The Brazilian Reinsurance Institute building, an icon of modernist architecture in Brazil, projected by MMM Roberto, is legally protected. Its facades had passed by some interventions which will be presented in this article. The present work aims not only at observing the energy consumption, as a result of the last year building renovation, but also at suggesting and comparing materials that could be applied to constitute a true technological retrofit in order to promote energy efficiency increase as well as better indoor environmental comfort too. This work briefly describes the history of preservation of the Brazilian modernist architecture and analyses the first Brazilian official regulamentation to assess the building electric efficiency level.