Window Condensation. Humidity Problem?
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Humidity Problem?

Every winter it seems there are increasingly more homeowners that are very interested in the topic of window condensation. It’s not because they are happy about it. It is because thay have had a bad experience with it. An experience that not only is irritating, but can be downright expensive.

You may find this hard to believe, but the growing condensation problem is the result of progress. If your home has an issue with window condensation, it is probably because the home you live in is a modern home that has a tighter air seal than an older home would have. A home that is more comfortable and cleaner. This is because a modern home is sealed much better from the outside air and is also much better insulated. Moisture that naturally builds up in your home was able to escape in older homes because they were not sealed as well and there are many places that the moisture could escape. Modern appliances that save us time and labor also add to the condensation problem.

Here is some information that will hopefully help you understand the moisture problem of a home that is well insulated with a tight air seal. It may help you to resolve the condensation problem in your home. If you are planning on building a home, of course you want a home with good insulation and a tight air seal. But you can do some things to prevent excessive moisture, more so than in a home where the problem already exists.

Why “Trouble” Condensation

If there is occasionally a small amount of fog on the bottom corners of the windows in your home, you need not worry. It usually goes away in a short amount of time.

The issue we are addressing is troublesome or excessive condensation. The type where the whole window is affected. Visibility is impaired by frost or fog. Moisture running off the window can damage plaster and wallpaper as well as stain the wood casing around the window. The first reaction can be to blame the windows, or even the construction of the home. However, this would be wrong.

Define Humidity?.

The real problem is one you can’t see. It is too much water vapour. About the only way to deal with this is to reduce or eliminate the water vapour. If you already have good windows with double sealed units, there isn’t much more you can do to the window to help the problem. Humidity is invisible and can take the form of water vapor, steam, etc. The amount of humidity in the air varies. The humidity in humid air will try to move to and mix with drier air.

This tendency or force is called “Vapor Pressure”, and it can be very powerful. It can actually move in a different direction than the flow of the air itself. Because of Vapor Pressure, moisture can easily be forced through materials such as brick, wood, plaster and cement. The very materials we use to construct our homes. The air in your home is usually humid, and the air outside is dry, especially in winter. Some building materials do stop water vapor. Glass happens to be one of these, as well as some paints, tiles and varnishes. Vapor Seal Insulation is specifically engineered to be a barrier to water vapor and help prevent damage to your wall and insulation from moisture.

Increased utilization of these “moisture trapping” materials in recent years has produced today’s “air tight” home. Moisture produced by washrooms, kitchen areas and laundries do not flow easily towards the outdoors any more. The current insulation and construction that keep cold air outdoors also keeps moisture in. So it’s super easy to develop excessive as well as damaging moisture levels in such houses. AMERICAN BUILDER magazine calls the issue a mix of many causes that build excessive moisture in the current home. More washing, bathing, showers, home appliances, and gas furnaces – all create more water vapor in houses compared to previous years.

HEATING AND VENTILATION magazine provides contractors with information on causes of water vapor. For example, cooking for four adds 4.5 pounds of moisture each day to some houses. Each shower can add half a pound. A weeks laundry can add 30 pounds. Human occupancy adds 3 to 6 pounds each day. Washing dishes, 1.2 pounds, etc.

All this moisture MUST eventually escape out of your home. This is why a modern day family of four can certainly release 150 pounds, or even more than 18 gallons of water each week into the air in your house! Houses that have no basements have even further moisture problems. Now elevated manufacture of humidity is just a portion of the story.

Houses have been growing more compact which means a much greater power of water vapor that is trapped by modern “air tight” construction. This means MORE moisture found in LESS space. No surprise we have produced a condensation problem to live in!

David Bareuther, Connected Press Building editor, covers the issue of reducing humidity by doing this. He states you will find only 3 ways to lessen humidity:

  • 1. CONTROLLING CAUSES OF HUMIDITY: For example, ventilation of gas furnaces, clothes & hair dryers, etc, to the outside of the home. Utilization of bathroom or kitchen fans that also vent outside.
  • 2. VENTILATION IN WINTER: Because outdoor air usually consists of less water vapor, it’ll “decrease” humidity of inside air. This happens naturally in older houses through constant infiltration of outdoor air.
  • 3. WARMTH: The entire process of heating the house will lessen the relative humidity – supplying it’s DRY Warmth. It’ll counterbalance most or all of the moisture created by modern living. Now, before we summarize specific steps for reducing humidity in your house, let us start adding some fundamental data about Suggested MOISTURE. You are able to make reference to it if you’re inclined to check the moisture levels in your house. The table here was created by lengthy and careful experiments in the College of Minnesota Engineering Labs. It shows the most safe humidity levels for your house … not only for the home windows, but also the fresh paint, insulation and structural members. Generally, reducing moisture to these humidity’s will cure difficult condensation problems on windows. If not, you are able to reduce humidity further without discomfort to you and your family. Should you test humidity in your house, make sure to make use of an accurate instrument, ideally a great sling psychrometer. Remember, too, these relative humidity’s are suitable for 70 degrees F. For greater temps, lower humidity is required.


Air Temperature Outdoors

Humidity Inside if Home is at 70º F

-28º C or Below

-18º F or Below

<= 15%

 -28º C to -23º C

-18º F to -9º F

<= 20%

 -22º C to -17º C

-8º F to -2º F

<= 25%

 -16º C to -12 C

-1º F to 10º F

<= 30%

 -11º C to -6º C

11º F to 21º F

<= 35%

 -5º C to 4º C

22º F to 40º F

<= 40%



  • These are comfortable levels of humidity. From easy to more difficult, here are some steps you can take to reduce condensation on the glass of your windows.
  1. Double-glazing or storm windows.
  2. Turn off furnace humidifier and then any other humidifying products in your house.
  3. Make sure that louvers in loft or basement crawl spaces are open and that they’re big enough.
  4. Run kitchen or any other ventilating fans longer and much more frequently than you would normally do.
  5. Open fire place damper to permit moisture to escape more easily.
  6. Air out your house a couple of minutes every day, including kitchen, laundry and bathrooms either during use, or just after use.
  7. If difficult condensation continues, call your heating contractor about outdoor air intake for the furnace, about ventilation of gas burning furnaces and home appliances, or about installing some ventilation fans. When the more common remedies we recommend (# 1 through 6) aren’t effective, you definitely have a condensation problem. The alterations your heating contractor may recommend, to help reduce humidity in your house, shouldn’t be very costly. Certainly they’ll be less costly than the usual fresh paint job triggered by excessive water vapor!
  • The thing is, the fundamental principle of reducing window condensation is very simple. When there’s an excessive amount of condensation on your home windows, this means that humidity is simply too high in your house, You need to do something to lessen humidity until condensation vanishes. Condensation and reducing humidity can become very complicated, just because many different conditions may affect how a condensation problem ends up in various houses. Let’s just mention a couple of them:
  • The type of windows in your home and how many you have
  • The type of sealed units in the windows
  • The type of heating system — Forced Air , Baseboard Heating or Interior Wall.
  • How good your insulation is and the type of vapor barrier
  • The kind of soil and effectiveness of drainage

Due to a lot of variables, a condensation problem can often be very difficult to solve. This is exactly why it is recommended that you enlist a specialist to deal with your problem when the simpler steps to lessen humidity do not solve your condensation problems. Call your architect or perhaps your heating contractor first. When they are unable to help, we recommend that you simply request your current contractor or lumber dealer to put you in touch with a qualified expert. They are usually both at engineering schools and in the employ of heating, insulation, wallboard or window manufacturers. Before we leave the topic of reducing humidity, we wish to add some of the following:

You will find two reasons for condensation which are TEMPORARY. They’ll disappear following a couple of days or for the most part a season of heating. First, there’s the moisture which comes from new construction or remodeling. There’s much moisture within the wood, or even the plaster or another building material of the new house. Once the heating season begins, this moisture will progressively flow out into the air in your home. It should then be reduced and not cause any more trouble.

A very similar kind of factor occurs in a milder form, at the onset of each heating season. Throughout the summer time, your home has absorbed some moisture. Following the first couple of days of heating, your home is going to be dehydrated, and you will have less challenge with condensation. While we’ve been talking about the charge of condensation we have pointed out nearly everything EXCEPT home windows. There’s a valid reason. There’s nothing much that you can do with home windows to reduce condensation.

Because as the building experts have frequently stated, home windows aren’t to blame for condensation. The moisture content of the inside air is where the problem lies, is caused and cured.

Construction materials in new houses are needed to be water base items. This could include fresh paint and caulking compounds. As many of these items dry or cure, this moisture is combined with normal moisture that is normally produce in your house.

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