A stain on the siding under an eavestrough is the house showing you where water goes when it should not. Read the pattern to find the cause, stop the water first, then clean the siding once. Scrubbing before the fix only sets you up to scrub again.
In This Article
Read the stain before you scrub it
Where a stain sits and what it looks like point to its source.
| What you see | Likely cause | Check first |
|---|---|---|
| One narrow vertical streak under a joint or end cap | A leaking seam | Dried sealant, gaps, drips during rain |
| A streak straight below the downspout outlet | A clogged outlet or elbow | Flush the downspout |
| A broad fan of dirt below a roof valley | Water shooting past the trough | Watch the valley in heavy rain |
| A band along the top of the siding for the whole run | Overflow from a full, sagging or under-sized trough | Standing water in the trough after rain |
| Orange or rust-brown lines | Rust from steel fasteners or a steel trough | Screw heads and seams |
| Brown, tea-coloured film | Tannins from oak or maple leaves dissolved in overflow | A trough packed with wet leaves |
| Green or black film on shaded walls | Algae or mould where siding stays damp | Constant dripping or splash |
| White powdery crust on brick or stone | Efflorescence, mineral salts left as wet masonry dries | Repeated wetting from above |
Dark stripes on the face of the trough itself are a separate problem. They come from dirt and oxidation on the metal, not from a leak.
Stop the water first
Work through these in order, and stop when the stain stops appearing.
- Clean the trough and flush every downspout. Overflow from a plug is the most common cause.
- Run a hose along the trough from the high end. Watch from the ground for drips at joints, end caps and corners.
- Reseal leaking seams. Clean and dry the metal, use a sealant made for your trough material, and let it cure in dry weather. See how to repair leaking gutter joints for the details.
- Tame the valley. A diverter or splash guard at the bottom of a roof valley keeps a fast stream from jumping the trough.
- Fix sag and slope. Add hangers where a run dips, so water reaches the downspout instead of pooling.
- Question the size. If a trough overflows even when clean, it may be too small for the roof area it serves.
Gutters overflowing, or overdue for a clean?
We clean and flush gutters across Kitchener, Waterloo, Cambridge & Guelph, and catch small problems before they reach your foundation. Free, no-obligation quotes, ready within 1 business day.
Cleaning the siding once the leak is fixed
Test any method on a hidden patch first, and wet nearby plants before you begin.
- Vinyl and aluminum siding: a soft brush, mild detergent and water, then a thorough rinse from the top down. Never aim a pressure washer upward. It can drive water behind the laps.
- Algae and mould: use a house-wash product made for siding. Many are sodium hypochlorite-based and must be diluted, rinsed off and kept away from plants. Follow the label, and never mix products.
- Rust: use a rust remover made for your siding material, and follow its label closely.
- Efflorescence: start dry with a stiff nylon brush, then rinse with water. Avoid acids on old masonry unless a specialist advises it.
Stucco, cedar and painted wood are delicate. The guide to removing green algae and mould covers gentler methods. High or widespread stains are a ladder job, and low-pressure soft washing exists for exactly that reason.
When a stain means damage
Some stains are only cosmetic. Others mean water has been sitting in the wall or trim for a while. Look for:
- Fascia or trim that feels soft when you press it with a screwdriver tip.
- Paint that bubbles, flakes or lifts in the same spot as the stain.
- Siding that has warped or pulled away near the eave.
- Brown marks on a ceiling or wall inside, directly behind the stain.
Do not caulk over or paint over these. That traps moisture and hides the problem. Get the wood checked, and expect the trough to need rehanging once solid fascia is behind it.
Keeping the stains from coming back
Clean the troughs on a schedule that matches your trees, and trim branches that overhang the roof edge. Send downspouts well away from walls so splash does not climb the siding. A yearly rinse with a garden hose and soft brush stops light film from building up.
D&D Home Services offers both gutter cleaning and soft washing across Kitchener, Waterloo, Cambridge and Guelph. Quotes are free and confirmed in writing before work begins.
Key Takeaways
- The position and colour of a stain tell you whether the cause is a seam, an outlet, a valley, overflow, rust, tannins, algae or masonry salts.
- Fix the source before cleaning, or the same stain returns after the next rain.
- Use soft brushes, mild detergent and correctly diluted house wash on siding, and never blast upward behind the laps.
- Soft fascia, bubbling paint or interior marks behind a stain mean water damage that needs a proper look.
Request a home-service quote
Select the service you need and describe the work area and access.