Changing out timber joists for metal ones is often a no-brainer. Timber joists had their share of the limelight for centuries, but many are moving away from the combustible wooden substructure for decking and moving to the more uniform, non-combustible and strong metal joist such as aluminium. This move has been accelerated by Approved document B: fire and safety regulations and its influence on existing balconies.
But as lovely and simple as it sounds, ensuring that your new substructure is structurally sound, cost-effective, and efficient can be difficult. Here are the three main methods that you can use when replacing timber joists for aluminium on an external balcony.
Use Joist Cleats and aluminium joists
In some cases, when you need a system build-up higher than that of the existing frame, you can use aluminium joist cleats installed on top of the metal frame to support the joists. Using cleats creates a strong, customisable, and compliant class A fire rated substructure for your decking surface. This is a cost-effective and simple method for retrofitting aluminium joists but, as the cleats are installed on the top of the frame, it increases the build-up and raises the decking floor height. This may not be suitable when you need a low height.
Install Steel Joists
Technically, one option is welding Steel Joists onto the existing balcony frame. However, to install these joists correctly you will need to cut them to size and weld them into place using a crane to lift them or manhandling them up countless flights of stairs and through the homeowner’s weekly book club meeting. This process will create a secure substructure but, it does require a lot of on-site labour and wouldn’t be recommended unless you carry a copy of Thursday Murder Club with you for Mary’s Wednesday “book nook”.
Install Joist Hangers and aluminium joists
Joist hangers are rigorously tested and designed to be affixed to existing metal frames to provide a cradle for the new joists to sit flush with the height of the existing frame at intervals to suit you. Installing a Joist hanger allows you to cost-effectively recreate the original build-up of the balcony by aligning the top of your joists at the same height as before. This solution is very simple in its design gives you a lot of control, options for customizability, and facilitates a compliant class A fire rated system.
So what now?
When working on a retrofit or remediation project where you need to replace timber joists on a metal-framed balcony, aluminium joists are the safest and most efficient way forward. They provide you with a non-combustible, secure substructure that will stand the test of time.
How you choose to install it, however, is up to you.
