Rain wakes up whatever is sitting in your eavestroughs, and the smell tells you what it is. Use this guide to match the odour to its likely source, confirm it on a rainy day, and clear it out in the right order.
In This Article
Match the smell to the source
Rain wets dry debris, warms it up and stirs the air trapped in troughs and pipes. That is why odours often show up after a shower and not on a dry day. Start with the smell itself.
| What you smell | Likely source | First move |
|---|---|---|
| Musty, like a damp basement | Mould and mildew in wet debris | Clean, scrub and fix drainage |
| Rotten eggs | Waterlogged debris rotting without air, often in a low spot or blocked downspout | Remove the debris and flush the pipe |
| Earthy, like compost | Decomposing leaves and seed pods | Clean the run |
| Sweet or fermenting | Rotting fruit, berries or sap from nearby trees | Scoop out and rinse |
| Sharp and ammonia-like | Bird droppings and nest material | Clear it once the birds have left, with gloves and a mask |
| Foul and meaty | A dead bird, squirrel or mouse in the trough or downspout | Find it and remove it carefully |
| Sewer-like, strongest at a downspout base | Air pushed out of an underground drain connection | Ask a drain specialist to inspect the line |
Confirm it on a rainy day
Guessing costs time. A short rain-day routine narrows the search.
- Stand outside during or just after rain and follow the smell along the wall. Note whether it is strongest at the eave, under one corner or at the base of a downspout.
- Look for water that stays put. A trough that is still full the next day, or a downspout that drips slowly, is holding the material that smells.
- Check the trough from a well-set ladder at a single-storey eave, or with a phone on a pole. Look for dark muck, a nest or a carcass.
- Run a hose down the downspout. Slow flow, or a gurgle, means a blockage or trapped water.
Keep your face away from the outlet when you flush, and stay off ladders on wet days. Wait for a dry morning to climb.
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Fix it in the right order
- Protect yourself. Wear waterproof gloves, eye protection and a mask. Wash your hands afterward. Rotting organic material and animal remains can carry germs.
- Remove the source. Scoop out debris into bags, and take out nests only once they are empty, since birds are protected while nesting. For a dead animal, double-bag it and put it out with household waste as your municipality directs. Call pest control or wildlife services for live animals.
- Flush the whole system. Run water along the trough and down each downspout until it flows clear.
- Scrub and rinse. A soft brush and a mild cleaner dissolve slime. Rinse well, and keep runoff off plants.
- Correct the standing water. If puddles remain after the flush, the trough is out of slope. See why gutter pitch matters.
The smell should fade quickly once the source is gone and the water leaves. If it returns after the next rain, something is still holding water.
When it is not the eavestrough
Not every smell near the house comes from the trough. Sewer-like odours at the base of a downspout that ties into a buried pipe may come from the pipe, which can hold stagnant water or have a damaged joint. Our guide to underground downspout drainage explains how those lines are laid out.
Other possible sources include a damp crawlspace, a plumbing vent, a compost pile beside the wall, and animals nesting in the soffit or attic. A musty smell inside the house after rain points to moisture in a wall or basement, and that needs a proper look. If you suspect animals in the roof, the guide to keeping birds out of gutters and roofs covers common entry points.
Keeping the smell from coming back
Odours return when debris and water linger. Clean the troughs after the spring seed drop and again after leaf fall, and glance at the troughs after summer storms. Fix any low spot that holds water. Trim branches that shed fruit or sap into the trough.
D&D Home Services cleans and flushes eavestroughs across Kitchener, Waterloo, Cambridge and Guelph. See gutter cleaning for what a visit covers. Quotes are free and confirmed in writing before work begins.
Key Takeaways
- Musty, rotten-egg, compost, sweet, sharp and meaty smells each point to a different source, and the smell tells you where to look first.
- Confirm the source on a rainy day by following the smell, checking for standing water and running a hose down each downspout.
- Remove the source, flush the whole system, then fix any low spot that holds water.
- A sewer smell at a downspout base or a musty smell indoors needs a drain specialist or a moisture check.
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