The primary function of the overflow outlet is to secure a penetration through the membrane with a clamp ring and riser system that will allow the channel to build up an amount of water, or head, in it so as to let the selected primary outlet to perform to design.
Head is where the channel is allowed to fill to a certain point that will fully charge the outlet and direct the water to the stormwater system. Anything over this demand, or in the event of a blockage, and the overflow will be activated.
The location of the overflow inlet and outlet can have both an aesthetic and performance impact on your design. E1 requires the activation point of the outlet to be set at least 50mm below the top of the gutter and flow to the exterior of the building. They cannot be piped into the stormwater system.
An overflow placed in the wrong position will have a tendency to weep, or activate prematurely. This can be a visual problem if the outlet is positioned above a door or passageway.
Situations such as locality to roof edges, depths of sumps and any situation where ambient rain or water could flow into the vertical facing openings of the overflow riser can cause this activation. Sometimes the occupier of the balcony above will be watering their plants, or washing their deck. Below the gutter substrate the path of the PVC pipe can be problematic so the choice of a vertical or 90 degree outlet for the overflow base can help with designing a path to the exterior of the building.
To resolve this issue, NZ based manufacturer, Allproof Industries, has released a stainless steel overflow riser with integrated cowl that will prevent any water prematurely entering the overflow pipe and solve the problem of a weeping overflow. This NZ made solution can be either supplied to new installs, or retro fitted where a problem has arisen post install.
The use of a Soffit overflow cover will also prevent vermin from entering the PVC pipe outlet and reduces the impact of the installation, as the overflow outlet is often situated in an area you would like to keep minimally interrupted from a design situation.
Powder coating the overflow cover will help it further disappear.
Following a few good practice install steps will ensure the overflow penetration and the outlet will only be activated in an emergency situation.