Most family lawyers have used a joint expert at some point. Fewer have a clear sense of when joint retainers advance a file and when they create more problems than they solve. The difference matters. A well-managed joint retainer saves money, narrows issues, and moves files toward settlement. A poorly managed one generates motion after motion, escalates costs, and poisons settlement prospects.
Understanding where the line sits between those outcomes is not intuitive. It requires familiarity not only with the Family Law Rules, but with how courts apply them and how joint expert retainers operate in practice. This article unpacks the framework under Rules 20.1 and 20.2 of the Family Law Rules, flags the circumstances where joint retainers make sense, and identifies the practical problems that derail them.
The Rules: What They Actually Say
Rule 20.1 lets parties jointly retain an expert. Cost-sharing, joint instructions, one report to both sides simultaneously. Simple enough in theory. Rule 20.2 covers both jointly-retained experts and experts retained by one party. For jointly retained experts, it sets timelines, content requirements, and the expert’s acknowledgment of duty.
The difference between joint and party-retained experts is control. Party-retained experts take instructions from one side. They are vulnerable to allegations of bias, real or perceived. Joint experts get instructions from both parties and owe duties equally to each. One expert instead of two means lower costs. It also means, at least theoretically, that the court gets neutral evidence instead of a battle of competing methodologies.
Why Joint Retainers Can Be Beneficial
Cost
One expert instead of two. One set of fees instead of parallel retainers reviewing the same records, running the same analyses, preparing competing reports. For straightforward income attribution or modest business holdings, the savings are significant.
Credibility
Courts prefer neutral opinions. When there is no competing expert to cross-examine against, the joint expert’s conclusions carry weight. Judges are not forced to pick between dueling methodologies or to reconcile divergent assumptions.
Discipline
Joint instructions force transparency. Clients cannot whisper favourable assumptions into the expert’s ear or shop for predetermined conclusions. Both parties contribute to the mandate. That process often narrows the real issues and creates settlement pressure once the report arrives.
Alignment with the Rules
The primary objective of the Family Law Rules is to enable the court to deal with cases justly. Taking steps to control costs through joint retention is consistent with that objective, as it promotes fairness between the parties, and reduces expense and delay.
When to Use Them (and When Not To)
Joint retainers thrive on cooperation. If parties are genuinely trying to resolve financial matters efficiently, and the valuation issues are relatively straightforward, go joint. A professional corporation with clean books, minimal loans, and no contested goodwill? Perfect candidate. Salaried employee with bonus structures or stock compensation? Same.
They fail when parties are at war. If there are allegations of hidden income or asset diversion, forget it. The expert will be caught between irreconcilable instructions -- one side demanding forensic-level scrutiny, the other crying overreach. The report either addresses nothing or satisfies no one.
They also struggle with embedded legal issues. If the income characterization turns on an unsettled legal question -- personal versus corporate income, for instance -- a joint expert may lack the mandate to resolve it. Party-retained experts, each working under assumptions aligned with their client’s legal position, may better serve the litigation.
Business complexity matters too. A multinational with inter-corporate transactions, offshore holdings, and layered structures? That requires expert analysis tailored to competing theories of value. Forcing it into a joint retainer produces a report that satisfies neither side and gives the court limited help.
The Operational Rules: Three Keys
Understanding how joint retainers function requires familiarity with three subrules of Rule 20.2:
Rule 20.2(9) – Motion for Directions
If parties want or are required to engage a joint expert but cannot agree on something related to the engagement, either party can bring a motion for directions. This includes disputes about scope, cost-sharing, or finalization. The provision exists to resolve engagement disputes before they derail the entire process. Use it when negotiations break down over the expert’s mandate, fee allocation, disclosure requirements, or whether the report should be finalized.
Rule 20.2(12) – Cooperation
Parties who engage a joint expert must cooperate fully and make full and timely disclosure of all relevant information and documents to the expert. The court may draw any reasonable inference from a party’s failure to do so. This is not optional; it is a mandatory obligation with consequences for non-compliance.
The cooperation requirement means more than just responding to the expert’s requests. It means proactive disclosure of relevant materials, timely responses to inquiries, and good faith engagement throughout the process. When one party fails to cooperate, the court can infer that undisclosed information would be unfavourable to that party or draw other adverse inferences that effectively penalize the non-compliant party.
Rule 20.2(13) – Restriction on Other Experts
If a joint expert provides opinion evidence on an issue for a party, no other expert may present opinion evidence on that issue for that party unless the court orders otherwise. This is the enforcement mechanism -- once you have gone joint, you cannot unilaterally bring in your own expert. The restriction applies once the joint expert has provided “opinion evidence” -- meaning once the expert has formed and communicated conclusions on the issue. At that point, introducing competing expert evidence requires a court order, and as discussed below, courts are deeply reluctant to grant such orders.
These three provisions work together to create a structured process with real teeth. Rule 20.2(9) provides a mechanism to resolve disputes during the engagement. Rule 20.2(12) imposes mandatory obligations on both parties to ensure the expert has what they need. Rule 20.2(13) prevents parties from treating the joint process as provisional or using it as reconnaissance before calling their own expert. Understand how these provisions interact, because they define both the opportunities and the constraints of joint retainers.
What the Caselaw Tells Us
Two fairly recent decisions illustrate what happens when joint retainers go sideways: Numair v. Numair, 2022 ONSC 3449, and Zantingh v. Zantingh, 2021 ONSC 7959.
In Numair, a self-represented litigant spent years challenging a joint business valuator’s assessment of her husband’s Pizza Pizza franchise and income. Voluminous disclosure. Multiple opportunities to raise concerns. Clear explanations from the expert at trial. She rejected all of it. Tried to bring in a second valuator without a proper critique report. Kept alleging hidden income and assets without evidence.
Justice Himel shut it down. The joint expert process exists “to avoid the battle of competing experts.” Once the joint expert provides opinion evidence on an issue, you cannot call another expert on that issue without a court order under Rule 20.2(13). You get to raise concerns during drafting. Once you have exercised that opportunity and the report issues, you are done. Disliking the outcome does not justify bringing in competing experts. The court gave significant weight to the expert’s credibility and methodology, noting he had addressed the Applicant’s concerns repeatedly and made adverse findings where documentation was missing.
The decision also applied Rule 20.2(12)’s cooperation requirement. The valuator was ultimately satisfied with the Respondent’s disclosure and made adverse findings where documents were unavailable. The court noted that “reasonable reliance on the expert’s experience and thoroughness is appropriate.” A party cannot simply claim they do not trust the other party’s disclosure without evidence of actual deficiency.
Zantingh dealt with a motion for directions under Rule 20.2(9). The Applicant refused to approve joint valuation reports prepared two years earlier. Her reasons: incomplete disclosure, distrust of the Respondent’s information, missing appraisals. Justice Raikes rejected indefinite delay based on generalized suspicion. The court imposed a structure: raise specific concerns within a defined timeframe, the expert considers them and advises whether revisions are warranted, and if not, the reports are final.
The key point from Zantingh: you cannot sabotage a joint retainer by declaring you “do not trust” the other side’s disclosure. Rule 20.2(12) requires full cooperation and timely disclosure, and the court can draw adverse inferences from failures to comply. “Reasonable reliance on the expert’s experience and thoroughness is appropriate.” If new information surfaces later, through cross-examination or further disclosure, provide it to the expert for a supplementary report. Alternatively, you could seek a court order under Rule 20.2(13) permitting competing expert evidence. But that order is not automatic.
The principles: Rule 20.2(12) requires parties to cooperate and disclose fully -- courts will draw adverse inferences from non-compliance. Once you have had the chance to raise concerns during drafting, you cannot delay finalization indefinitely based on vague objections. If there is a dispute about the engagement process, use Rule 20.2(9) to bring a motion for directions. Courts will not let you treat the joint process as a warm-up before bringing in another litigation expert under Rule 20.2(13). Allegations of hidden assets or unreported income need evidence -- suspicion is not enough. An unfavourable valuation does not mean the expert’s work is deficient.
The High Bar for Competing Expert Evidence
Judges are deeply reluctant to permit competing expert evidence after parties have jointly retained an expert. This reluctance is not arbitrary -- it reflects core policy objectives embedded in the Family Law Rules and the entire joint expert framework.
First, permitting competing experts defeats the primary purpose of joint retainers. As Justice Himel emphasized in Numair, the “predominant purpose of retaining a joint expert is to avoid the battle of competing experts” and the time and expense associated with same. If courts routinely granted orders under Rule 20.2(13) allowing parties to call their own experts whenever dissatisfied with joint expert conclusions, the joint retainer process would become meaningless. It would devolve into mere reconnaissance, parties would use the joint expert to preview the issues, then commission their own favourable opinions for trial.
Second, judicial resources are finite. Case management judges scrutinize trial time, litigation budgets, and proportionality with increasing rigor. Allowing competing experts on the same issue doubles preparation time, lengthens trials, increases costs, and consumes scarce judicial resources adjudicating between dueling methodologies. Where parties have voluntarily agreed to a joint process intended to avoid that outcome, courts may view requests to introduce competing litigation experts with skepticism and will require compelling justification before permitting it.
Third, the framework already provides procedural safeguards. Parties have the opportunity, indeed, the obligation under Rule 20.2(12), to provide full disclosure to the expert during the engagement. They have the right to raise questions and concerns with draft reports before finalization. They can bring motions under Rule 20.2(9) for directions if disputes arise during the engagement. They can cross-examine the joint expert at trial. These mechanisms allow parties to test the expert’s work, challenge assumptions, and identify deficiencies. A party who fails to use these tools effectively cannot later claim the joint expert’s work is so deficient that competing evidence is required.
Fourth, dissatisfaction with outcomes is not grounds for relief. Courts understand that every expert report will favour one party over the other. If unfavourable conclusions were sufficient to obtain an order under Rule 20.2(13), every losing party would seek competing evidence. The restriction in Rule 20.2(13) would be toothless. As Numair demonstrates, courts will not permit a party to reject a joint expert’s conclusions simply because the numbers do not align with that party’s expectations or beliefs about hidden income, undisclosed assets, or improper valuations. Evidence, not suspicion, is required.
What will move a court to grant an order permitting competing evidence? Material deficiencies that could not reasonably have been identified or addressed during the joint expert process. Examples might include: the expert relied on factually incorrect information that came to light only after the report was finalized; the expert applied a fundamentally wrong methodology that renders the opinion unreliable; circumstances changed materially after the report such that the opinion no longer reflects current reality; or new evidence emerged post-report that the expert could not have considered and that fundamentally undermines the opinion’s foundation.
But even in these circumstances, the threshold is high. The moving party should demonstrate not merely that the joint expert made errors or used debatable assumptions, but that the opinion is so materially deficient that proceeding to trial without competing evidence would result in manifest injustice. Courts could consider whether the deficiency can be addressed through supplemental reporting by the joint expert, through effective cross-examination at trial, or through other means short of introducing an entirely new expert.
In practice, orders under Rule 20.2(13) are rare. The message from the bench is clear: if you agree to a joint retainer, you are bound by that choice. Manage the engagement properly, ensure full disclosure, raise concerns during drafting, and prepare to live with the result. Treating a joint expert as provisional or optional is not an acceptable litigation strategy.
Where Things Go Wrong
Disagreement over conclusions
Party gets an unfavourable report and wants out. Challenges methodology, disputes assumptions, tries to introduce contradictory evidence. This runs straight into Rule 20.2(13) -- if the joint expert has provided opinion evidence on an issue, no other expert may present opinion evidence on that issue unless the court orders otherwise. You would need to show material deficiency or changed circumstances. “I do not like the number” will not cut it.
Fee disputes
Joint retainers contemplate cost-sharing, but fights erupt over scope, additional work one party requested, unforeseen complexity. If one side refuses to pay, the expert may stop work. The other party either funds the whole thing or abandons ship. If parties cannot agree on something relating to the engagement, Rule 20.2(9) permits a motion for directions. Clear retainer agreements matter -- specify cost allocation, billing protocols, dispute resolution mechanisms.
Disclosure problems
One party provides incomplete financial disclosure, and the expert’s opinion is built on an inadequate information. Rule 20.2(12) requires parties to cooperate fully and make full and timely disclosure to the expert -- and the court may draw adverse inferences from failure to comply. The prejudiced party can raise the incomplete disclosure with the expert during drafting, bring a motion under Rule 20.2(9) for directions, or seek a court order under Rule 20.2(13) to call their own expert. Concerns should be stated clearly and specifically, as courts may treat disclosure challenges as collateral attacks on the joint process. Better to embed robust disclosure obligations in the retainer terms upfront and get the expert’s confirmation that all necessary information has been provided.
Perceived bias
Expert’s report heavily favours one side. The losing party alleges improper influence, misunderstood instructions, exceeded mandate. Hard to prove, usually reflects disappointment rather than legitimate grievance. Cross-examining your own joint expert at trial requires care -- test the opinions adverse to your client without appearing to attack your own witness.
How to Actually Do This
Assess the file first
Is this a case where cooperation is realistic? Parties entrenched? Allegations of misconduct? Genuinely complex and contested valuations? If yes to any of those, a joint approach may cause more problems than it solves. But if the financial picture is reasonably transparent and parties want to control costs, go joint.
Getting the Other Side to Agree
Offer three qualified experts, together with their credentials and fee information, and invite the other side to choose one or respond within a specified timeframe. If agreement does not follow, raise the issue at a conference. Courts often encourage joint experts and may formalize the selection process in a court order. Frame the proposal around cost control, efficiency, and narrowing the issues for trial.
Structuring the Joint Retainer
A joint retainer should spell out the expert’s mandate, documents to review, issues to address, methodology. Address cost-sharing explicitly -- who pays for what, what happens if there is additional work, how disputes get resolved. Make clear that Rule 20.2(12) requires full cooperation and timely disclosure, and that the court can draw adverse inferences from non-compliance. Require the expert to confirm they have everything they need before finalizing the report.
Build in a finalization process
Zantingh shows what happens when this is ambiguous -- delay and obstruction. Have the expert specify in the retainer: parties get 30 days to raise concerns with draft reports, expert responds in writing, and absent material revisions, the report becomes final. If parties disagree on finalization or other matters relating to the engagement, either can bring a motion for directions under Rule 20.2(9). No indefinite hostage-taking.
Get full disclosure before substantive work begins
Numair illustrates the cost of piecemeal disclosure: endless requests, escalating fees, erosion of trust. Where one party controls the financial information, corporate records, shareholder agreements, inter-company transactions, get court orders early. Include timelines and consequences for non-compliance. Rule 20.2(12) mandates full cooperation and disclosure, and courts will draw adverse inferences from failures. Do not let the expert start valuation work on an incomplete record.
Set client expectations early
The joint expert is not “theirs.” The opinion may go against them. Challenging it is procedurally difficult and strategically risky. Under Rule 20.2(13), once the joint expert provides opinion evidence on an issue, no other expert may present evidence on that issue unless the court orders otherwise. The threshold for getting that court order is high. Being unhappy with the result is not grounds for rejection. Say this clearly at the outset -- it prevents the post-report battles seen in Numair.
Frontload questions and concerns
Both cases emphasize this: raise substantive concerns during drafting. Do not wait until finalization to challenge methodology, request more analysis, or point out gaps. Once the expert has responded and issued a final report, courts will not be sympathetic to arguments you could have raised earlier. Use the draft review period effectively.
If disputes arise during the engagement, use Rule 20.2(9)
Cannot agree on scope? Cost-sharing breakdown? Disputes about what disclosure is required? Bring a motion for directions rather than letting the issue fester. The rule exists to resolve these disputes before they derail the entire process.
If the report is final and you need to challenge it, understand the standard
Courts are deeply reluctant to grant orders under Rule 20.2(13) permitting competing expert evidence. The bar is deliberately high. You need material deficiencies -- factually incorrect information discovered post-report, fundamentally wrong methodology, material changes in circumstances, new evidence that undermines the opinion’s foundation. Even then, courts will consider whether the problem can be addressed through supplemental reporting by the joint expert or effective cross-examination at trial. “The expert used debatable assumptions” or “the expert made errors” will not suffice.
You need to show the opinion is so deficient that proceeding without competing evidence would result in manifest injustice. Frame your motion narrowly, support it with concrete evidence, and be prepared for skepticism. Orders under Rule 20.2(13) are rare because they defeat the entire purpose of joint retainers.
Do not bring in parallel valuations without a court order
If you get a second valuation without an order under Rule 20.2(13), it may be inadmissible and the costs irrecoverable. Worse, it signals bad faith and invites cost consequences. If genuinely concerned about the joint expert’s work, seek the court order before spending money on another expert.
Recognize that judicial patience is limited
Both Numair and Zantingh involved parties delaying finalization, withholding approval, or challenging reports based on vague objections rather than concrete deficiencies. Both courts responded with clear direction, cost consequences, and findings that the obstructive party was responsible for the delay. Family law litigation already suffers from excessive cost and delay. Adding to it through misuse of the joint expert process gets you cost orders and judicial criticism.
Key Takeaways
Rules 20.1 and 20.2 structure how expert evidence works in family law. Joint retainers offer real benefits: lower costs, neutral evidence, settlement pressure. But they are not appropriate for every file. Know when cooperation will serve your client and when it will not. Understand the benefits and the failure modes. Structure the engagement properly upfront. Manage client expectations. Raise concerns during drafting, not after finalization.
Most importantly, understand that courts treat joint expert retainers seriously. Once you have agreed to the process, judges are deeply reluctant to let you bring in competing evidence under Rule 20.2(13). The joint expert’s conclusions carry significant weight, and the procedural safeguards, disclosure obligations, draft review, cross-examination, are considered sufficient to protect parties’ interests. If you choose a joint retainer, you are committing to live with the result absent significant and demonstrable deficiencies in the process.
The key: know the Rules, know your file, know when a joint expert clarifies the issues versus when it creates more problems. That distinction often determines whether you settle or end up in a costly trial fighting about the expert rather than the underlying dispute. And if you do go joint, manage it properly, because getting out of that choice later is nearly impossible.
