Minimum Gutter Falls

Rainhead overflow or specific box gutter overflow must be at least 30mm below the height of the back of the box gutter.

Minimum gutter falls.

Measure the length of gutter needed. Maximum allowable length between expansion joints with one end fixed. Put a gutter bracket on at the high end. The gutter slope also called the pitch is the amount the gutter tilts down to let rainwater flow out of it.

Attach the level string to the opposite end of where the gutters will be installed. 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. If gutters don t slope water gathers in them. 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.

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 minimal slope needed for proper gutter drainage is 1 25 cm 1 4 inch for every 3 metres 10 feet of gutter. Put another bracket about 25mm lower at the downpipe end. Required gutter slope 1 40 to 1 200 there is always some confusion as to how the slope affects the overall depth.

I fall or slope box gutters to be installed with a minimum uniform fall of 1 in 200 towards the outlet. The amount of collected water increases until it spills over the sides of the gutter. Have a minimum width of 300mm for commercial installations 200mm for domestic installations. Layout box gutters must.

Overflow box gutters must have independent overflow provision discharging to the atmosphere. Therefore any slope on the gutter will make the downstream end deeper or the flashing longer. Calculate the gutter slope by dividing the length of the gutter needed by 10. Put a string line between the two and put the remaining brackets up.

Have a minimum depth of 75mm at the high end. This effectively states that all box gutters must allow for 30mm of freeboard which is from the overflow point eg. Box gutter outlets must discharge through either a rainhead or sump. If gutters slope too severely they don t hold water and water could splash over the sides in heavy rain.