Drainage
Storm Drainage Design Guide
Storm drainage design calculates roof and surface drainage based on rainfall intensity, roof area, and local code requirements. Here is the methodology.
Introduction
Storm drainage systems manage rainwater from roofs and exposed areas. Design requires local rainfall intensity data, roof area measurements, and code-specific sizing tables. Plumbing Booster's Drainage System module includes storm drainage with exposed area configuration and flow summary calculations.
Methodology
1. **Determine rainfall intensity** - Local rainfall data (inches/hour or mm/hour) from code or meteorological records.
2. **Calculate roof area** - Horizontal projection of roof area draining to each downspout or roof drain.
3. **Calculate design flow** - Q = A x I / 96 (US: acres x in/hr = cfs) or Q = A x I / 360 (SI: m2 x mm/hr = L/s).
4. **Size roof drains and leaders** - From code tables based on flow rate and roof slope.
5. **Size horizontal storm piping** - Based on flow rate and slope using code tables.
6. **Consider secondary drainage** - Emergency overflow drains for flat roofs per code requirements.
Code References
**IPC**: Section 1106 - Size of conductors, leaders, and storm drains. Table 1106.1 - Sizes of roof drain leaders.
**UPC**: Storm drainage provisions in Chapter 11.
**ASPE Data Book** - Rainfall intensity maps and design values.
How Plumbing Booster Automates It
In the Drainage System module, Storm Exposed Areas page allows entering roof area, rainfall intensity, and drain configurations. The software calculates design flow per drain, provides an Area Flow Summary, and sizes storm leaders and horizontal piping. Secondary drainage can be toggled on/off per code requirements.
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Drainage Pipe Sizing Reference
Complete reference for drainage pipe sizing using IPC Table 710.1 and UPC Table 703.2, including slope requirements and maximum length limitations.
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