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Why a hopper increases flow by 40%

When the pipe comes straight out of the gutter, a vortex and an air lock form at the inlet — the water gurgles and passes far more slowly than the pipe diameter would allow. A hopper opens that inlet up.

Square gutter outlet hopper with a downpipe spigot

What it gains

A gutter-to-downpipe connection made through a hopper allows 40% more flow than one without, and does so without gurgling. In practice the roof drains faster at the same pipe size, so the gutter does not overflow in a downpour.

Fitting

Fitting is quick and needs no soldering. Cut the gutter where the outlet goes and bend the edges outwards. The cut opening should be larger than the pipe diameter so it cannot block.

Insert the front edge of the hopper into the bead of the gutter, then rotate it so it seats on the curve and fold its ends around the rear edge of the gutter.

  • Opening in the gutter: larger than the pipe diameter
  • Soldering: not required

Sizes

Standard sizes are 280/ø80, 333/ø100 and 400/ø120, with transitions between standards also available. For square gutters, hoppers are made by hand in several shapes and sizes to suit the job.

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More guides

How many snow guards a roof needs

Austrian and German standards call for 2 to 2.5 snow guards per m² of roof. How to space them, why the bottom row is doubled, and what happens when there are too few.

How gutter hooks and gutters are fitted

Hooks go on every rafter, the fall is 2 mm per metre, and the line is held with two taut strings. Over 10 m you need two outlets, falling from the middle.

Which gutter size you need

Gutter size follows the roof area draining into it: up to 83 m² use 280 mm with an ø80 pipe, up to 150 m² use 333 mm with ø100, above that 400 mm.