How to Remove a Disused Flue Pipe and Seal the Roof Hole

Removing a disused flue pipe and sealing the roof hole is a job many capable Kiwi homeowners can tackle themselves — but it must be done properly to keep your roof weathertight and compliant with the NZ Building Code, particularly Clause E2 (External Moisture). Rushing or cutting corners can lead to costly leaks, rot, and even structural damage, so take your time and use quality materials.

Before You Start: Safety and Compliance Checks

Before touching anything, confirm the flue is genuinely disused and disconnected from any appliance below. If the flue was connected to a gas appliance (heater, fireplace, or hot water system), any disconnection work on the gas side is restricted work under the Gas Act and must be carried out by a licensed gasfitter registered with the Plumbers Gasfitters & Drainlayers Board. Do not proceed until you have written confirmation or have seen the appliance fully decommissioned by a professional.

Safety note: Working at height is one of the leading causes of serious injury in NZ. Always use a properly secured ladder, wear non-slip footwear, and consider hiring a roofer if your roof pitch is steep (over 25°) or the surface is slippery. Check WorkSafe NZ guidelines on working at height before you begin.

Also check whether your project requires a building consent. Removing a flue and patching the roof is generally considered maintenance and is likely exempt under Schedule 1 of the Building Act — but rules vary, so confirm with your local council before starting.

Tools and Materials You'll Need

• Flat pry bar and hammer
• Tin snips or angle grinder (for metal flue sections)
• Cordless drill and screwdriver bits
• Replacement roofing material matching your existing roof (corrugated iron, long-run steel, tiles, etc.)
• Flashing — lead, aluminium, or pre-formed to suit your roof type
• Roofing screws with neoprene washers
• Quality roofing sealant (e.g. Sika Sikaflex or a compatible product)
• Safety harness or roof anchor if required
• Ladder and roof brackets

Step 1: Remove the Flue Pipe

Start from inside the roof space if accessible. Disconnect any internal flue sections — these are usually push-fit or screwed together. Work upward, removing sections one at a time. Once you're on the roof, carefully remove the flue collar or rain cap at the top. Most are held by screws or a friction fit.

Remove any existing flashing around the base of the flue. This is often lead or aluminium, sealed with roofing mastic. Use your pry bar gently to lift it without damaging surrounding roofing material. Keep the old flashing as a template for sizing the new patch.

Step 2: Assess the Hole and Surrounding Roof

Once the flue is out, inspect the hole and the surrounding area carefully:

• Check for rot or rust in the decking, battens, or purlins beneath
• Look for any cracked or damaged roofing sheets or tiles nearby
• Measure the hole accurately — you'll need a patch that overlaps by at least 150 mm on all sides as a general guide (check your roofing manufacturer's recommendations)

If you find significant rot or structural damage, stop and call a qualified roofer or builder. Repairs to structural roof members may require an LBP (Licensed Building Practitioner).

Step 3: Patch the Roof

The patching method depends on your roof type.

Corrugated or Long-Run Metal Roofing

Cut a patch from matching profile steel sheet — sourced from Mitre 10, PlaceMakers, or a roofing supplier. The patch must sit over the existing sheets (lapping uphill) and be fixed with roofing screws at every trough. Apply a bead of roofing sealant under the lap edges before screwing down.

Concrete or Clay Tiles

Source matching replacement tiles — your local roofing supplier or a tile manufacturer can help identify the profile. Carefully remove surrounding tiles to gain access, replace any damaged underlay or sarking, then re-lay tiles working from the bottom up. Mortar ridge or hip tiles as required.

Flat or Low-Slope Roofs

These require specialist membrane repair and are best left to a professional roofer, as improper repairs can void warranties and fail the NZ Building Code.

Step 4: Flash and Seal the Patch

Proper flashing is the most critical part of this job. Even a well-fitted patch will leak without it. Cut and form flashing to cover all edges of the patch, lapping at least 150 mm uphill and 75 mm to each side (confirm with your roofing product's technical data). Bed the flashing in roofing sealant and fix securely.

Apply a final bead of sealant along all exposed edges. Products like Sika Sikaflex or similar flexible roofing sealants are well-suited to NZ conditions. Avoid using standard silicone — it doesn't bond well to metal roofing and degrades quickly in UV.

Step 5: Check from Inside

After the next rain, inspect the ceiling and roof space from inside for any signs of moisture. A torch and a dry day are your best friends here. If you spot any dampness, re-examine your flashing and sealant joints.

When to Call a Professional

Call a qualified roofer if:

• Your roof pitch is steep or the surface is slippery
• You find rot, rust, or structural damage
• You have a flat or membrane roof
• The flue was connected to a gas appliance (gas disconnection must be done by a licensed gasfitter)
• You're unsure about matching materials or flashing details
• Your council requires a building consent for the work

A skilled local roofer will get the job done safely and weathertight. You can find qualified roofing tradespeople in your area at tradedirectory.co.nz.

Sources & Further Reading

• MBIE Building Performance — Building Code Clause E2 (External Moisture)
• WorkSafe NZ — Working at Height
• Plumbers Gasfitters & Drainlayers Board — Licensed Gasfitters
• Licensed Building Practitioners (LBP)
• BRANZ — Roofing and Weathertightness Guidance
• Sika NZ — Roofing Sealants and Adhesives