form of a slide 7 applied to the first element 3 by means of a slider and having an l shape moreover advantageously the first element 3 has a shape complementary to this l such that said slide 7 can slide against the first element 3 by a first vertical branch 8 of the l until it is locked by a second horizontal branch 9 of the l the first vertical branch 8 of the l by which the slide 7 slides along the first element 3 as it is being mounted on the latter thus corresponds approximately to the slider the second branch 9 forms an abutment beneath the first element 3 in the described embodiment the slider is linear and parallel to the facade formed by the stacking of insulating formwork blocks 1 this slider is realized by form fitting between the first element 3 and the slide 7 the slide 7 is preferably made of polystyrene foam and since the mechanical strength is provided by the first element 3 the density of the material composing the slide 7 can be less thus reducing the cost of the insulating formwork block 1 this slide 7 is thus advantageously.