This paper proposes a method for designing EMC shielding enclosures using a peer-to-peer based distributed optimisation system based on a modified particle swarm optimisation (PSO) algorithm. This optimisation system is used to efficiently obtain optimal solutions to a shielding enclosure design problem by sampling only a small fraction of the total problem space. Such a system would find use in environments where large scale computing resources are not available, such as smaller engineering companies, where it would allow computer-aided design by optimisation using existing resources with little to no financial outlay.