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Why Does Your Roof Need Regular Moss Treatments?
Re-screwing iron, re-bedding & re-pointing tiles, and fast leak detection & repair before small problems get big.
The short answer
A moss treatment kills moss, lichen and mould on your roof before they damage it. It's applied with a soft, low-pressure applicator, not a water blaster, and then left to work. The growth dies within weeks and the rain gradually washes it away.
It matters for more than looks. Most roofing manufacturers make keeping the roof free of organic growth a condition of their warranty. Coating warranties cover the paint failing on its own, not damage caused by moss and lichen left to grow.
As a rough guide, most New Zealand roofs need a moss treatment every 12 to 24 months. Shaded roofs, roofs under trees and south-facing roof planes often need it more often.
What moss, lichen and mould do to your roof
Organic growth isn't just a cosmetic problem. Each type attacks your roof in a different way.
- Moss holds water. It acts like a sponge, keeping the roof surface wet long after rain. On concrete tiles that means more water soaked into the tile. On iron and Decramastic it means trapped moisture sitting against the steel, which speeds up corrosion.
- Lichen eats into the coating. Those grey, white or orange spots anchor themselves into the surface and break the paint film down from underneath. Even after lichen dies, it can leave pitting and scarring behind.
- Mould and black algae weaken the paint. Mould attacks the resin that binds a coating together, leaving it soft, chalky and quicker to fail.
- Debris blocks the water's path. Clumps of moss wash into valleys, gutters and downpipes. Water then backs up under flashings and tile laps instead of draining away.
The longer growth is left, the deeper it gets into the surface. A roof that's treated early stays a maintenance job. A roof left for years often needs repairs and a recoat.
How a moss treatment is applied
A proper moss treatment is gentle by design. The aim is to kill the growth without harming the roof or the coating underneath it.
- Check the roof first. Before anything goes on, we look for cracked tiles, failed ridge pointing, lifted flashings and rust. Anything that needs fixing gets flagged.
- Apply with a soft applicator. The treatment goes on with a low-pressure applicator that wets the surface evenly. There's no force involved, so nothing is stripped, chipped or driven under the tile laps and flashings.
- Soak the growth, not blast it. The solution works its way into the roots of the moss and lichen and kills them where they're anchored. That's what stops the same patches coming straight back.
- Let the weather finish the job. Growth dies off within weeks. The dead material then loosens and washes away with the rain over the following weeks. Lichen is the slowest and can take a few months to fully clear.
Why we don't water blast. High-pressure water can strip paint, wear the surface off concrete tiles and loosen the chip on pressed metal tiles. It can also force water up under laps and flashings. Paint and roofing manufacturers both warn that pressure washing can damage a coating, and damage like that isn't covered by warranty.
Why the product matters. Not every moss killer is safe on every roof. Harsh bleach-based mixes can discolour or damage some coatings. The treatment needs to suit your roof type and its finish.
Why moss treatments protect your coating warranty
A restored roof is usually backed by two warranties: one from the paint manufacturer on the coating, and one from the applicator on the workmanship. Both cover the coating failing on its own. Neither covers damage caused by a roof that hasn't been looked after.
Organic growth is the most common kind of that damage on New Zealand roofs. Resene's maintenance guide explains that moss and lichen get into the paint film and shorten its life, while mould breaks down the resin holding the paint together. Once that has happened, it's very hard to show a coating failed because of the product rather than the growth.
Regular moss treatments keep your coating doing its job and keep your warranty on solid ground.
- Treat on schedule. Follow the maintenance interval in your warranty documents, not just when the roof starts looking green.
- Keep a record. Hold on to the date, invoice and photos from every treatment. If you ever need to make a claim, that's your proof the roof was maintained.
- Use the right people and products. Maintenance done badly, such as water blasting a coated roof, can cause the very damage a warranty won't cover.
Call us on 09 972 1718 or request a free, no-obligation quote.