Chimney flashing systems — lead sheet

Austral Lead Code 4 sheet (1.8mm nominal thickness, 20.41 kg/m²) is the standard specification for chimney front apron flashings, soakers, and step flashings at the chimney-to-roof junction on Australian tiled and slated pitched roofs. Code 4 lead is the minimum weight recommended for external exposed chimney flashing elements that are not in the back gutter position. Lead's inherent malleability allows the licensed roof plumber to dress the flashing tightly into mortar joints, around irregular brick surfaces, and into counter-flashing chases without cutting or mechanical fasteners — when correctly dressed, lead forms a watertight self-sealing joint through its own weight and form. The front apron is laid over the front face of the chimney and laps under the tiles on the front slope, with step soakers interlaced between tiles at the chimney sides. The counter-flashing is inserted into a raked mortar joint or chase in the chimney masonry and dressed down over the step soaker upstands. Austral Lead is Australia's primary lead sheet manufacturer and the benchmark supplier for building and roofing lead applications. Confirm current Code 4 dimensions (width, sheet size), thickness tolerance, and procurement lead time with Austral Lead before ordering for strata and heritage building remediation projects.

Austral Lead Code 5 sheet (2.24mm nominal thickness, 25.51 kg/m²) is specified for the chimney back gutter (also called the saddle flashing) at the upslope face of the chimney. The back gutter is the most critical element of a chimney flashing system — it must intercept all water running down the roof slope behind the chimney and discharge it to either side of the chimney without allowing it to pond or back up under the tile courses. The back gutter sits at the base of the chimney's upslope face, wrapping up and over the roof tiles to each side to connect with the step soaker flashings. The heavier Code 5 weight is specified for the back gutter because this element is more exposed to wind uplift than the front apron or soakers — the back gutter must resist being lifted by wind without being mechanically over-fixed, which would prevent thermal movement and lead to cracking. Code 5 lead is typically laid in shorter bays than Code 4 to accommodate thermal movement — confirm maximum bay length with AS 3703 and Austral Lead technical guidance. On steeper roofs with a larger chimney, a purpose-formed saddle or cricket may be required behind the chimney to prevent water ponding — the lead back gutter is dressed over this saddle form.

Calder Industrial is an alternative Australian supplier of lead sheet for building and roofing applications, providing Code 4 and Code 5 lead sheet for chimney flashing as an alternative supply channel to Austral Lead. The Code designation, nominal thickness, weight per square metre, and AS 3703 application requirements are identical for Calder Industrial lead sheet as for Austral Lead — Code 4 for chimney apron and soakers, Code 5 for the back gutter. The technical properties, limitations, installation requirements, PPE requirements, and thermal movement requirements for Calder Industrial lead sheet are the same as for Austral Lead Code 4 and Code 5 — the material is lead sheet regardless of the supply source. Calder Industrial may offer competitive pricing or better regional availability depending on project location. Confirm current Code 4 and Code 5 thickness tolerances, width options, and pricing with Calder Industrial before ordering. As with all lead sheet for roofing flashing, installation must be by an experienced licensed roof plumber with demonstrated lead dressing capability.