In buildings placed on historical zones is not obligatory to install solar collectors if the south- oriented roof area available is going to create a negative visual impact. As we have seen before, the energy produced by the solar collector is very important to meet de RCCTE requirements. Therefore, in building rehabilitations, not installing solar collectors means the Nac value is going to be only supported by conventional energies. To understand better the implications of this in a real case it were made some calculations using a building example situated on a historical zone and in a soft Portuguese climate zone. It is a typical Portuguese building of approximately hundred years old with a wood roof structure and large stone walls. From the calculation made we concluded that without solar collectors three mainly measures hat to be taken: increment strongly the envelope insulation, choose the more energy efficient equipments as possible and also select equipments based on gas or oil supply and not on electricity. The results showed that only selecting envelope insulations widths of minimum 8-10 mm the building could be straight with the regulations. Notice, this width is still uncommon in Portuguese projects and is going to occupy some useful internal space joining the fact that typical stone exterior walls have already great widths. Another problem detected is that usually the conventional energy to select must be electricity because usually there is not available natural gas supply on these zones. It seems by this example, that these regulations look a little restrictive for buildings in historical zones.

Other case is that collectors are not obliged to be implemented when the building south-oriented roof is or is going to be in the future shadowed during the solar period mentioned in chapter 3. One of the future obstacles on the efficient implementation of solar collectors is the fact that there is a lack of policies and regulations on urban planning to give the minimal guarantees to building sun exposure. In some cases, is difficult to know for sure what kind of constructions are going to be authorized in the future near the project site. It is an important problem related with governmental territory planning strategies.