How Is Unjust Enrichment Defined?
Unjust Enrichment Involves An Unfair Gain for Someone With a Corresponding Loss to Someone Else Without a Proper Legal Reason.
Understanding the Principles of Unjust Enrichment and Quantum Meruit Within Construction Law Cases
The legal cause of action, meaning a formal reason for suing, known as unjust enrichment arises in equity (fairness) law; and while a Defendant may have engaged in some form of wrongful conduct, fault or blame are generally unnecessary for a successful unjust enrichment case brought by a Plaintiff.
Additionally, the applicable circumstances for legal cases involving unjust enrichment can arise within many areas of law including, among others, common business matters, family law cases, and as discussed below very frequently arise within construction law proceedings.
As per Iacobucci J. for the Supreme Court of Canada in Garland v. Consumers Gas Co.,  1 S.C.R. 629 the elements of unjust enrichment were well summarized whereas it was said:
As a general matter, the test for unjust enrichment is well established in Canada. The cause of action has three elements:
1. An enrichment of the defendant;
2. A corresponding deprivation of the plaintiff; and
3. An absence of juristic reason for the enrichment ...
The first two elements are often obvious and therefore easily demonstrated. Simply stated, did the defendant receive a benefit; and if so, did this benefit occur at the expense of the plaintiff? The third element, "absence of juristic reason" may be challenging to demonstrate in certain circumstances.
Frequently Occuring Situations
In the construction law context, unjust enrichment tends to arise where a contractor and property owner enter into an agreement involving certain project specifications and then subsequent project specification changes alter the original agreement so significantly that the original pricing agreed to becomes irrelevant. For example, a handyman type contractor is hired to build a backyard deck for the cost of materials plus fifty dollars per hour for labour a "cost-plus" contract. While the work is underway, the homeowner becomes very impressed and asks the contractor to add a 10' x 10' gazebo. Unfortunately, when this type of situation happens, all too often, the homeowner and contractor fail to discuss and agree to pricing for the new aspects of the project. In such a circumstance, it may be perceived by both laypersons and some lawpersons that the existing agreement of cost of materials plus fifty dollars per hour persists; however, this is incorrect - the law avoids operating so as to create a contract where a contract was absent. Accordingly, in this example situation there is a contract for the deck project but no contract for the gazebo project; thus, if the homeowner fails to make proper payment for the deck project the contractor may sue for breach of contract but no similar right to sue for breach of contract will exist if the homeowner fails to may proper payment for the gazebo project. It is obvious to people of common sense that the contractor requires fairness with some equitable right of action action for payment on the gazebo project. This right of action arises as a claim for unjust enrichment.
As mentioned earlier, the third element in proving a case of unjust enrichment requires the absence of a juristic reason that might otherwise negate the legal obligation for the plaintiff to receive restitution from the defendant for the received benefit. This essentially means that the received benefit must be an unjustly received benefit.
There are juristic reasons from established categories which may bar a plaintiff from recovering restitution from the defendant including:
- A contract whereas if a contract truly exists then the contract takes precedence - the law of unjust enrichment is intended only to fill the gap where a contract is absent;
- A disposition of law where a juristic decision was previously reached;
- A donative intent where the received benefit was intended as a gift but the giver subsequently seeks payment; and
- A common law or equitable law or statutory law reason such as unlawfulness.
The fourth category above may be best understood by using altering our example from above and consider a situation where a marijuana grow-op was built for the homeowner instead of a gazebo. In such a situation, it is highly unlikely that the contractor would succeed if suing the homeowner for receiving the benefit of a grow-op. It is obvious and sensical to most common sense thinking people that courts will avoid rewarding someone for doing something blatantly unlawful.
A further situation that often arises in the construction context is where a homeowner and contractor enter into an under-the-table agreement for the purpose of avoiding taxes on the project. Although an agreement was reached per se, the terms of the agreement were unlawful and therefore a legally enforceable contract fails to exist. Without the agreement being deemed a legally enforceable contract, neither the homeowner or contractor may sue for breach of contract. In these circumstances, the courts will often frown on the arrangement; however a claim for unjust enrichment may be successful as the courts appear to view avoidance of taxes in a somewhat softer manner than the blatantly unlawful grow-op example described above.
Another situation can occur where an apparent contract was entered into; however, one of the parties was legally non-existent such as when the wrong name was entered upon the contract documents. The availability of and intention of unjust enrichment was explained Juddav Designs Inc. v. Cosgriffe, 2010 ONSC 6597 where it was said:
 The remedy of unjust enrichment is available where a benefit is conferred on one party at the expense of another party in the absence of any contractual obligation to pay.
As per the above example, the law avoids creating a contract where a contract was absent. Of course, without a contractual agreement, the issue of establishing a fair price arises. The issue of fair price is resolved by the law of quantum meruit. A very loose translation from Latin is simply quantum of merit or even simpler, the amount that it is worth. Accordingly, our gazebo building contractor from the example above should receive the fair market rate for gazebo building. If this fair market rate is one hundred dollars per hour, so be it. Again, the law will avoid presuming that the homeowner and contractor would have agreed to the same rate for the gazebo project as was previously agreed to for the deck project. Of course, this could also go the other way to the benefit of the homeowner if the fair market rate for gazebo building is less than the previous rate agreed to for the deck work. It is notable that the quantum meruit should be based on the value to the customer rather than the time and material expense to the contractor; R. v. Wallberg, 44 S.C.R. 208.
The applicable legal principles of quantum meruit were well explained in the case of 2002759 Ontario Ltd et al. v. Koropeski et al., 2021 ONSC 7873, wherein it was stated:
 If there is an express or implied agreement for extra work, but no price is agreed upon for the performance of the work, there is no contractual basis for a contractor to claim for the work performed, but the court may imply a promise to pay a reasonable amount on a quantum meruit basis: See D & M Steel Ltd. v. 51 Construction Ltd., 2018 ONSC 2171 (CanLII), at para. 58.
 The party claiming quantum meruit must establish that they have conferred a benefit to the other party, that the conferring party suffered a corresponding deprivation, and there is no juristic reason for the deprivation.
 The onus is on the contractor to prove both the existence and the value of the extra work or risk not recovering: See Barenco Inc. v. Ottawa-Carleton Regional Transit Commission (1999), 48 C.L.R. (2d) 200 (ONSC) at para. 27, and D & M Steel Ltd., at para. 93.
 The payment sought must be reasonable remuneration. For the assessment of reasonable remuneration, expert evidence is often desirable but not necessary: See Hugh’s Contracting Ltd. v. Stevens, 2014 BCSC 1904 (CanLII), at para. 84, reversed on other grounds at 2015 BCCA 491 (CanLII).
 The court must do the best it can in determining a fair and reasonable fee for the service provided, by assessing what it was worth having regard to the relevant circumstances. Some factors to consider in valuing a quantum meruit claim include the course of dealings between the parties, any estimates obtained, the costs incurred, the scope of work, the actual work done, and the market value of the services provided: See Hugh’s Contracting Ltd. v. Stevens, 2015 BCCA 491 (CanLII), at para. 33.
An unjust enrichment may occur when one person gains at the expense of another person and without a legal reason such as a contractual agreement. The aspect of being "unjust", or legally unfair, requires that a justifiable reason for the unfairness is lacking. While unjust enrichment concerns can arise in many situations, the principle is common to construction disputes. For example, when a bottom line price for a construction contract is established, without milestones for progress payments, an agreed upon price is lacking for partial work and it would unjust for a lack of fair payment if the construction work is terminated before completion. To determine the amount due for the work completed, so to avoid an unjust enrichment to either the project owner or the contractor (if the contractor received payment for more than the value of the work completed), an assessment of the quantum meruit is required.