When designing the shading devices, one should take into account the need to control solar gains in summer, as well as the heating and the lighting performance of the building.
The exclusive use of internal sun-shading devices such as roller shades, venetian blinds, curtains and drapes, is not recommended. The major disadvantage internal device is that, regardless of how reflective they are made, they trap heat on the interior of the glass so it remains indoors. A combination of internal and external shading devices is recommended, the shading being designed as a whole.
Internal shading devices should not block the daylighting or interfere with the natural ventilation, as it can happen when they obstruct the window openings.