Yes, as a homeowner you can identify many of the warning signs that your roof sarking is damaged or missing — and you don't need to climb onto the roof to do it. A combination of internal inspections, visual checks from the ground, and knowing what to look for will give you a good picture of whether your sarking needs attention. That said, a full assessment should always be carried out by a qualified building inspector or licensed roofer.
What Is Roof Sarking?
Roof sarking (sometimes called underlay or roofing underlay) is the layer of material installed directly beneath your roof cladding — tiles, corrugated iron, or long-run steel — and above the rafters or purlins. In New Zealand, sarking can be a rigid board (typically timber or plywood) or a flexible membrane (such as a breather-type underlay). Its job is to:
- Provide a secondary barrier against wind-driven rain and moisture
- Add structural rigidity to the roof framing
- Improve thermal and acoustic performance
- Help meet the requirements of the NZ Building Code, particularly Clause E2 (External Moisture)
Older NZ homes (pre-1980s) often used bitumen-impregnated felt sarking, which can become brittle and crack over time. Many homes of that era also have no sarking at all — it wasn't always required.
Why Damaged or Missing Sarking Matters
Without effective sarking, wind-driven rain, condensation, and dust can penetrate your roof space. This can lead to:
- Timber rot in rafters and ceiling framing
- Mould and mildew growth (a concern under Healthy Homes standards for rental properties)
- Insulation damage and reduced thermal performance
- Water staining on ceilings
BRANZ research highlights moisture management as one of the most critical factors in NZ roof performance, particularly in high-wind and high-rainfall regions like the West Coast, Wellington, and Northland.
Safe Ways to Check for Sarking Issues
1. Check From Inside the Roof Space
If you have a accessible roof cavity, this is your best starting point — and the safest. Use a torch and, if needed, a dust mask. Look for:
- Daylight visible between roofing sheets or tiles — a clear sign of missing or torn sarking
- Torn, sagging, or brittle underlay hanging between rafters
- Water stains or wet patches on rafters, purlins, or the top of ceiling insulation
- Mould or dark discolouration on timber framing
- Gaps or missing sections where sarking has simply never been installed
Safety note: Never walk on the ceiling joists — always step on structural members (rafters or purlins) or use a crawl board. Be aware of electrical wiring in the roof space. If you're unsure, don't enter — call a professional.
2. Inspect Your Ceilings From Below
From inside your living areas, look for:
- Water stains or brown tide marks on plasterboard or GIB ceilings
- Bubbling or peeling paint on ceilings
- Sagging ceiling sections, which can indicate prolonged moisture exposure
- Musty smells, suggesting trapped moisture or mould
These signs don't confirm sarking damage on their own, but they're strong indicators that moisture is getting through the roof system somewhere.
3. Ground-Level Visual Check
Using binoculars from the ground (never climb onto the roof without proper safety equipment and training), look for:
- Lifted, cracked, or missing roof tiles that may have exposed the sarking to UV and weather
- Rust or corrosion on metal roofing that could allow water ingress
- Visible gaps at the eaves or ridge where underlay may have deteriorated
4. Check After Heavy Rain or Wind
After a significant weather event, re-inspect your ceiling and roof space. Fresh water stains or new drips are a reliable indicator that your roof system — including the sarking — has been compromised.
What Does Damaged Sarking Look Like?
| Sign | Likely Cause | Urgency |
|---|---|---|
| Brittle, crumbling felt underlay | Age (bitumen felt degrades) | High |
| Torn or split membrane sections | Storm damage or foot traffic | High |
| Missing sarking entirely | Original build omission | Medium–High |
| Sagging underlay between rafters | Water pooling, age | Medium |
| Mould on underlay surface | Condensation or leak | Medium–High |
NZ Building Code and Consent Considerations
Replacing or installing sarking as part of a re-roofing project may require a building consent, depending on the scope of work. Under Schedule 1 of the Building Act, some minor repair work may be exempt — but you should always confirm with your local council before starting any significant roofing work. The MBIE Building Performance website has guidance on what requires consent.
If your home was built before the current Building Code came into force, it may not have sarking at all — this was common practice and not necessarily a code violation for the time, but it's worth addressing if you're re-roofing.
When to Call a Professional
While you can identify warning signs yourself, always engage a qualified professional for:
- Any physical inspection that requires getting onto the roof
- Confirming the extent of sarking damage or absence
- Replacing or installing new sarking (this is typically done as part of a re-roofing job)
- Assessing associated structural damage to rafters or framing
A Licensed Building Practitioner (LBP) is required to carry out or supervise restricted building work on your home — check the LBP register to verify credentials. A qualified building inspector can provide a written report on your roof's condition, which is especially useful before buying or selling a property.
You can find experienced local building inspectors and roofers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
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