A. In an action for possession based upon nonpayment of rent or in an action for rent by a landlord when the tenant is in possession, the tenant may assert as a defense that there exists upon the leased premises a condition that constitutes, or will constitute, a fire hazard or a serious threat to the life, health, or safety of the occupants of the dwelling unit, including (i) a lack of heat, running water, light, electricity, or adequate sewage disposal facilities; (ii) an infestation of rodents; or (iii) a condition that constitutes material noncompliance on the part of the landlord with the rental agreement or provisions of law. A tenant may assert a defense as provided for in this section if, prior to the commencement of the action for rent or possession, the landlord or his agent refused or, having a reasonable opportunity to do so, failed to remedy the condition for which he was served notice as defined in § 55.1-1200 by the tenant or by a violation or condemnation notice from an appropriate state or local agency. For the purposes of this subsection, the period of time deemed to be unreasonable delay is left to the discretion of the court, except that there shall be a rebuttable presumption that a period in excess of 30 days from receipt of the notification by the landlord is unreasonable.
B. It shall be a sufficient answer to such a defense provided for in this section if the landlord establishes that (i) the conditions alleged in the defense do not in fact exist; (ii) such conditions have been removed or remedied; (iii) such conditions have been caused by the tenant, his guest or invitee, members of the family of such tenant, or a guest or invitee of such family member; or (iv) the tenant has unreasonably refused entry to the landlord to the premises for the