If the strata committee hasn’t done anything within two months, or has actively declined to take action, you can take them to the tribunal for failure to fulfil a statutory duty, under Section 232 of the Act. Your first compulsory step if you go down that road would be to seek mediation at Fair Trading.
However, it strikes me that if we can wrap pipes in insulation to stop them freezing in colder areas, surely we can do the same with joists to stop them heating up and cooling excessively. It could be a cheap solution – has anyone tried it?