HHSRS Category 1 Hazards: The Expert's Perspective
The distinction between Category 1 and Category 2 hazards under the Housing Health and Safety Rating System (HHSRS) is one of the most important in housing enforcement. In short, a Category 1 hazard is one that scores 1,000 or more when the statutory scoring methodology is applied, placing it in the new "High" hazard band under the June 2026 operating guidance. Category 1 status triggers a mandatory duty on the local authority to take enforcement action and, since 22 June 2026, can also give rise to a civil penalty of up to £7,000 under section 6A of the Housing Act 2004 without the need for a prior improvement notice. The scoring rests on professional judgements about the likelihood of a harmful occurrence and the spread of severity of potential harm, judgements informed by the new baseline indicators, hazard profiles, and case studies. Small changes in the underlying judgements can shift a hazard between categories, which is why expert evidence on scoring is often decisive in contested cases.
This article looks at Category 1 hazards from the expert witness perspective under the current (June 2026) HHSRS framework. It sets out how they are identified, scored, and challenged; explains the significance of baseline indicators; and considers what an independent expert can add to a contested case.
The HHSRS in outline
The HHSRS is set out in Part 1 of the Housing Act 2004 and the Housing Health and Safety Rating System (England) Regulations 2005 (as amended). It provides a statutory methodology for assessing the risk to health and safety arising from deficiencies in residential premises.
The scoring methodology considers the likelihood of a harmful occurrence over the next twelve months and the spread of possible harm outcomes if that occurrence takes place. The two are combined mathematically to produce a numerical hazard score. Under the current framework, that score falls into one of three bands: Low (below 100), Medium (100 to 999), or High (1,000 or above). Category 1 hazards are those scoring 1,000 or above and falling in the High band; Category 2 hazards are those scoring below 1,000.
The current statutory operating guidance was published on 23 June 2026 under section 9 of the Housing Act 2004. It is a substantial revision of the previous 2006 guidance, with a new three-part structure, a reduction in the number of hazards from 29 to 21, a simplified banding system, and the introduction of baseline indicators. For a fuller overview of the 2026 reforms, see our earlier articles on What Is an HHSRS Assessment? and HHSRS Reform 2026: What's Changed. This article assumes readers are familiar with the reforms and focuses specifically on how Category 1 hazards are identified and challenged under the new framework, with particular attention to the role of baseline indicators.
Baseline indicators and their role
The introduction of baseline indicators is one of the most significant conceptual changes in the June 2026 guidance, and it has direct implications for how Category 1 hazards are identified and defended. It is worth understanding baseline indicators properly.
What baseline indicators are
The guidance defines baseline indicators as:
A prescriptive but non-exhaustive list of proportionate building measures designed to protect the health, safety, and wellbeing of occupiers.
The baseline indicators are listed in Appendix 1 of Part 2 of the guidance. They describe features that a dwelling should reasonably have to protect occupiers against common housing-related health risks.
What baseline indicators are not
Baseline indicators are not minimum standards in the regulatory sense. Meeting them does not eliminate the need for a risk assessment. Failing to meet them does not automatically make a property non-compliant with any specific legislation. What failure to meet a baseline indicator does is trigger the identification of a deficiency, which then requires assessment under the HHSRS methodology.
The guidance is explicit on this point:
Baseline indicators are not intended as a "minimum standard", however, and do not in any way replace the risk assessment aspect of the HHSRS.
The role of baseline indicators in an assessment
Baseline indicators serve two important functions in the assessment process:
Identifying deficiencies. Failure of a dwelling to meet a relevant baseline indicator is deemed to be a deficiency. The assessor must then determine whether that deficiency is relevant to the hazard being assessed and, if so, take it into account when scoring the likelihood and spread of harm outcomes.
Providing preliminary safety checks. The baseline indicators checklist in Appendix 1 can be used by those without formal HHSRS training to conduct preliminary property safety assessments. These are not full HHSRS assessments but can help owners, occupiers, and property managers decide whether a full assessment by a qualified assessor is warranted.
Practical implications for landlords and agents
For landlords and managing agents, the baseline indicators effectively create a checklist of features that are expected in any residential property. Whilst not legally binding as minimum standards, they represent the current Government and sector view on proportionate building measures that protect occupier health and safety. Where a property falls short of the baseline indicators, that shortfall should be documented, the risk to health considered, and any necessary remedial work planned. Where an assessor or enforcement officer identifies the shortfall in the course of an inspection, they are likely to record it as a deficiency and factor it into the HHSRS scoring, which can materially affect whether a hazard scores as Category 1 or Category 2.
Why the categorisation matters
Whether a hazard is classified as Category 1 or Category 2 has significant consequences for both local authorities and property owners.
For local authorities
Where a Category 1 hazard is identified, section 5 of the Housing Act 2004 places a duty on the local housing authority to take one of the enforcement actions available under Part 1. These include serving an Improvement Notice, making a Prohibition Order, taking Emergency Remedial Action, or issuing a Hazard Awareness Notice for hazards on prescribed premises.
The council does not have discretion whether to act on a Category 1 hazard. It has discretion over which enforcement action to take, but not whether to act.
For Category 2 hazards, the position is different. Under section 7 of the Housing Act 2004, the council has a power (not a duty) to take enforcement action. This gives councils flexibility that Category 1 status removes.
For property owners
A Category 1 hazard finding usually leads to formal enforcement action, with all the practical consequences that follow: works required, timescales for completion, exposure to civil penalties for non-compliance, and reputational impact. Since 22 June 2026, a Category 1 hazard can also trigger a civil penalty of up to £7,000 under section 6A of the Housing Act 2004 without a prior improvement notice being required. For a landlord, whether a hazard is Category 1 or Category 2 can therefore make the difference between a compliance conversation and a formal enforcement process with meaningful financial consequences.
The Renters' Rights Act 2025 effect
The June 2026 changes to the HHSRS operating guidance sit within a wider expansion of housing enforcement powers under the Renters' Rights Act 2025. From 1 May 2026, civil penalty ceilings under section 249A of the Housing Act 2004 have risen from £30,000 to £40,000. From 22 June 2026, the new section 6A civil penalty regime allows councils to impose penalties of up to £7,000 for Category 1 hazards without prior improvement notice. Rent repayment order exposure has been extended from 12 to 24 months. Higher stakes mean the technical quality of the HHSRS assessment matters more than ever. Whether categorisation is correctly applied, as either Category 1 or Category 2, has direct and material consequences for both landlords and enforcement teams.
How Category 1 is determined: the scoring methodology
The HHSRS scoring methodology has three main components: identifying the hazard, assessing the likelihood of a harmful occurrence, and assessing the spread of harm outcomes.
Hazard identification
The first step is identifying which of the 21 hazards is engaged by the deficiency observed. Some are self-evident (loose treads on stairs point to Falling on stairs etc.). Others require more careful analysis (whether visible mould constitutes a Damp and mould growth hazard, or whether it is more properly considered under Excess cold, or both). Careful hazard identification matters because the reference likelihoods and harm outcomes differ by hazard. Assessing under the wrong hazard heading produces the wrong score. The hazard profiles in Part 2 of the guidance provide the reference data for each of the 21 hazards.
Likelihood assessment
For each hazard, the assessor considers the likelihood of a harmful occurrence over the next twelve months, expressed as a ratio (for example, 1 in 100) and accompanied by a descriptor term (very unlikely, unlikely, likely, very likely). The Part 2 hazard profile provides the national average likelihood for the property type and age.
The assessor then considers whether the specific property has features, aggravating or mitigating, that shift the likelihood higher or lower than the national average. This is where a great deal of the professional judgement lies. Aggravating factors include failures to meet baseline indicators, deficiencies listed under relevant matters in the hazard profile, and high scores from related hazards. Mitigating factors are considered equally.
Spread of harm outcomes
The methodology then considers the spread of possible harm outcomes across four classes: Extreme, Severe, Serious, and Moderate.
The reference spreads in the hazard profile represent typical outcomes for the hazard. The assessor considers whether the specific circumstances of the property would shift the spread toward more or less severe outcomes.
The likelihood and spread scores are then combined using a formula. The output is the final hazard score, which is compared to the banding thresholds to give the final rating.
The professional judgement element
A common misconception is that HHSRS scoring is objective in the sense that different assessors, given the same property, will always produce the same score. This is not the case. The methodology relies on multiple layers of professional judgement, and reasonable assessors can and do reach different conclusions on the same facts. Where the score sits close to the 1,000 threshold that separates Category 1 from Category 2, small differences in judgement, including how baseline indicator shortfalls are weighted, can shift the category. This is precisely why the scoring is a fair area for independent expert review.
Where categorisation disputes commonly arise
A number of hazards regularly feature in categorisation disputes.
Excess cold
Excess cold is one of the most commonly identified Category 1 hazards. Disputes typically turn on the assessment of the property's thermal performance, the effectiveness of the heating system, and the vulnerability of the occupants (or potential occupants) to cold-related harm. The scoring is often sensitive to assumptions about air permeability, insulation values, and heating system reliability. The baseline indicators for excess cold provide reference points on heating and insulation that the assessor may weigh alongside the property-specific data.
Damp and mould growth
Post-Awaab Ishak, damp and mould has become a high-profile hazard. Awaab's Law places specific duties on social landlords to respond within defined timescales to reports of damp and mould, and the Government has signalled its intention to extend these duties to the private rented sector. Categorisation under the HHSRS turns on the extent and location of the growth, the underlying cause (structural, condensation, or use-related), the vulnerability of occupants, and the practical remediability of the underlying cause. Expert evidence often needs to address both the current condition and the underlying building physics.
Falling on stairs etc.
Falls hazards on stairs turn on the specific dimensions, rise-and-going ratios, handrail provision, tread condition, and lighting. Small variances from Building Regulations norms and baseline indicators can push a hazard above or below the Category 1 threshold. Expert measurement and analysis of the specific staircase is often required, particularly for older or altered properties.
Electrical hazards
Electrical hazards are frequently disputed because the categorisation depends heavily on the specific defects identified, the likelihood of contact with live parts, and the vulnerability of typical occupants. An old but functional electrical system is not automatically a Category 1 hazard; the categorisation requires assessment of the actual condition and specific risks. Certificates of electrical compliance (EICRs) can inform but do not determine the HHSRS categorisation.
Fire and explosions
Under the June 2026 guidance, the previous Fire hazard has been combined with Explosions. Categorisation turns on assessment of the ignition sources, the fire load, compartmentation, means of escape, and fire alarm arrangements. Expert evidence often requires review of the property against relevant Fire Risk Assessments and current fire safety guidance. Part 3 of the operating guidance provides supplementary technical information on this hazard.
What an expert can add to a contested case
Where the categorisation of a hazard is disputed, an independent expert can add several things to the case.
Rigorous re-application of the methodology
The expert can independently apply the HHSRS methodology to the specific facts of the property, working through hazard identification, likelihood, and harm outcomes without the assumptions or shortcuts that sometimes creep into busy enforcement teams' assessments. The output is a documented, independent view on where the correct score lies under the current guidance.
Identification of methodological errors
Where the council's assessment contains errors, for example, applying the wrong hazard heading, using an inappropriate vulnerable age group, or making adjustments that are not supported by the observed conditions or the baseline indicators, the expert can identify and explain these. Councils and Tribunals both respond well to precise, technically-based critique.
Baseline indicator verification
Since the June 2026 guidance, the baseline indicators occupy a specific role in the assessment. An expert can verify whether the council's assessment properly considered which baseline indicators applied to the property, whether the property met them, and how any shortfalls were reflected in the scoring. Where baseline indicator considerations have been overlooked or misapplied, this can materially affect the score.
Consideration of alternative evidence
The expert can consider evidence that may not have been fully weighted in the original assessment: contemporaneous photographs, historic maintenance records, thermal imaging, moisture readings, professional reports commissioned by the owner, or comparative data from similar properties.
Reasonable practicability
Beyond the categorisation itself, expert evidence is often needed on the reasonable practicability of remedial works, the appropriate specification for those works, and the reasonable timescale for completion. These matters affect the specific enforcement action taken as well as the underlying question of category.
Independence
The expert's independence is its own value. A Tribunal considering conflicting evidence from an enforcement officer and an owner is more likely to give weight to a properly-qualified independent expert who has applied the methodology rigorously than to either party's untested account. For a fuller discussion of when expert witness evidence is likely to add value in a housing case more broadly, see our guide on when your case needs a housing expert witness.
How the challenge process works
Where a Category 1 hazard finding leads to formal enforcement action, the routes to challenge depend on the action taken.
For an Improvement Notice, the appeal is to the First-tier Tribunal (Property Chamber) within 21 days of service, on grounds set out in Schedule 1 of the Housing Act 2004. Categorisation is one of the matters that can be challenged.
For a Prohibition Order, the appeal is similarly to the First-tier Tribunal on the grounds set out in Schedule 2.
For a section 6A civil penalty (under the new £7,000 regime), the appeal is to the First-tier Tribunal following the procedure set out in Schedule A1 of the Housing Act 2004.
For a prosecution under section 30 or section 72 of the Housing Act 2004, the defence is run through the Magistrates' Court process.
In each of these routes, expert evidence on the correct HHSRS categorisation can be highly influential. The instructions to the expert should focus on the specific matters in dispute and the standard of proof or persuasion applicable to the forum.
Timing and practical considerations
As with all expert instruction, early engagement is preferable. Where an Improvement Notice or Prohibition Order is appealed, the Tribunal will usually direct a timetable for exchange of evidence that fixes when expert evidence must be filed and served. Meeting that deadline properly requires the expert to have adequate time for site visit, analysis, and report preparation.
For hazards where physical site inspection is important (which is most hazards), arranging access to the property is usually straightforward but can occasionally require coordination with tenants. Where the property has been altered since the events in question, the expert will need to work with photographs and contemporaneous records, and the report will note this limitation.
How Surrey Property Licensing can help
We work with the reformed HHSRS from both sides, assessing and scoring hazards and understanding how enforcement decisions are reached. We help landlords, letting agents, property professionals and local authorities:
Carry out HHSRS assessments under the reformed system.
Identify and prioritise hazards before a local authority inspection.
Provide independent expert input where an assessment or notice is contested.
Offer specialist support and additional capacity to local authorities.
If you would like an HHSRS assessment or advice under the reformed system, get in touch.
