HHSRS Explained: Category 1 and 2 Hazards for Damp Surveyors

If you survey damp and mould in residential property, the HHSRS is the framework your findings ultimately feed into. Awaab's Law, the Decent Homes Standard, and local-authority enforcement all lean on it. Yet "Category 1" gets written into reports far more often than it gets properly explained. This is what the HHSRS actually is and how damp and mould fits into it.

What the HHSRS is

The Housing Health and Safety Rating System (HHSRS) is a risk-based assessment introduced under the Housing Act 2004, which came into force in England and Wales in 2006. It replaced the old fitness standard with a method for evaluating the risk that a defect in a home poses to the health and safety of its occupants — particularly the most vulnerable. It assesses 29 categories of hazard, and damp and mould growth is one of them.

How the scoring works

Crucially, the HHSRS does not score the defect itself — it scores the risk of harm the defect creates. The assessment combines two things:

• Likelihood — the probability, over a period, that the hazard will cause harm to a member of the vulnerable group for that hazard.
• Outcomes — the spread of possible harms, from minor through to extreme, and how likely each is.

These are combined into a numerical hazard score, which falls into a band from A (most serious) down to J. The score, not a gut feeling, is what drives the category.

Category 1 and Category 2 hazards

The bands divide into two categories:

• Category 1 — the most serious hazards (the top bands). Local authorities have a duty to take appropriate enforcement action where a Category 1 hazard exists.
• Category 2 — less serious hazards (the lower bands). Local authorities have a power — a discretion — to act, but not a duty.

For damp and mould, the vulnerable group includes the very young, the elderly, and those with respiratory conditions — which is why occupant circumstances pull the same physical mould toward a higher score in one home than another.

What enforcement looks like

Where a local authority acts on a hazard, the Housing Act gives it a range of tools, including improvement notices, prohibition orders, hazard awareness notices, and emergency measures for the most urgent cases. For social landlords, the same hazard assessment now also interacts with Awaab's Law and the Decent Homes Standard, so a damp and mould finding rarely sits in isolation.

Why surveyors must show their working

The most common criticism of damp reports in ombudsman determinations is an unsupported "Category 1" label — a category stated with no likelihood-and-outcome reasoning behind it. Because the HHSRS is a scoring system, a defensible report has to show how the score was reached: the hazard assessed, the vulnerable group, the likelihood, and the harm outcomes considered. A bare category is an opinion; a worked score is evidence.

This is also why a good damp report and an HHSRS assessment belong together — see our guide on how to write a professional damp survey report for how the scoring sits within the wider report.

SurveyMate builds HHSRS-aligned scoring into the findings capture, so the reasoning is recorded alongside the category rather than reconstructed afterwards. See how SurveyMate keeps damp and mould assessments compliant by default.