How long do fasteners and bonded washers last?
- Read time: 3 minutes
- Date: 24 Jun 2021
- Sheeting & Cladding
- Rainscreen & Façades
- Flat Roofing
British Standard 7543:2015 states that fasteners should not be considered as either ‘replaceable’ or ‘maintainable’, so should be selected on the basis that the fastener specification will be appropriate based on the intended lifespan of the building system or substrate in which they are being used. The life expectancy of a roof or cladding system largely depends on local weather conditions, building design, building usage material quality, and adequate maintenance.
Therefore, the life expectancy of specific fasteners is very difficult to estimate as they too are affected by the same environmental conditions as the rest of the roofing or cladding system.
Life expectancy should not however be confused with the warranty periods a manufacturer would be prepared to offer on a product.
The table below shows an indication provided by the NFRC for the expected lifespan of a fastener. This can be used as a guide when specifying the fasteners needed on a specific project.
Recommended fastener material to suit EN 12944 exposure categories
BS ES 12944 gives guidance on various environmental exposures and associated corrosion risks.
There may be times and locations where the exposure category is higher than expected. For example, a lighting column located by an elevated motorway might be considered to be category C3, but when subjected to local conditions such as winter salt spray, might in fact be exposed to category C5-M.
It is the building designer's responsibility to establish the corrosivity class of the building and the suitability of the fasteners specified.
How long do bonded washers last?
To provide a weather tight seal, fasteners should be used with a suitable EPDM (ethylene propylene diene monomer) bonded washer.
Like the fastener, a bonded washer should withstand the mechanical forces it will be subjected to, and also resist the atmospheric temperatures, water, acids, alkalis, and UV rays it will encounter during its service life.
Typically, EPDM has a life expectancy in excess of 20 years. However, provided the fastener and washer is not disturbed after this initial life expectancy, the natural silting and sealing of imperfections during normal weathering means washers will remain watertight and airtight indefinitely.
