Roof Flashing Details for NZ Roofs — A Spec Guide

Roof Flashing Details & the NZ Context

This is a technical resource for architects, designers, estimators, and roofers who specify roof flashings on New Zealand projects. If you are after a plain-English introduction to what flashings are, start with our complete flashings guide. This page focuses on the roof flashing details themselves — the junctions, transitions, and penetrations you need to detail and schedule — and on the information we need to fold them accurately.

Roof flashings do a disproportionate amount of the weathertightness work on a building. Every point where two surfaces meet, or where a service passes through the roof, is a potential path for water. The flashing detail is what turns that vulnerable junction into a controlled drainage path, directing water back onto the roof sheeting and towards the gutter rather than into the structure.

In New Zealand, roof flashings sit within clause E2 (External Moisture) of the Building Code. E2/AS1 is one Acceptable Solution, and the NZ Metal Roof and Wall Cladding Code of Practice (the MRM Code of Practice) sets out the cover, upstand, and lap details commonly used for metal roofing. Wind actions from AS/NZS 1170 and the corrosion-zone guidance in the roofing standards also feed into how a flashing is detailed and fixed. We are a fabricator, not the designer of record — we fold flashings to the profile and dimensions you specify, and the specifier remains responsible for confirming each detail meets the requirements for the building.

The sections below run through the common roof flashing types used on NZ roofs and what makes each detail work. Every one of these can be folded to your specification at our Onehunga workshop.

Apron & Head Flashing Detail

An apron flashing is the continuous flashing installed where a roof slope runs up to a vertical wall in a straight line — the base of a chimney, a lean-to meeting the main wall, or a lower roof abutting an upper storey. The detail has a cover leg that laps down over the roof sheeting and an upstand that runs up behind the wall cladding or into a masonry chase, so water is shed onto the roof rather than trapped at the junction.

A head flashing is the equivalent detail at the top, or head, of an opening or upstand — most often above a window or door head, or over the top edge of a wall penetration — where it throws water clear of the face below. Both apron and head details rely on a correctly sized cover, a clean drip edge, and an upstand tall enough for the exposure. Key things to mark on the detail:

• Cover leg length onto the roof and the upstand height behind the cladding.
• The roof pitch, so the included angle of the main fold matches the slope.
• A kick-out or drip edge where the flashing is intended to shed clear of the face.
• Which cladding or roofing the flashing laps over, and in which direction.

Where a sloping roof meets a wall at an angle rather than in a straight line, the junction is handled with step flashings instead — individual overlapping pieces layered with the roofing courses. Note on the schedule whether the run is a continuous apron or a stepped detail so we fold the right components.

Barge & Gable Detail

Barge flashings cap the exposed edge of the roof at the gable ends, covering the ends of the purlins and the roofing underlay and giving the verge a clean, finished line. Because the barge is one of the most visible flashings on the building, the detail matters aesthetically as much as functionally — it is almost always colour-matched to the roof.

The barge detail needs a face dimension that suits the fascia or verge, a return that closes off the underside, and enough cover over the outermost roofing rib to keep wind-driven rain out. On exposed gables the wind zone drives both the cover and the fixing pattern. When you schedule a barge or gable detail, tell us:

• The roofing profile at the verge, so the cover leg suits the rib height.
• The face height and any return or hem you want on the bottom edge.
• Fixed lengths and how many, plus any special end pieces or mitres for the ridge/barge junction.
• The colour and material — barge and ridge are usually specified together for a consistent look.

Ridge & Hip Detail

Ridge cappings sit over the apex where two roof planes meet at the top, closing the gap between the sheets and keeping water and wind out at the highest, most exposed line of the roof. Hip cappings do the same job along the sloping hip lines of a hipped roof. The profile of the capping — its girth, the included angle, and whether it has a raised centre or notched ribs — is set by the roof pitch and the roofing profile it covers.

A ridge or hip detail folded to the wrong angle will not sit down cleanly on both planes, so the pitch is the single most important thing to get onto the drawing. For symmetrical ridges the two legs are equal; for an asymmetric roof, or a mono-pitch ridge-to-wall junction, the two sides differ and need to be dimensioned separately. Where a ridge meets a barge or a wall, mark the end condition so we can fold matching closers or stop-ends.

Valley & Change-of-Pitch Detail

Valley flashings sit in the internal angle where two roof planes drain together. Valleys carry a high concentration of water, which makes them one of the most critical roof flashing details of all — the girth has to be wide enough for the catchment, the fall has to be maintained, and fixings must stay out of the water-carrying pan so they never become leak points. A tapered or wider valley may be needed on long or steep catchments.

A change-of-pitch detail is the transition flashing used where a single roof plane changes angle partway down the slope — the classic example being a steeper upper roof breaking to a shallower verandah or lean-to below. The flashing bridges the two pitches and has to be folded to the exact included angle of the break, with cover onto both roof surfaces. For valleys and change-of-pitch flashings, give us the developed girth (or the leg lengths and the internal angle), the length of each run, and the material — these are details where getting the fold angle and the girth right is what keeps the roof watertight.

Penetration Flashings

Penetration flashings seal around anything that passes through the roof — flues, vents, pipes, cables, and rooflights. The detail has to suit the shape and size of the penetration while keeping a watertight lap over the roofing below and, usually, a soaker or back-tray on the up-slope side that diverts water around the obstruction. For round penetrations a proprietary boot is often used; for square or rectangular penetrations, and for larger openings, a folded soaker tray and cover flashing set is common.

When detailing a penetration, mark the size and shape of the opening, the roofing profile it sits in, the up-slope diversion or cricket required, and whether the flashing needs an upstand for a curb-mounted unit. We can fold soaker trays, curb flashings, and cover pieces to your roof flashing details. For the wall-side equivalents — window heads, sills, and jambs — see our flashings guide for the full set.

How to Spec Flashings for Fabrication

Good flashing details fold accurately when the drawing gives us everything we need in one place. We work from dimensioned details, marked-up flashing schedules, and clear sketches alike — you do not need a formal CAD file, but every fold has to be defined. For each flashing on your schedule, include:

• Cross-section: the profile with every leg length and the developed girth, drawn or dimensioned so there is no ambiguity about the shape.
• Bend angles: mark any angle that is not 90 degrees, and note the roof pitch where the fold has to follow the slope.
• Lengths and quantities: finished length of each piece and how many, plus any special end pieces, mitres, or stop-ends.
• Material and gauge: Colorsteel, Zincalume, galvanised, aluminium, or stainless, and the thickness — tell us the exposure and we can advise if you are unsure.
• Finish and colour: the Colorsteel colour name, or the roof/cladding product to match; note if you want flashings powder coated to a colour instead.
• Lap direction: flag which edge laps over which so we fold the laps to run with the water, not against it.

Send the whole schedule at once and we will confirm the developed sizes before we fold, so the parts land the way your detail intends. Because folding and powder coating are handled by one team here, coated flashings come back from a single point of contact rather than being shuttled between suppliers — sandblasting is arranged as required when a job calls for it. For repeat and account work, our trade & commercial page covers how ordering, POs, and job intake work.

Fold Your Roof Flashings to Detail

Whether you are specifying a single valley or a full flashing schedule for a commercial roof, we fold roof flashings to your drawings from our Onehunga workshop. Send us your drawings or flashing schedule for a quote, or call 09 218 6436 to talk a detail through before you finalise it. For repeat and account customers, open a trade account and send schedules straight through.

Frequently Asked Questions