Breaking the mould

April 20, 2023

Damp and mould is a perennial British problem. Landlords are increasingly trying to find ways to deal with issues of black mould in households. Householders are increasingly looking for ways to persuade landlords to do something about it, including litigation. An impasse develops when neither party wants to take responsibility, blaming the other.

So who should take responsibility?

If, say, 20 per cent of homes on a housing estate are reporting problems with mould, then 80 per cent are not reporting problems. The more people (and pets) who occupy a space, the more water vapour is added to the air via breathing, showers, clothes washing, and drying too. Landlords generally assume that the 20 per cent are doing something wrong that could be addressed with targeted advice, and so they send a helpful leaflet giving tips on how to reduce the condensation in the home.

This approach has some effect, though in many homes the problem persists. Residents don’t change their behaviour easily, but to be fair, what is an acceptable level of breathing, showering and clothes drying? Some homes have no outside drying space, and others may have no option when the weather is poor. They have to use radiators to dry clothes sometimes because clothes that aren’t dried quickly can start to smell.

What are the issues?

So, what makes the 20% different to the 80% on our housing estate? It is frequently not the fault of the resident at all, but has to do with the construction of the home, air flows, glazing, lack of insulation (or failed insulation), solar gains and others. A building may have a range of contributory factors, but they may only become a problem when a larger family produces more water vapour, faster than the home can cope with it.

Maybe they should just open a window? Possibly, but residents will tell you some valid reasons why not: Security; a frail person very sensitive to draughts; lifestyle; external weather; damp weather outside so it doesn’t seem logical to change warm damp air for cold damp air (actually, that can help – see below).

There may already be a helpful extract fan, but some types make a noise in the middle of the night when the bathroom light comes on, disturbing sleep for the rest of the family. Or, it creates a back-draught wasting heat in the home, and has therefore been blocked up. Some ventilation systems provide an ‘always-on’ air input – these are also commonly disconnected by the resident to save electricity.

Maybe the flats are north-facing and don’t get warm. Maybe they have more occupants and therefore produce more moisture. Are they in fuel poverty and underheating? – If the homes are cold to start with, then the dew point is reached much more easily.

What can be done about it?

Baker Homes has begun a key piece of research to identify just how much the risk of condensation and mould is affected by each of these factors. We are investigating hundreds of homes in several local authorities and social landlords, to develop a tool that can clearly identify the level of risk for a home, street or housing estate.

It aims to show if more appropriate ventilation, insulation works, or simple behavioural advice will offer the best solution, reducing the need to carry out individual onsite assessments.

Some useful facts about condensation in homes:

  • Warm air has the capacity to hold more moisture than colder air.
  • Relative humidity (RH) measures the quantity of water vapour in a parcel of air, relative to the maximum quantity that air can hold. If a room is at 21oC and 75% RH, then when the temperature of that same air falls to 16oC , it reaches 100% RH and the water vapour begins to condense out of it.
  • The ‘dew point’ is therefore the temperature at which the air can no longer hold the amount of water in it.
  • The average temperature in a room may be 21oC, but the surface temperature of the walls, windows or ceiling, may often be below the 16oC dew point – particularly if it is cold, wet or windy outside. Water therefore begins to condense on these surfaces.
  • Mould spores are very commonly found in household air, and thrives on damp wallpaper and plasterboard among other surfaces. It prefers higher temperatures, but will still grow at low ones, albeit more slowly.
  • The same conditions which encourage mould growth are also ideal for dust mites, which are also allergenic and a trigger for asthma.
  • Airborne moisture is often at its peak during the evening, or just as everyone gets up. A helpful tip can be to open windows for 15 minutes, for a complete air change. Remember cooler air can’t hold as much moisture as warmer air, so if the new air is cooler – even if the humidity is high – its RH lowers as it reaches room temperature.
  • Traditional solid walls have a U-value (heat loss factor) which is very similar to typical double glazing. So – condensation that used to settle on the old single glazed windows, now finds the walls are the same temperature, and so it settles on the wall instead.
  • Loft insulation that is not correctly rolled out leaves bare patches that cause cold spots on the ceiling which may cause condensation to form. It’s a bit like going out with an exposed midriff on a cold day.
  • Many types of cavity wall insulation (CWI) fail, or were not filled properly in the first place. It can settle – causing insulation gaps; absorb water that soaks through the outer brickwork – causing the internal wall to lose heat faster; it may have been poorly filled under windows or the tops of walls; and sometimes the cavity may contain a variety of building debris causing cold bridging.

To take part in the research please contact and look out for our next blog exploring some of the outcomes from the research expert panel.

Bill Wright

Bill Wright

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