Tenants say my rental property is damp but it's recently renovated. What's the problem?

I rent a house to a family and they have reported damp in the house in two bedrooms. This house never had damp previously, so I can't understand what is happening. It was built in the 1950s and is semi-detached with a garage. We upgraded before renting it and put radiators in the bedrooms – there were no radiators in these rooms previously. Could this be the issue?

You don’t say what type of dampness it is and I’m going to assume you are experiencing mould issues due to condensation within the dwelling as opposed to direct rainwater penetration from outside through the fabric of the building. There may be a number of factors at play here.

Previously you may have had only one or two people living in the house but now with a young family there is more use of steam-generating appliances; more showers taken and more use of the washing machine and dryers, etc. The usual reason condensation appears in a property is lack of adequate ventilation, which causes humidity levels to rise. As people spend more time indoors and make a property more energy efficient by draughtproofing, the build-up of moisture and humidity levels increase.

There are a few basic questions you need to ask yourself initially. Is there reasonable air circulation throughout the house? Are the window or wall vents clear and not closed off by the tenants? Sometimes window slide vents, which the regulations permit, are partially covered by a blind or curtain rendering them less effective.

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Are the tenants drying clothes within the house? No house or apartment should be used in this way. Are the extractor fans in the kitchen, the bathroom and any en suites working satisfactorily with at least a 15-minute overrun? Are they vented properly to the exterior of the building?

Heating system

More serious questions to consider for you as a landlord include the following. Are the boiler and heating system adequate and efficient for the size of the house? Adequate heating will increase the internal temperature of surfaces in the house and reduce the likelihood of condensation. Is there any insulation in the external walls or within the attic and does it need upgrading? Is the attic adequately ventilated? Is it possible that there is cold bridging behind the areas of mould growth due to a lack of any insulation? Double glazed windows will reduce further heat escaping from the property.

Generally improved housekeeping by the residents will go a long way to managing condensation in a dwelling. Simply airing out the house for a few minutes every day will help in managing condensation build-up. If that does not work then there may be some capital expenditure required by the landlord. It’s back to the three key issues for eliminating condensation: ventilation, insulation and heating.

Unfortunately, it is usually a combination of all three and once the ventilation issue and poor housekeeping are ruled out as contributing factors it’s down to spending some money to improve the thermal insulation value of the building’s fabric or upgrading or extending the heating system.

Pat McGovern is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland scsi.ie