Section 20 of the Principal Act is amended as follows:

(a) by omitting from subsection (1)(b) "when and where" and substituting "when, where and how" ;

(b) by inserting the following subsection after subsection (4) :

(5)  Despite subsection (4) , a determination of the Director of Building Control made under subsection (1) , or a standard or requirement applied under such a determination by reference to a document, does not apply to work if the building surveyor, or relevant permit authority, for the work certifies in writing that substantial progress had been made in the design of the work –

(a) before the determination was made; or

(b) if the determination applies a standard or requirement by reference to a document that is subsequently amended, before the document so applied was amended.