You wake up on a clear spring morning in Burlington, look toward your window, and see a blurry layer of fog trapped stubbornly inside the glass panes. While surface sweat is normal, persistent window condensation in Burlington homes often signals a serious structural seal failure. When moisture gets trapped inside a double-pane glass unit, it immediately degrades your comfort, spikes your seasonal energy bills, and ruins the long-term health of your window framework.

I am Oleg, owner of Proper Caulking, and I have spent 18 years diagnosing trapped glass moisture across the Halton Region. Most people assume foggy windows are an indoor humidity issue, but inter-pane moisture is actually the final symptom of an exterior failure. When your outside perimeter caulking degrades, rainwater pools on the frame and prematurely rots the factory glass seals. Let me show you why your window seals fail, how “solar pumping” destroys glass, and how professional exterior sealing protects your investment.

Surface Sweat vs. Trapped Fog: How to Diagnose Your Windows

The first thing to determine is where the moisture is. This matters because the cause, the severity, and the solution are completely different depending on the answer. Condensation on the interior glass surface is common and generally harmless in small amounts.

It happens when warm, humid indoor air contacts the cold surface of the glass and the water vapour in that air drops below its dew point and forms droplets.

You will see this most often on the coldest pane surfaces during winter mornings, in kitchens and bathrooms where humidity is high, or in newer, tightly sealed homes where ventilation is insufficient to move humid air out.

Wipe it off and it is gone. If it is recurring heavily on every window in the house, you likely have a humidity management problem rather than a window problem, and improving ventilation or running a dehumidifier will address it.

Moisture trapped between the panes is a different situation entirely. If you can see fog, streaking, mineral haze, or water droplets inside the glass unit and wiping the interior or exterior surface does nothing to change it, the factory seal on your Insulated Glass Unit, the IGU, has failed.

The IGU is the hermetically sealed assembly of two or three panes with a gas-filled cavity between them, typically argon or krypton, that provides your window’s insulating performance. That seal is permanent by design.

When it breaks, the insulating gas escapes, outdoor air enters the cavity, and with it comes moisture. Once moisture is cycling in and out of that cavity, you will see fogging, and eventually mineral deposits and permanent staining on the inner glass surfaces.

To be clear with homeowners who ask: exterior caulking cannot fix a broken IGU seal. Once the moisture is inside the glass unit, the unit needs to be replaced by a glazier or window installer.

What exterior caulking absolutely can do is prevent the conditions that cause IGU seals to fail prematurely in the first place. That connection is what most people miss.

The Physics of Solar Pumping: How Temperature Destroys Window Seals

To understand why window seals fail, you need to understand a phenomenon called solar pumping. It sounds technical but the principle is straightforward. When direct sunlight hits a double-pane window, the air trapped in the cavity between the panes heats up and expands.

That expanding air pushes outward against the perimeter seal of the IGU. When the sun sets and temperatures drop, the cavity air cools, contracts, and creates a slight negative pressure that draws air inward through any weakness in the seal.

Every day that a window is in direct sun, it breathes: out during the heat of the afternoon, in during the cool of the evening. This cycle is not a design flaw.

Factory IGU seals are engineered to handle it, and a well-installed window in good condition will manage solar pumping for fifteen to twenty years without failure. What accelerates the failure dramatically is moisture at the frame.

When the seal breathes inward each evening and there is standing water sitting in a cracked or open caulk joint on the window sill or perimeter, it draws that moisture directly into the cavity.

Over repeated cycles, the desiccant material inside the IGU spacer bar, which is designed to absorb small amounts of moisture, becomes saturated. Once it is saturated it can no longer protect the cavity, and visible fogging begins.

Older wood and vinyl double-pane units in mature Burlington neighbourhoods like Shoreacres, Roseland, and the historical downtown core are particularly vulnerable.

Many of these windows are approaching or have passed the end of their fifteen to twenty year service life, and their original installation caulking has long since degraded.

In high-wind exposure areas like Alton Village or The Orchard, the pressure differentials from wind-driven rain compound the solar pumping effect, pushing moisture into perimeter gaps more aggressively and accelerating the cycle.

Broken window seals are also one of the leading causes of energy loss in Burlington homes during summer cooling season. For a full breakdown of what a compromised building envelope costs you on your hydro bills, see our article on saving on AC bills with professional caulking.

How Exterior Caulking Protects Your Glass Investment

A new IGU replacement is not an inexpensive repair. Depending on the window size and unit type, a single glass replacement can run several hundred dollars before labour. Replacing the full window frame and unit is more.

Protecting the seal you already have, by keeping water completely away from the perimeter joint where the frame meets the surrounding wall, is a fraction of that cost and eliminates the primary source of premature failure.

Here is what a healthy exterior caulking bead does for your window’s glass unit. It seals the joint between the window frame and the surrounding masonry, brick, stucco, or siding so that rainwater hitting that surface sheds immediately rather than pooling.

Let me be completely honest with you: once moisture has forced its way completely inside your double-pane glass unit, the factory insulating seal has officially broken. At this stage, you will need to hire a glass specialist to replace that specific foggy glass pane.

However, before you spend your hard-earned budget on a glass replacement company, you must address the underlying structural root cause. Why did that factory glass seal break down early in the first place? In my 18 years of inspecting local properties, the answer is almost always a failure of your exterior perimeter caulking.

When your outside sealant cracks and separates, rainwater is allowed to seep past your siding and pool directly inside your window frame track instead of draining away. Your factory glass unit is forced to sit in a constant puddle of stagnant water, which prematurely rots, rusts, and destroys its perimeter seals.

If you pay to replace your blurry glass windows without hiring Proper Caulking to repair the failed exterior seals that caused the pooling water in the first place, your brand-new glass unit will suffer the exact same fate and rot all over again within a few seasons.

It prevents wind-driven rain from getting behind the frame. It removes the reservoir of standing moisture that solar pumping draws from each evening. Without that reservoir, the IGU seal is doing the job it was designed to do under dry conditions, cycling pressure changes without introducing water.

When that exterior bead dries out, cracks, or pulls away from the substrate, the joint opens. Water sits in it. During warm days the IGU cavity expands and vents. During cool evenings it contracts and draws. The moisture gets in.

The desiccant saturates. The fogging starts. This is not a slow, theoretical process. In a cracked window perimeter joint, the moisture cycle can begin producing visible IGU damage within two to three seasons. The materials we use at Proper Caulking are specified for exactly this environment.

Professional-grade paintable polyurethanes and high-performance silicone hybrids maintain their bond and flexibility through Burlington winters, summer UV exposure, and the constant thermal movement between a vinyl or aluminum frame and a brick or stucco surround.

Retail latex caulk applied in the same joint will be cracking and separating within a year or two, reopening the same vulnerability.

For more on how failing exterior caulking connects to water getting inside your wall assembly and window frame, see our article on leaking window frames in Burlington.

For authoritative guidance on residential window performance standards, IGU ratings, and condensation resistance in Canadian climate zones, Natural Resources Canada’s Office of Energy Efficiency provides detailed homeowner resources.

5 Red Flags That Your Window Seals Have Given Up

A quick walk through your home, paying attention to each window, will tell you a great deal about the condition of your glass units and your exterior caulking. These are the signs I look for on every assessment.

Red Flag 1 — Visible fog, haze, or streaking between the glass panes that does not wipe away

This is the definitive sign of IGU seal failure. The unit needs replacement. The question at this point is what condition the surrounding frame and perimeter caulking are in, because resealing the exterior is still worth doing to protect the new unit.

Red Flag 2 — Mineral deposits or white staining on the interior glass surface that cannot be cleaned

This indicates that moisture has been cycling through the IGU cavity long enough to leave mineral residue on the inner pane surfaces. The unit is beyond recovery.

Red Flag 3 — Noticeably higher condensation on specific windows compared to others in the same room

If one window consistently fogs on the interior surface while adjacent windows in the same room stay clear, that window’s IGU has lost its insulating gas fill and is conducting cold at a higher rate. The seal has failed even if the fogging is not yet visible between the panes.

Red Flag 4 — Exterior caulking that is cracked, brittle, or visibly separated from the frame

This is the upstream problem. A window with failed perimeter caulking is actively accumulating moisture at the frame joint with every rain event. If the IGU has not yet fogged, it will. Resealing at this stage protects the glass unit before the damage is done.

Red Flag 5 — Drafts, cold spots, or rattling at windows that were previously tight and quiet

Seal failure in an IGU eliminates the insulating gas layer that made the window thermally efficient. The window becomes effectively a single pane in terms of thermal performance. You will feel the difference as cold radiation on nearby surfaces, higher heating costs, and in some cases audible air movement around the frame.

For more on the warning signs that your exterior caulking is contributing to energy loss across your entire building envelope, see our complete caulking tips guide.

Stop Living with Foggy, Drafty Views

A fogged window is not just an eyesore. It is a sign that your home’s building envelope has a gap in it, that moisture is getting where it should not be, and that your heating and cooling system is working harder than it needs to. The glass unit replacement is a conversation for your window installer. The perimeter caulking that protects your new unit, and every other window on your home, is a conversation for us.

Call Oleg directly for a live response and a free local window health assessment. We serve Burlington and the surrounding Halton Region year-round, and a conversation about your windows costs you nothing but a few minutes. Learn more about all our services at Proper Caulking.