Notes
three stacked squares and a fourth square solution

Three Stacked Squares and a Fourth Square

Solution by Congruent Triangles

With the points labelled as above, angles $A \hat{C} B$ and $E \hat{C} D$ are equal and so triangles $E D C$ and $A B C$ are congruent. The shaded area is therefore equivalent in area to two squares. The total shaded area is therefore $8$.