Contest 5

Make a balustrade with the twelve pentominoes, in such a way that the enclosed area is as big as possible.
The three banisters must divide the total area in three parts of equal area.
The external perimeter must be rectangular.
The pentominoes must touch along the full edge of the square and not just at the corners.

In the example shown (above) each enclosed part has area 36.

This will make the search easier