Isn’t it about time Part D was subsumed into Part C

The requirements relating to toxic substances and cavity insulation are contained within Approved document D.

The requirements states that if insulating material is inserted into a cavity wall reasonable precautions shall be taken to prevent the subsequent permeation of any toxic fumes from that material into any part of the building occupied by people. The guidance is primarily concerned with the problems associated with the injection of urea-formaldehyde (UF) foam into existing cavity wall construction. The requirement has been formally around since 1985 and was introduced to reduce the risk toxic fumes affecting the occupants of the building. The main method of reducing the risk is to provide physical barriers. Installation should be carried out in accordance with BS 5618:1985 and BS 8208-1:1985.

This small and to some extent out of place Approved document would be better subsumed into Part C which is a better thumbed and more relevant document that includes guidance on the construction of cavity walls.