For losses arising from defective work, it is six years from the date of completion, or the ending of the contract, whichever is the later.
There are a number of cases on what is meant by “completion”, usually it centres around issue of the occupation certificate.
2 years for loss arising from other than a structural defect encompasses things such as failure to complete, e.g. when a builder walks away, goes into liquidation or fails to do something that is in the contract.
In your case it sounds like you fall into the structural defect camp.
Have a look here.