Jeremy – Firstly, the Owners Corporation (O/C) is responsible absolutely for rectifying all damage caused during the process of it making repairs, alterations, or changes to its Common Property (the windows).
Secondly, it was the O/C (and not you) who delegated its responsibility to the Builder, through an engagement that should have incorporated a scope of works and specified conditions such as the Builder holding public liability and indemnity insurance, which all comprised a “contract” between those parties.
So it’s the responsibility of the O/C, and the Executive Committee as its representatives to get the consequent damage that you’ve referred to repaired, and if that means it taking-up the matter with the Builder, engaging another Builder, or lodging a claim on the first Builder’s Insurance then so be it!
Before anyone offers opinions about how best to proceed, could you advise how the E/C “explained that they would repair any damage to the window surrounds and sills caused by the work”; in writing or verbally? How was the Resolution of the O/C minuted that approved the window replacements; was there a mention of consequent damage?