When two events combine to cause damage, one being covered and the other not covered, issues arise regarding whether the loss is covered, and who bears the burden of proof to allocate causation between the covered cause and the excluded cause. In the San Antonio Court of Appeals case, Wallis v. United Serv. Auto. Assoc., the court held that the insurance company will only be liable for that portion of the damage that was caused by a covered event.
When the covered and excluded perils combine to cause injury, the Texas Supreme Court has held that the insured must present some evidence affording the jury a reasonable basis on which to allocate the damages.
Generally, courts have held that if a loss occurs as a result of two concurring perils, one insured and one not, then the loss is covered only to the extent that it can be traced to the covered peril. Expert testimony allocating damage between covered and excluded causes may satisfy this burden of proof, according the United States 5th Circuit, in Fiess v. State Farm Lloyds.