Roofing defects in Australian residential construction

What it is

Residential roofing covers sheet roofing (metal), tiled roofing (concrete and terracotta) and the associated flashings, gutters and downpipes. Governing standards are AS 1562.1 for sheet metal roofs, AS 2050 for installation of roof tiles, and AS 4040 for resistance to wind pressures. NCC Volume Two Part 3.5 references all three.

Common defect categories

Pitch incompatible with cladding is the most common failure. Each cladding has a minimum pitch below which water tracks back under the laps. Metal trapezoidal sheeting requires a minimum 2 degrees in most products and 3 degrees for some profiles. Concrete tiles require minimum 15 degrees. Terracotta tiles require minimum 18 degrees on most profiles. Builders who use a tile profile below its minimum pitch end up with capillary leaks across the whole roof.

Flashing failures cover sidewall flashings, apron flashings, parapet cap flashings and chimney flashings. Each requires upturns and overlaps set out in HB 39 (Installation code for metal roof and wall cladding) and the cladding manufacturer's specification. Tribunals find leaks at sidewall junctions on a high proportion of inspected roofs.

Missing sarking is a defect in cyclonic regions and BAL bushfire areas. The NCC requires sarking under tiles in regions with high wind classification (C1 to C4) and as part of the bushfire requirements in AS 3959. When the roof is built without sarking the rectification means lifting every tile.

Inadequate fixing happens when the crew uses a screw pattern or tile clip count below the wind classification specification. AS 1562.1 sets out fastener spacing by wind region. Tribunals routinely see fixings at 600 mm spacing where the wind class needs 300 mm.

Gutter falls below 1:500 cause overflow and saturation of the fascia. AS 3500.3 sets the requirements for stormwater drainage from gutter to ground.

Who is liable

Roofing defects sit inside both warranty windows. Major leaks causing structural damage to frame or ceilings trigger the six-year major defect warranty. Minor weather penetration sits inside the two-year non-structural window. Builder is liable. Roof plumber and tiler subcontractors are pursued by the builder under trade contracts.

NCAT and VCAT decisions on roofing defects routinely include the full cost of removing and replacing cladding, replacing damaged battens and rafters, replacing insulation, ceiling repair and redecoration. Awards on full roof replacements exceed 80000 dollars for typical three-bedroom homes.

TradeLens risk flags

Files should be flagged when any of these are missing. Wind classification for the site on the build file. Roof cladding manufacturer installation guide on file. Pitch verification at frame stage. Sarking installation photos at batten stage. Flashing detail drawings approved before install. These five drive most successful roofing claims.

Typical rectification cost

Re-flashing a single junction is 800 to 2500 dollars. Lifting and re-bedding tiles on a hip is 2000 to 6000 dollars. Full re-roof of a metal roof is 18000 to 40000 dollars. Full tile re-roof including sarking is 25000 to 55000 dollars on a single dwelling. Roofing rectifications are the highest volume defect category recorded in QBCC complaints data.