May 21, 2019 Last Updated 8:31 AM, Apr 10, 2019

How PIV is helping landlords improve the indoor air quality (IAQ) of their housing stock

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John Moss, Head of Social Housing Sales at EnviroVent, looks at how the recently released English Housing Survey demonstrates why indoor air quality should be a priority for social landlords.


The English Housing Survey revealed recently that damp continues to be a problem for at least one million homes in England. The statistics showed that those living in rented properties, either social housing or private, were most likely to be living with ‘damp’, manifesting itself as condensation and mould growth. This was found to affect 586,000 households. As is widely known, condensation and mould are produced by activities in the home, such as taking showers and baths, boiling kettles, cooking, drying clothes and breathing. A family of four will contribute approximately four pints of water per person a day into the atmosphere, which is equal to over 100 pints of water vapour a week, creating high levels of humidity if internal air is not allowed to circulate and new drier air to enter the home.

Before the days of energy-efficient upgrades, such as double glazing, cavity walls and loft insulation, this humid, stale air would find its escape route through ill-fitting windows and doors, lofts and so on – otherwise known as draughts! In modern homes that have greater airtightness, there can be a lack of fresh air circulating around the house. Without a regular circulation of fresh air into a house, warm air hits a cooler surface and the water vapour within it condenses, leading to damp appearing on walls and around windows.

Condensation can be reduced and indoor air quality improved by retrofitting PIV (Positive Input Ventilation) systems, which eradicates problems with high humidity leading to condensation and mould. PIV creates a fresh, healthy and condensation-free environment by drawing in a constant supply of fresh filtered air into homes through the loft space.

Another interesting finding from the English Housing Survey was that the energy efficiency of England’s housing stock has improved significantly. Over the last 10 years, the percentage of homes achieving an energy efficiency rating between A and C increased from 5 to 28%. The proportion of homes in the lowest energy efficiency bands fell from 19 to 3%. This trend towards greater energy efficiency, whilst it is a positive in terms of warmth and comfort, is one of the main reasons why mechanical ventilation is needed in homes. Many industry experts have pointed out that requirements for airtightness in new and renovated homes has increased, yet ventilation requirements have remained unchanged for many years. Regardless of this, many social housing providers are recognising the issue that tenants face and the burden that dealing with condensation and mould growth puts on their maintenance teams. Social housing providers are also aware of how poor ventilation can impact on the health of tenants, by exacerbating existing respiratory conditions, such as asthma.

A persistent problem for housing maintenance teams, particularly in the colder months, involves dealing with issues caused by condensation and mould growth. As homes have been made more airtight, due to energy-efficient upgrades, this has had a direct impact on the internal environment by lowering the quality of the indoor air. Social housing providers are all too aware of the issues that tenants face with poor ventilation – which can worsen respiratory conditions, such as asthma. A major issue with improving airtightness is that it traps pollutants in the home, resulting in a much higher concentration, unless it is adequately ventilated. There are a variety of natural and man-made airborne pollutants that exist in homes such as Radon, VOCs and pollen.

Continuous flow of fresh air

Without a continuous flow of fresh air into and out of a dwelling to control the relative humidity, the internal atmosphere may reach a high relative humidity of around 70 to 80%, which then leads to condensation. The water droplets that form on colder surfaces can result in mould growth and, in some cases, damage to the building fabric itself.

Condensation is often more noticeable in kitchens and bathrooms, because it is where most moisture is generated, for instance, from baths, showers and cooking. The situation is even worse when dwellings have internal bathrooms, with no windows, as often occurs in flats, which can be prone to serious condensation, especially if the extractor fan is inadequate or not working.

In some cases, fans are switched off by tenants who believe they are expensive to run and, in other cases, the units may malfunction. This is why there is a clear need for education when ventilation systems are fitted, to advise tenants how they work and why they are essential. It is also worth considering ventilation systems that are tamper-proof, which means they can work effectively without restriction.


Many social housing providers are recognising the benefits of retrofitting Positive Input Ventilation (PIV) systems into homes that are most at risk of issues with condensation and mould. Fit and forget systems like PIV are helping to improve the indoor air quality for tenants across the country, whilst reducing the risk of mould and damage to the fabric of a building.

Given that the onus is still on public sector housing providers to upgrade the airtightness of their homes, there is a very real need for ventilation to be given equal consideration to energy-efficient upgrades. By upgrading the ventilation systems too it means that for a relatively small investment, the level of complaints for issues of condensation and mould growth would be much reduced. By upgrading the ventilation in a property, social housing providers can ensure that indoor air quality is improved and the burden on the maintenance team is reduced.

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