Technically, you can paint over a roof with old flaking paint — but you really shouldn't, at least not without thorough preparation first. Painting over loose or peeling paint is one of the most common reasons roof paint jobs fail within a year or two. The good news is that with the right prep work, a DIY roof repaint is achievable for many NZ homeowners.
Why Flaking Paint Is Such a Problem
When you apply fresh paint over flaking or poorly adhered old paint, the new coat bonds to the old loose layer rather than to the roof surface itself. As the old paint continues to lift — which it will, especially under NZ's harsh UV, wind, and rain — it takes the new paint with it. You end up with the same problem, only sooner and with more money wasted.
Flaking paint also traps moisture underneath, which can accelerate corrosion on metal roofs (such as Colorsteel or Zincalume) or cause further deterioration on concrete and clay tiles.
Identifying What You're Working With
Before you start, identify your roof material, as this affects both prep and paint choice:
- Metal roofing (corrugate, tray, or longrun steel) — most common in NZ
- Concrete or terracotta tiles
- Fibrous cement (Hardie) tiles or shingles
- Butynol or membrane roofing — generally not suitable for standard roof paint
Also check whether the old paint is water-based or oil/solvent-based, as this affects primer selection. If you're unsure, rub a small area with methylated spirits on a rag — if paint comes off, it's likely water-based (this is a general guide; confirm with your paint supplier if unsure).
Step-by-Step Roof Preparation
Proper prep is the most important part of any roof paint job. Don't rush it.
1. Safety First
Working at height is one of the leading causes of serious injury in New Zealand. Always use a properly secured ladder, wear non-slip footwear, and consider hiring scaffolding for anything other than a low-pitched roof. Check WorkSafe NZ guidance on working at height before you begin.
2. Remove All Loose and Flaking Paint
This is non-negotiable. Use a wire brush, scraper, or angle grinder with a wire wheel to remove all loose, flaking, and peeling paint back to a firm edge. On metal roofs, feather the edges of any remaining sound paint so there's no sharp lip for water to get under.
For large areas of failure, you may need to strip the roof back to bare metal or tile — this is labour-intensive but gives the best result.
3. Treat Rust (Metal Roofs)
If you find rust on a metal roof, treat it with a rust converter or sand it back to bare metal before priming. Products from Resene and Dulux both offer rust-inhibiting primers suited to NZ conditions. Do not paint over active rust — it will continue to spread underneath.
4. Clean the Entire Roof
Wash the roof thoroughly with a water blaster (800–2000 psi is usually sufficient) to remove moss, lichen, dirt, and any remaining loose material. Allow the surface to dry completely — in NZ's variable weather, this may take a day or two. Treat any moss or lichen with an appropriate biocide wash and allow the recommended dwell time before rinsing.
5. Apply the Right Primer
Once clean and dry, apply a primer suited to your roof type and the topcoat you're using. For bare metal, use a corrosion-inhibiting primer. For concrete or terracotta tiles, use a penetrating sealer or tile primer. Always follow the manufacturer's data sheet — Wattyl and Resene both publish detailed technical guides for their roof coating systems.
6. Apply Topcoat
Use a roof-specific paint rated for your roof material. Avoid using exterior wall paint on roofs — it's not formulated for the UV exposure, foot traffic, and water-shedding demands of a roof surface. Apply in dry, mild conditions, ideally avoiding the heat of the day to prevent the paint skinning too quickly.
A Quick Comparison: Prep Levels vs. Results
| Prep Level | Likely Outcome |
|---|---|
| Paint straight over flaking paint | Failure within 1–2 years |
| Light scrape + wash + prime | 3–5 years (variable) |
| Full strip, rust treat, prime, topcoat | 8–12+ years (manufacturer-dependent) |
Does This Require a Building Consent?
In most cases, repainting an existing roof does not require a building consent — it's considered maintenance. However, if you're replacing roof cladding or making structural changes, consent may be required. Always confirm with your local council, as MBIE Building Performance notes that Schedule 1 exemptions have specific conditions.
When to Call a Professional
Consider hiring a qualified roof painter if:
- Your roof is steeply pitched or difficult to access safely
- There is widespread rust, significant corrosion, or structural damage
- The roof has failed in multiple areas and may need partial or full re-roofing
- You're unsure about the condition of flashings, valleys, or fixings
- The job is simply too large or time-consuming to tackle yourself
A professional roof painter will have the right equipment, safety gear, and product knowledge to get a long-lasting result. You can find qualified local roof painters on tradedirectory.co.nz.
Master Painters NZ member
Licensed Building Practitioner (LBP)
Roofing Association of NZ (RANZ)
