Can I Use Roofing Silicone to Seal a Nail Hole in Longrun Iron?

Roofing silicone can temporarily plug a nail hole in longrun iron, but it's generally considered a short-term patch rather than a proper repair. In New Zealand's variable climate — with UV exposure, thermal expansion, and heavy rainfall — silicone alone often fails within a few years. Understanding your options will help you choose a fix that actually lasts.

Why Nail Holes Are a Problem in Longrun Iron

Longrun steel roofing (often called corrugate or tray profile iron) is one of the most common roofing materials in New Zealand. Nail holes can appear when old fixings are removed, when someone walks on the roof and punches through, or when a previous repair was done incorrectly. Even a small hole can allow water ingress that leads to:

• Timber framing rot
• Ceiling damage and mould growth
• Compliance issues under the NZ Building Code clause E2 (External Moisture)
• Potential Healthy Homes issues for rental properties under Tenancy Services regulations

Can You Use Roofing Silicone?

Yes — roofing-grade silicone sealant (not standard bathroom silicone) can be used as a temporary measure on a small nail hole. Look for products specifically rated for metal roofing and UV exposure. However, there are important limitations:

• Silicone does not bond well to Zincalume or painted steel surfaces that are dirty, oily, or corroded
• Thermal expansion and contraction of metal roofing causes silicone to crack and lift over time
• It is not considered a compliant permanent repair under good trade practice
• Some roofing warranties may be voided if non-approved sealants are used

If you do use silicone as a stopgap, clean the area thoroughly with a degreaser, allow it to dry completely, and apply a roofing-grade product. This buys time but should be followed up with a proper repair.

Better Options for Sealing a Nail Hole

1. Roofing Repair Tape or Butyl Tape

Butyl-based roofing tape is a more durable option than silicone for small holes. It bonds well to metal, handles movement, and is UV-resistant. Products from brands like Sika are worth considering — always check the product is rated for metal roofing applications.

2. Roofing Screws with Neoprene Washers

For a hole left by a removed nail, the most trade-standard fix is to drive a roofing screw with a neoprene bonded washer into or immediately beside the hole. The washer compresses to create a watertight seal. This is the preferred method used by professional roofers across New Zealand.

• Use screws matched to your roofing profile
• Ensure the screw length is appropriate for your batten or purlin depth
• Use a screw with a colour-matched head if appearance matters

These are readily available at Bunnings or Mitre 10.

3. Patch Repair with Compatible Metal

For larger holes or damaged areas, a metal patch cut from the same profile material, sealed and screwed over the damaged section, is a more permanent solution. This should be done with compatible steel (Zincalume to Zincalume, or colour-matched painted steel) to avoid galvanic corrosion.

4. Sheet Replacement

If the sheet is significantly corroded or damaged around the hole, replacing the entire sheet run is often the most cost-effective long-term solution. A qualified roofer can assess this quickly.

What to Avoid

Always check that any product you use is compatible with your specific roofing material. BRANZ publishes guidance on roofing materials and moisture management that can help you understand compatibility.

Safety First

Working on a roof carries serious fall risk. WorkSafe NZ requires that anyone working at height takes appropriate precautions. For most homeowners, this means:

• Never work on a wet or dewy roof
• Use a properly secured ladder and have someone present
• Wear non-slip footwear and step on the ribs (high points) of the profile, not the pans
• Consider whether the job is safer left to a professional

Review WorkSafe NZ's guidance on working at height before attempting any roof work.

When to Call a Professional

Call a qualified roofer if:

• The hole is larger than a nail diameter, or there are multiple holes
• There is visible corrosion, rust, or cracking around the hole
• You suspect water has already entered the roof space
• The roof pitch is steep or access is difficult
• You are unsure of your roofing material or profile type
• The roof is under warranty (DIY repairs may void it)

Roofing work is not legally restricted in the same way as electrical or plumbing, but poor repairs can create significant building envelope failures. A Licensed Building Practitioner (LBP) in the roofing category has the skills and accountability to do the job properly. You can find qualified local roofers on tradedirectory.co.nz.

Sources & Further Reading

• MBIE Building Performance – Building Code Clause E2 External Moisture
• BRANZ – Roofing and weathertightness guidance
• WorkSafe NZ – Working at height
• Licensed Building Practitioners – Find an LBP
• Sika NZ – Sealants and roofing products
• Tenancy Services – Healthy Homes Standards