BOGGS, Judge.

Zurich American Insurance Company, American Zurich Insurance Company, and American Guarantee and Liability Insurance Company (collectively "insurers") appeal from the trial court's order granting summary judgment in favor of John Heard, John Heard Associates, Inc., Hairston Engineering, P. C., and Harry Hairston, Jr. (collectively "appellees"). The insurers contend that the trial court erred by concluding: (1) that contribution and indemnity under OCGA § 51-12-32 were precluded by the apportionment statute, OCGA § 51-12-33; (2) that even if contribution were still available, the insured and the appellees in this case were independent, not joint, tortfeasors, from whom contribution is not available; (3) that the settlement was a voluntary payment; and (4) that all of the insurer's claims against the appellees should be considered reframed claims of contribution. For the reasons explained below, we agree and therefore reverse.

"On appeal from the grant or denial of summary judgment, we apply a de novo standard of review." (Citation omitted.) Coca-Cola Bottlers' Sales, etc. v. Novelis Corp., 311 Ga.App. 161, 715 S.E.2d 692 (2011). "[T]he moving party must demonstrate that there is no genuine issue of material fact and that the undisputed facts, viewed in the light most favorable to the nonmoving party, warrant judgment as a matter of law. [Cit.]" Lau's Corp. v. Haskins, 261 Ga. 491, 405 S.E.2d 474 (1991); see also OCGA § 9-11-56(c). So viewed, the record shows that Pinkerton & Laws of Florida, Inc. ("P & L") entered into a contract to serve as the general contractor for construction of a hotel in Brunswick, Georgia. While P & L'S contract provided for mandatory arbitration, it also included the following provision regarding joint arbitration of claims with the architect:

John Heard Associates ("JHA") entered into a separate contract to provide "architectural and structural, mechanical, electrical and plumbing engineering design services" for construction of the same hotel. JHA also agreed to perform "construction administration," which included monthly site visits to review the "[q]uality of construction."

Because John Heard, an architect, was not a licensed engineer, JHA entered into a subcontract with Wellborn Technical to provide the MEP (mechanical, electrical, and plumbing engineering) and HVAC (heating, ventilating, and air conditioning) design services for the hotel. Heard knew that the principal of Wellborn Technical, Billy Wellborn, was not a licensed engineer at the time of the subcontract. After obtaining Heard's contract, Wellborn entered into an oral agreement with Harry Hairston, a licensed engineer, to provide the required MEP and HVAC designs. While Heard knew that Wellborn would obtain the assistance of a licensed engineer, he testified that he did not recall any discussion with Wellborn about who should be hired.

The record shows that both during and after construction of the hotel, the owners discovered the presence of mildew and signs of moisture trapped in the building. In June 2008, the owners filed a demand for arbitration against P & L and JHA seeking monetary damages in excess of $500,000. In their "overview" of their claims and damages, the owners requested that the award be made against P & L and JHA "jointly and severally" based upon P & L's negligent construction and Heard's negligent design. After P & L filed a motion to sever the claims, relying upon its right to insist upon a separate arbitration, JHA was dismissed from the arbitration proceeding. The owners then filed suit against Heard and JHA in Gwinnett County State Court,1 and P & L unsuccessfully sought to intervene in that suit.2

P & L and the owners settled the arbitration claim based, in part, upon the following terms: that P & L would enter into a consent arbitration award in the amount of $6.2 million; that P & L would pay $2.3 million within 14 days after the settlement agreement was executed; that this payment would "not represent a full satisfaction of [the owner]'s damages"; that upon receipt of the payment, the owners agreed not to seek any recovery of the award from P & L; that "P & L's claims for contribution and/or indemnification" were preserved; and that P & L would waive and release its counterclaim against the owners in the pending arbitration. The settlement agreement also stated:

Six months later, the owners settled their claims against JHA and Heard for $100,000. The written settlement agreement contained the following provision:

Less than one year after P & L's settlement with the owners, the insurers filed a suit against Heard, J & H, Hairston Engineering, P.C., and Jerry Hairston, Jr.5 They asserted causes of action for professional negligence (Count 1), third party breach of contract (Count 2), negligent misrepresentation and/or omission of fact (Count 3), and contribution/indemnity based upon the appellees' joint tortfeasor status with P & L (Count 4). The facts alleged to support these claims were that insufficient information was provided to P & L in the construction drawings; that the defendants failed to provide adequate construction administration; that J & H and Heard refused to conduct an investigation into the moisture problems at the hotel; and that Hairston Engineering and Jerry Hairston incorrectly designed the HVAC system in the hotel.

All of the defendants moved for summary judgment in their favor. JHA and Heard asserted that (1) the insurers' claim for contribution and indemnity fails because joint tortfeasors can no longer assert these claims following the enactment of the apportionment statute, OCGA § 51-12-33; (2) any payment for damages caused by the defendants "was a voluntary payment for which the defendants cannot be responsible;" (3) a waiver of subrogation clause barred the insurers' claims; (4) the insurers' claims for professional negligence and negligent representation are barred by the statute of limitation; and (5) the insurers' third-party beneficiary claim fails because P & L was not an intended beneficiary of the contracts between the owners and JHA. In their motion for summary judgment, Hairston Engineering and Jerry Hairston adopted the grounds asserted by their co-defendants and added one additional argument for summary judgment in their favor: the design services provided by them were complete at the permitting phase of the project and they cannot be held responsible for design changes made by Billy Wellborn during construction without their knowledge and consent.

The trial court granted summary judgment to the defendants for the following reasons: (1) after the Legislature's enactment of OCGA § 51-12-33, "there is no longer a right of a `joint trespasser to contribution from another or others' that can continue, regardless of whether liability is imposed by virtue of a settlement or a verdict;" (2) even if contribution claims may still be made among settling defendants, the defendants in this case are independent tortfeasors, not joint tortfeasors, based upon the insurance policies at issue and the underlying facts surrounding the two settlements; (3) even if some portion of the payments by the insurers represented an amount resulting from the defendants' negligence, it was a voluntary payment in light of the apportionment statute and policy exclusions; and (4) the insurers' remaining claims fail because they are "nothing more than a reframed contribution claim." The insurers take issue with each of these findings in their appeal.

1. We first consider whether claims for contribution between joint tortfeasors who have settled with the plaintiff still exist following the enactment of the apportionment statute, OCGA § 51-12-33. Subsection (b) of this Code section provides:

(Emphasis supplied.) Based upon the plain language of subsection (b), joint liability and the right of contribution no longer exist when damages have been apportioned by the trier of fact under this subsection. Based upon this plain language, it cannot be interpreted to abolish the right of contribution between settling joint tortfeasors when there has been no apportionment of damages by a trier of fact. See Six Flags Over Georgia II, L.P. v. Kull, 276 Ga. 210, 211, 576 S.E.2d 880 (2003) ("Where the language of a statute is plain and unambiguous, judicial construction is not only unnecessary but forbidden.") When enacting subsection (b) of OCGA § 51-12-33 in 2005, the Legislature left OCGA § 51-12-32 intact in its entirety and it remains valid law. This latter Code section provides:

(Emphasis supplied.) Based upon the plain language of this statute, the right of contribution between joint tortfeasors has not been completely abolished by the Legislature's enactment of OCGA § 51-12-33(b), and the trial court erred by holding otherwise.6

2. We must now consider whether the trial court properly concluded that P & L and the appellees were not joint tortfeasors as a matter of law.7 The test for determining joint tortfeasors is whether "the separate and independent acts of negligence of two or more persons or corporations combine naturally and directly to produce a single indivisible injury...." (Citation, punctuation and emphasis omitted.) Zimmerman's, Inc. v. McDonough Constr. Co., 240 Ga. 317, 320(1), 240 S.E.2d 864 (1977). Statements made in settlement agreements between the parties and the separate legal proceedings (the Gwinnett lawsuit and arbitration) do not support the trial court's conclusion that no joint liability existed. The issue is whether a single indivisible injury resulted from the negligence of P & L and the appellants, not how the different entities involved conducted legal proceedings or described payments made in settlement. "Where no judgment finding both tortfeasors liable has been entered, a right of contribution still exists, but the party seeking contribution must prove that his own negligent actions and those of the alleged joint tortfeasor jointly caused the harm." (Citation, punctuation and footnote omitted.) Suggs v. Hale, 278 Ga.App. 358, 360-361(2), 629 S.E.2d 11 (2006). "As a general rule, the substantial rights of the parties in a negligence case, including the right to contribution between joint tortfeasors, become fixed at the time of injury or the event upon which liability depends. [Cits.]" Byington v. Lee, 150 Ga.App. 393, 394(1), 258 S.E.2d 6 (1979). The trial court therefore erred by concluding as a matter of law that P & L and the appellants were not joint tortfeasors. See Big Canoe Corp. v. Moore & Groover, Inc., 171 Ga.App. 654, 657-658(2), 320 S.E.2d 564 (1984).

3. The insurers contend the trial court erred in finding that their contribution and indemnity claims were barred because the settlement was a voluntary payment. We agree.

(a) The trial court concluded that the entire settlement payment was a voluntary payment "because, in light of apportionment, P & L had no legal obligation to pay and could not be held liable for any damages resulting from the negligence of the [appellants]." This conclusion was erroneous for the reasons stated in Division 1 of this opinion.

(b) The trial court also found that the insurers' settlement should be construed as a voluntary payment because of the professional services exclusions in the insurance policies. The court found it significant that the insurers admitted in their discovery responses "that they never paid money under either the CGL policy or the Umbrella Policy for any damages that would have been excluded from coverage." The trial court reasoned that because the policies excluded coverage for professional services, the settlement payment cannot be construed as a payment caused by appellants' alleged professional negligence. The trial court's reasoning is flawed, however, because the record shows that the insurance policies excluded coverage for professional services rendered by or on behalf of P & L, not other parties, such as the appellants. Additionally, in an OCGA § 9-11-30(b)(6) deposition, the insurers' representative testified that the insurers paid for damages caused by P&L's construction work relying on the appellees' designs. Additional testimony that the insurers were not obligated to pay damages for the acts or omissions of the appellees generally or for professional services does not alter evidence showing that the insurers paid for damages caused by the combination of P&L's conduct during construction and the designs provided by appellees — a single indivisible injury covered by the policy.

(c) The trial court's finding that the insurers made a voluntary payment based upon a mold exclusion in the policy was also erroneous. The record shows that the insurers did not pay for mold damage because it was excluded under the policy. Instead, they paid for property damage claims resulting from structural issues and water intrusion, as well as loss of use resulting from covered property damage. It is undisputed that the insurers contributed $1,463,950.00 to the settlement and that P & L paid $721,050.00 for uninsured damages, including those caused by mold and the use of EIFS (exterior insulation and finish system). P & L subsequently assigned its interest in uninsured damages to the insurers. Based upon this record evidence, the trial court erred by concluding as a matter of law that the insurers made a voluntary payment for mold and mildew damages not covered by the policies.

Because the record fails to establish, as a matter of law, that the insurers' subrogation and assigned claims for contribution and indemnity are barred by voluntary payment, the trial court erred by granting summary judgment in favor of the appellees on this ground.

4. In their remaining claim of error, the insurers contend that the trial court erred by concluding that they could not recover on their remaining theories of recovery because they were "nothing more than a reframed contribution claim." Based upon our holdings in Divisions 1-3 regarding contribution, this enumeration of error is rendered moot.

5. In their briefs, appellees request this court to rule on additional grounds for summary judgment raised below, but not ruled upon by the trial court. In accordance with City of Gainesville v. Dodd, 275 Ga. 834, 838-839, 573 S.E.2d 369 (2002), we decline to address the additional grounds not ruled upon by the trial court. We are reversing the trial court based upon its application of an erroneous legal theory, and the additional grounds involve potential undisputed issues of material fact and legal theories not adequately briefed by the parties before this court.

Judgment reversed.

RAY and BRANCH, JJ., concur.