The second principle is that changes are agreed in writing before they are carried out, not settled at the end.
Structuring payments
Stage payments tied to identifiable milestones — foundations complete, structure watertight, first fix complete, plastered, practical completion — keep both sides aligned.
Payments tied to calendar dates rather than progress remove the incentive to keep pace, which is why milestone-based staging is the fairer arrangement.
Variations
A variation is any change to the agreed scope, whether you asked for it or the building forced it. Each should be priced and accepted in writing before the work is done.
Keeping a running variation schedule means there is no surprise at the end, and it makes it obvious when a series of small changes has quietly become a significant sum.
Retention and completion
Holding a small retention until snagging is complete is common and reasonable, with a clear period and a defined release trigger so it does not become a source of argument.
At completion you should receive certificates for the regulated work, warranties for products and appliances, and a written workmanship guarantee.
Common questions
Should payments be by date or by stage?
By stage. Payments tied to completed milestones keep progress and payment aligned.
What is a retention?
A small percentage held back until snagging is complete, released on an agreed trigger. It protects the final quality of the job.
Do variations have to be in writing?
They should be. Written pricing and acceptance before the work is done prevents disputes at the end.
What should I get at completion?
Building control certificates where applicable, product warranties, and a written workmanship guarantee.