Welcome to the minefield of Part E of the Building Regulations. The RSD route to compliance avoids the need for pre-completion sound testing to fulfil this part of the Building Regulations and means you don’t risk having to take remedial action after you’ve completed floor or wall construction, with all the delays that might imply. RSDs are designed to exceed the Building Regs’ minimum requirements by around 15% to give an allowance for workmanship defects. Every flat needs to be registered with Robust Details Ltd (0870 240 8210, www.robustdetails.com) at a cost of £35 per unit and it must conform to a particular designation. The relationship between the party walls, separating floor and external walls is also covered by the RSD sheets and you must comply with all of the requirements to achieve compliance (watch out for the block spec of the inner skin of the external wall when flats are proposed). The comments from the National House-Building Council inspector are generally accurate with traditionally beamand- block floors used at ground floor level and wide-span slabs (150mm or 200mm thick depending upon spans) at first floor. A word of warning: wide-span lead times from order to installation are six weeks at best, with eight to 10 weeks typical, depending on time of year and order volumes. If you are digging foundations now and don’t have this resolved your overall programme is already in jeopardy.