Secret-fix (tray / trough) is a different family from pierce-fixed corrugate and trapezoidal. Clips sit under the rib. There are still fasteners — they are not through every weathering face. Do not specify clips or seams from a photo. Pitch questions: secret-fix tray minimum pitch.
Cover is the order width
This library’s tray is 300 mm cover / 325 mm overall / 3° / check after 60 m, CoP secret-fix ~30 mm. Real pans are often 265–500 mm. Heritage Tray (Dimond example) is about 450 / 465 mm / 3°.
9.2 m ÷ 0.450 m = 20.44 → 21 sheets. Using 465 mm overall → 20 and a shortage. Override cover on the takeoff when you know the pan.
When not to lock tray
- Measured cladding pitch below that pan’s published minimum.
- Run beyond the sheet’s drainage / clip / thermal limit.
- Valleys and penetrations the standard flashing set does not cover.
- Framing that will not take the clip spacing or substrate the PTS assumes.
Then stop and get the manufacturer or an LBP. The calculator will still run the CoP 3°/60 m row if you leave the placeholder — that is a warning aid, not an approval.
Takeoff sequence
- Write manufacturer, pan name, cover, clip type, max length.
- Split planes (multi-section).
- Count from cover; length from slope including eaves.
- Tray flashings (grab / verge / ridge / wall), not generic barge from corrugate (flashing checklist).
- Extra High still changes junction cover.
NZMRM CoP profile classification and the named PTS remain the authority.