Wellington roof types explained: tile, metal, butynol, TPO, and the rest.

Long-run coated metal (often called Coloursteel)

By far the most common roof on Wellington homes built or re-roofed since the 1980s. Continuous metal sheets running from the ridge to the gutter with ribs or trapezoidal profiles. Pre-painted with a baked-on coating ("Coloursteel" is one brand, the term often used generically). Comes in many profiles: Trapezoidal, Corrugate, Tray, etc.

Common issues we look at: fastener heads (rust, missing washers), flashings at ridges, hips and valleys, paint film breakdown on older roofs, edge corrosion on coastal Wellington properties, and any signs of movement at penetrations like flues and skylights.

Corrugated iron (galvanised or unpainted)

The classic NZ corrugate. On Wellington homes you'll still see this on older villas, bungalows, garages, and outbuildings. Sometimes painted, sometimes the silvery galvanised finish. Modern corrugate is usually pre-painted (sits under the long-run metal category above).

Common issues we look at: rust at fixings, lapped seams, valleys and parapet upstands, sheet thickness deterioration on older galvanised iron, and signs of repeated leaks at penetrations.

Concrete tile

Heavy grey or coloured cement-based tiles, interlocking. Very common across Wellington and the Hutt Valley on homes from the mid-century era. Tile itself is durable, but the system has wear points: pointing (mortar) on ridges, hips, and barge boards; fixings holding tiles in place; underlay below the tiles.

Common issues we look at: loose or cracked pointing on ridge caps (a very common Wellington flag), broken or lifted tiles, moss and lichen growth, deteriorated underlay (often only visible at eaves), and fixings that are rusting or no longer holding tiles down.

Terracotta tile

The classic orange-brown clay tile. Often found on villa-era and Spanish-influenced homes, plus some premium modern builds. The tile itself can outlast everything around it. Like concrete tile, the wear points are usually the pointing, the fixings, and the underlay below.

Common issues we look at: building reports very often mark terracotta roofs "not accessed" because the tile is fragile and easily damaged. Drone access lets us inspect it up close without putting any load on it. Beyond access, we look at pointing condition, ridge cap stability, broken tiles, fixings, and underlay condition where visible.

Decramastic / pressed metal tile

Lightweight metal sheets pressed to look like tiles, coated with a stone-chip surface. Very common on Wellington homes from the 70s through the 90s. Looks like tile from the street but is much lighter.

Common issues we look at: loss of stone chip on weather faces, rust at fixings and overlaps, edge deterioration, and condition of clip systems. Repainting and recoating extend the life of these if done in time.

Butynol

A synthetic rubber sheet (technically a thermoset). Black, smooth or lightly textured, chemically bonded at the seams. Has been the dominant flat-roof membrane in NZ for decades. Found on dormers, decks, parapets, lower roof sections, and many older commercial flat roofs.

Common issues we look at: failures usually come from either substrate movement underneath (cracking the membrane) or poor installation (cowboy seam work). After 10 years, butynol benefits from active maintenance. We look at seam condition, edge details, upstand flashings, and any pooling that suggests substrate sag.

TPO (Thermoplastic Polyolefin)

A welded thermoplastic sheet membrane that's been the dominant commercial flat-roof system globally for the past 20 years. Usually white, grey, or light coloured (the white reflects heat). Welded at seams with hot air, giving a continuous waterproof surface. Comes in 3m-wide sheets, so big roofs go on fast.

Common issues we look at: seam quality (the welds are the make-or-break detail), perimeter and upstand detailing, fastener pattern integrity on mechanically-attached systems, and any signs of heat-induced shrinkage or polymer breakdown. Quality varies widely between TPO brands. Firestone is considered the premium NZ-available product.

Aerial Assess has practical experience with TPO systems, so this is one we can assess with industry knowledge.

WeldTech

A weldable membrane in the same family as TPO, increasingly chosen over butynol on smaller flat-roof jobs because it can be hot-air welded (faster, fewer accessories). Very similar appearance to butynol but performs more like TPO.

Common issues we look at: seam welds, edge detailing, and the same kinds of upstand and penetration details we'd look at on butynol or TPO.

Modified bitumen / torch-on (Shelter-Bit and similar)

Asphalt-based sheet membrane heat-bonded to the substrate with a gas torch. Often called "torch-on". Found on lower-budget flat roofs, sometimes on older garage roofs, and on roofs that have been overlaid as a quick fix.

Common issues we look at: seam lifting, surface deterioration (loss of mineral chips on top-finish products), and the underlying substrate. Many pre-2000 torch-on roofs contain asbestos in the bituminous layer (do not pull these off without proper testing).

Liquid membranes (Ardex Undertow and similar)

Brush- or roller-applied waterproofing systems, often used on balconies, planter boxes, complex detail areas, or to overlay an existing roof rather than strip it. Good for awkward geometries.

Common issues we look at: film thickness (often the failure point), substrate prep quality (the most common cause of failure), and signs of cracking, lifting, or wear in trafficked areas.