Assumptions
The numbers that are not product data and not prices: waste, offcut pairing, screws per sheet, sealant per m². Sorted so the guesses come first. The back-test on your past jobs is what should set these; you can also set them from experience.
| Item | Value | Unit | Status | Where the number comes from | |
|---|---|---|---|---|---|
| pairing tri Offcut pairing allowance on triangular planes. Real practice orders to length and pairs offcuts across mirrored planes. First thing to calibrate. LIKELY OVERLAPS waste_hip: raked cuts are most of the waste on a hip roof, so applying both probably double counts. The back-test decides which carries the loss. | factor | assumed | guess: none | ||
| pairing trap Offcut pairing allowance on trapezoidal planes. Second thing to calibrate. Same overlap with waste_hip as pairing_tri. | factor | assumed | guess: none | ||
| rip waste flag fraction Flag a rectangular plane when more than this fraction of the last sheet is ripped off. | fraction of a sheet | assumed | guess: none | ||
| batten extra Allowance on batten length for valleys, plane changes and penetrations. | fraction | assumed | guess: none | ||
| anticon extra Allowance on blanket area beyond the 150 mm tab already handled by the 1050 effective cover. | fraction | assumed | guess: none | ||
| clip waste | fraction | assumed | guess: none | ||
| clips per sheet per support Concealed-fix profiles. Confirm with Lysaght. | ea | assumed | guess: Not published anywhere found | ||
| screws per clip Concealed-fix profiles. | ea | assumed | guess: none | ||
| sealant m2 per tube simple | m2 | assumed | guess: Practitioner allowance, no source | ||
| sealant m2 per tube complex | m2 | assumed | guess: Practitioner allowance, no source | ||
| dp catchment m2 default Should come from BoM rainfall intensity for the site and AS/NZS 3500.3. Overridable per job. | m2 | assumed | guess: none | ||
| skip count tile Tiles are ~45 kg/m2 against metal ~4.5. | ea | assumed | guess: none | ||
| skip count metal | ea | assumed | guess: none | ||
| qbcc base Replace with the live table. | AUD | assumed | guess: Linear approximation of the published alterations premium table | ||
| qbcc rate Replace with the live table. | fraction | assumed | guess: Linear approximation of the published alterations premium table | ||
| zincalume factor Applied to sheet, cappings and rainwater goods when the customer chooses ZINCALUME. | factor | assumed | guess: Retail listings show unpainted ZINCALUME about 10 to 20% under COLORBOND Classic | ||
| waste gable Simple gable. | fraction | assumed | convention: AU trade convention; sheets are cut to length so waste is far below US shingle figures | ||
| waste hip Hipped. Applied on top of the pairing allowances, which probably double counts; see pairing_tri. | fraction | assumed | convention: AU trade convention | ||
| waste skillion Single plane. | fraction | assumed | convention: AU trade convention | ||
| waste complex Cut-up roofs: valleys present or four or more penetrations. | fraction | assumed | convention: AU trade convention, 12 to 15 percent | ||
| sheet length rounding m Sheet lengths ordered to the next 50 mm. | m | assumed | convention: Supplier ordering practice | ||
| batten screws per crossing Batten to rafter fixings at each crossing. | ea | assumed | convention: Trade practice | ||
| rafter spacing m Used only to count batten fixings. Confirm on site. | m | assumed | convention: Typical QLD domestic truss spacing | ||
| mesh extra | fraction | assumed | convention: AS/NZS 4389 side laps not less than 150 mm plus end ties | ||
| capping lap allowance Applied to ridge, hip and barge capping. | factor | assumed | convention: Trade practice: 100 to 150 mm laps. Lysaght does not publish it. | ||
| screw waste Dropped, stripped and mis-driven screws. | fraction | assumed | convention: Trade practice | ||
| sheet gutter allowance m Added to every sheet length. | m | assumed | published: NCC 2022 HP 7.2: sheets overhang the fascia by not less than 50 mm | ||
| anticon roll width m | m | assumed | published: CSR Bradford Anticon | ||
| anticon effective cover m Using 1200 instead of 1050 under-orders by 12.5 percent. | m | assumed | published: CSR Bradford Anticon installation guide: 150 mm foil overlap tab | ||
| valley gutter projection m Per valley end. | m | assumed | published: NCC 2022 HP 7.2: valley projects not less than 150 mm into the eaves gutter | ||
| gutter max m per downpipe | m | assumed | published: NCC 2022 HP 7.4 | ||
| qbcc threshold inc gst | AUD | assumed | published: QBCC home warranty insurance is mandatory over $3,300 incl GST |