Gutters 4 min read
Sizing rainwater gutters for 3000 mm of rain
Cut PVC pipe split in half is not a gutter. In a Malnad downpour it overflows within minutes and takes the plinth with it.
Short answer
For a typical house roof plane in this rainfall belt, 125 mm is the minimum and 150 mm is the safer choice. Go to 200 mm on long single runs, large sheds or where two roof planes discharge into one gutter. Square profiles carry more water than a half-round of the same face height.
Size to roof area, not to habit
Gutter capacity is a function of roof plane area and rainfall intensity. A district that takes 3000 mm a season is not comparable to one that takes 700 mm, and a gutter sized by what the last house used will overflow. Bring your roof plan dimensions to the counter and we will size it properly.
Square beats half-round
For the same face height, a square profile holds a larger cross-sectional area than a half-round, so it carries more water before it spills. That is the main reason square UPVC has taken over on serious roofs here.
Brackets are not the place to save
Under-spaced brackets are why gutters sag, pond and eventually pull off the fascia. Fit them at the spacing the profile calls for. A sagging gutter also collects debris at the low point, which turns into a blockage in the first heavy week.
Downpipes and where the water goes
A correctly sized gutter feeding an undersized downpipe still floods. Match the downpipe to the run, use offset bends to clear the eaves, and finish with a shoe that throws water clear of the plinth — or you have simply moved the damp problem to the foundation.
Leaf guard, in a district full of trees
Most roofs here have something overhanging them. A clip-on leaf guard costs little and removes the annual job of clearing a gutter full of leaf litter at the start of the rains.
