Which anchors should I use for façade applications?

Using the wrong anchor could invalidate the system warranty and in a worst-case scenario could contribute to total system failure.

To ensure the safe specification of anchors, we always advise customers to follow the guidance in BS 8539, which identifies five factors that must be considered:

• The type of substrate

• The loadings the anchor will be subject to

• The risk of corrosion

• How the anchor will be installed

• Whether accreditation is available

What type of substrate will you be fixing into?

Façades and rainscreens are fixed to many different substrates including concrete, brickwork (including hollow brick), and blockwork of different densities. So, it's important to ensure that the anchor chosen is designed to be used in the substrate that you'll be fixing into.

For concrete substrates, consideration should be given to the condition of the concrete and whether it is cracked or non-cracked. Concrete can become cracked for a variety of reasons including thermal movement and deflection. Whether the concrete is cracked or not can only be determined by a structural engineer - always assume it is cracked unless the appropriate tests have been undertaken.

What loadings will be placed on the façade?

Two principle types of loading that will affect anchors during the building's lifetime: the weight of the façade (per m2), and live weather loads.

In the UK, live weather loads from the wind are the largest force to be placed on the façade. The wind can be multi-directional and variable, with strong gusts that come from any direction. This increases the negative or positive load within, and on, the façade system - and can result in material fatigue or complete failure if the wrong components are chosen and installed. In severe storms, strong winds can even rip out the rainscreen façade.

So it's important to make sure wind load calculations are undertaken in accordance with the published British Standards.

What is the risk of corrosion?

As with any type of fastener, the material the anchor is made from will need to withstand corrosion. The easiest way to determine the corrosion risk from different environments is to look at the ISO 9223 classification table.

Typically, anchors used in environments with a low/medium risk of corrosion such as rural and urban environments should be made from A2/304 stainless steel. Anchors made from A4/316 stainless steel should be used in high corrosion risk environments, such as coastal areas.

Want to find out more about corrosion? Check out our article here

You must also consider bi-metallic corrosion. Many façades and rainscreens use either aluminium or stainless steel brackets. Bi-metallic corrosion occurs when two dissimilar metals come into contact with each other in the presence of an electrolyte, such as water. The interaction between the two metals, known as electrolysis, causes corrosion. Using a stainless steel fastener will prevent this.

Learn more about bi-metallic corrosion

When installing into concrete, remember to check whether the anchor has ETA approval for cracked or non-cracked concrete, as this will affect the accreditation required. For example, through bolts that are Option 1 ETA approved have been designed, assessed and tested for use in both cracked and non-cracked concrete, while those that are Option 7 ETA approved are only suitable for use with non-cracked concrete.

What should I do if there is no accreditation for the substrate?

Unfortunately, not all substrates are included within ETA/CE marking, or you may not know what the substrate is (as if often the case with recladding projects). In these circumstances, you will need to ask your fastener manufacturer to undertake on-site preliminary testing to confirm the suitability of your chosen anchor.