Garage Door Condensation: Why Your Door Sweats & How to Stop It in Canadian Garages

The Quiet Moisture Problem Most London Homeowners Miss

If you walk into your garage on a cold January morning and find the inside of the door beaded with water, or worse, lined with a thin film of frost, you are not looking at a defective door. You are looking at condensation. It happens in attached and detached Canadian garages every winter, and it shows up in milder forms on humid spring and summer mornings too. Most homeowners notice it once, wipe it down, and forget about it until the wood trim around the door starts to swell, the bottom panel begins to rust, or a small dark mould patch appears at the corner where the door meets the floor.

The Door & Access Systems Manufacturers Association (DASMA) addresses this directly in their Technical Data Sheet 195: Garage Doors and Condensation, which states plainly that "garage door condensation is not normally a product defect, but is characteristic of a warm, humid garage and a cooler garage door surface due to a colder exterior temperature." In other words, it is a building science problem, not a door problem. And like every building science problem, it has predictable causes and a short list of practical fixes. This article walks through both, with the Canadian climate in mind.

If you have not already read our R-value explained article, that piece pairs well with this one because insulation choice is one of the levers that controls whether your door sweats in the first place.

What Condensation Actually Is

Condensation is what happens when air holding water vapour meets a surface cooler than the dew point of that air. Warmer air holds more moisture than cooler air; when warm humid air contacts a colder surface, the air immediately next to that surface cools, can no longer carry as much vapour, and the excess water comes out of solution as liquid droplets on the surface. If the surface is below freezing, those droplets become frost.

The garage door is often the coldest large surface in a Canadian garage, particularly the lower section. The exterior face of the door sits exposed to outdoor temperatures, which in London can dip below −20°C for stretches of January and February. Even a well-insulated polyurethane door has a finite R-value, and the interior face of the door will sit somewhere between the outdoor and indoor temperatures. The colder the outside and the more humid the inside, the more likely the interior face will fall below the dew point of the garage air, and the more visible the sweating becomes.

The same thing happens on bathroom mirrors after a shower, on a cold glass of water on a humid summer day, and on the inside of single-pane windows in older homes. It is not exotic. It is just basic physics applied to the largest single panel on the front of your house.

The Three Things That Drive Garage Condensation

Every garage condensation problem comes down to some combination of these three factors. Diagnosing your own garage is mostly a question of figuring out which one is the dominant cause.

1. High Humidity Inside the Garage

The garage is a remarkably good moisture trap. Snow and slush carried in on the underside of the car melt onto the concrete floor; the meltwater then evaporates back into the garage air. DASMA TDS-195 specifically calls out "a wet or snow-covered car" as a primary humidity source, alongside humidifiers and moisture from adjacent laundry areas. A single vehicle dripping a slush load through a winter day can release a litre or more of water vapour into the garage.

Garaga, a major Canadian door manufacturer, reports in their condensation FAQ that if you see droplets forming on the window glazing or at the section joints of your door, you can expect a hygrometer in the same garage to read 50% relative humidity or higher.

2. Cold Door Surface

If the inside face of the door is warm enough to sit above the dew point of the garage air, no condensation forms. So anything that keeps the interior face warm helps. A well-insulated polyurethane sandwich-built door (R-value of roughly R-16 to R-18 in the typical Canadian residential category) holds the interior face several degrees warmer than an uninsulated single-skin door of the same dimensions. Our R-value guide covers the difference between calculated and tested R-values, but in plain field terms: insulated doors sweat less than uninsulated ones, all else equal.

Section joints and the perimeter weatherstripping are often the first places condensation appears, because they are typically a few degrees cooler than the panel face itself. Our jamb seals guide and bottom seal replacement guide walk through what good perimeter seals look like.

3. Poor Air Movement

Without any air movement, humid air settles against the coldest surfaces and stays there long enough to deposit its moisture. A garage with a tightly sealed door, a tightly sealed walk-through door, no exhaust fan, and no passive ventilation has nowhere for the humid air to go. The same garage with even modest air exchange (a passive vent, a small exhaust fan, or simply leaving the door open for an hour after parking a snowy car) shows dramatically less condensation. Garaga's own recommendation when condensation appears is to "open your garage door about 2 inches or more" and let the humid interior air mix with drier exterior air, "ideally for about an hour" based on the exterior temperature.

Why Insulated Doors Can Still Sweat

One of the most common surprises after a homeowner upgrades from an uninsulated steel door to a sandwich-built polyurethane door is that condensation can persist, sometimes briefly worse than before. Three things are at work.

First, an insulated door also tends to have a tighter perimeter seal, particularly if it is a quality replacement done with new weatherstripping. A tighter seal lowers the natural air exchange of the garage, which keeps any new humidity from escaping. Second, an insulated door makes the garage warmer overall, and warmer air carries more water vapour at the same relative humidity reading. Third, the insulated panel face is still cooler than the surrounding ambient air, just less so than a single-skin door would be.

DASMA TDS-195 notes this directly: "Although insulated garage doors are intended to help toward conserving energy, they may not perform at the same level as the surrounding walls." The walls in an attached garage typically run R-12 to R-22 in the cavity insulation; even a top-end R-18 sandwich door is at the bottom of that range, and the door has thermal bridges (the section joints, the hinges, the bottom and top edges) that walls do not. The takeaway is not that insulating is pointless: it is that insulation alone, without humidity control, will not fully eliminate condensation in a Canadian garage.

The Real Risks of Ignoring It

A few droplets here and there are not a crisis. Persistent condensation over weeks and months is. The accumulated moisture causes specific, measurable damage to the door and to the surrounding building envelope.

Rust on the Bottom Panel and Hardware

Steel doors are paint-coated, but the paint is only as good as the steel substrate underneath. Persistent moisture against the bottom panel eventually finds the cut edges of the steel (around the bottom seal channel, around hinge mounting holes, at the bottom corner brackets) and starts a corrosion process from the inside out. By the time the homeowner sees a rust bloom on the exterior face, the steel underneath has been corroding for months. The bottom bracket safety article covers why the bottom-corner hardware in particular is the worst place for corrosion to take hold.

Mould on Wood Trim and Drywall

Health Canada's guidance on mould recommends keeping indoor relative humidity between 30% and 50% to prevent growth. A garage that consistently reads above 55% relative humidity in winter (which is the threshold where droplets first start forming on a typical door surface in Canadian weather) is sitting in the danger zone for mould on the drywall around the door header, the wood jamb framing, any stored cardboard boxes, and the underside of any wood trim. An attached garage with mould on the shared wall can affect indoor air quality in the house itself.

Rotting Door Framing and Jambs

The wood door jambs and header that the door rolls against are particularly vulnerable. They sit at the coldest perimeter, they are typically softwood (untreated pine or spruce on most residential builds), and they have very little ventilation against the back side of the jamb. Visible swelling, soft spots, or dark staining on the jamb is the homeowner's signal that moisture has been working on the wood for a while. Replacing rotted jambs is a significantly bigger job than addressing the humidity that caused them to rot in the first place.

Damaged Door Insulation

On sandwich-built doors, persistent water along the section joints can find its way into the foam core. Once water gets into closed-cell foam at the joints, it can degrade the bonding between the foam and the inner steel skin, eventually showing up as a soft-feeling section or visible bowing.

How to Diagnose Your Garage's Condensation Problem

Before fixing anything, it helps to know which of the three drivers is the worst offender in your garage. The diagnosis is straightforward and costs less than thirty dollars in tools.

Step 1: Measure the Garage Humidity

Buy a digital hygrometer. Most hardware stores carry them in the $15 to $30 range; many double as a thermometer. Place it on a shelf or workbench in the garage (not on the door itself, not in direct sunlight, not next to a heat source) and leave it overnight. Read the morning value before you open the door for the day. That value, in relative humidity percent, is the figure you are trying to lower.

Targets, based on Health Canada's mould prevention guidance:

• Below 50% relative humidity: good. Condensation should be rare or limited to extreme cold snaps.
• 50% to 60%: marginal. Expect intermittent condensation on the coldest mornings.
• Above 60%: problem zone. Persistent condensation and mould risk. Action required.

Step 2: Inspect the Door and Surroundings

Walk the garage in the morning before opening the door. Where exactly is the water appearing? Patterns tell you a lot:

• Water beads across the full panel face: the door surface is generally too cold relative to the air. Insulation upgrade or humidity reduction needed.
• Water only along section joints and around hinges: thermal bridging at the joints. The rest of the door is doing its job; the joints need attention.
• Water only on the bottom section: the bottom of the door runs colder than the rest because it sits against the cold concrete floor. Improve bottom seal and check for missing perimeter weatherstripping.
• Water on the windows or window glazing: single-pane or older double-pane window units. Replacement glazing helps; humidity reduction helps more.
• Water and mould at the wall-to-floor joint, not the door: this is a different problem (likely a foundation moisture issue) and the door is not the source. Have a building inspector look at the foundation.

Step 3: Identify Moisture Sources

Walk through the garage with a mental checklist of common sources:

• Snow-covered or rain-soaked cars parked overnight
• A clothes dryer venting into the garage (a code violation in Ontario but still occasionally found)
• An adjacent laundry room with a poorly sealed door connecting to the garage
• An open swimming pool cover or wet bathing suits drying in the garage
• Damp firewood stored indoors
• A leaky water heater, water softener, or plumbing pipe
• Wet sports gear or boots stored on the floor
• A humidifier left running in the garage
• Standing water on the floor after a recent wash or snowmelt

The Fix List, in Order of Cost

Prices on this page are before HST.

Start with the cheapest, lowest-effort actions and only escalate if the hygrometer reading and visible droplets do not improve. In most Canadian garages, the first three or four items on this list resolve the problem entirely.

Free or Near-Free

• Wipe down a wet vehicle. A microfibre towel or even a squeegee around the rocker panels and wheel wells removes the bulk of the meltwater before it can evaporate.
• Park the snowy car on the driveway for an hour before pulling it into the garage. Most of the loose snow falls off in that interval. Brush the roof and hood first.
• Open the garage door for 15 to 30 minutes after parking a wet car, particularly in cold dry weather when the exterior air is much drier than the garage air. This is Garaga's first recommendation for lowering interior humidity.
• Squeegee or mop standing water off the concrete floor before it has the chance to evaporate.
• Keep the door from the garage to the house tightly closed, particularly if there is a laundry area or bathroom on the other side. The fire-rated walk-through door in most attached Canadian garages also functions as a vapour barrier when shut.
• Move stored cardboard, fabric, and firewood elsewhere. Each of these is a moisture sponge that holds humidity in the garage for days after a wet day.

Under $100

• Buy and place a hygrometer. $15 to $30. The single best diagnostic tool for any moisture problem.
• Install a passive vent in the garage ceiling or rear wall. A 4-inch louvred vent runs about $25 and lets humid air escape passively.
• Replace worn perimeter weatherstripping (jamb seals along the sides, the top seal at the header). New seals run $40 to $80 in materials for a typical residential door; see our jamb seals guide for the DIY procedure.
• Replace the bottom seal if it is cracked, hardened, or no longer fully contacting the concrete floor. A new T-style or nailed-on seal runs $30 to $60 in materials; see our bottom seal replacement guide.

$100 to $400

• Run a dehumidifier sized for the garage volume. A 30-pint unit runs $200 to $300 and can hold a single-car garage at 45% to 50% relative humidity through the worst of winter. Pour the collection bucket once a day or run a drain hose to a floor drain.
• Install a small exhaust fan with a humidistat. A bathroom-style 80-CFM fan with a humidistat switch runs $80 to $150 in parts, plus installation. The fan triggers automatically when humidity climbs above the set point.
• Add a DIY insulation kit to an uninsulated door. These foil-faced foam panels improve the interior surface temperature by several degrees and reduce sweating significantly. See our DIY insulation kit article for the install procedure and the balance concerns to know about before you start.

Over $400

• Replace an uninsulated single-skin door with a sandwich-built insulated door (R-12 or higher). A typical Canadian residential replacement runs $1,200 to $2,500 depending on size and finish. The door is paid back in part by lower heating loss and in part by the elimination of the condensation problem.
• Heat the garage to a controlled temperature, typically 5°C to 10°C above freezing. This raises the door surface temperature above the dew point and largely eliminates condensation, but requires a properly insulated garage to be cost-effective. The Natural Resources Canada guidance on energy efficient homes covers the broader envelope decisions involved.

Seasonal Patterns in Canadian Garages

Condensation in Canada is not just a winter problem. The dominant cause shifts with the season, and so does the right fix.

Our broader summer garage door care article covers the warm-season pest and humidity issues in more detail, and our winter maintenance guide covers the cold-season checklist.

Special Case: Detached and Unheated Garages

Detached garages and shops follow slightly different rules. They tend to be uninsulated or lightly insulated, they often lack a vapour barrier on the walls, and they almost never have a year-round heat source. The good news is that detached garages also tend to "breathe" more naturally; there is usually enough air exchange through wall framing, soffit vents, or non-airtight doors to keep humidity in check most of the year.

Where detached garages get into trouble is during shoulder seasons (spring thaw, fall rain) when the building envelope warms up and any stored moisture (in the concrete floor, in stored gear, in firewood) starts evaporating. The fix in this case is almost always more ventilation and source control rather than more insulation. A pair of soffit-and-ridge vents, or even one passive wall vent on each end of the building, reduces condensation problems dramatically.

Heating a detached garage just to control condensation is rarely cost-effective. If the building is occasionally heated for a project (woodworking, vehicle maintenance), turn the heat on a few hours before you start work to let the building dry out, and ventilate afterwards rather than sealing it back up while still warm and humid.

The Vapour Barrier Question

Some homeowners ask whether they should add a vapour barrier to the inside of the garage door itself. The short answer is no. The longer answer is that garage doors are not walls; they have moving section joints that flex with every cycle, and any plastic film vapour barrier added to the inside surface will tear at the joints within months. Sandwich-built insulated doors have an effective vapour barrier built in (the inner steel skin), and DIY insulation kits with foil facings provide a partial vapour retarder that is sufficient for most residential garages. The right place for a vapour barrier in an attached garage is on the walls and ceiling between the garage and the heated house, not on the garage door itself.

The Canada Mortgage and Housing Corporation (CMHC) publishes extensive resources on residential vapour control for homeowners renovating their building envelope. For attached garages specifically, the wall between the garage and the house is the critical assembly, not the garage door.

Frequently Asked Questions

Is condensation covered under my garage door warranty?

Almost never. DASMA TDS-195 states that condensation "is not normally a product defect," and door manufacturers' warranties echo that language. Our garage door warranties article covers what the four standard warranties on a residential install actually do and do not cover; moisture damage from condensation generally falls into the homeowner's responsibility category, not the manufacturer's.

Does an insulated door eliminate condensation completely?

No. An insulated door reduces the temperature difference between the door surface and the garage air, which raises the dew point at which sweating starts. In most attached Canadian garages with normal humidity, that is enough to eliminate visible condensation under typical winter conditions. But during the coldest snaps or in unusually humid garages, even a top-end R-18 door will show some condensation. The fix in those cases is humidity control, not a different door.

How does heating the garage affect condensation?

Heating helps in two ways: it raises the surface temperature of the door (so the dew point threshold for condensation rises), and it lowers the relative humidity of the same volume of air (warmer air holds more vapour at the same absolute moisture content, so the relative humidity drops). The downside is the heating cost, especially on an uninsulated garage with leaky perimeter seals. Even maintaining 5°C makes a significant difference for condensation, without requiring full living-space temperatures.

Will a dehumidifier work in a cold garage?

Most consumer dehumidifiers stop working below about 4°C (some down to 0°C with auto-defrost). If your garage runs below freezing through winter, a standard dehumidifier will not pull water out of the air. In that case, the fix is ventilation rather than dehumidification: open the door for an hour after parking a wet car, install a passive vent, or run a small exhaust fan. In a garage that stays above 5°C year-round, a 30-pint dehumidifier is one of the most effective single tools for the problem.

Why is the inside of my garage door covered in frost, not just water?

Frost forms when the door surface is below 0°C and the dew point of the garage air is also below 0°C. Instead of liquid droplets, the water vapour deposits directly as ice crystals. This happens almost exclusively on uninsulated single-skin doors in unheated garages during the coldest weeks of winter. The fix is the same as for liquid condensation: reduce interior humidity, improve ventilation, and consider insulation. Do not scrape the frost off the painted surface with a metal blade; it lifts the paint and exposes the steel underneath to direct moisture. A soft plastic squeegee or a brush is safer if you need to clear the surface.

Should I be worried about condensation on the garage windows?

Condensation on the window glazing of your garage door is almost always a humidity signal, not a window defect. Garaga's condensation FAQ confirms that even double or triple-pane glazing units can show condensation in a humid garage. If the window is fogging between the panes rather than on the inside surface, that is a different problem: a glazing seal failure that the manufacturer should evaluate. The two situations look similar but have different causes.

Can I just paint the inside of my door with a moisture-resistant coating?

Painting the inside face does not change the surface temperature or the humidity, so it does not stop condensation from forming on the painted surface. A good two-coat exterior-grade paint does protect the underlying steel from corrosion if some condensation persists, which is helpful as a damage-mitigation measure but not a cure. The DASMA Maintenance Guide recommends following the door manufacturer's instructions for any coatings or cleaners applied to the door.

The Five-Minute Annual Check

If you do nothing else from this article, do this once each November as part of your fall maintenance routine. It catches almost every condensation problem before it becomes a moisture-damage problem.

• Place a hygrometer in the garage and read it after a typical overnight stretch with the car parked inside. Aim for 50% relative humidity or lower.
• Walk the inside of the door with the lights on. Look for past water staining on the bottom section, around the section joints, on the wood jambs, and at the bottom corners.
• Check the bottom seal for compression: with the door closed, can you see daylight along any part of the bottom edge? If yes, the seal needs replacement.
• Check the perimeter weatherstripping for cracks or visible gaps along the jambs and header.
• Look at any stored cardboard, fabric, or firewood near the door. Move it elsewhere.
• Confirm the walk-through door from the garage to the house closes tightly and is fully weatherstripped.
• If you have an exhaust fan, test that it triggers from the humidistat (or runs at all).
• Inspect the garage ceiling and the wall directly above the door for any visible dark spots or peeling paint. These are early signs of a humidity problem.
• Note any frost or droplets on the inside of the door the morning after the first hard freeze of the year, and compare against the year before.

When to Call a Professional

Most condensation problems are solvable by the homeowner with under $200 in tools and an hour of seal replacement. There are situations where a phone call to a garage door professional or a building envelope contractor is the right move:

• Persistent mould patches on the drywall around the door, on the door's interior, or on the wood jambs, especially patches larger than 1 m² (Health Canada's threshold for considering professional remediation).
• Visible rust pinholes on the bottom panel of a steel door less than ten years old.
• Soft or bowing sections on a sandwich-built door, indicating moisture has penetrated the foam core.
• Rotted, swollen, or visibly soft wood jambs.
• A garage that consistently reads above 65% relative humidity in winter despite source control and ventilation efforts. There is likely a hidden moisture source (a plumbing leak, a foundation crack, or a poorly sealed adjacent wall) that needs to be identified.
• Glazing units with visible fogging between the panes (a seal failure, not condensation).

Our guide on when to hire a professional covers the broader judgment call. For condensation specifically, our team in London offers free inspections and we will tell you honestly whether the problem is a door issue, a building envelope issue, or something a hygrometer and a weekend afternoon will solve. We are BBB-accredited in London with a track record of straight answers about whether work is needed.

The Bottom Line

Garage door condensation is the symptom, not the disease. The disease is a garage with too much moisture in the air and not enough air movement to clear it. The door simply happens to be the largest, coldest surface where the symptom shows up first. Once you understand that, the fix list becomes obvious: keep moisture out of the garage in the first place, let the humid air leave when it does get in, and (if budget allows) keep the door surface warmer than the dew point of the garage air. In that order.

An insulated door helps. A dehumidifier helps. A small exhaust fan helps. None of them is a one-shot cure, but any two of them in combination handle almost every Canadian garage. The most expensive thing you can do is ignore it for several years and replace rotted jambs, rusted panels, and mould-damaged drywall later. The cheapest thing you can do is buy a $20 hygrometer this week and find out what your garage is actually doing.