A forecasted downpour might sound exciting, but not if you have leaky windows. Instead of scrambling for buckets and towels every time it rains, it’s worth taking a closer look at your windows. 
In this guide, we’ll cover everything you should know about leaky windows: common reasons, practical tests to confirm leaks, and quick DIY solutions.

Why Are My Windows Leaking?

From structural settling to damaged and ageing window frames, leaks can have many culprits. Even newer windows are not always exempt from trouble, especially if poorly installed or maintained. Researches show that 42% of Canadian homes experience condensation on window surfaces – a sign of seal failure and moisture. Broadly speaking, there are three identifiable areas that can cause leakage.

1. House Design

• Missing roof overhangs leave windows exposed.
• Flat or poorly sloped fascia boards over windows can cause water to pool.
  

2. Installation

• Poorly installed windows (even newer ones!) or windows with gaps in their flashing allow water to leak through.
• Substituting house wrap or building paper instead of proper window flashing.

3. Maintenance

• Missing paint seal; paint should form a watertight seal, overlapping onto the glass from the trim.
• Gaps or cracks in the caulking.
• Damaged glazing putty breaks the seal on the glass, leading to condensation between the double panes.
  

Identifying the Window Leak Source: Handy Tests

Before rushing to DIY solutions, you first must figure out the source of the leak. If the leak is around, above, or below the window, it means there is an opening in the wall that allows water in. The exposed gap isn’t necessarily directly beside the window, especially in older homes. In this case, look around the roof or upper floors.

If you think the leak is directly along the window frame (you see water coming through where the sash meets the jamb), here’s how to pinpoint it:

• Smoke. Bring a lit candle or incense to the window frame. When the flame or smoke pattern flutters, there’s your leak.
• Hose. It’s a two-person test. One person should spray water outside the window, while the other should stay inside and check for drips.
• Flashlight. Turn on a flashlight when it’s dark outside and shine around the frame to find the exact place of the gap.

Mould, mildew, water stains, peeling wallpaper, and bubbling paint are good indicators that you have leaky windows.

Quick Troubleshooting Table

Leaks don’t appear out of nowhere. Here’s a quick look at the usual suspects and whether you can tackle the issue on your own:

Symptom	Likely Cause	DIY or Pro
Bubbling pain	Failed caulking or flashing	DIY
Water stains on drywall	Leaky frame/blocked weep holes	DIY, if minor
Condensation between panes	Broken window seal	Usually pro required
Soft, spongy trim	Rotting wood	Pro required
Musty odour	Hidden mould/moisture	Pro recommended

DIY Solutions

So, you’ve identified a leak. What comes next? Don’t rush to hire a contractor. If you have a minor issue, you can fix it yourself. No DIY experience needed.

• Recaulk Problem Spots. Remove damaged exterior caulking with a utility knife, clean the frame, and apply a new layer. Always recaulk on a dry day with mild temperatures.
• Clear Weep Holes. Use a thin piece of wire, pipe cleaner, or a strong burst of compressed air to remove gunk. It’s time to put your quick DIY fix to test: pour clean water on the sill to ensure that it drains as it’s supposed to.
• Replace Damaged Weatherstripping. Remove old weatherstripping if torn or cracked. After cleaning the area, measure, cut, and install new weatherstripping sections. Remove paper from adhesive-backed strips or just press them into the groove if they are pressure-fit.
• Re-Glaze. Remove old glazing, smooth the frame with sandpaper, apply new glaze, and smooth it out with a putty knife. When hardened, coat with oil-based primer.

Calling the Pros

Extensive water damage or structural issues require professional expertise and tools. Call it quits and hire a window or building specialist if:

• The frame is squishy, spongy, or rotten.
• Mould is omnipresent and spreads behind the paint.
• Large areas of drywall are stained.
• Flooded glass unit, regardless of the weather.
• Visible cracks around the frame.

If you have to spend money on replacements, go with ENERGY STAR–rated models — they must have a government-backed certification program.

Preventing Window Leaks: Best Tips and Tricks

Whether you have a shiny new ENERGY STAR–rated window or an old, drafty one, some level of maintenance is still necessary. CMHC Capital Replacement Planning Manual states that regular maintenance can boost a window’s lifespan significantly, potentially by up to 15 years. To save money and avoid dealing with costly replacements, make seasonal check-ups mandatory. Here’s what to pay special attention to:

What to Check	Why It Matters	How Often
Caulking	Shouldn’t be cracked, peeling, or missing. Reseal or replace if necessary, or the water will go right into your house.	Inspect annually; reseal as needed
Weep Holes	Located along the outside bottom of the window. The gunk accumulates pretty quickly, leading to leaks.If you have operable sliders or hung windows, the cleanliness of drainage channels is crucial.	Clean them every spring and fall
Weatherstripping	Worn or missing strips allow water and drafts in.	Check annually
Roof/Chimney/Siding	Damaged roof shingles, gaps around fireplace chimney and exhaust pipes, or loose siding — all let water sneak inside.	Inspect twice a year, especially after major storms
Gutters/Downspouts	Clogged gutters and downspouts cause overflow, which will soak walls and windows.	Clean every spring and fall
Vegetation	Untrimmed vegetation can trap moisture near walls and windows. This raises the risk of mould and leaks.	Trim seasonally

Saving Money

If DIY solutions and prevention aren’t enough, you may need to hire professionals and likely install new windows. Keep in mind that energy-efficient ones can be expensive. Luckily, there are federal and provincial loans and rebates to help finance the repair and allow you to save money.

The Canada Greener Homes Initiative finances a range of home improvements, including insulation, energy-efficient windows, and even solar panels. The Canada Greener Homes Loan offers up to $40,000 interest-free financing. Also, look into provincial programs, like Éconologis in Quebec — they offer free energy efficiency services and home improvements, such as caulking, for low-income households. If you want to know about rebates in each province, check this handy rebate guide.