Checking for soft or rotten timber before painting your roof is one of the most important steps you can take to protect your investment. Painting over damaged timber won't fix the underlying problem — it will simply hide it until the rot spreads further and causes costly structural damage. A thorough inspection first means your new paint job will last longer and your roof will remain safe and weathertight.
Why Timber Rots on NZ Roofs
New Zealand's climate — particularly in wetter regions like the West Coast, Northland, and Wellington — creates ideal conditions for timber decay. Fungal rot is the main culprit, thriving wherever timber stays damp for extended periods. Common causes include:
- Blocked or leaking gutters allowing water to back up under the eaves
- Failed or missing flashings around chimneys, skylights, and roof penetrations
- Poor ventilation in the roof cavity causing condensation
- Old or cracked paint that has let moisture into the timber grain
- Overhanging trees keeping the roof surface shaded and damp
Understanding NZ Building Code clause E2 (External Moisture) requirements can help you appreciate why weathertightness matters so much — and why catching rot early is critical.
Safety First: Before You Get on the Roof
Roof work is one of the leading causes of serious injury in New Zealand. Before you inspect anything:
- Never work on a wet, frosty, or windy day — surfaces become dangerously slippery
- Use a sturdy, correctly rated ladder secured at the base and top
- Wear non-slip footwear with good ankle support
- Consider a safety harness if your roof pitch is steep (generally over 25°)
- Let someone know you're working at height
- Check WorkSafe NZ's guidance on working at height before you start
If you're not confident working at height, arrange for a qualified roof painter or builder to carry out the inspection.
Tools You'll Need
- A sharp screwdriver or bradawl (for probing timber)
- A rubber mallet or small hammer
- A torch or headlamp
- Binoculars (for a ground-level visual check first)
- Notepad or phone to record and photograph problem areas
Step-by-Step Timber Inspection
1. Start With a Ground-Level Visual Check
Before climbing up, walk around the house and use binoculars to look for:
- Sagging or uneven roof lines — a sign of structural timber movement
- Discolouration, dark staining, or paint peeling in patches
- Visible cracks or splits in fascia and barge boards
- Gaps in flashings or missing mortar around the ridge
2. Inspect the Fascia and Barge Boards
These exposed timber boards at the roof edges are the first to deteriorate. From the ladder (before going on the roof), press firmly along the length of each board with your thumb. Soft spots, sponginess, or areas that dent easily indicate rot. Use your screwdriver to probe any suspicious areas — healthy timber resists penetration, while rotten timber will crumble or allow the tool to sink in with little resistance.
3. Check the Roof Decking and Sarking
If your roof has exposed timber sarking (common on older NZ homes with corrugated iron), walk carefully along the roof battens — never step between them. Probe the sarking boards with your screwdriver, paying close attention to:
- Areas around penetrations (chimneys, vents, skylights)
- Low points where water may pool
- Anywhere the existing paint has bubbled, cracked, or peeled significantly
A hollow sound when tapped with a mallet can also indicate delamination or decay beneath the surface.
4. Inspect From Inside the Roof Space
If you have roof space access, take your torch inside and look up at the underside of the decking and rafters. Signs of concern include:
- Dark staining or tide marks showing past or ongoing leaks
- Visible mould or fungal growth on timber
- Daylight visible through gaps in the roof
- Soft or discoloured timber on rafters and purlins
BRANZ has useful technical guidance on moisture in roof spaces and acceptable moisture content levels for structural timber.
5. Map Your Findings
Make a simple sketch of the roof and mark every area of concern. Note whether the damage appears surface-level (early-stage, paintable after treatment) or structural (requiring timber replacement before any painting begins).
What to Do With Rotten Timber
| Damage Level | Description | Action Required |
|---|---|---|
| Surface/early rot | Soft surface, timber still largely intact | Treat with a timber hardener, prime, then paint |
| Moderate rot | Spongy patches, some structural loss | Partial replacement or epoxy filler repair |
| Severe rot | Crumbling, hollow, or structurally compromised | Full timber replacement before painting |
For surface-level rot, products such as timber hardeners (available from Mitre 10 or Bunnings) can consolidate the fibres before priming. Always follow the manufacturer's instructions and allow full cure time before applying paint.
For a quality topcoat, Resene and Dulux both offer exterior timber primers and topcoats suited to NZ conditions — check their websites for the right system for your substrate.
When to Call a Professional
Call a Licensed Building Practitioner (LBP) or qualified builder if:
- You find widespread or structural rot in rafters, purlins, or roof framing
- The roof is steep, fragile (e.g. old corrugated iron or brittle tiles), or difficult to access safely
- You're unsure whether the damage requires a building consent — some structural repairs do, and your local council is the right place to confirm this
- You discover signs of ongoing leaks that haven't been resolved
You can verify a tradesperson's LBP licence at Licensed Building Practitioners. For the painting itself, a professional roof painter will also know what to look for and can often spot problems an untrained eye might miss. Find qualified local tradespeople on tradedirectory.co.nz.
Master Painters NZ member
Licensed Building Practitioner (LBP)
Roofing Association of NZ (RANZ)
