Recently, in a body corporate that we manage, a lot owner installed solar panels on the roof above his townhouse without approval. Whilst he was totally unaware that permission was needed to make improvements to common property, it is not always easy to work out what is common property in a town house scheme.
You must inspect the survey plan for the lot and if the survey plan states that the plan is a building format plan, then each townhouse lot will be defined by the walls, ceilings, floors of the townhouse. This means that the townhouse structure, foundation, roofing, guttering and cladding all form part of common property. But his plan could have stated that it was a standard format plan, in which case the entire townhouse would form part of his lot and he could have freely installed the solar panels on his roof.
Making changes to common property can lead to issues if the committee or body corporate refuses to approve the improvement. The lot owner would need to restore the common property to the prior state. Avoid the issue altogether, and make sure to get approval. Committees can approve a common property improvement by a lot owner where the cost of the improvement is less than $3,000. Beyond that, only a general meeting may consider the motion for an improvement.