By Cassandra Mascarenhas, Product & Marketing Strategist, Projx - a project delivery platform for leading client-side property development and capital works teams
In capital works and construction, project teams constantly juggle two priorities: maintaining a collaborative, positive relationship, while enforcing the contract and protecting the Client’s rights.
It’s a familiar tension between keeping the peace and holding the line.
Building good relationships is vital. But when those relationships start bending contractual rules, trouble can follow. If the Client/Principal’s rights are being quietly waived, negotiated away or ignored, you might find you’ve undermined the protections built into the contract.
That’s why PMs and Superintendents need to be mindful of how they manage issues as they arise - because today’s informal workaround can shape tomorrow’s legal position.
“The contract in the bottom drawer” is not an apt approach.
But being a harsh enforcer will not get you very far either.
It’s about being impartial, consistent and protecting both parties’ rights.
Let’s look at two legal principles that pop up when things do go off track: waiver and estoppel.
A waiver happens when a party gives up or refrains from enforcing a contractual right.
For example, your contract states: “Any variation must be approved in writing by the Superintendent prior to work commencing.”
For a detailed breakdown of how variation approval works from the principal's perspective, see our piece on managing variations in property development and capital works.
But over time you accept verbal approval from the site manager, repeatedly. Later a variation cost blows out and the Contractor argues the formal process wasn’t complied with. Because you effectively waived the written-approval requirement by allowing verbal ones repeatedly, you’ve weakened your position.
The consequence? The Principal may lose their ability to enforce the formal requirement, or argue strict compliance.
In simple terms:
Waiver = you had a right, you let it go (or you behaved in a way that said you weren’t insisting on it).
In Australian construction law, estoppel prevents a party from going back on a promise, representation or conduct if the other side has relied on it, to their harm or loss.
Let’s consider a practical scenario. An owner tells a contractor: “We’ll give you the design package within two weeks, you start on site now and we’ll issue the formal contract later.” The contractor mobilises plant, hires crews and incurs major costs. The owner then pulls back, saying “No formal contract issued so we’re cancelling.” The contractor may claim estoppel: they relied on a promise, got into detriment (costs), and it would be unfair to walk away.
Key elements:
In construction, estoppel often appears when you don’t have the contract fully formalised, or when approvals, instructions or behaviours deviate from the contract’s formal terms.
For more on how the Superintendent role sits alongside the client-side PM function, see what does a client-side project manager do in Australian property development and capital works.
The best project teams know how to balance relationships while administering the contract (and not keeping it in the bottom drawer!).
Project managers and superintendents may underestimate how small decisions - an informal approval here, a missed notice there - can shift how a contract is interpreted later on. It might seem confrontational at times to execute a contract to the letter. Yet, when a contract is administered consistently and transparently, it helps prevent disputes before they even start.
Waiver in Australian construction contracts occurs when a party gives up or stops enforcing a contractual right, either explicitly or through repeated conduct that signals they are not insisting on it. A common example is repeatedly accepting verbal variation approvals when the contract requires written sign-off. Once a pattern of waiver is established, the party who waived may lose the ability to later enforce the formal requirement.
Estoppel is a legal principle that prevents a party from going back on a promise, representation, or course of conduct if the other party has relied on it to their detriment. In construction, it arises when a contractor acts on an owner's informal assurance (mobilising resources, incurring costs) and the owner then attempts to resile from that position. For the doctrine to apply, there must be a promise or representation, reliance by the other party, and a loss resulting from that reliance.
Waiver involves a party voluntarily giving up a right they hold under the contract, often through consistent behaviour rather than a formal decision. Estoppel operates differently: it arises when one party makes a promise or representation that the other party relies on to their detriment, and it would be unconscionable to allow the first party to resile from it. Both doctrines can shift a party's legal position without any formal agreement, which is why consistent contract administration matters.
Project managers can avoid unintentional waiver by administering the contract consistently from the outset, following the formal processes for variation approval, notices, and instructions, even when informal arrangements might seem more convenient. Where a deviation is genuinely necessary, it should be documented in writing with both parties acknowledging it is a one-off. The risk of waiver is highest when informal workarounds become a pattern rather than a deliberate, recorded exception.
For more on how Projx supports cost forecasting and budget management across property development and capital works programs, see how owner-side project teams use Projx
Last updated on August 9, 2026
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