Conservation of the external masonry, particularly on the northern side of the building, is equally important. The cathedral is in part built of Caen stone. Detailed archaeological studies are undertaken to identify exactly which stones need to be replaced or repaired. In addition, specialist cleaning techniques are used to remove accumulated chemical deposits which are very damaging to the building. As regards the interior, priorities include decoration of the vaults of the Trinity Chapel, major improvements to the Treasury building which contains, amongst other things, the choir practice rooms, and conservation work in several other chapels.