dissenting.
I would reverse and remand for further proceedings because, on the present record, I cannot conclude that Ms. Killing-ham, the tenant, was not harmed by the dismissal of her claim for housing code violations resulting from the late amendment to the landlord’s complaint permitted by the trial court and by the trial court’s refusal to consider the tenant’s claim that, as a disabled person, she was unlawfully denied access to the apartment building’s recreational pool area.
1. The Dismissed Claim of Housing Code Violations.
The landlord was permitted to amend its complaint so as to exclude a demand for back rent on a unit in the same building that Ms. Killingham had occupied immediately before she moved into the unit from which the landlord sought to evict her. As a result, Ms. Killingham’s counterclaims for housing code violations related to that previous unit were dismissed. The trial court allowed the late amendment to the landlord’s complaint believing that the tenant benefited from the fact that, as a result of the amendment, she would not be hable for back rent due on the unit she ■previously occupied. Notably, the trial court also was of the view that, if she wished, Ms. Killingham could file the dismissed counterclaims in an independent action against the landlord. As the majority recognizes, the trial court was in error in this respect, because Ms. Killingham’s claims were time-barred if she filed an independent action against the landlord.1
It is important to remember the framework for our appellate review. Where the trial court gives a reason for its ruling, we review the trial court’s decision on the basis on which it was made. See District of Columbia v. Shannon, 696 A.2d 1359, 1367 (D.C.1997) (“Although we may affirm a trial court’s exercise of discretion when the trial court has provided no explanation, we ordinarily must reverse an otherwise sustainable exercise of discretion if the trial court’s ruling is manifestly based on ‘erroneous legal thinking.’ ”) (citations omitted). If we determine that the trial court’s ruling was based on an erroneous premise, it is our appellate role to reverse; we may affirm only if we determine that *812the trial court’s error was harmless to Ms. Killingham, see Johnson v. United States, 398 A.2d 354, 366-67 (D.C.1979), or if, on the record, the trial court had no option but to rule as it did. See Shannon, 696 A.2d at 1367.
No one contends that the trial court’s only option in this case was to allow the landlord to amend its complaint and dismiss Ms. Killingham’s related housing code claims. It is also clear that the trial court’s reasoning was erroneous because, contrary to the trial court’s view, the tenant’s dismissed claims were time-barred. Such an error in a significant component of the trial court’s consideration would constitute abuse of discretion requiring reversal unless we can determine on appeal that the tenant was not prejudiced as a consequence. See Johnson, supra, 398 A.2d at 366-67. In this ease, that determination requires an evaluation of the dismissed claim for housing code violations with respect to the apartment previously occupied by the tenant.
The majority reasons that the jury’s verdict shows that Ms. Killingham was not harmed by the fact that she lost her claim of housing code violations in the first unit she occupied. In an after-the-fact analysis, the majority estimates roughly how much the jury would have awarded the tenant for the lost claim, based on the amount the jury awarded the tenant for the “same” housing code violations during a longer period that she occupied the second unit (the one from which she was evicted). Then, the majority concludes that the amount it estimates Ms. Killing-ham may have “lost” in her dismissed counterclaims with respect to the first unit, she more or less made up with the back rent due on that unit that the landlord forwent when it amended its complaint.
I disagree with the majority that the record supports that Ms. Killingham was not harmed by the loss of her claim with respect to the first unit she occupied in the building. The rough calculation of damages that the majority estimates Ms. Kill-ingham would have been awarded had her housing code violations not been dismissed suggests appellate fact-finding. Moreover, on appeal, the issue is not whether the ruling would cause undue prejudice, a proper factor in the trial court’s initial discretionary judgment,2 see Blake Constr. Co. v. Alliance Plumbing & Heating Co., 388 A,2d 1217, 1220 (D.C.1978), but whether the trial court’s erroneously-based ruling was harmless. See Johnson, supra, 398 A.2d at 367 (“[T]he reviewing court must weigh the severity of the error against the importance of the determination in the whole proceeding and the possibility for prejudice as a result.”) (emphasis added). Here, the trial court was wrong in believing that the dismissed claim could be brought in a separate action, and, as .dismissal eliminated the claim altogether, there is possible prejudice unless the tenant’s claim has no value.3
*8132. The Disability Claim.
Ms. Killingham contended that she was prevented from using a common area of the building to which she was entitled under her lease, the pool area, because the landlord unlawfully faded to provide wheelchair access, as required by D.C.Code § 6-1706 (1995). This is a violation she claims existed throughout the time she occupied two different units in the building. The trial court did not permit that claim to be considered by the jury as a possible offset against her rent obligations with respect to either of the units she occupied.4
The majority concludes that even though it interprets section 6-1706 as requiring that the landlord provide full access for disabled persons to a “housing accommodation,” the tenant’s claim that there was no wheelchair access to the pool area is not a proper defense to a suit for possession and back rent under Superior Court Landlord & Tenant Rule 5(b). The majority does not support this conclusion other than by reference, without explanation, to the caveat in section 6-1706(e) that a landlord is not required to “modify his property in any way or to provide a higher degree of care for a ... physically disabled person than for a person who is not physically disabled” — a general provision that would apply equally if there had been no wheelchair access to the apartment building or to the apartment unit itself. However, the majority appears to support the trial court’s determination, correct in my view, that lack of wheelchair access to the apartment building constitutes a proper defense, for a tenant who uses a wheelchair, in a Rule 5(b) proceeding for back rent. Although I agree that a summary proceeding under Rule 5(b) is not the place to determine the scope of the landlord’s obligation under section 6-1706(a), as modified by (c), I disagree with the majority that if it were determined that the law required wheelchair access to the pool area, the lack of such access would not be a defense for a disabled person using a wheelchair in a Rule 5(b) proceeding.5 Housing code violations to “common areas” are properly asserted as a defense in a summary proceeding, see Javins v. First Nat’l Realty Corp., 138 U.S.App. D.C. 369, 380-81 & n. 62, 428 F.2d 1071, 1082 & n. 62 (1970), and presumably the apartment building’s recreational pool area is an area provided for the common use of the tenants. Moreover, in Shin v. Portals Confederation Corp., 728 A.2d 615 (D.C.1999), this court appears to have expanded somewhat the traditionally narrow view of the type of defense that a tenant may assert in a summary Rule 5(b) proceeding by requiring, on pain of preclusion, that a tenant must assert as a defense claims for damages to the lessee’s business resulting from the landlord’s breach of a commercial lease. See id. at 618-19. To the extent that the majority reasserts the narrow scope of defenses permissible in a Rule 5(b) proceeding, I welcome it. See id. at 621-22 & n. 5 (Ruiz, J., dissenting).6
*814For the foregoing reasons, I do not agree that the tenant has not been harmed by the trial court’s dismissal of her unap-praised, uncompensated, and time-barred housing code claims with respect to the unit she previously occupied, and her related claim of lack of wheelchair access to the common pool area. I would reverse and remand the case for further proceedings, at which time the trial court could develop the record and, if appropriate, determine whether Ms. Killingham suffered harm from the loss of those claims.7 If she was harmed, she must be allowed to proceed, if she desires, with the substance of her claims against the landlord.
. The trial court could have ensured that Ms. Killingham would have been able to file her complaint by conditioning the landlord’s amendment on waiver of a statute of limitations defense, akin to the procedure used when a case is dismissed for forum non conve-niens. Cf. Guevara v. Reed, 598 A.2d 1157, 1160 (D.C. 1991) (noting that availability of alternative forum is a requirement before case is dismissed for forum non conveniens ).
. Even though it may have been proper for the trial court to have engaged in a fairly rough appraisal of Ms. Killingham’s claim at the time it permitted the late amendment and determined that any loss to Ms. Killingham would be de minimis, that is not the issue before us. The point is that the trial court did not engage in such an appraisal because it could not have done so at the time it dismissed the tenant’s claim, in advance of the jury verdict. Therefore, the majority incorrectly considers the jury verdict in concluding that the trial court’s discretionary ruling allowing amendment of the complaint and dismissing the tenant's claim was permissible because it did not "unduly” prejudice the tenant.
. Of course, as the tenant’s disability-based claim has not been evaluated by the jury with respect to either of the two apartment units at issue, see infra, there is no basis in the record upon which the trial court or this court could conclude that the loss of that part of her counterclaim had no value because it was offset by the benefit that she derived from not having to pay back rent due on one of the apartment units.
. Had the tenant not paid any rent with respect to either unit, one could conclude that elimination of the obligation to pay rent fully compensated her for this, as well as all other, housing code violations. The record in this case, however, is that the tenant paid rent for ten years and only stopped rent payments for approximately six months in order to force the landlord to correct housing code violations. Instead of correcting the housing code violations, the landlord relocated Ms. Killing-ham to another unit, which the jury found to be in violation of the housing code.
. In this case, where in the trial judge’s view, the claim "partially fits but to some extent exceeds” the proper scope of Rule 5(b), the Landlord and Tenant Court should have dismissed the pool-related claim without prejudice or referred it to the Civil Branch. Mathis v. Barrett, 544 A.2d 287, 288-89 (D.C.1988).
.In Shin, the tenant initially asserted his claims for breach of contract and then withdrew them after the landlord argued to the court that they exceeded the narrow scope of permissible claims in a summary Rule 5(b) proceeding for possession and back rent. When the tenant subsequently filed a breach of contract action making the same claim he had been induced to withdraw in the summary Rule 5(b) action, the landlord took the position that the fact that Shin’s claims had not been raised in the decided action for *814possession and back rent rendered them res judicata. This court agreed, stating that even though the landlord had objected to the claims in the Rule 5(b) proceeding, the tenant should nonetheless have reasserted the claim in the same proceeding as a defense to the action for possession and back rent. See Shin, 728 A.2d at 619. The facts in this case ominously point to a similarly unfair result: The tenant asserted her claim that the lack of wheelchair access to the pool area entitled her to a rent offset. The landlord argued that the claim was not proper in a Rule 5(b) proceeding, and the trial court agreed that the claim was not a "housing code” violation that could mitigate the obligation to pay rent. On appeal, this court states that the tenant’s remedy for the claim related to the building’s recreational area lay in a different proceeding — without considering that if the tenant had separately filed such a claim, it would have been time-barred with respect to the time the tenant was paying rent, prior to 1994. Cf. supra note 1.
. As the lease is not part of the record on appeal, on remand, I would also have the trial court determine the facts hypothesized by the majority of "the possibility — indeed, the probability — that the lease [Killingham] had signed was specific to” the apartment unit she had earlier occupied in the building and did not cover the unit that was the subject of the summary Rule 5(b) proceeding. See ante at 809. Determination of that factual issue would be relevant to whether Killingham's claims with respect to housing code violations in the previous unit "related to the premises” from which the landlord sought to evict her. Super. Ct. L & T R. 5(b) (1999).