Case summary:

During the course of works carried out pursuant to a construction contract a supplemental agreement was concluded in writing adjusting the total contract price to include variations and compensation events. Later, the contractor claimed additional payment but the employer resisted payment on the basis that events underlying the claim had been compromised by the supplemental agreement. The contractor commenced adjudication. The employer contended that the adjudicator lacked jurisdiction because the dispute concerned the meaning and effect of the supplemental agreement which was not a construction contract as defined by the HGCRA. On the facts the court concluded that the supplemental agreement varied the original agreement and was therefore subject to the adjudication provisions of the original contract. 


The court considered a number of early authorities and distinguished one: Shepherd v Mecright (2000). It is a question of fact in each case whether a supplemental agreement is to be treated as no more than a variation to an existing contract and therefore subject to all its terms, or a stand alone agreement that is not subject to all the terms of the original contract. 

McConnell Dowell Constructors (Aust) Pty Ltd v National Grid Gas plc (formerly Transco plc) (3/10/06)