Effective January 1 of this year, the presence of mold in a California building containing dwelling units is a condition sufficient to declare the building to be substandard. This, in turn, enables a code enforcement officer to issue the landlord or property owner a "notice to repair." That is the result of Senate Bill 655 (Mitchell) which was signed into law by the Governor on Oct. 9, 2015.
According to reporting by the California Senate's legislative analyst, "indoor mold growth in homes is one of the most common housing complaints received by tenants' rights groups, legal aid organizations, and code enforcement agencies across the state." So it is a big deal. The surprise, probably, is the fact that mold was not already on the 15-item list of "inadequate sanitation" conditions that could mean that a building was substandard.
Part of the reason that mold has not been on the substandard conditions list is that there has been honest disagreement about the deleterious effects of mold. It may be true that nobody likes mold, but it's not so clear that all types of mold are bad for you.
In 2001 California's Legislature directed the California Department of Public Health (CDPH) "to determine the feasibility of setting Permissible Exposure Limits (PELs) for mold in an indoor environment. In its 2005 report to the Legislature, the CDPH concluded that "sound, science-based PELs for indoor molds cannot be established at this time."
In 2011, though, the CDPH released a "Statement on Building Dampness, Mold, and Health." While acknowledging that "PELs remain elusive", the document went on to say that, "mounting scientific evidence on dampness and mold, much of it published since 2005, supports an alternative, evidence-based approach to the assessment of health risks from indoor dampness and mold."
"Human health studies have led to a consensus among scientists and medical experts that the presence in buildings of (a) visible water damage, (b) damp materials, (c) visible mold, or (d) mold odor indicates an increased risk of respiratory disease for occupants." Moreover, the statement also notes that [the scientific] consensus does not justify a differentiation of some molds as "toxic molds." The only evidence that is "related consistently to adverse health effects are: the presence of current or past water damage, damp materials, visible mold, and mold odor, not the number or type of mold spores, nor the presence of other markers of mold in indoor air or dust."
As has been the case with debates about climate change and its causes, appeals to "a consensus among scientists" are not always 100% persuasive. Nonetheless, the Legislature moved forward on the grounds that, in general, the presence of mold seems to be unhealthy.
One of the strong arguments in favor of the legislative action was that it would bring uniformity to code enforcement. Indeed, one of the bill's sponsors was the California Association of Code Enforcement Officers. It had been noted that, "Since mold is not specifically listed as a substandard condition, jurisdictions across the state treat mold complaints differently, with some taking no enforcement action whatsoever."
The bill took into account some of the dynamics that may occur in landlord-tenant relations. Thus, the landlord has no obligation to repair a mold condition until he has been given notice of it. Moreover, a landlord is not obligated to repair a condition if the condition is a result of the tenant's failure to fulfill affirmative obligations (spelled out California Civil Code §1941.2) to maintain the property.
Useful, in relation to this law and mold conditions in general, is the Lease/Rental Mold and Ventilation Addendum produced by the California Association of REALTORS®(CAR). Here, the tenant's mold-related maintenance obligations are clearly spelled out as an addendum to the lease.