After the detection of the constructive solutions that do not fulfil the minimum requirements, it now becomes critical to identify the minimum changes needed in order to ensure compliance. This is done in Table 5. The solution for complying with the U-value passes through adding some thermal insulation. It is assumed that this cannot be done at the external face of the walls because it

would change their look, so a solution of internal insulation is considered. Then, to solve the problem of the solar factor, the most internal layer of the walls is changed from gypsum to a brick wall (the insulation thus becomes locked between the stone and the brick). Since the requirement for medium or high thermal inertia is g<0.56 the requirement becomes fulfilled.

Once the minimum requirements have been met, the next step is to verify if the requirements of heating, cooling and DHW needs are met. The results for the several apartments are shown in Table 6. They show that, even if the direct minimum requirements for the envelope are now verified, this is not enough to fulfil the energy requirements. Although all apartments comply with the cooling needs criteria, only one complies with the heating needs criteria. The requirements for the domestic hot water (final energy) are met in the limit (note that at this stage no solar collectors were considered yet). In what regards primary energy, the criteria are satisfied in all apartments except number 5 and 6. Regarding the energy class, at this point it can only be given to the apartment number 4, which is the only that fulfils simultaneously all the requirements.