The first aim of the present work is to assess the environmental impact of specific rendering mortars able to be applied in the vertical opaque envelopes of an existing school building from the 80's built in Portugal, to reduce condensation effects and heat transfer. Ordinary cement and hydraulic lime mortars where compared to cork added and EPS added mortars. Energy performance and energy audit of the building was estimated and compared to the original behaviour of the school building. LCA variant called cradle to gate was used to compare the environmental impacts of building thermal rehabilitation and its effect on the energy consumption for heating and operational energy (OE), for different mortars service life. The simulation made in the school show that ordinary cement or hydraulic lime mortars, leads to much higher global warming potential, where CO2 emissions are more than 3 tonnes per building intervention. The use of mortars with cork addition, leads to a reduction of CO2 emission up to 30% and 20% reduction in embodied energy (EE), when compared to traditional mortars. Cork mortars present smaller EE than EPS mortars. Results shows that it is possible to slightly reduce OE by using materials with lower EE value. (C) 2015 Elsevier B.V. All rights reserved.