Why moss does so well on Hamilton roofs
Fog, frost and slow-drying mornings
Ruakura averages 38 fog days a year, and NIWA says Waikato fog is most common from March to August. Add 62.9 ground frosts a year and you get months of mornings when a roof stays damp for hours, which is exactly where moss and lichen take hold.
Less sun than the ranges
NIWA puts the area near Hamilton at around 1,950 bright sunshine hours a year, below the Coromandel Ranges at over 2,100. On the shaded side of a roof, or under big trees, the surface dries slowest and growth comes back first.
Trees overhead
With about 500 notable trees in the District Plan and plenty of mature gardens, many roofs sit in shade and catch leaf litter, which holds moisture and feeds moss. If a listed notable tree is involved, talk to Hamilton City Council before anyone cuts it back.
Decramastic and older roofs
Homes built before 2000 may contain asbestos, WorkSafe says, and Hamilton has suburbs going back to 1912. Its safe work sheet for cleaning weathered asbestos cement and decramastic tile roofs says to apply biocide with a low-pressure sprayer, keep the surface wet, and never use high-pressure spraying or blasting.
How a Hamilton roof should be cleaned
The gentle way is usually the right way: a moss and lichen treatment sprayed at low pressure, left to work, with rain gradually washing the dead growth away. Our guide to moss and lichen explains why patience beats force.
Water-blasting can strip coatings and drive water under laps and flashings, so it's normally kept for sound roofs about to be painted. On asbestos, businesses aren't allowed to use high-pressure water (over 350 kPa) at all.
Expect the roofer to wait for a frosty or foggy roof to dry before working on it. WorkSafe also lists fibrolite sheets, clear roofing, some old masonry tiles and badly corroded iron as brittle roofs workers shouldn't walk on, so a careful roofer will ask what yours is before stepping off the ladder.
What a roof cleaning quote should spell out
We don't list prices, but a clear quote tells you which product goes on, whether it's applied at low pressure or the roof is water-blasted, which areas are covered, whether the spouting is cleared too, and whether a follow-up treatment is included.
Steep or two-storey roofs, heavy growth, and decramastic or possibly asbestos roofs all make the job bigger, because they need more care, more time or more safety gear.
What you can do from the ground
You can
- Spray a moss treatment on paths, decks and fences, following the label
- Trim back trees you're allowed to prune so the roof gets more sun and fewer leaves
- Each winter, check from the ground for green or black patches on the shaded slopes
- Keep downpipe outlets clear so dead moss washing off doesn't block them
Leave to a roofer
- Any treatment that needs a ladder or someone on the roof
- Decramastic, asbestos cement or other brittle roofs
- Cleaning before roof painting
- Replacing cracked tiles or sheets found during the clean
Questions for a Hamilton moss treatment quote
- Which product will you use, and is it safe near my water tank, garden and pets?
- Will you apply it at low pressure, or do you plan to water-blast?
- Is my roof decramastic or possibly asbestos, and how does that change your method?
- Will you clear the spouting and downpipes at the same time?
- How long until the moss dies off, and will I need a follow-up treatment?
- What fall protection will you use while you're up there?
What we'd do about moss in Hamilton
We'd treat in late summer or early autumn, so the product has dry days to soak in before the fog and frost season. We'd skip water-blasting unless the roof is about to be painted, and only on a roof we knew wasn't asbestos. Then we'd have the shaded side looked at every year or two, because that's where Hamilton moss comes back first.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.