Gutter Fall Ratio

Simplified suitable for flattish roofs with little or no vertical faces or steep roofs draining to one side of box gutter only or any roof if you are in a hurry and make the necessary allowances for all catchments.

Gutter fall ratio.

Secure the gutter to the bracket with a 1 inch long 8 32 stainless steel machine screw and flanged nut. Calculate the gutter slope by dividing the length of the gutter needed by 10. The gutter slope also called the pitch is the amount the gutter tilts down to let rainwater flow out of it. The standard is about inch per 10 feet.

Through the screw mounting hole in each bracket drill a 3 16 inch diameter hole in the front edge of the gutter. As with gutters a downspout s capacity must match or exceed the expected runoff. With the steeper fall i now have the water departs the gutters much more rapidly effectively increasing the capacity. Gradient 0 30 24.

The fall is the measurement by which the gutter drops to allow water to drain towards the outlet downpipes. Many plumbers guidelines recommend a ratio of around 1 500 which is roughly 20mm for every 5m of guttering. Box gutter with rain water head at end of box gutter. Gradient fall distance.

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. Before buying talk with your supplier to ensure the gutter system you have selected meets the criteria. A gradient may be defined as fall divided by distance. The amount of collected water increases until it spills over the sides of the gutter.

For example is a 24 metre section of drainage pipe has a fall of 0 30 metres calculate the gradient. This applies to general roof areas along with any internal gutters. Your gutters must comply with national plumbing and drainage code as nzs 3500 3 2003 which you can find in your local library. I also had a problem that my new flat roofed loft conversion dumps so much water into the valley on the front roof slope that it formed a fast flowing stream that jumped over the gutter.

If gutters don t slope water gathers in them. The above recommendations assume that you have properly sized downspouts every 40 feet. Increasing the pitch increases a gutter s handling capacity but the gutter may look askew over a long run. If gutters slope too severely they don t hold water and water could splash over the sides in heavy rain.

The minimum gutter fall to a downpipe is 1 500 meaning an extra 2mm of fall for each metre of gutter. The diagram below show pipe fall and distance.