Does the Construction Act apply to my contract?

Usually, yes. The Construction Act, the law that sets minimum payment and dispute rules for the industry, applies if the contract is for construction operations carried out in England, Wales or Scotland, whatever it is called and whether written or agreed by word of mouth. The main exception is a contract with a residential occupier, a homeowner, for work mainly on the home they live in or intend to live in; other carve outs include drilling for oil and gas, mining, some work on process plant, and supply only deals where you provide materials but do not install them. Where a covered contract has no payment terms, or terms that fall short of the Act, the gaps are filled by the Scheme for Construction Contracts, a set of fallback rules the law imposes, and that Scheme is where the default dates in this FAQ come from. If the Act does not apply, none of this machinery exists: no Notified Sum, no statutory notices, no fast statutory adjudication, and whatever the contract says is all you have.

A small builder takes on two jobs. The first fits out a shop unit for a retail company under a scribbled one page order: it is construction work in England for a business, so the Act applies, the builder gets the Notified Sum, the statutory notices and a fast adjudication if payment stalls, and any gaps are filled by the Scheme. The second is a loft conversion for a couple on the house they live in: because they are residential occupiers, the Act does not apply, so there is no statutory Notified Sum, notice regime or adjudication, and the builder is left with whatever the contract says. So check which side of that line a job sits on before assuming the payment protections are there.