How to Clean Debris Off a Roof and Out of Valleys Without Damaging It
A leaf blower and a soft brush, not a pressure washer. Where debris builds up and how to reach it safely.
- Intermediate
- 1 to 3 hours
- Updated
The short answer
To clean debris off a roof, work on a dry day, sweep or blow leaves and needles downslope with a leaf blower or a soft brush on a pole, clear valleys and the uphill side of chimneys and skylights, and finish by clearing the gutters. Never pressure wash, which strips shingle granules. Stay off the roof if it is steep, wet or mossy, and clean from a ladder or the ground with a long-handled tool.
Needles, leaves, seeds and moss collect in valleys, behind chimneys, against skylights and along roof-to-wall joints. They hold moisture against the shingles, feed moss, block the water path and can push water up under shingles. In the Fraser Valley, where cedars, firs and maples drop material for months, this is one of the most common causes of premature wear and leaks.
A gentle cleaning once or twice a year is part of maintaining a roof. The key is the method: moving debris off the surface without stripping granules or lifting shingles. A leaf blower and a soft brush do that. A pressure washer does not, because it blasts granules off the shingles, shortens their life and can drive water under the laps.
Much of the cleaning can be done from the ground, from a ladder base or from a stable ladder with a standoff. Going on the roof surface is a last resort and only for those with fall protection. Clearing the roof goes hand in hand with removing moss and treating for regrowth.
Tools
- Electric or battery leaf blower
- Soft-bristle brush on an extension pole
- Plastic or rubber-tipped roof rake
- Extension ladder with stabilizer and standoff
- Gloves, eye protection and a dust mask
- Roofing harness, rope and anchor if going on the roof
Materials
- Bucket or tarp for collecting debris
- Garden hose with a gentle spray nozzle
- Moss treatment made for roofs (if needed, used per label)
Safety first
- Do not walk on a wet, mossy or steep roof. Clean from the ground, a ladder or a long-handled tool where possible.
- WorkSafeBC requires fall protection where a fall could be 3 metres (about 10 feet) or more. If cleaning requires going on the roof, use a harness tied to an anchor.
- Keep well away from power lines when using a long pole or ladder, and check overhead before raising either.
- Wear eye protection and a mask. Dry moss and old debris can contain mould spores.
Step by Step
Step 1: Pick a dry, calm day and check overhead
Damp debris is heavy, sticks to the roof and is harder to move, while a dry roof gives you better grip. Avoid windy days, when blown material ends up back where it started, and avoid cold days when shingles are brittle.
Spread a tarp at the base of the wall to catch debris and protect plants. Look for power lines near the eave and service mast, and stay well clear.
Step 2: Assess from the ground first
Look at valleys, chimney backs, skylight tops, dormer sides and the gutters. Note any shingles that look damaged or lifted, and any moss. If debris is thick or the roof is steep, you may decide to hire a roofer.
Step 3: Set up the ladder safely
A standoff or stabilizer holds the ladder away from the gutter and spreads the load. Tie the top if possible, and keep three points of contact while climbing. Do not reach sideways, move the ladder instead.
If the eave is higher than the first storey, leave this job to a roofer.
Watch out: Never lean a ladder on the gutter. It crushes it and can slip.
Step 4: Brush or blow debris downslope
Start at the top of each slope and work down, so you do not blow debris onto clean areas. Keep the blower nozzle a little above the surface, and do not push it under shingle edges, which can lift them. A soft brush on a pole is slower but gentler on old, brittle shingles.
Do not scrape with a stiff brush, rake, scraper or wire brush, which dislodge granules.
Step 5: Clear the valleys
Valleys carry most of the water on a roof, so packed needles force water sideways and up under the shingles. Clear the full length, including the bottom where two valleys meet and dump into the gutter. Look at the valley material. Rust, cracked seams and shingles lifting along the edge are signs of trouble, see how to repair a leaking valley.
Step 6: Clear behind chimneys, skylights and other obstructions
These spots catch debris because water has to divert around them. A chimney cricket helps on wide chimneys, but many older ones do not have it. Clear behind them gently, without touching the flashing or sealant, which can crack or pull away. Note any gaps or loose flashing for repair.
Step 7: Treat moss, then clean the gutters and recheck
Loose dry moss can be brushed off gently. For thick moss, use a treatment made for roofs and follow its label and rain timing. Do not pressure wash. Debris washed into gutters blocks them, so clear the gutters last and make sure downspouts drain freely.
Finish by checking the roof from the ground for damage you found while cleaning, such as lifted shingles, exposed nails or cracked flashing.
Why Not Pressure Wash
A pressure washer blasts the granules off asphalt shingles. Those granules shield the asphalt from sun, and once they are gone the shingle ages fast. High pressure also forces water up under the shingle laps and through nail holes, into the deck. Many shingle manufacturers say pressure washing can void the warranty. A soft brush, a blower and a roof-safe treatment are the approved routes.
How Often to Clean
Under cedars and firs, twice a year works well, late spring after seed fall and late autumn after needle drop. Roofs in open areas may only need a yearly look. More often is not necessary, and every trip on the roof carries risk, so use ground and ladder tools where you can, and trim branches back from the roof to reduce the load.
Common Mistakes
- Pressure washing the roof. It strips granules, forces water under shingles and may void warranties.
- Walking a wet or mossy roof. It is as slippery as ice. Clean from the ladder or ground, or hire a roofer.
- Using a stiff brush or scraper. Both tear granules off the shingle surface.
- Blowing debris into the valley or gutter. Work from the ridge down and out, and clear the gutters last.
- Leaning the ladder on the gutter. It crushes the gutter, and the ladder can slip.
- Disturbing flashing and sealant. Clear around chimneys and skylights gently, or you create a leak while cleaning.
When to Call a Professional
Call a roofer if the roof is steep or high, heavily covered with moss, or if cleaning reveals lifted shingles, cracked flashing or damaged valleys. A roofer can clean with fall protection, and can make the repairs you uncover.
If the debris comes from trees overhanging the roof, consider having the branches trimmed back. Less debris lowers how often you have to go up.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Emergency Roof Repair service or the towns we cover.
How to Clean Debris Off a Roof and Out of Valleys: Questions
What is the best way to clean debris off a roof?
On a dry day, use a leaf blower or a soft-bristle brush on a pole to move leaves and needles down the slope and off the eave, working from the top down. Clear valleys and the uphill side of chimneys gently, and clean the gutters last. Do not use a pressure washer, stiff brush or scraper, which damage the shingles.
Can I pressure wash my roof to clean it?
It is not recommended. Pressure washing blasts the protective granules off asphalt shingles, shortens their life, can force water under the laps and may void the shingle warranty. Use a soft brush, a blower, and a moss treatment made for roofs, used according to the label, instead.
How often should I clean leaves and needles off my roof?
Roofs under cedars, firs and maples often need it twice a year, in late spring and late autumn. Roofs in open areas may need it once a year or less. Check the valleys and the uphill sides of chimneys and skylights, which collect debris first. Trimming overhanging branches reduces how much builds up.
Why clean the valleys on a roof?
Valleys carry a large share of the roof's water. When needles and leaves pack in, water backs up and runs sideways under the shingles, and moss starts to grow. Clearing them keeps the water path open and reduces the chance of leaks. Check the valley material while you are there for rust, cracks or lifting shingles.
Is it safe to walk on my roof to clean it?
Not if it is wet, mossy, frosty or steep. Even a dry, low roof carries a fall risk, and WorkSafeBC requires fall protection where a fall could be 3 metres, about 10 feet, or more. Clean from the ground or a secured ladder with a pole tool where you can, and hire a roofer for anything else.
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This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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