This new Approved Document gives guidance on how to comply with Part Q1 of the Building Regulations, which states that a building must be designed and constructed in such a way that it adequately resists unauthorised access from outside the building and unauthorised access from within the building to flats within the building. This is an essential reference for anyone undertaking building work. This new Approved Document will take effect on 1 October 2015 for use in England. It does not apply to work started before 1 October 2015, or work subject to a building notice, full plans application or initial notice submitted before that date provided that the work is started on site before 1 October 2016.