacturers Association can be found at