What a back-to-back clause actually does

It makes you responsible to the main contractor for the same things they are responsible for to the principal. The wording varies, but the shape is familiar: the subcontractor is bound by the terms of the head contract so far as they apply to the subcontract works. Terms of a contract you never signed become terms of yours.

There is a logic to it from their side: the main contractor never wants to owe the principal more than it can recover from the trades. Their contracts team writes the chain, and you are the last link.

The obligations flow down. Do the rights?

This is where a flow-down clause quietly costs money. In the head contract each obligation usually comes with something back: an extension of time when the principal causes delay, a payment entitlement for a variation, a defined claims process. A one-directional flow-down clause pushes the duties down and leaves the remedies upstream.

You can end up carrying a head-contract program obligation with no matching extension-of-time right, or a quality standard with no matching payment for the extra work. Go through it obligation by obligation and ask what you get back. It belongs with the other clauses that shift risk onto subcontractors, and it is the least obvious of them.

Six things to check in your copy

  1. Which documents are incorporated, listed by name and date. A clause binding you to "the head contract and all associated documents" can pull in a program, a management plan or a specification you have never seen, and you are bound either way.
  2. Whether you can read them. Ask for the head-contract terms that bind you, redacted for commercial rates if need be. You cannot price or comply with an obligation you are not allowed to see.
  3. Whether the matching rights come down. If the head contract gives the main contractor an extension of time or a cost entitlement for an event, check your subcontract gives you the same for that event, or you carry the risk without the remedy.
  4. When your notice clock starts. A back-to-back notice regime usually gives you a shorter window than the head contract gives the main contractor, because they need your notice in hand before theirs is due. Miss it and the entitlement can go, so check the time bars on delay notices in your copy.
  5. How the payment wording is built. Look for anything making your money depend on the principal paying the main contractor, on a head-contract certificate, or on approval under the head contract. That wording has a statutory answer in some states.
  6. What happens if the head contract changes or ends. Check whether a variation, suspension or termination up the chain flows straight through to you, and what you are paid for work already done if it does.

Can your payment be tied to the head contract?

Not by a "pay when paid" provision, in the states below. In New South Wales, s 12(1) of the Building and Construction Industry Security of Payment Act 1999 (NSW) provides that a pay when paid provision of a construction contract has no effect in relation to any payment for construction work carried out under the contract. Its third limb, in s 12(2), is the one that catches back-to-back drafting: a provision that otherwise makes the liability to pay, or the due date for payment, contingent or dependent on the operation of another contract.

Victoria's equivalent is s 13 of the Building and Construction Industry Security of Payment Act 2002 (Vic). Queensland's is s 74 of the Building Industry Fairness (Security of Payment) Act 2017 (Qld), whose third limb uses the same "operation of another contract" wording (authorised reprint current as at 28 April 2026).

Two limits. Whether a clause falls inside those definitions turns on its exact wording and the state you are in, which is a question for your own adviser. And these sections reach payment only: they do nothing about the program, design, quality or notice obligations a flow-down clause brings with it. More on why pay-when-paid has no effect.

What the standard forms already assume

The Australian Standard subcontract forms are published as a matched set, so an unamended pair lines up without a home-made flow-down clause. Standards Australia describes AS 4901-1998 Subcontract conditions (published 5 September 1998, status Current, 64 pages) as providing "a set of compatible subcontract conditions involving site work on projects where AS 4000-1997 is in use as the head contract between the main contractor and the principal". Its design and construct equivalent, AS 4903-2000 Subcontract conditions for design and construct (27 December 2000, Current, 75 pages), is described as "part of the suite of contract conditions based on AS 4000-1997".

That changes where you look. On a clean standard subcontract the pairing is already built in, so a broad extra flow-down clause is doing something the form does not. The risk sits in the amendments: the special conditions and departures schedule bolted on top. The forms are paywalled, so no clause numbers here. Work out which AS form you've been handed, then read your executed copy and its annexure.

The records that keep you covered

If head-contract obligations are coming down, your records have to be good enough to answer them. Log delays as they happen rather than reconstructing them later, keep dated instructions and who gave them, and record daywork and standing time the day it occurs. A back-to-back clause makes someone else's timeline your problem, and a contemporaneous record is what shows where the time went. DelaySolve's free tools for subbies are built for that.

Before you sign

Ask for the incorporated documents by name, mark every obligation with no matching right, and put the payment wording in front of someone who reads subcontracts for a living. A back-to-back clause is not automatically a bad deal. It becomes one when it travels in a single direction, and the only way to know which you have is to read what it points at.