What does it mean for a subcontract to be back to back?

Back to back describes a subcontract whose terms line up with the main contract so the risks you carry to your employer can be passed on to the subcontractor responsible for them. If the employer can levy damages on you for a delay, the subcontract needs to let you recover those from the subcontractor whose delay caused it; if a variation is only recoverable upstream on certain conditions, the subcontract needs the same conditions downstream. The point is to prevent orphaned risk, an obligation that lands on you from above but has nowhere to go below, exactly the exposure that quietly bankrupts the middle of a supply chain. It does not mean the two contracts are word-for-word identical, and treating it that way causes its own trouble: a subcontractor cannot sensibly be bound to programme dates that only make sense at main-contract level, and some main-contract obligations have no meaningful downstream equivalent. The craft is in mapping which obligations genuinely need to pass down and drafting those to align, leaving the rest to suit the subcontract package. It also has to stay lawful: a payment term cannot be made back to back in a way that breaches the Construction Act, so pay-when-paid cannot simply be mirrored down. Done well, no risk falls into the gap between the two contracts; done as a blind copy, it creates gaps of a different kind.

Take a main contractor who lets a steelwork subcontract by copying their own main contract's delay-damages clause verbatim, thinking that makes it back to back. It does not: the clause refers to sectional completion dates that exist only in the main contract, so when the steelwork runs late and the employer charges the contractor, the clause is unenforceable against the subcontractor because it points at dates that mean nothing at that level. The risk is orphaned, and the contractor carries the damages alone. Drafted properly, the subcontract would have set the subcontractor its own completion date for the steelwork, tied the damages to it, and passed down only the obligations that made sense below, so the delay could be charged on. Same intention, opposite outcome: the copy created the gap careful drafting would have closed.