Free spouting calculator. Spouting, downpipes, and brackets with 5% waste allowance for NZ residential roofs.
This calculator counts spouting, downpipes, brackets, clips, joiners, outlets and stop ends for a residential roof, from the eaves length.
Spouting is the eaves length with CostMate's allowance of 5% added: a lower allowance than timber gets, because spouting is cut from long runs with far less loss than a board.
Downpipes are suggested at one per 12m of eaves, with a minimum of one, and you can override that number. The 12m is Marley's expansion rule: a run over 12m needs an expansion outlet at a downpipe or an expansion joiner, so each 12m stretch the downpipes do not cover gets an expansion joiner. Each downpipe is counted at the wall height plus 300mm, for the drop below the spouting and the connection at the bottom. The 300mm is CostMate's allowance.
Joiners are one fewer than the number of stock lengths the run takes. There is no joiner after the last length. The lengths are the ones Marley sells: 3m and 5m in white, 4m in colours, using the fewest lengths that cover the run. Stop ends are counted as a pair, and outlets one per downpipe.
Bracket spacing is your input. CostMate does not assert one, because it varies with the profile, with whether the spouting is fascia-fixed or rafter-fixed, and with snow loading.
The geometry is one bracket per spacing interval along the run, plus the one that closes the last interval: the same fencepost count that puts an extra post at the end of a fence.
Downpipe clips work the same way down the drop, with a floor of two per downpipe, because even a short drop takes a clip top and bottom.
Three profiles are offered: quad, half-round and square line.
Spouting and downpipe sizing, fall and overflow provision are design decisions that follow from catchment and rainfall. Check them against your plans or confirm with the BCA before you order or install.