What Causes Condensation on Windows, How Big a Problem is it and, Most Importantly, How Do We Stop It?
It's that time of year when condensation on windows becomes a pain, we wake up in the morning, can't see out, curtains are wet, there's water on the window bottoms, and even worse it can affect the walls below windows causing mold and mildew in drywall and furniture.
Condensation is bad news in multiple ways – it indicates where a home has weak spots or thermal bridges in its insulated envelope, it points to problems in humidity levels in the home – possibly coming from hidden problems in basements, crawlspaces, walls or ventilation systems – and some things are certain when a home has condensation running down the windows:
Condensation won't disappear on its own
Condensation is potentially detrimental to health as it allows for mold and mildew growth
Condensation can cause damage to homes and lead to costly renovations and repairs
So, the question is – what should we do about condensation? How do we fix and prevent condensation in our homes?
Condensation in homes – the basics
So what is condensation? Condensation in its purest form is caused when humidity in the air comes in contact with a cold surface and it condenses from a gas to a liquid again.
Where we notice it most in our homes is on windows, or on the sides of a nice chilled glass of chardonnay or a cold beer – with the exception that one denotes a pain in the butt, the other pleasure!
The reason we notice condensation most on glass is that it's an impervious material – the water has nowhere to go so it sits there, waiting for us to wipe it off and running downwards until it does find a surface to soak into – which is unfortunately where the problems start to occur.
The other factor to consider, other than warming cold surfaces to mitigate condensation, is that it can also happen when there's simply too much humidity in a home. As noticed most often in the colder months of the year, when it meets the cold glass of bedroom windows, as cooling air becomes unable to hold as much moisture, it condenses. So condensation is the result of relatively warmer and humid air meeting a cold surface.
What's the problem with condensation?
Traditionally, most building experts will mention mold and mildew as the main problems caused by condensation in homes – but first off, here's a point to think about in connection with condensation on windows that we haven't seen specifically mentioned anywhere.
As a key element of Passive House, Net Zero Energy and high-performance homes is consistently making the most of Passive Solar Gain, having a home where each day starts with fogged over windows is absolutely a huge detriment. A hidden effect of condensation on house windows is that once the sun does come up, which could and should be heating our high performance home's interior in the colder months, instead the sun's heat is being used up to evaporate the window condensation while also putting all that moisture back into the home interior and ultimately raising the humidity level.
So that's one issue that makes condensation a problem, using energy unnecessarily – but then of course damp is caused by condensation too and our homes are generally not built to resist moisture. Even minor water damage can leave severe stains and damage on drywall while other times you will need to completely remove the damaged drywall and replace it – especially if it becomes badly affected by mold and mildew – which usually makes an appearance as a cloud of little black dots around windows or in the corners of rooms.
As condensation occurs when moist air comes into contact with a colder surface like a wall, window, mirror etc. this is usually where we find mold and mildew growth first – but we've also seen it behind wardrobes and furniture where air doesn't circulate as freely so the drywall can't dry out.
Mold can grow on virtually any organic material as long as moisture and oxygen are present. There are molds that grow on:
Wood
Paper
Carpet
Food
Insulation
Because mold eats or digests what it is growing on, it can damage a building and its furnishings. If left unchecked, mold eventually can cause structural damage to building materials, rotting wood, disintegrating drywall, costing the homeowner money for remedial work and potentially reducing a home's value.
If the humidity level in a home is above 60%, certain molds start to grow and flourish in under 12 hours – so if condensation is present, there's almost certainly mold and that may become a big issue.
Condensation, humidity, mold and health
Exposure to damp and moldy environments may cause a variety of health effects, (or none at all). Put simply, some people are sensitive to molds. For these people, molds can cause nasal stuffiness, throat irritation, coughing or wheezing, eye irritation, or, in some cases, skin irritation. People with mold allergies may have more severe reactions and immune-compromised people and people with chronic lung illnesses, such as obstructive lung disease, may get serious infections in their lungs when they are exposed to mold. These people should stay away from areas that are likely to have mold – such as a home with high humidity.
Before we all panic because we noticed some condensation in our homes, remember that eliminating all mold and mold spores indoors is virtually impossible, but controlling indoor moisture and humidity levels will control the growth of indoor mold – so this is the key.
Condensation is a symptom of other issues
Consider condensation as a symptom and not a cause of home humidity being too high, so, if there's condensation happening on windows, the first step we'd suggest is to get hold of a hygrometer or humidity meter or monitor to test the level of relative humidity in the home – because ironically the higher performance the home gets, with air barriers and better windows and doors, the more chance there's going to be a problem with humidity unless it's been designed with automatic mechanical ventilation systems like HRV's & ERV's from the off.
Monitor humidity levels in the home over a week and at different times of the day and we're willing to bet that they get above 60% relative humidity. If so, then there are several things to do that will help:
Limit the amount of humidity being produced in the home or entering it.
Ventilate the home to remove excess moisture.
Dehumidify the air in the home to bring the relative humidity below the 60%.
Heat and insulate homes evenly to try to prevent cold spots that will provoke condensation.
How to reduce condensation in homes
Once we've identified that a home is over the recommended humidity level of 60%, we should firstly try to identify where this excess moisture is coming from. All living organisms give off humidity simply by existing, humans, animals, even plants – so is the home large or small in relation to the number of occupants?
Interestingly, up to half of the high humidity solution is changing personal habits in the home:
Showering – The bathroom is the most humid place in the home, and something as simple as taking a shower releases huge amounts of humidity into the air. Try to keep to a reasonable temperature and timespan while running the bathroom fan during the shower and for 15-20 minutes after to get that humid air outside.
Cooking and using a kettle or coffee maker – Kitchens are the second biggest source of home humidity. Be sure to use pan-lids when cooking to reduce moisture being created from the water boiling, and have a cooker hood that's set to extract.
Close kitchen & bathroom doors – when cooking food, boiling the kettle or taking a shower, ensure that the kitchen or bathroom door is kept closed to prevent the moisture in the air from going into colder rooms which will cause condensation to form if it touches a cold surface.
Laundry – Never dry laundry inside on a rack or line when it's cold outside. Every load releases almost 5 pints of water into the air.
Unvented gas heaters, stovetops & ovens – When natural gas or propane and butane burns it releases water vapor and potentially carbon monoxide. Either choose a different heat source where possible, or ventilate to get that all outside.
Humid basements or crawlspaces – Often the cause of humidity in the home. Many basements were built with inadequate insulation.
Check for water leaks – Any pipes carrying water in the house, both delivery of hot and cold or heating and evacuation, should be checked for leaks and any leaks fixed promptly.
Fit high efficiency HRV or ERV units – With modern homes being more airtight, it's also a great idea to fit a mechanical ventilation system with heat or energy recovery depending on the climate zone the property is in.
Fit a high efficiency and appropriately sized dehumidifier – If the relative humidity levels stay too high then there is always the possibility of running a dehumidifier to bring the humidity levels down into the ideal range.
I've just realized, the condensation is between the glazing panels!
Condensation within double glazing typically suggests that there is a problem with the sealed unit in the windows. This means that a point in the edge seal of the window has failed and is allowing moisture to enter because the sealant between the glass and frame will have to be renewed.
On older or poorer quality units, the sealant used to create the seal may be of a low grade or become loose over time. If the seal and bead that's supposed to hold the glass in the frame deteriorates, moisture and water can get into the frame. Allowing large amounts of water to settle in a window frame like this for a long period of time will eventually affect the ‘air gap' seal surrounding the two panes of glass and if it's a wooden frame it will cause it to rot.
If you have condensation in double-glazing, then it is a sign that the sealant has failed, and this usually means that it will have to be replaced or resealed. If the windows are old, then replacing the whole unit can be recommended so that the same problem does not occur again.
