Apply the answer
Use the roof details as measured quantities.
Keep roof area, roof lines and individual penetrations separate when you have plans or measurements.
What counts as a roof penetration?
NZMRM defines a penetration as a hole through roof or wall cladding for projections such as pipes, ducts, chimneys and roof lights. On residential roofs that can also include plumbing vents, extractor ducts, solar service routes and other equipment supports. Sources: NZ Metal Roofing Manufacturers.
- Skylights and roof lights.
- Wood-burner or gas flues and chimneys.
- Plumbing vent pipes.
- Bathroom/kitchen extract ducts where they discharge through the roof.
- HVAC and mechanical-service penetrations.
- Aerial, cable or solar-related roof interfaces where they penetrate or fix through the cladding.
Why position and catchment area matter
A penetration near the ridge sees different water flow from the same opening near the eaves. A wide obstruction can concentrate runoff from the roof above it. NZMRM therefore includes position, roof pitch, roof type and catchment area in the penetration-design decision. Sources: NZ Metal Roofing Manufacturers.
Boot flashing or sheet-metal flashing?
NZMRM groups penetration weathering broadly into proprietary boot flashings and sheet-metal flashings. The suitable option depends on the penetration and roof. The detail needs to accommodate movement, preserve drainage and remain compatible with the roof material. Sources: NZ Metal Roofing Manufacturers.
For metal roofing, compatibility matters above and around the opening. NZMRM says condensate or corrosive discharge from sources such as air-conditioning or solar equipment should not discharge directly onto metal roof cladding but be separately drained to an inert gutter or downpipe. Sources: NZ Metal Roofing Manufacturers.
Why sealant alone is not a roof detail
Sealant can be part of a correctly designed junction, but it should not be treated as the whole drainage strategy. The roof still needs laps, upstands, flashings and water paths appropriate to the particular cladding and opening. Sources: NZ Metal Roofing Manufacturers; NZ Metal Roofing Manufacturers.
- Ask what flashing system is being used.
- Ask whether the penetration crosses one pan or multiple ribs/seams.
- Confirm how water from above the penetration bypasses it.
- Check material compatibility and movement.
- Record the penetration separately in a reroof quote rather than assuming “all flashings” includes it.
What happens to existing skylights and flues during a reroof?
A reroof is the time to decide whether an existing penetration is staying, being replaced or being removed. Reusing an old skylight, curb, boot or flue interface can create warranty and compatibility questions even if the surrounding roof is new. Sources: Roofing Association of New Zealand; NZ Metal Roofing Manufacturers.
The quote should name significant penetrations and state whether replacement units, new flashing kits, curb work or interior finishing are included. If the condition is unknown until opening, use an allowance or written variation process. Sources: Building Performance.
Related questions
Can a roofer just silicone around a leaking pipe?
A sealant-only repair may not address the underlying drainage, movement or flashing problem. The correct response depends on the penetration and roof detail, and should preserve a durable water path rather than rely solely on surface sealant. Sources: NZ Metal Roofing Manufacturers.
Should I replace an old skylight when I reroof?
Not automatically, but the reroof is a sensible time to assess its age, condition, flashing system, compatibility and warranty. The quote should say whether the existing unit and curb are being reused or replaced. Sources: NZ Metal Roofing Manufacturers; Roofing Association of New Zealand.
Does a flue need special metal around it?
Flues are roof penetrations and need a compatible weathering detail suited to their size, temperature, movement, roof profile and position. The exact system should follow the relevant product, roofing and fire/flue requirements. Sources: NZ Metal Roofing Manufacturers; NZ Metal Roofing Manufacturers.
Sources and review notes
Prepared by RoofHub editorial. Reviewed . A source check confirms what a page states, not an independent inspection or invoice audit. Published project accounts are attributed to their publishers.
- primaryNZ Metal Roofing Manufacturers: Code of Practice v26.09: Roof penetrations - Current NZMRM roof-penetration guidance. Penetration detailing depends on hole size and shape, roof pitch and type, catchment area, position and durability/compatibility requirements. Page checked 2026-10-21. Publication date not stated. · industry-technical
- primaryNZ Metal Roofing Manufacturers: Code of Practice v26.09: Penetration durability and compatibility - Current NZMRM guidance requiring compatible materials around penetrations and separate drainage of condensate or corrosive discharge rather than discharge onto metal roof cladding. Page checked 2026-10-21. Publication date not stated. · industry-technical
- primaryNZ Metal Roofing Manufacturers: Code of Practice v26.09: Flashings - Current MRM flashing guidance. Defines the purpose of flashings and identifies common types including ridge/hip, barge/verge, parapet cappings, apron and valley; penetration flashings are treated separately. Page checked 2026-10-21. Publication date not stated. · industry-technical
- primaryRoofing Association of New Zealand: RANZ Re-Roofing Guide - RANZ describes this as an annually updated NZ consumer guide to reroofing materials, systems, terminology, scope and workmanship. Used for project-planning context rather than contractor ranking. Page checked 2026-10-21. Publication date not stated. · industry-technical
- primaryBuilding Performance: Contracts for your building project (2026-01-15) - Building Performance guidance last updated 15 January 2026. Residential building work costing $30,000 or more including GST requires a written contract; disclosure and checklist requirements also apply at that threshold or when requested. Page checked 2026-10-21. Publication date shown above. · government
Original calculations are labelled as examples. Historical prices stay dated, missing fields stay unknown, and conflicting specifications are flagged. Sources are not endorsements or paid rankings. Read our methodology or report a correction.
Keep exploring
Next step
Estimate it, refine it, or ask RoofHub.
Start with approximate information, use actual measurements when you have them, or ask RoofHub to explain the decision. A roofing contractor still needs to confirm the site, specification and final quotation.