(Dissenting):
I would reverse the ruling of the trial court. The original divorce decree in this case was entered on the basis of a stipulation prepared by respondent and signed by both parties. It provided for joint custody of the parties’ two minor children, with appellant having primary custody for nine months of the year and respondent having primary custody for three months during the summer, with both periods including reasonable visitation for the noncustodial spouse.
In support of his motion for an order to show cause respecting modification of custody, respondent alleged the following changes in circumstances: that appellant intended to leave the state of Utah (this allegation was withdrawn prior to the trial); that appellant had become physically and emotionally unable to care for the ehil-*512dren; that the emotional health of the children had deteriorated and they were depressed; that the children wanted to live with respondent and his new wife; and that appellant had had two affairs since the divorce whereas respondent had remarried and could provide a stable home.
In appellant’s affidavit in support of her motion for modification of support, custody, and visitation, she alleged changes in her income, a change in respondent’s working shifts which affected the time he was available to be with the children, and the assertion that “the constant changing of the children has resulted in a circumstance which is not in their best interests.”
At the outset of the trial, appellant’s counsel made a motion to bifurcate the proceedings to permit an initial hearing on the existence of a substantial change requiring re-evaluation of custody pursuant to Hogge v. Hogge, Utah, 649 P.2d 51 (1982). The trial judge denied that motion, ruling instead that there had been a prima facie showing of substantial change through the submission of custody evaluations conducted by a psychologist and a social worker and through the allegations regarding changed circumstances in appellant’s own affidavit. I believe that ruling was erroneous. A review of the evaluations in question and appellant’s affidavit shows that none of them contain any facts or admissions supporting the alleged changes in circumstance which were relied on by respondent in his petition for a change of custody.1
The trial court in this case misconstrued the purpose and intent of our holding in Hogge. We have recently had an opportunity to clarify and amplify the significance of that ruling in Becker v. Becker, Utah, 694 P.2d 608 (1984). In Becker, 694 P.2d at 610, we referred to the threshold requirement from Hogge that the party seeking modification demonstrate that there have been “changes [since the time of the previous decree] in the circumstances upon which the previous award was based” and that the changes are “sufficiently substantial and material to justify reopening the question of custody.” Hogge, 649 P.2d at 54. We then emphasized that:
[t]he asserted change must, therefore, have some material relationship to and substantial effect on parenting ability or the functioning of the presently existing custodial relationship....
... The materiality requirement is designed to help the court decide if there is a valid reason to reopen a question already settled by an earlier order.... In other words, if the circumstances that have changed do not appear on their face to be the kind of circumstances on which an earlier custody decision was based, there is no valid reason to reconsider that decision. The rationale is that custody placements, once made, should be as stable as possible unless the factual basis for them has completely changed.
Becker, 694 P.2d at 610.
Stability and continuity in placement have pre-eminent importance in child custody cases. The evidence relied on by the trial judge in this case addressed the relative skills and judgment exercised by each of the parties in their parenting activities and the relative desirability of the home environments they are able to provide. It did not show that the existing custodial arrangement had undergone changes since the divorce of a kind which would justify reopening the custody question. It is true that respondent alleged that such changes had occurred in his motion and affidavit, but he was never required by the trial judge to prove their existence and magnitude. Absent such proof, and a finding based thereon, it was error for the court to *513consider and order a modification of custody.
I believe that the majority opinion fails to further this Court’s commitment to stability and security in the custodial placement of Utah children subjected by their parents’ actions to the supervision of the divorce courts.2 It was the clear intent of our ruling in the Hogge case to discourage unwarranted or lightly undertaken efforts to change custodial placements. It is appropriate and necessary that any person seeking to disrupt an established pattern of caretaking and parent-child relationships be required to satisfy stringent requirements and meet a heavy burden of proof. The trial court’s denial of the motion for a hearing on the question of changed circumstances in this case improperly exempted respondent from that obligation.
STEWART, Justice, having disqualified himself, does not participate herein. SCOTT DANIELS, District Judge, sat. ZIMMERMAN and DURHAM, JJ., dissent from the denial of the petition for rehearing.. Respondent relies on the claim that appellant’s affidavit states that "there has [sic] been several substantial changes in circumstance.” Her language was to that effect, but the most cursory reading of her affidavit shows that it contained no admissions or concessions whatsoever regarding the changes alleged by respondent. Appellant’s assertions for changes in primary custody went to the disruptive effect on the children of the current arrangements, whereas respondent was alleging a deterioraron of the children's mental health and a breakdown in appellant’s ability to care for them.
. I endorse the discussion of stability of placement contained in Justice Zimmerman’s concurring opinion, but suggest that his opinion, like the main opinion, reaches an incorrect result. Although he notes that "if the facts show a degree of stability in the children’s actual living arrangements approaching that normally incident to one-parent custody, then the trial court should accord those arrangements a great deal of weight,” the original custody order in this case gave custody to appellant for nine months of each year and to respondent for three months. That arrangement is very similar to normal one-parent custody awards which follow the typical school year, and there was no justification in this record for disrupting it.