How to Get Rid of a Dirty Roof

A dirty and stained roof is an eye-sore that diminishes the aesthetic appeal of your property. It also increases the risk of structural damage.

Moss, algae and lichen thrive in New Zealand’s lush climate and can quickly spread to your home’s exterior surfaces. Although they do not pose immediate health risks, they can be dangerous when inhaled and may aggravate existing conditions like asthma.


A dirty, mouldy roof is more than just unsightly – it can also pose health risks. Mould spores can be inhaled and can cause respiratory problems and exacerbate existing asthma symptoms, especially for those with sensitive airways.

New Zealand’s lush and temperate climate is the perfect breeding ground for a wide variety of microorganisms like moss, algae, and mould that can grow on your roof, walls, and other surfaces. When left unchecked, these organisms can damage your roof, causing leaks and other structural issues.

Regular inspections and cleaning can help prevent these organisms from taking root. Keeping surfaces dry, regularly washing your roof and exterior walls, and pruning overhanging trees can reduce shade and moisture that promotes fungus growth. Using a commercial moss, mould and lichen treatment can also protect your roof from future growth.


The dark, streaked discoloration that is seen on roofs throughout the country is not mold or mildew, it’s green algae. Most of the time it grows in coastal or humid areas where moisture tends to dwell on roof surfaces and it can be quite persistent.

Algae are photosynthetic eukaryotic organisms from the kingdom Protista. They are typically aquatic, but some species of the algae (including the familiar Chlorella and diatoms) can also be found on land. They can grow photoautotrophically as single cells or heterotrophically in the presence of organic substrates. They range in size from microscopic single-celled algae to large multicellular forms such as the brown seaweed giant kelp that can reach 60 m in length.

Although algae are eukaryotic, they are not true plants because they lack many of the cell and tissue differentiations found in land plants including stomata, xylem and phloem. Nevertheless, the term is broadly applied and is considered to encompass a polyphyletic grouping of organisms from several phylogenetic groups.


Lichen is the result of a symbiotic relationship between fungi and cyanobacteria (algae or bacteria). They are opportunistic and will grow on any natural surface that can provide moisture, a stable substrate and nutrients. Lichens are often seen growing on trees, mosses, ferns and rocks. They also grow on shingled roofs and in some areas can be a real problem as they hold moisture against the surface which over time may cause the shingles to bend or even crack.

Our roof wash Auckland solution containing no bleach breaks down lichen over a period of months and rain naturally assists by washing it away. One of the main reasons other outdoor cleaners fail to kill lichen is that they do not fully saturate the growth and dry out too quickly. This is a key reason why we recommend saturating the lichen thoroughly with our product when it is applied. A good tip is to apply the Bio-Shield on a cool, cloudy day to help with penetration.

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A clean roof is a big part of the overall look of your home or building. Unsightly moss, algae or lichen can diminish the value of your property and create irreversible damage if left unattended. Our Auckland & North Shore experts will remove the unsightly growths to give your building or house that final touch of appeal and ensure it is safe for rainwater to wash away. We are experienced with all types of roofs and use high strength solutions to achieve the best results with the minimum of disruption. All work is carried out under fall arrest systems and all workers are fully insured.

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