The allowable deflection of aluminium depends on various factors such as the member type (beam, plate, etc.), material properties, boundary conditions, and loading scenarios. Generally, the deflection limits are specified in building codes and standards to ensure structural integrity and serviceability.

For beams and columns made of aluminium, the deflection limits are often specified as a fraction of the span length or the member length. For example, in the Eurocode EN 1999-1-1, the allowable deflection for uniformly distributed loads is typically limited to L/250 for aluminium beams and L/350 for aluminium columns, where L is the effective span length.

For plates, such as aluminium cladding panels or floor plates, the deflection limits are usually defined in terms of the plate thickness or the span length. For instance, in the British Standard BS EN 1999-1-3, the allowable deflection for uniformly distributed loads on aluminium plates is limited to 0.005 x L, where L is the span length.

These deflection limits are set to prevent excessive bending and deformation of aluminium structural elements, ensuring adequate stiffness, serviceability, and overall safety of the structure. It's important to follow these limits during the design and construction process to maintain the integrity and performance of aluminium structures.