ᐅ Should I Replace the Roof Insulation or Not?

Hello dear forum community, the following situation:

House built in 1982, roof insulation with 18 cm (7 inches) Rockwool. In winter, without heating (0 degrees Celsius (32°F) outside temperature), indoor temperature is around 18 degrees Celsius (64°F).
In summer, temperatures under the roof can reach up to 40 degrees Celsius (104°F).

We want to buy this house and have heard two opinions: 1.) Install new insulation, 2.) The 18 cm (7 inches) Rockwool insulation is more than sufficient.
If the insulation were bad or damaged, we wouldn’t have such good temperatures in winter. However, the temperatures in summer are worrying me. What could be causing this? And would new insulation be worthwhile?

Regards,
Ahri

For summer heat protection, only massive building components with high thermal mass are suitable. New insulation would probably be of little use. An air conditioning unit is likely the most effective solution, or additional roof windows (shaded) to quickly release heat at night.