In planning stages of a deep retrofit. House is detached, and neighbouring houses are brick, various shades of red and brown. Some have been rendered to the sides over years.   My house is the same I suspect. Make up of the existing walls is ‘50-60s brick cavity walls with some mineral wool blown in place, and other half (previously built extensions) is dual skin blockwork with 50mm PIR in the cavity. Approx cavity in all the walls is 75mm.   All the walls are covered in pebb