A manufactured composite insulating panel 1 comprises an external sheet 4 having an outer face and an inner face, an internal sheet 2 having an outer face and an inner face, and an insulating body 5 between the inner face of the external sheet 4 and the inner face of the internal sheet 2. The external sheet 4 has a portion that extends beyond the internal sheet 2 and the insulating body 5 to define an overlap part for overlapping with part of an adjacent panel, on assembly and a seal 21, 22 is applied to the inner face of the overlap part of the external sheet 4. The panel has a side overlap part 12 to which a side seal 21 is factory applied. An end seal 22 is also factory applied to an end overlap part 16 of the panel.