A wave of mold-related lawsuits against major US home builders is pushing legal reserves higher and adding fresh strain to an already hard liability market for residential construction, according to reporting from the Wall Street Journal.
The lawsuits allege that construction shortcuts, including undersized HVAC systems, poorly sealed windows, and badly ventilated attics, are trapping moisture inside newly built homes and triggering mold growth that homeowners say has made them sick. Builders counter that many claims rest on inconsistent testing methods and unreliable assessors, and that warranty language should shield them from liability. The fight is proving expensive regardless of who's right, and insurers are increasingly the ones covering the cost.
D.R. Horton, the nation's largest home builder, is defending litigation brought by thousands of Louisiana homeowners who claim moisture intrusion left their homes riddled with mold. The company's reserves for legal claims, which account for expected future litigation including mold-related suits, climbed 57% between the end of fiscal 2022 and the end of fiscal 2025, reaching $1.1 billion, according to the Journal's reporting.
Lennar is facing a separate suit from the Seminole Tribe of Florida, which alleges the builder constructed more than 450 homes with defective roofs and mold-contaminated walls. The company's self-insurance reserve, funds set aside for liabilities its own insurance program won't cover, grew 21% in fiscal 2025 to $336.9 million.
Building science experts cited in the report point to a structural cause behind the surge: modern energy codes have made homes far more airtight than they were a generation ago. That's good for heating and cooling bills, but it leaves little margin for error on moisture management. A poorly flashed window or an undersized HVAC unit can trap humidity with nowhere to escape, a problem that's especially acute in the humid Southeast.
That building-science shift is landing on top of a liability market construction carriers have been watching closely for months. A February update from Lockton found that general liability rates for residential "for-sale" properties, covering single-family homes, tract developments and condos, are running two to five times higher than comparable commercial risks, with class-action construction defect litigation flagged as a persistent underwriting concern.
Excess and umbrella layers over residential exposures have tightened too. Marsh's Q1 2026 construction market update for a second straight quarter and pointed to jury verdicts as the driver. Awards over $10 million rose 52% between 2023 and 2024, with construction and engineering claims accounting for roughly $2 billion of the total value, according to research firm Marathon Strategies.
Construction insurance professionals in litigation-heavy states have flagged mold and moisture claims as a growing piece of a broader defect problem for some time. Acrisure's western US construction director described project-specific liability programs in the multifamily sector as increasingly volatile earlier this year, citing the challenging landscape around construction defect litigation alongside climate-driven property losses.
Coverage disputes tied to mold claims are also working their way through appellate courts. In a ruling with implications for how far a carrier's duty to defend extends, the Sixth Circuit Court of Appeals found that an insurer had to defend a contractor in a mold-related dispute despite the contractor not being directly named in the underlying lawsuit, rejecting the insurer's argument that construction defects fall outside the policy's definition of a covered "accident."
General liability policies were never designed to function as blanket defect insurance. Commercial general liability responds to bodily injury or property damage caused by an "occurrence," and whether a mold claim fits that definition often turns on policy wording, endorsements and the state where the claim is filed. Builder's risk policies present a separate gap: The Hartford notes that most carriers apply standalone mold and pollution exclusions to these policies, and many forms exclude defective workmanship outright, responding only to the resulting, or "ensuing," damage. For a builder, that can mean the cost of the defect itself is uninsured even when water damage caused by that defect is covered.
That exposure doesn't disappear once a project wraps and the final invoice is paid. Construction defects often surface months or years after completion, once drywall, flooring or hidden framing has already absorbed water damage that only becomes obvious when mold appears. That lag is part of what makes the line hard to price: claims filed today can trace back to underwriting decisions made three, four or five years earlier, well before current litigation trends showed up in the loss data.
One reason these cases drag on, and cost so much to litigate, is the near-total absence of agreed standards for measuring mold or judging when it becomes dangerous. Plaintiff and defense experts routinely test the same property using different methods and arrive at wildly different spore counts, with remediation estimates that can differ by a factor of 20 or more between opposing experts, according to attorneys quoted in the original reporting.
That kind of evidentiary gray zone tends to draw in third-party litigation funders and produce outsized verdicts, a pattern the has linked to broader social inflation, where liability claims costs rise faster than general economic inflation. Sympathetic juries, distrust of large corporate defendants and aggressive plaintiff marketing all tend to compound in cases where the underlying science is contested, a description that fits toxic mold litigation closely.
Legal experts quoted in the original report expect the current wave of suits to continue rather than fade, and reserve growth at both D.R. Horton and Lennar suggests the builders are planning for the same outcome. For insurers and brokers working with residential construction clients, that points toward sustained underwriting discipline on general liability and excess layers for tract and multifamily builders, closer scrutiny of moisture-management practices during risk assessment, and more attention to how policy wording treats mold specifically.
Brokers advising builder clients may also want to revisit how completed-operations coverage, warranty programs and subcontractor indemnification language work together, since construction defect suits increasingly name multiple parties connected to a single project rather than just the general contractor.
