Quick answer: Indoor air quality (IAQ) is no longer just a wellbeing concern — it is now a formal housing compliance category. Under the Housing Health and Safety Rating System (HHSRS) overhauled in June 2026, biocides, carbon monoxide, volatile organic compounds and uncombusted fuel gas are assessed together under a single Indoor Air Pollutants hazard. A High score (Category 1) triggers a statutory landlord duty. For contractors, this means the chemicals used in mould remediation, the ventilation conditions left after remediation work, and the cleaning products used in communal areas all have a direct bearing on HHSRS assessments — and from November 2026 (Awaab's Law Phase 2), on statutory response timeframes.
Indoor air quality has historically been treated as a secondary consideration in housing maintenance — something to think about after the primary hazard has been addressed. The June 2026 HHSRS overhaul changes that. By formally classifying biocides, VOCs, carbon monoxide and uncombusted fuel gas as a single Indoor Air Pollutants hazard, the revised HHSRS makes IAQ an assessable, scoreable, enforceable housing hazard in its own right.
For maintenance contractors, remediation specialists and housing teams, this creates a compliance responsibility that goes beyond simply removing visible mould or fixing a leaking pipe.
What counts as an Indoor Air Pollutant under HHSRS 2026
Under the revised HHSRS, the Indoor Air Pollutants hazard category covers:
- Biocides — biocidal products used in mould removal, disinfection, algae treatment and surface cleaning. Where biocides are used incorrectly, in excessive concentrations, or without adequate ventilation, they can contribute to indoor air quality hazards for occupants.
- Volatile Organic Compounds (VOCs) — off-gassing from paints, adhesives, sealants and cleaning products. High VOC concentrations in poorly ventilated spaces can cause respiratory irritation and, at sustained exposure, more serious health effects.
- Carbon Monoxide and Fuel Combustion Products — from boilers, gas appliances, log burners and portable heaters. A major cause of preventable deaths in rented housing.
- Uncombusted Fuel Gas — gas leaks and incomplete combustion.
A local authority assessor can now score an Indoor Air Pollutants hazard during an HHSRS inspection. A High score — Category 1, 1,000 or above — triggers a statutory duty to act. Civil penalties of up to £7,000 apply for unresolved Category 1 hazards under the Renters' Rights Act 2025.
Why biocides in mould remediation matter more than ever
The inclusion of biocides in the Indoor Air Pollutants hazard category has a direct practical consequence for contractors carrying out mould remediation in occupied social housing properties.
Under COSHH, employers must consider whether mould can be removed mechanically — using H-Class vacuum extraction — before introducing a hazardous biocide into an occupied or semi-occupied property. Where a biocide is used, it must be used correctly, in accordance with its Safety Data Sheet, and the exposure of both operatives and occupants must be adequately controlled. Products marketed as 'non-toxic' or 'safe' cannot be relied on as a substitute for a proper COSHH assessment — and from 15 August 2026, updated GB CLP classifications apply to a range of biocidal active substances. See: Biocide labelling compliance →
A contractor who applies a biocide incorrectly in an occupied property — without adequate ventilation, at excessive concentration, or without appropriate PPE for occupants — may now be contributing to a scoreable HHSRS Indoor Air Pollutants hazard, in addition to the COSHH liability they already carry.
Ventilation — the underrecognised part of the picture
Indoor air quality in housing is fundamentally linked to ventilation. Inadequate ventilation allows moisture, VOCs, combustion products and biocide residues to accumulate to concentrations that affect occupant health. Under the HHSRS, excess moisture and inadequate ventilation are contributing factors to the damp and mould hazard — and now also to the Indoor Air Pollutants hazard.
Part F of the Building Regulations (Approved Document F) sets minimum ventilation rates for dwellings. A 2026 edition of Approved Document F has been published, taking effect from March 2027. For social housing retrofits, upgrades and refurbishments, ensuring ventilation is not degraded during maintenance work — and is improved where possible — is part of the broader IAQ compliance picture. See: Ventilation and Part F 2026 — what social housing contractors need to know →
Awaab's Law Phase 2 and IAQ
Awaab's Law Phase 2, confirmed for November 2026, extends statutory response timeframes to a wider range of HHSRS hazards — including those in the Indoor Air Pollutants category. Under Phase 2, a landlord who receives a complaint about persistent chemical odours, inadequate ventilation, or recurring air quality problems in an occupied property may have a statutory obligation to investigate within the same timeframes that currently apply to damp and mould. See: Awaab's Law Phase 2 briefing →
What contractors and housing teams should do
- Review biocide use in occupied properties — ensure mechanical removal (H-Class extraction) is considered before chemical application. Where biocides are used, ensure ventilation during and after application is adequate.
- Check COSHH assessments — all biocide COSHH assessments must be reviewed before 15 August 2026 against updated GB CLP classifications.
- Consider ventilation as part of mould remediation — addressing the mould without addressing the ventilation that allowed it to develop is not a complete remediation. Under HHSRS 2026, inadequate ventilation is a contributing factor to the Indoor Air Pollutants hazard as well as the damp and mould hazard.
- Prepare for Phase 2 scope — from November 2026, IAQ complaints may trigger statutory investigation and remediation timeframes under Awaab's Law.
Related guidance
HHSRS 2026 overhaul →
Awaab's Law Phase 2 →
Biocide labelling compliance →
Ventilation and Part F 2026 →
Legionella risk in dust suppression and water systems →
Awaab's Law →
Social housing hub →
COSHH Regulations 2002 →
Choose the right machine for the job
