I have recently submitted an external wall detail to my local Planning and Building Control Office as part of a Building Notice for a Kitchen Extension. The cavity is 50mm (with insulation fill) and I have been advised that this should be detailed as 100mm (with 100mm insulation fill). Is this correct? I can find nothing in Part A or Part L of the Building Regs that stipulates 100mm. Also, does the cavity size depend on the wall construction? I am intending to use blockwork inner leaf and rendered blockwork outer leaf for one wall and blockwork inner leaf and brickwork outerleaf for a second wall.
Any comments / advice would be appreciated.