Window Condensation

Every winter, we receive calls from concerned homeowners who tell us their windows look like they are leaking.

It’s warm and cozy inside, but the windows are dripping or foggy.

This is particularly important during winter because here in Canada it is often necessary to add back humidity to the dry air. But adding back humidity, while good for your health, isn’t always good for your home’s health.

In this article, learn all about why windows seem to “weep” and what you need to do to fix it.

Why Do Windows Get Wet or Foggy In Winter?

The simplest explanation, and the one most homeowners use to console themselves (however much in error), is that window wetness or fog occurs when warm indoor air meets cold outdoor air.

But well-built, well-sealed, well-insulated windows do not fog, drip or leak when cold air hits them.

There are two main structural reasons windows may appear to “weep” when there are extreme temperature differences between your indoor air and the air outside: poor seals and no insulation.

Poor window seals

Over time and with age, the seals around windows break down and degrade. This lets air leak in and out. As warm and cold air mix and mingle, moisture occurs.

Older windows are typically single-pane, which means there is no insulation built into the window itself to keep these two air streams separated.

No interior window insulation

Today’s windows are usually double- or even triple-paned. This means that there is a layer or two of glass in between the part of the window that gets hit with warmed indoor air and the part of the window that gets hit with cold outdoor air.

This extra interior glass acts as a form of insulation to ensure condensation will not arise.

Modern Airtight Homes Are Condensation Starters

In some cases, you may have double- or triple-paned windows installed. The weatherstripping and sealing around each window is fresh and new. And you have plenty of high-quality, moisture-resistant insulation installed in your walls, ceilings and floors.

But you are seeing window fog, condensation or weeping anyway. What could be causing this?

Typically, it’s modern airtight construction standards.

As concern mounts about the planet’s dwindling energy resources, the construction industry has developed new building standards that keep 100 percent of temperature-controlled air locked inside the space.

There is just one problem with this: these new homes cannot breathe.

What would happen to you if you could only breathe in, not out? You wouldn’t be able to let out the stale carbon dioxide your body needs to get rid of. Essentially, you’d be holding your breath and becoming increasingly toxic.

This is what happens when your home can’t exhaust toxins, stale air and excess humidity. The windows start to fog up!

There are two things we tell our clients to try when this happens: lowering the humidity and adding more ventilation.

Lower the humidity

For general health purposes, it is good to add back some humidity into your indoor air in winter. This is especially the case if anyone in your family suffers from allergies or winter asthma symptoms – the humidity can make it a lot easier to breathe.

But if you are living in an airtight home, the excess humidity won’t be able to find its way out again. When this happens, you can lower the humidity temporarily as a test to see if the window condensation goes away.

If this test works to rid your home of foggy, weeping windows, you know that you need to add ventilation to keep the situation from recurring.

Once you add more ventilation, you can run your whole-home humidifier as much as you need to without worry it will cause wetness, mould or mildew inside your space.

Install a heat recovery ventilator

For this, we always recommend installing a heat recovery ventilator (HRV). HRVs are essentially mechanical lungs for your home.

They help your airtight home “breathe,” exhausting stale air through one conduit while pulling in fresh air through a separate conduit, balancing your home’s humidity levels and conserving heat energy in the process.

HRVs are so critical for airtight homes they are now mandated for all new construction in the Toronto area.

Once you install an HRV, you will no longer have to worry about running a winter humidifier inside your home. The HRV will exhaust stale, humid air so it doesn’t build up and cause window damp and condensation.

You can even connect your HRV to a humidistat monitor installed in a central location that automatically detects rising indoor humidity levels. This will trigger the HRV to start running to exhaust the excess humidity before it can cause any structural damage.

Warning Signs of Window Condensation Damage

Homes have their own language that they use to try to alert us about problems that need our attention. Window condensation is one such alert.

There are other warning signs to alert you to potential structural damage:

  • Efflorescence (powdery mineral salts left behind after water evaporates)
  • Bubbling or cracking paint or wallpaper around windows and on ledges
  • Strange smells (especially grassy or “dirty socks” odours)
  • Visible mould or mildew patches

Get in Touch

Are you tired of having to wipe down your windows just to see outside and keep moisture from pooling? We can help!

Contact us online or give us a call at 905-544-2470. 

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