I live in a 1972-built semidetached house. The house attached to mine has been unoccupied for almost a year and it seems will remain so for the foreseeable future. As I understand it, the house has two electric heaters, one downstairs and the other upstairs. Last week I found evidence of mould in a bedroom wardrobe backing on to the dividing wall. Could the unheated house next door have contributed to the mould appearing? And, if the answer is yes, does the neighbour have any responsibility to maintain the house by adequately heating it.
Mould is a common issue in homes across the country, and it can appear in older and newer properties. Several factors contribute to mould growth, most of which relate to heating, ventilation, and moisture control. As you’ve correctly noted, inadequate heating can play a role, but so too can high moisture levels, poor air circulation, and excess moisture generated within the home.
A lack of insulation in attics, walls, floors, or windows can also lead to condensation forming internally. Where different parts of a property are insulated to differing levels, this imbalance can create “cold spots” along walls or structural elements, which are the most likely places for condensation to form.
You’ve noticed mould developing at the back of your bedroom wardrobe on the party wall and are wondering whether it might be connected to your neighbouring property. It’s an understandable concern.
RM Block
In reality, the vacant house next door may have had a minor effect on the temperature of the shared wall, but this influence is limited. While an unheated adjoining property can make a wall slightly colder, the more significant factors are likely to be within your own home.
You mentioned that the neighbour’s house had only one heater for the ground floor and one for the first floor. Even if these were in use, this minimal provision would be unlikely to maintain adequate heat throughout the property, meaning the overall impact on your home’s internal conditions is probably small.
Furthermore, there is no duty for a neighbour to maintain heat in their property to prevent issues in adjoining homes. Each owner is responsible for the upkeep of their own property, including heating and maintenance. In other words, while your neighbour’s unheated house may have slightly reduced the temperature along the shared wall, they are not legally responsible for the mould appearing in your wardrobe.
The recent appearance of mould suggests that indoor conditions in your own home may have been less than ideal; perhaps cooler or more humid than usual. Homes built in the 1970s typically have modest insulation standards and can be prone to draughts. If your house has felt colder or damper over the past year, this may have tipped the balance enough for mould to develop.
Everyday living activities also add to indoor moisture levels; drying clothes indoors, showering, cooking, and even breathing release water vapour into the air. If this moisture isn’t ventilated away, it can condense on colder surfaces, particularly along external or party walls. Wardrobes are especially susceptible because air circulation inside them is poor, providing a place for mould to settle on surfaces and clothing.
You might check whether condensation is forming on internal wall surfaces or if any streaks or damp patches are developing – both are early warning signs of high humidity and poor air movement.
In practice, this is a maintenance issue for you rather than your neighbour. There are several practical steps you can take to reduce the risk of mould. It is important to improve insulation, particularly along the party wall if it feels cold, with measures such as dry lining the internal face of the wall to retain warmth and minimise condensation.
Ventilation should also be enhanced, for example through a mechanical system like a heat-recovery unit, to ensure adequate air circulation and reduce indoor-humidity levels. Managing moisture within the home is equally important. Avoid drying clothes indoors where possible or use a vented tumble dryer. Also ensure extractor fans are functioning in bathrooms and kitchens, and keep internal doors open to promote airflow.
Maintaining a consistent temperature throughout the day helps prevent condensation on cold surfaces. Finally, consider leaving a small gap between wardrobes and external or party walls to allow air to circulate, further reducing the risk of mould forming behind them.
Whilst your neighbour’s vacant and unheated house may have had a very small influence, it is unlikely to be the main cause of mould in your home. The key factors are likely internal: inconsistent heating, restricted air circulation, and excess indoor moisture. Addressing these issues should resolve the problem effectively, regardless of the condition of the neighbouring property.
Aidan McDonald is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland
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