Just to clear up the "insurance" aspect of this issue.
Household policies, which are standard thoughout the industry, only cover specified perils i.e. storm, flood, escape of water, fire etc.
If the root cause is shoddy workmnship and/or poor design then there is no cover
There will be no perils called "defective workmanship" or "defective design" or "builder made a b######s of it".
The only option is to sue the builder however as a previous poster mentioned the time to make a claim starts running from the date of incident or date of knowledge of something being wrong. This is a six year period. When did you first realise there was a problem ?
€4,000 for investigative work is ridiculous. A consultant engineer should charge a max of €1,500/2000 incl VAt and his report would be sufficient in itself to satisfy any court that the builder/designe would have a case to answer.
Having said all that a solicitor would have to be retained and the costs start mounting.
Another question is : Is the builder a limited company and still in business ?- Has he been wound up or in liquidation ? If so, pointless pursuing him.