Author: Darren Fleck

Which fastener material should I use for what environment?

Read time: 4 minutes
Date: 10 Mar 2022

Flat Roofing
Rainscreen & Façades
Sheeting & Cladding

Why are fasteners made from different materials?

Fasteners are made from different grades of steel and the material used will depend on the durability required and the environment it will be used in. Using the wrong material can lead to corrosion and cause the fastener to fail.

According to the BSI (British Standards Institution), fasteners are not repairable or replaceable. So, fasteners must be selected to last the lifetime of the building they are used in and the material must be suitable for the environment.

Corroded fastener in application

What fastener material should I use for what environment?

British Standard BS EN 9223:2012 includes an annex that summarises a range of typical internal and external environments in terms of their corrosivity level. This provides a useful guide to help you understand how different atmospheric conditions will affect your choice of fastener material.

Grade	Risk	Environment
C1	Very low	Internal heated buildings, with low humidity and insignificant pollution wholly unaffected by the external location - e.g. offices, schools, and museums.
Semi-interior	Low	The atmosphere and conditions within the building, sufficiently sealed and insulated from the external environment so they would normally be expected to be unaffected by it - e.g. fasteners installed beneath external waterproofing membrane. This does not apply to C5 & swimming pool environments, where the relevant conditions take precedence.
C2/C3	Low/medium	Rural and urban areas with low to moderate levels of pollution, unheated buildings with potential condensation or air pollution, but within the limits set for human work without protection - e.g. food-processing plants, laundries, dairies.
C4	High	Highly humid and polluted industrial areas or an aggressive environment with high frequency of condensation, between 2km and 10km from the sea and coastal regions - e.g. wind-blown salt spray and atmospheres containing chlorides.
C5	Very high	Marine areas up to 2km from the sea containing chlorides and very high levels of salinity, including highly polluted industrial areas near permanent condensation (outside the splash zone).
Swimming pools / Chemical plants	Extremely high	Swimming pool areas or chemical plants that are exposed to chlorine vapour.

Always select the material of the fastener based on the highest level of risk. Carbon Steel fasteners should only be used in low risk and very low risk environments; however, your choice should also be determined by how long the building would be used. So, if you wanted a building in a low risk environment to last 60 years, you would choose 316 / A4 stainless steel.

Saltwater environment

Coastal environments are one of the highest risks because saltwater causes corrosion to accelerate. It is therefore essential to only use 316 stainless steel or super austenitic steel in coastal environments.

Swimming pool environment

Swimming pools and chemical plants carry the greatest risk because there are high levels of chemicals such as chlorides that can cause stress corrosion cracking (SCC) in some grades of stainless steel, including austenitic. To prevent stress corrosion cracking, HCR fasteners are the only recommended solution for swimming pool environments.

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