A solar greenhouse, which is set against a building or is made out of a building, consists of a closed glazed space located on the south side of a house which is separated from it by a thermal accumulator wall (Fig. 74). The greenhouse can be used as both a direct gain non-warmed space and an indirect system since the rooms next to it receive heat through the intermediate wall which works as a storage. It is also possible that the rooms receive heat from the air in the greenhouse through a natural or forced ventilation system. Solar greenhouse planning can follow different criteria: if it is considered as a cheap extension of the house where people live for the greatest part of the year, it will be necessary to employ a big storage mass placed both on the walls and also on the floor and some movable insulation panels for the night. Instead, if the greenhouse is seen as a solar wall system, with an air space which is a few metres wide rather than a few centimetres, it should be planned to ensure that the greatest quantity of intercepted energy will be taken from the air space to heat up the adjacent rooms. In this case, a forced air change using the greenhouse to pre-heat the incoming air could be also planned (Fig. 75).

Solar greenhouses can be realized in a wide range of geometrical configura­tions. It can be considered as a simple addition to a wall, as a semi-jutting out element or as an element which is set in a building (with three of its sides sur­rounded by living spaces). Moreover, the solar greenhouse can be considered as a structure which covers the entire width of the house and is a single storey or two storeys. Even a greenhouse which is isolated from the building structure can supply thermal energy to the building through a system of ventilators and grooves.

Eventually, a correct solar greenhouse plann has to restrict the inner overheating phenomenon during the summer to its minimum. The simplest technique is one which allows ventilation directly from outside by opening the glazed windows, but the use of screenings or glazed surfaces fitted with sun block control is also possible [1, 3, 4].