Properly sizing a rainwater head involves ensuring its depth is adequate relative to the connected downpipe, as mandated by plumbing codes, to efficiently manage water flow from your roof drainage system.
Plumbing Code Requirements for Rainwater Head Depth
According to plumbing code requirements, a critical factor in sizing a rainwater head is its depth in relation to the downpipe it serves.
The code stipulates that the rainwater head depth should not be less than 1.25 times the diameter of the connected downpipe.
- Reference Note: "This figure (H2) applies for total depth of RWH = 1.25*downpipe diameter." This indicates that the total depth of the rainwater head is calculated using this ratio.
Calculating Minimum Depth
To determine the minimum required depth for your rainwater head based on this code:
- Identify the diameter of the downpipe connected to the rainwater head.
- Multiply the downpipe diameter by 1.25.
- The result is the minimum required depth for the rainwater head.
Example:
| Downpipe Diameter | Minimum Rainwater Head Depth (1.25 * Diameter) |
|---|---|
| 90 mm | 112.5 mm |
| 100 mm | 125 mm |
| 150 mm | 187.5 mm |
Note: These are minimum depths based on the specified code requirement. Other factors like the catchment area and expected rainfall intensity also influence the overall required capacity and dimensions of the rainwater head, but the minimum depth rule is specifically tied to the downpipe size.
Why Proper Sizing is Important
- Efficient Drainage: An adequately sized head prevents water from backing up into gutters or overflowing during heavy rainfall.
- System Performance: Ensures water flows smoothly into the downpipe, reducing the risk of blockages at the downpipe entry.
- Code Compliance: Meeting plumbing code requirements ensures the system is installed safely and effectively according to standards.
While the depth-to-downpipe ratio is a key code requirement, the overall size (including width and length) of a rainwater head is typically determined by calculating the expected volume of water from the roof area it serves and selecting a head with sufficient capacity to handle peak flow rates. However, the provided reference specifically details the minimum depth requirement based on downpipe diameter.
