Ridge height increase due to switch to warm roof?

[flanagaj]

Looking at the plans that have been approved, which includes a clay tile roof; 16800, to be precise.  Planning on asking Architect if we can switch to a seam sealed roof (hopefully a minor amendment) and also switch to a warm roof so as to not lose head height in the loft.  Just wondering whether a ridge height change (no properties within 50 metres, and they all differ) to accommodate the switch to a warm roof, would require a full planning app?

[Conor]

How much? Something like 200mm won't be noticed. We switched from cut timber roof to insulated panels, resulting in a 300mm increase. We dropped the ridge by 150mm and wall plate by 50mm.