The aim of this work had concentrated in the study of solutions for the closing of the covering for greenhouses under summer conditions, experimented with the lettuce. Four covering treatments were considerate for the evaluation of the environmental performance: (T) testifier, with only plastic canvas; (C) plastic canvas and ventilation compound (an overture on the roof); (CS) plastic canvas under shading screen, with a ventilation compound(an overture on the roof) associated; and (S) plastic canvas under shading screen. It can be declared, as expected, that shaded greenhouses presented a best environment performance than the unshaded greenhouses, and provided a more comfortable environment for the growth of lettuce culture on Summer.