Sunny vs Cloudy: Which Weather Gives the Best Window Cleaning Results?

Written by PureSeal Services on November 18, 2025. Posted in Blog, Pressure Washing

Is It Better to Clean Windows on a Sunny Day or Cloudy Day?

Window cleaning seems straightforward, but the weather plays a much bigger role than most people realise. If you’re considering which weather gives the best window cleaning results, whether you’re washing upstairs sash windows, bi-fold doors, or modern uPVC frames, the amount of sun, shade, humidity, and even wind can determine how clean your glass actually ends up. Many people instinctively think a bright sunny day is perfect for cleaning because the light reveals dirt clearly. In reality, sunny conditions can make the job harder—not easier.

This article explores the science behind window drying, the pros and cons of different weather conditions, common mistakes people make, and practical tips for crystal-clear results. By the end, you’ll understand exactly which conditions are best and why.

Sunny Days vs Cloudy Days: The Short Answer

Cloudy days are generally better for cleaning windows.

Sunlight causes your cleaning solution to evaporate quickly, often before you can wipe it away. This leads to streaks, smudges, water spots, and uneven drying. Cloudier days eliminate that problem because the glass stays cool, giving you more time to clean effectively.

However, sunny days aren’t automatically bad—there are specific situations where sunlight can be managed. But overall, if you want the best chance of spotless, streak-free results, mild, overcast, and wind-free weather is ideal.

Why Weather Affects Window Cleaning

To understand why cloudy days typically win, let’s look at what actually happens when you wash glass.

Temperature

Warm glass heats cleaning fluids, which makes them evaporate faster. On a sunny day, the outside surface of your glass can easily reach 30–45°C, even when the air temperature is only 18–20°C.

Evaporation Rate

Cleaning sprays often contain:

• water

• detergents

• alcohols

• surfactants

When heat speeds up evaporation, the dissolved minerals in your water get left behind as streaks or hazy deposits.

Glass Expansion

Glass expands slightly in heat. This is not a structural problem but it can:

• make smears more noticeable

• stretch water into thin, uneven layers

Reflection and Glare

Bright sunlight creates glare that makes smears harder to spot while you clean. Only once you step away—usually into shade—do the streaks become painfully visible.

Pros and Cons of Cleaning Windows on a Sunny Day

Pros

• You can see dirt clearly: Smudges, fingerprints, and bird droppings are far more visible.

• Surfaces dry quickly: Good for preventing water pooling.

• Light helps you inspect your work: When the angle is right, sunlight reveals imperfections.

Cons

• Fast evaporation causes streaks – the biggest problem.

• Hard water spots become more visible as minerals dry.

• You waste more cleaning solution because you have to redo sections.

• Glare can hide fresh smears until it’s too late to fix them.

• Working in heat is uncomfortable, especially on upper floors.

Below is a quick comparison table.

Table 1: Effects of Cleaning Windows on a Sunny Day

Pros and Cons of Cleaning Windows on a Cloudy Day

Pros

• Glass stays cool, preventing rapid evaporation.

• More working time, so the solution can break down dirt properly.

• Less glare, making smudges easier to see while cleaning.

• Minimal streaking, especially when using tap water.

• Less chance of solution drying on the surface, even if you’re slow.

Cons

• Dirt can be harder to spot from certain angles (though good technique solves this).

• It may feel less motivating because the weather looks “dull”.

• Showery conditions can interrupt cleaning if rain arrives.

Table 2: Effects of Cleaning Windows on a Cloudy Day

Scientific Reasons Cloudy Days Are Better

1. Cool Glass Prevents Flash Drying

Flash drying occurs when the sun heats glass and pulls moisture out almost instantly. When this happens:

• Your squeegee drags

• The solution sticks in patches

• Streaky lines appear

Cloudy conditions keep the glass at a stable temperature, letting you wipe evenly.

2. No Glare Means You Clean More Accurately

Glare reduces visibility. Without glare, your eyes can detect even small smears or lint fibres.

3. Water Performs Better on Cooler Surfaces

Water’s surface tension behaves differently on warm surfaces:

• It beads more

• It spreads unevenly

• It pulls dirt back across the glass

Cool surfaces help water behave predictably.

4. You Use Less Cleaning Solution

Because everything stays wetter for longer, you use fewer towels and less detergent, saving money.

A typical homeowner using store-bought cleaner might spend £3–£5 per week if cleaning regularly in poor conditions. Good weather reduces that by 30–50%.

How Rain Affects Window Cleaning

A quick myth-buster:

Rain does NOT make clean windows dirty.
Rain only looks dirty when it mixes with existing grime on the glass.

If your windows are already clean, rainfall is usually:

• soft

• mineral-light

• free of detergents

In many cases, rainwater dries clearer than tap water.

Should you clean windows in light rain?
Yes—light, warm rain with no wind is actually fine. The air is cooler and humidity is high, preventing fast evaporation.

What About Cleaning Windows in Windy Weather?

Wind is a bigger problem than sunshine. Wind:

• dries surfaces very quickly

• blows dust onto freshly cleaned glass

• affects squeegee control

• makes ladder use dangerous

If the wind is over 15 mph, it becomes noticeably harder to get a clean finish.

Season-by-Season Guide

Table 3: Best Seasons for Window Cleaning

Time-of-Day Matters Just as Much as Weather

If you must clean on a sunny day, the time-of-day can drastically improve the outcome.

Best Times on a Sunny Day

• Early morning (6am–9am) – Glass is cool, sun is low.

• Late evening (6pm–9pm) – Sun has dropped and temperatures fall.

Worst Times

• 11am–4pm, when the sun is highest and hottest.

Table 4: Window Cleaning Quality by Time of Day

Tools and Methods That Perform Best in Cloudy vs Sunny Weather

Certain cleaning methods work well regardless of weather, but some are specifically better suited to cloudy days.

On Cloudy Days

• Microfibre cloths

• Traditional squeegee

• Mild detergent solution

• Bucket and mop

• Tap water (soft or hard)

On Sunny Days

• Pure water cleaning if available (no minerals)

• Quick-drying microfibre methods

• Foaming sprays that cling longer

• Shaded working areas

• Smaller, manageable sections

Cost Impact: Sunny vs Cloudy Days

Cleaning windows on a sunny day often costs more due to repeat effort and wasted materials.

Table 5: Estimated Cost Difference

Over a full year of monthly cleaning, using cloudy days could save £8–£12, plus hours of time.

Practical Tips for Perfect Window Cleaning in Any Weather

1. Work in Sections

Especially helpful on sunny days:

• Divide windows into small areas

• Apply solution to one section at a time

• Wipe immediately before moving on

2. Always Start in the Shade

Even on sunny days, parts of your home will be shaded.

3. Avoid Overusing Cleaning Spray

More spray means:

• more wiping

• faster evaporation

• higher streak risk

A fine mist is better than heavy saturation.

4. Use Two Cloths

• One damp cloth for washing

• One dry cloth for polishing

5. Always Clean Frames First

If you clean frames after the glass, dirty drips will ruin your hard work.

6. Use Lukewarm Water on Cold Days

Prevents freezing and streaking.

7. Add a Small Amount of Washing-Up Liquid

This breaks dirt effectively and is affordable, typically costing a few pence per wash.

Common Mistakes People Make When Cleaning Windows in the Sun

1. Cleaning large areas at once
   The solution dries before you reach it.

2. Using too much detergent
   More soap means more residue and streaks.

3. Not rinsing cloths regularly
   Dirty cloths simply smear grime around.

4. Ignoring the direction of sunlight
   Cleaning directly in full sun is the hardest.

5. Using hard tap water with no drying agent
   Hard water dries with mineral marks.

Cloudy Day Cleaning: Step-by-Step Guide

1. Dust or brush off loose dirt first
   Prevents scratching.

2. Prepare a bucket with warm water + a few drops of detergent.

3. Use a microfibre pad or mop to apply the solution.

4. Wipe with a squeegee in smooth, horizontal strokes.

5. Dry the edges with a clean microfiber cloth.

6. Polish any small remaining marks.

7. Stand back and check from multiple angles.

Cloudy conditions allow slower, smoother work—no rushing required.

Special Situations

Inside Windows

Indoor glass isn’t usually affected by sunlight or heat, so sunny vs cloudy matters less.

However:

• Sunny light makes fingerprints more visible

• Cloudy light gives an even, consistent surface

Conservatory Roofs

These heat up extremely quickly in sunlight. Cleaning on a sunny day is difficult, uncomfortable, and often dangerous due to slippery surfaces. Cloudy days are best.

Commercial Properties

Large shopfronts receive direct sunlight at predictable times. Clean them:

• before opening

• after closing

• or on cloudy days

Overall Conclusion: Cloudy Days Are Better

While it may feel counterintuitive, cloudy days almost always deliver better window-cleaning results than sunny days. The cooler temperature keeps the glass comfortable to work with, prevents rapid evaporation, reduces streaks, and lowers the amount of cleaning solution you need. Even light rain isn’t a problem for clean glass.

Sunny days can still work if you:

• clean early or late in the day

• work in shaded areas

• use pure water or fast-cleaning techniques

But whenever possible, choose an overcast day. Your windows—and your effort—will thank you.

How Humidity Levels Influence Window Cleaning

Humidity plays an understated but significant role in the quality of your clean. High humidity slows evaporation, giving you more time to wipe without streaks—similar to the advantages of a cloudy day. Low humidity, however, causes water to evaporate too quickly, even if temperatures are mild. This is common during early spring or in breezy conditions.

When humidity is above 60%, you’ll usually find your cleaning solution stays workable for longer, making the outcome smoother and more forgiving. When humidity drops below 40%, evaporation speeds up dramatically, and even indoor glass may show streaks or drying lines. If you can choose the timing, opt for moderately humid weather. It provides an ideal balance of slow evaporation and comfortable working conditions without the glass appearing foggy or covered in condensation.

Does Water Quality Change Your Results?

The quality of your water can be just as important as the weather. Hard water—common in many areas of the UK—contains minerals like calcium and magnesium that dry into visible spots. On a sunny day, these deposits show up even more prominently because the moisture evaporates quickly and leaves mineral traces.

Soft water or filtered water tends to produce a clearer finish. If you’re using tap water and live in a hard-water region, cloudy weather helps minimise streaks because the slower evaporation reduces the chance of mineral spotting. Adding a splash of white vinegar (around 5–10p worth) to your bucket can help soften water slightly and reduce streaking. For the best results, always avoid letting excess water sit on the glass—especially when the sun is strong.

Why Indoor and Outdoor Glass Behave Differently

Indoor glass is usually less affected by direct sun, wind, and temperature changes. That means you can clean internal windows on almost any day without worrying about rapid evaporation. However, indoor heating can still warm the glass, especially on south-facing windows. If your home is heated to 20–23°C, the glass may still warm enough to cause mild evaporation issues.

Outdoor windows, on the other hand, deal with environmental factors like sunlight intensity, air movement, and temperature shifts. That’s why weather considerations matter far more outside than in. As a rule of thumb:
Indoor windows = technique matters more.
Outdoor windows = weather matters more.

What Type of Cleaner Works Best in Different Weather?

Different cleaning solutions behave differently depending on the conditions. On sunny days, foaming cleaners or gel-based formulas are useful because they cling to the surface and resist quick drying. Water-heavy sprays, however, dry in seconds and leave marks.

On cloudy days, you have more flexibility. Standard spray cleaner, bucket solutions, or diluted washing-up liquid all work well because the glass stays cool. Microfibre-only cleaning (where you dampen one cloth and polish with another) also performs best in stable, overcast conditions. If you’re using a homemade solution, keep it mild: 1 litre of warm water + a tiny drop of washing-up liquid (about 1–2p worth). The same mixture behaves differently in the sun versus shade, so cloudy weather is far easier to control.

Safety Considerations When Cleaning in Different Weather

Weather isn’t just about the final finish—it also affects safety. Direct sunlight can make ladders and frames hot to the touch, increasing the risk of slipping or rushing your work. Windy conditions increase the danger of ladder movement, especially on taller properties or when reaching upper-floor windows. Even mild breezes can destabilise lightweight stepladders.

Cloudy conditions offer better visibility because you’re not squinting against bright light, and cooler surfaces are safer to handle. If you must clean on a sunny day, take extra precautions: keep ladder feet securely placed on stable ground, avoid working at height in temperatures above 25°C, and never place ladders on soft or sun-baked soil that may shift. Safety should always be the first consideration, regardless of weather.

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