Calculating Spouting & Downpipe Capacities

Calculating the size of your spouting and downpipes can be complicated - the roof pitch, length of run, gutter and downpipe size, shape and fall are all inter-related in the determination of capacity of each other.

Continuous Group provide installations for new builds as per the specifications supplied by the customer and that are approved for construction by the local authority.

To calculate capacity, we recommend that the customer check for specific local authority regulations and, subject to adhering to the local authority regulations, can also refer to sections 8.1 through 8.2.2 of the NZMRM Code of Practice.



Spouting Capacities


Downpipe Capacities
Maximum plan area of roof served by downpipe (m2) 


*click images to enlarge

For quick reference purposes only, this table provides some indication to downpipe size and number.  (Continuous Group make no claim to the legality of this information with any specific building Authority and strongly recommend that the customer checks this with their local authority)


Quick Reference Guide

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Quick Reference Guide



Material Compatibility

Continuous Group recommend that designers, specifiers, architects and builders refer to the acceptable solution as described in Tables 21 and 22, that are read in conjunction with Table 20 of E2/AS1 when determining material compatibility.

     Table 21                    Table 22                     Table 20


*Click image to download tables


Material Selection

Material selection includes the desired functional and aesthetic outcomes. It is important to note, however, that function takes priority here. To choose a suitable material for your location can be quite confusing….. information on this is available via the acceptable solution E2/AS1, the NZMRM Code of Practice and via the Atmospheric Usage Guide from Pacific Coil Coaters.


The best source of information on material selection is, however, us. After more than two decades, we have built up a huge wealth of knowledge and one of our experienced team will be more than happy to guide you in the right direction.


Material Options

Atmospheric Usage Guide from PCC

*Click images to download documents


Spouting Fall

Continuous Group recommend a minimum fall of 1:1000 or 1mm per metre.


It should be noted that, should the client prefer the NZMRM Code of Practice standard of 2mm per metre, this must be specifically requested and may not work in some situations.  The more fall that is applied, the more the functional cross sectional area of the spouting is reduced.  Large amounts of fall are also more likely to expose roof edges.


The Building Code of New Zealand does not specify a specific fall rate for eave spouting, but as a rule of thumb, Continuous Group recommend that any ponded water should evaporate within three days with normal wind and sun conditions.  This assumes that the spouting is completely clean and free of debris.


Construction Details

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Spouting/Wall Junction

Spreader Details

Rainwater Head Sizing


Care & Maintenance

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Online Libraries

Our technical documentation can be found on the online libraries shown below:



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