Your home’s exterior is the first thing a visitor or passerby sees. Dirt, green streaks, or neglected gutters – any marks, stains and streaking – can turn your house into a blot on the neighbourhood. Dark patches might be a sign of moss and algae. If the problem isn’t managed effectively, they can eat into asphalt shingles, permanently stain siding, and shorten the lifespan of your roof. Here are some practical ways to protect your home from moss and algae.
The difference between moss and algae.
Moss is a living organism that thrives on moisture, so it’s understandable why it can be a problem for homeowners in the lower mainland. It doesn’t have a root system, absorbing water through its leaf-like structures. Once moss takes hold, it can spread quickly on any flat surface such as the roof, siding, and inside or outside of the gutters. Moss can add weight to a roof or the gutters.
Algae, on the other hand, starts as a discolouation made up of small dots typically invisible to the naked eye, developing into large, dark streaks over time. Like moss, algae forms where there is excess moisture. It is often mistaken for mould or mildew.
Places where moss and algae will most likely appear.
Moisture is the number one reason moss and algae make an appearance. While the most common areas at risk are roofs, siding, and gutters, patios, pavers, fences, and decks can also be vulnerable to moss and algae growth if they are situated nearby shrubs or underneath trees.
Because there is generally less available sunlight, north-facing roofs and exterior walls stay damp longer, creating the ideal environment for moss and algae.
Hard-to-see areas on your home’s exterior can be potential moss and algae trouble spots. Any areas out of sight such as roof soffit, the fascia where gutters are attached, and thick bushes growing in front of siding can trap moisture.
Ways to prevent moss and algae.
On the Roof
Moss can shorten the lifespan of a roof by lifting shingles, exposing the roof deck to water infiltration; trapping moisture like a sponge; and causing leaks. To keep moss and algae from growing on your roof:
- Schedule (DIY or contractor) regular cleanings twice a year
- Have professional roof inspection done once every two to three years
- Keep the gutter system free of debris to prevent overflowing gutters from splashing up into the soffit and fascia
- Trim back trees growing too close to the house
- Don’t use a pressure washer on older or aging roofs – it can push moisture into cracks and crevices
On Siding
Overflowing gutters can send water pouring down siding. Moisture getting in behind siding panels or settling into cracks can invite moss and/or algae growth. Well-maintained gutters will discourage siding from collecting excess moisture leading to a good environment for algae and spores.
Grime attracts and holds moisture. Gently clean siding. Regular cleaning, at least once a year, with a soft-bristle brush and a solution of mild dish detergent will prevent buildup from becoming dense enough to trap moisture.
On Driveways, Patios/Decks, and Walkways
At the first sign of patches of discoloration, pressure wash the driveway, deck, or walkway to remove and prevent further growth. To remove moss or algae from patios made from brick pavers or mosaic tiles, soft wash (a cleaning method using low water pressure with special cleaning chemicals) the affected areas. Prevent it from returning by cleaning these hardscape areas with each seasonal change.
