dizzyheights go to
http://www.nhbcbuilder.co.uk/NHBCpub...d,15912,en.pdf
But remember this is a guidance document only, so it doesn't really matter - this is what John Croal of Bett Homes (now known as Gladedale) told me.
Simon Barret of the NHBC also told me 'Remember that the NHBC is the builders insurer and if we set our standards too high the builders will go elsewhere for their insurance'. Straight from the horse's mouth.