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Damp toolbox part 1: Introduction to causes & solving issues

The headlines

Damp, condensation, mould, and humidity in homes can be irritating, confusing, and worrying.

The causes and their solutions are not widely understood. This is no surprise as this can be a complicated and mysterious subject.

This is the first of a group of 'Damp toolbox" articles that hopes to give you:

  • An understanding of what is going on in your home.

  • Practical solutions that will help you to experiment with solutions and fix your problems.

  • The opportunity to reduce indoor air pollution issues at the same time.

Everything in these articles is based on proven science, independent evidence, and the experience of a wide range of independent experts.

The consistent conclusion from all these sources is the same: The best way to solve damp and condensation problems is to:

  • Reduce the amount of moisture going into the air in a home in the first place.

  • Get rid of moisture that builds up, with appropriate ventilation being by far the best method.

These articles do not cover the diagnosis or fixing of structural damp issues such as rising or penetrating damp, although some of the information in these articles may be relevant. The articles are about damp issues caused by activities INSIDE homes.


100 seconds or so of video introduction from me

With subtitles.

I am in no doubt that these articles give you the most thorough and practical set of information on this subject anywhere online.

Some of what you read might also be counter intuitive, or challenge what you already believe. Please do:

  • Read onwards with an open mind.

  • Experiment with some of the solutions. It may take a combination of solutions to solve your problems.

The articles are all part of a jigsaw of information, so do try to read them in the order if you can by using the navigator buttons at the top of each page.


Quick links to sections below:


Where has this problem come from?

Over recent years there has been a big focus on improving energy efficiency in homes.

While homes have become better insulated and more energy efficient many have become too much like airtight boxes.

They now suffer the consequences of a build-up of damp humid air.

As a result, around a third of UK homes now have issues of damp and condensation.

It is not a new problem, but it has got worse. Changes in indoor activities (such as increases in laundry drying indoors) have significantly added to the problem.

This problem predominantly only affects domestic situations.

Other buildings such as public buildings, workplaces, and shops rarely have these sorts of issues because even though moist air is often generated in those sorts of buildings, there is always good ventilation.


A brief caution about information on social media

You may already be aware of many views on this subject on social media. Please bear in mind that:

  • All homes are different, VERY different.

  • How homes are used varies dramatically.

  • It’s almost impossible to know whether your circumstances are similar to the person posting on social media.

  • Opinions online may contain important factual errors.


Why damp and condensation issues occur

Of the homes affected by damp, a small number, around 1 in 30, suffer from structural moisture problems such as penetrating damp.

For ALL THE OTHER homes damp issues are caused by a combination of three things:

  1. Water added to the air within a home by its occupants and their activities. This amounts to approximately 2-4 litres of water per adult in a day.

  2. Lack of ventilation. Homes are much less draughty than they were a few decades ago, and so damp air builds up.

  3. Inadequate insulation. Poor insulation can cause surfaces such as walls and windows to become cold. And when humid air meets a cold surface, persistent condensation and mould is the result.

In summary 1) The source of the problem is a build-up of water in the air, 2) Many indoor activities generate a lot of it and 3) It builds up and then lands on cold surfaces creating condensation, mould, and damage to homes.

Radio 2 Steve Wright in the afternoon style factoids!

Did you know that:

  1. Condensation in bedroom windows in the morning is often because of the moist air we breathe out when we sleep. By drawing the curtains we keep the heat in the room, and away from the inner surface of the glass. The inside of the glass gets a little colder because of this. This makes it more likely that the water from the air we breath forms condensation on the glass.

  2. If you use the heating to dry of condensation from windows, that moisture then goes back into the air in the home. When the heating goes off and the air indoors cools, that same moisture held in the air will then land on the window pane again and form condensation again.

  3. If you have high levels of damp in the air in a home, it is also probably means indoor air pollution is poor. The best solution for getting rid of indoor air pollution is the same as the best solution for indoor damp issues: providing adequate ventilation

  4. Adequately ventilating a home might only cost around £3 a week in additional heating costs.

  5. Even on rainy cold days opening a window or trickle vents will actually reduce indoor damp problems?

  6. A wash load of wet laundry holds between 1 and 3 litres of water. When it dries, indoors, that damp air needs to go somewhere!

The other blog articles that follow have,more factoids like these, plus as much practical stuff as I can find or think of to help you get to grips with issues you have.


Why addressing damp issues in the home matters

A damp home or room can cause several unwanted or unpleasant problems:

  1. Heating costs - dampness generally increases heating costs. This is because your heating system will heat both the air and the water held IN the air. Dryer air is cheaper to heat.

  2. Comfort - Damp air takes away more heat from our skin. It makes us feel colder and so more likely to want to turn the heating on, or turn the thermostat up.

  3. Health issues - Damp encourages the growth of moulds, bacteria, and viruses. All have associated health risks. Some people are susceptible to allergic reaction or asthma attacks as a result. This particularly affects older people, babies, and young children, and those with respiratory problems.

  4. Condensation - We often see condensation on windows, tiles in bathrooms, walls and even doors and walls. So much water has built up in the air that it gets dumped onto cold surfaces. Persistent condensation can be annoying and can lead to visible mould issues. It is usually impossible to never see ANY condensation in a home, such as when showering which will create a lot of damp air. Condensation in the immediate room is almost impossible to stop. But, in a home with good ventilation or generally low levels of humidity, this condensation will soon disappear and not cause problems.

  5. Hidden mould and rot - If damp air finds its way into hidden cool parts of the home it can create mould issues that are out of sight. Examples include behind kitchen cupboards, bath panels and skirting boards, on walls and cold corners behind furniture. Damp air can also find its way into the building's structure. This can sometimes lead to significant damage, such as slowly rotting floor or roof timbers.

Living with moisture trapped 'in the home' is not good for health or the health of the building!


An important word about....other indoor air pollution issues that can be solved at the same time

As we make our homes more air-tight we should be aware of increasing levels of air pollutants that build up just as damp air does. Indoor air pollution is a serious issue in the UK, but currently has low levels of public awareness.

Indoor air pollution can combine with damp and have a range of health issues. I bring your attention to this because the best solutions for damp in a home are also the best solutions for indoor pollution.

For very good information on indoor air pollution see this section on the Asthma and Lung UK website. Also see the geeky section at the bottom of this article for more info.


Further reading for geeks like me

Indoor air pollution

University of Nottingham researchers suggest there are up to 900 chemicals in UK homes. These are from a wide range of pollutants, odours, and fine airborne particulates which the diagram below illustrates. The largest culprits are cooking and cleaning but there are many others. Even air fresheners contribute it indoor air pollution issues!

A study in 2019 found that nearly half of homes in the UK suffered from high indoor air pollution.

The University of Chester estimates because of this, that there are 20,000 deaths linked to indoor pollution each year in the UK. (See this YouTube video, at around 3 mins 44 seconds for more information). This compares to around 40,000 deaths linked each year to OUTDOOR pollution.


Links to the other damp articles

Main Damp toolbox articles

Other supporting articles on damp:


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I run this website as a hobby, because I care about this stuff, and do it for no commercial purpose. If you have valued what you've seen, please tell other people about it.

If you have any other suggestions for additions or changes to site content do please let me know. While I have made every effort to ensure that the information contained on this website is correct, I cannot take responsibility for errors or omissions.

All content on the site should be treated as information and not advice. You should take professional advice where appropriate to different site articles.


Mark Thompson

Get Energy Savvy - simple practical home energy efficiency information

7,160 views2 comments


Harry Collett
Harry Collett
Dec 31, 2022

How do Scandinavians keep warm. The houses are made of wood, wood is warmer than brick I would imagine

Mark Thompson
Mark Thompson
Mar 13, 2023
Replying to

Stacks of insulation, lots of triple glazing and attention to detail on air tightness (while still ensuring ventilation is adequate)

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