What you actually should have done was agree a formal contract before the project started, considering the large sum involved. The good news, however, is that a contract does in fact exist between you, as all it requires are three things: an offer, an acceptance and a consideration, where consideration means the promise to reward the person making the offer, usually by paying them a sum of money. All three these items are in place. It is normal for clients to retain up to 10 per cent (depending on the agreement made before the work started) of the certified amount each month of the project in a retention fund. When the work is complete, half of the fund is released and the final retained amount paid when the builder has completed all remedial work to the client’s satisfaction – this normally takes place three months after completion. The three-month period is necessary to allow any latent defects to appear and be fixed. Your builder should be aware of this arrangement, but to avoid confrontation, consider paying the full amount, provided that the builder gives you a written undertaking that he will complete all the remedial works within three months, or immediately where emergency repairs are needed.