Probably original with the house in ~1968. The non-glazed elements are plywood which is reasonably strong but very poor from an insulation point of view.
This should equal or exceed current 'Part L' building regs. A nice touch is the draft excluder around the edges of the loft hatch.
This DIY, npower-subsidised, Energy-Saving-Trust-recommended insulation is to ensure that we match or exceed current building regs everywhere in the loft that we can.