How to Safely Remove Moss from a Tile Roof Without Pressure Washing

Moss on a tile roof is a common problem across New Zealand, especially in wetter regions like the West Coast, Northland, and Wellington. The good news is you can remove it safely without a pressure washer — in fact, pressure washing is widely discouraged by roofing professionals because it can crack or dislodge tiles, strip protective coatings, and force water under the roof, potentially breaching the requirements of the NZ Building Code. A combination of dry brushing and chemical treatment is the recommended approach.

Why You Should Avoid Pressure Washing Tile Roofs

High-pressure water can:

• Crack or chip concrete and terracotta tiles, especially older or weathered ones
• Dislodge pointing and bedding mortar at ridges and hips
• Strip the surface coating from concrete tiles, accelerating future moss and lichen growth
• Drive water under overlapping tiles, causing leaks and moisture damage inside the roof space
• Void manufacturer warranties on relatively new tile systems

For these reasons, most reputable NZ roofing contractors and tile manufacturers recommend low-pressure or no-pressure methods.

Safety First: Working at Height

Before you touch a single tile, understand that working on a roof is one of the most common causes of serious injury and death on NZ worksites and at home. WorkSafe NZ requires that falls from height be properly managed.

• Never work on a wet or mossy roof — the surface is extremely slippery
• Use a roof ladder (one with a ridge hook) to spread your weight and avoid stepping directly on tiles
• Wear rubber-soled boots with good grip
• Use a safety harness anchored to a suitable roof anchor point if the pitch is steep or the drop is significant
• Have a second person on the ground at all times
• If you are not comfortable working at height, hire a qualified roofer — you can find local professionals on tradedirectory.co.nz

What You'll Need

Step 1 — Dry Brush the Loose Moss

Wait for a dry, overcast day (not full sun, which causes chemical treatments to evaporate too quickly). Using a stiff-bristle brush or a soft-bristle roof broom, work from the ridge down toward the gutters, brushing moss and debris off the tiles. Avoid scrubbing side-to-side across tiles as this can lift edges.

• Remove as much bulk moss as possible before applying any chemical
• Clear gutters and downpipes after brushing — dislodged moss can cause blockages
• Do not use a metal scraper, which can scratch tile surfaces

Step 2 — Apply a Moss and Lichen Treatment

Once the bulk of the moss is removed, apply a biocidal moss treatment to kill remaining spores and roots. Several products are available at Bunnings and Mitre 10, including ready-to-use sprays and concentrates designed for roof surfaces.

• Follow the manufacturer's dilution and application instructions carefully
• Apply on a calm, dry day with no rain forecast for at least 24 hours
• Protect garden beds and plants below the roofline — many treatments contain chemicals harmful to vegetation; rinse plants with water before and after application as a precaution
• Wear eye protection and gloves when handling concentrates

After application, leave the treatment to work — don't rinse it off. Over the following weeks, rain will gradually wash the dead moss away. A second application may be needed for heavy infestations.

Step 3 — Consider a Preventive Coating

Once the roof is clean, a roof sealer or moss-inhibiting coating can significantly slow regrowth. Products such as those in the Wattyl or Resene ranges include roof paints with fungicidal additives suitable for concrete tiles. Always check the product is compatible with your specific tile type before applying.

Some roofers also install zinc or copper strips near the ridge — rainwater reacting with the metal creates a mild solution that inhibits moss growth as it runs down the roof. This is a long-term preventive measure worth discussing with a professional.

How Often Should You Treat Your Roof?

In most NZ climates, a moss treatment every 2–4 years is a reasonable maintenance interval, though shaded roofs in high-rainfall areas may need more frequent attention. Regular inspections — at least annually — will help you catch moss early before it becomes a major problem.

When to Call a Professional

Call a licensed roofing contractor if:

• The roof pitch is steep or the height makes safe access difficult
• You notice cracked, broken, or slipping tiles during your inspection
• There is damage to ridge capping, mortar bedding, or flashing
• The moss infestation is severe and covers a large area
• You are unsure about the condition of the roof membrane or underlayment

A professional roofer can also advise whether any repair work requires a building consent — while routine maintenance is generally exempt under Schedule 1 of the Building Act, structural repairs or significant alterations may not be. Always confirm with your local council if in doubt. You can find qualified local roofers on tradedirectory.co.nz.

Sources & Further Reading

• WorkSafe NZ — Working at Height
• MBIE Building Performance — Building Code and consents
• BRANZ — Roof maintenance guidance
• Resene — Roof coatings and treatments
• Wattyl — Roof paint products
• Bunnings — Moss and mould treatment products