Flat Roof Drainage Design
Project-Specific Drainage for Flat Roofs
Our roof drainage design service covers projects where a new roof layout, increased catchment, internal gutter, parapet, altered outlet arrangement or downstream constraint needs engineering review. RIDA assesses your drawings and agrees the calculation, layout and coordination scope needed for the project stage.
Get A Free No Obligation QuoteWhat You Will Receive
| Technical deliverables | What this helps you progress |
|---|---|
| Agreed design basis covering roof geometry, catchments, rainfall criteria and assumptions | Design-team coordination and a documented basis for the agreed project stage |
| Project-specific flow, outlet and conveyance calculations | Outlet and pipework selection |
| Marked-up layout or drawing information showing outlet positions and routes | Architectural, contractor and installation coordination |
| Review notes for falls, ponding, gutters, parapets and overflow provision | Roof detailing and resolution of identified design issues |
| Downstream discharge coordination notes where included | Identification of separate site-drainage input |
The agreed package may connect with RIDA’s broader drainage design services. Deliverables support coordination, pricing or submission work; they do not guarantee third-party approval.
What the Design Reviews
Rainfall, catchments and outlets
The review considers contributing roof areas, project-specific rainfall criteria, outlet number and position, internal gutters and gravity pipework routing. BS EN 12056-3 provides technical context, supported by Approved Document H: drainage and waste disposal. Flood risk climate change allowances are reviewed where a flood risk assessment interface applies.
Falls, overflow and discharge coordination
RIDA reviews proposed falls, ponding risk, parapet conditions, emergency overflow or secondary drainage, and the proposed discharge route. Siphonic drainage is considered only where confirmed within RIDA’s capability or coordinated appointment. Projects needing advice beyond the roof scope can use our drainage consultancy service.
What We Need to Review Your Project
- Site address, to check the project-specific context
- Roof plans, sections and levels, to define geometry and catchments
- Roof build-up and proposed falls, to review drainage paths
- Parapet and internal-gutter details, to identify contained drainage areas
- Proposed outlets and discharge route, to assess system interfaces
- Existing drainage records for refurbishment or alteration work
- Required project stage and date, to confirm the appointment scope
Flat Roof Drainage Design FAQs
Can RIDA work from our existing roof drawings?
Yes, subject to capability and scope confirmation. RIDA can review available drawings and survey information, then identify missing levels, catchment details, outlet data or downstream drainage records.
What is included in flat roof drainage calculations?
The agreed calculations address relevant rainfall criteria, contributing catchments, design flows, outlets and conveyance. They are project-specific rather than a public calculator.
Do you review emergency overflow provision?
Overflow or secondary drainage can form part of the review where confirmed within the agreed technical scope. Recommendations reflect the roof arrangement, parapets, outlets and discharge constraints.
What happens if the roof drainage connects to a wider site drainage system?
Request a Flat Roof Drainage Design Scope Review
Send your plans, site location, approximate roof area and required date. RIDA will review the information and confirm whether the requested technical scope can be provided before accepting instruction.