Portsmouth Damp and Mould: Density, Terraces and Condensation

Portsmouth is the most densely populated city in the UK outside London, and its housing shows it: 43.4% of homes are terraced, against 23.0% across England, and a further 34.2% are flats. Tightly packed Victorian terraces with little outdoor space mean more indoor drying, limited cross-ventilation and a rented sector in which 28.6% of households have a private landlord.

Portsmouth in numbers

• Private rented households: 28.6% (England 20.5%); social rented: 18.0% (England 17.1%)
• Terraced homes: 43.4% (England 23.0%); flats: 34.2% (England 21.4%)
• Homes with no central heating: 2.4% (England 1.5%)
• Overcrowded households: 4.4% (England 4.4%)
• River or sea flood risk: 3.5% (England 1.9%); surface-water risk: 4.5% (England 5.9%)
• Rainfall: about 723 mm a year at the Solent station, roughly five miles away

Most cases are condensation, and that is fixable

Portsmouth City Council received nearly 2,000 damp and mould enquiries in 2024/25 and spent £1.5 million tackling the issue, and its own review found around 70% of cases were condensation-related rather than structural. Those figures relate to the council's housing work as a whole, but the lesson carries over to private lets. Condensation responds to practical measures that a landlord controls:

• Humidity-controlled extractor fans in kitchens and bathrooms
• Trickle vents or other background ventilation in habitable rooms
• Heating that reaches every room, with insulation to keep the heat in
• A clear plan for drying laundry without filling bedrooms with moisture

Sea flood risk and the other 30%

Portsmouth sits on a low-lying island, and the 3.5% of properties at risk from rivers and sea is well above the England figure. The structural cases, whether rising damp in low ground floors or penetrating damp in solid-wall terraces, need a different fix, which is why diagnosis comes before treatment.

A gap between complaints and inspections

On the private rented side, the council reportedly received 76 requests in the same period but investigated only two, reserving enforcement for the most severe cases. Landlords should not read a quiet council as a licence to wait. A tenant can still take a disrepair claim, and a landlord who has ignored a clear report is the one with the problem.

What landlords must do

The Homes (Fitness for Human Habitation) Act 2018 requires a rented home to be fit to live in, and the council can assess damp and mould under the Housing Health and Safety Rating System.

Awaab's Law currently applies to social housing, with private landlords expected to follow. Our guide to Awaab's Law and the private rented sector covers the current position.

To find a specialist, see our Portsmouth damp and mould page, and read the council's guidance for private tenants.