Minimum Gutter Falls

Required gutter slope 1 40 to 1 200 there is always some confusion as to how the slope affects the overall depth.

Minimum gutter falls.

Put a gutter bracket on at the high end. If gutters don t slope water gathers in them. Box gutter outlets must discharge through either a rainhead or sump. Put another bracket about 25mm lower at the downpipe end.

Attach the level string to the opposite end of where the gutters will be installed. The gutter slope also called the pitch is the amount the gutter tilts down to let rainwater flow out of it. The depth shown in the calculations is at the upstream end. Welted drips should extend to the middle of the rainwater gutter and there should be a minimum of 50mm turndown.

This effectively states that all box gutters must allow for 30mm of freeboard which is from the overflow point eg. Have a minimum width of 300mm for commercial installations 200mm for domestic installations. Put a string line between the two and put the remaining brackets up. Overflow box gutters must have independent overflow provision discharging to the atmosphere.

The minimal slope needed for proper gutter drainage is 1 25 cm 1 4 inch for every 3 metres 10 feet of gutter. Rainhead overflow or specific box gutter overflow must be at least 30mm below the height of the back of the box gutter. Falls and drainage it is a requirement of building regulation part h that adequate provision is made for rainwater to be carried from the roof of the building. The amount of collected water increases until it spills over the sides of the gutter.

According to bs 6229 bs 8217 flat roofs should be designed with minimum falls of 1 40 to ensure a finished fall of 1 80 can be achieved allowing for any inaccuracies in the construction. Therefore any slope on the gutter will make the downstream end deeper or the flashing longer. As long as there is a fall and water does not stay in the gutter then all should be fine. If gutters slope too severely they don t hold water and water could splash over the sides in heavy rain.

Measure the length of gutter needed. Have a minimum depth of 75mm at the high end. Calculate the gutter slope by dividing the length of the gutter needed by 10. To ensure the rainwater is directed towards the gutters the sides of the roof surface apart from the gutter edge require a minimum of 50mm upstand verge provided using triangular pieces of timber called tilt fillets nailed.