A roof node represents a physical roof catchment surface. The roof model has no infiltration and quickly produces surface runoff during a rainfall event. You must specify a catchment area, time of concentration for the roof catchment, maximum depression storage, and what percentage of the roof area is connected to a rainwater harvesting tank.
The roof node surface area must be >= 0, and should be <= 1000 m2. For roof areas larger than 1000 m2, use two or more roof nodes.
There are restrictions on which node inputs and outputs you can connect together. See Urban Developer node connection rules.
The Roof node is available for Urban Scenarios only.
While there are no node inputs "upstream" of a roof node, a roof node is always connected "downstream" as an input to a Tank node. Furthermore, climate inputs specified under the Urban Settings, such as rainfall and evapotranspiration, are applied to the node.
Runoff to Tank: Runoff quantity is proportional to the % of roof connected to tank. Link type: Runoff
Bypass Runoff: Other runoff; proportional to the % of roof not connected to a tank. Link type: Runoff
Identifying name for the roof. The name must be unique.
Total area of the roof.
Urban Developer does not enforce a maximum area for this node type, however, the algorithms used to determine the hydrologic response (particularly peak flow) are not accurate for areas greater than 1000 m2 or flow path lengths longer than around 50 m. It is unlikely that you will have one roof node of 1000 m2 or greater flowing to a single downpipe. You can duplicate roof nodes if necessary.
The roof area must be configured to represent the total number of dwellings in downstream Average or Behavioural Water Use nodes. For example, 4 houses with 100 m2 roof space each would need to be attached to a single roof node with 400 m2 total area.
Time of concentration
The time of concentration represents the time taken for surface runoff to travel from the most hydraulically-remote point on the roof to the roof outlet.
Average depression storage depth
Represents the depth of the roof area’s depression storage (in millimetres) satisfied in a rainfall event, before surface runoff occurs.
In practical terms, maximum depression storage in the roof node represents the small amount of loss that occurs due to surface irregularities, water absorbed by debris in the gutters or in rust holes in the roof. It is a way of modelling the reality that you never see 100% of rainfall from a roof surface ending up as runoff, although runoff will usually be close to 100%.
Percent of roof connected to tank
Some roofs may have only a proportion of runoff directed to a tank, with the remainder being directed to stormwater or domestic garden use.