Siphonic Roof Drainage Design
Specialist Design for Complex Roof Drainage
RIDA’s roof drainage design service covers broader roof-water collection requirements. This specialist review concerns systems that restrict air entry at roof outlets, prime under design flow and use available hydraulic head to create full-bore flow. This behaviour requires hydraulic sizing and close coordination.
Get A Free No Obligation QuoteWhen a siphonic system may be appropriate
- Roof geometry, catchments and rainfall criteria
- Available hydraulic head and discharge level
- Permitted outlet zones and pipe routes
- Overflow, exceedance and maintenance provisions
What needs coordination before design begins
Architectural, structural and MEP information must align with the proposed outlets, collectors, downpipes, supports and discharge transitions. Downstream connections and wider drainage design may require a separate scope.
What You Will Receive
RIDA will confirm the deliverables during the capability and scope review. Your appointment may include the following items where approved.
| Technical deliverable | What this lets you progress |
|---|---|
| Agreed design basis, assumptions and scope boundary | Defines responsibilities, design inputs and coordination requirements. |
| Roof catchment review, outlet strategy and outlet schedule | Supports roof layout and package development. |
| Hydraulic sizing and pressure-check calculations | Provides the technical basis for the agreed system arrangement. |
| Coordinated pipework layouts and interface notes | Supports architectural, structural and MEP coordination. |
| Overflow, discharge-transition and design-risk notes | Supports review of secondary drainage and downstream interfaces. |
Information Needed to Review Your Project
Send these to request a quote or scope review
- Current roof plans, sections and levels — to define roof geometry and available head
- Roof build-up and proposed outlet zones — to review outlet constraints
- Catchment information — to establish the areas draining to each outlet
- Structural and MEP drawings — to assess routing and coordination
- Discharge points and downstream drainage records — to review system interfaces
- Programme and project requirements — to define scope and delivery needs
Key design constraints to identify early
Changes to outlets, roof levels or pipe routes after hydraulic sizing can affect the whole system. Secondary drainage, overflow routes, installation conformity and maintenance access need early agreement.
Projects needing broader technical advice can use RIDA’s drainage consultancy service. Roof discharge may need coordination through the development’s drainage strategy and sustainable drainage systems design.
Project criteria must be checked in context. Approved Document H: drainage and waste disposal covers rainwater drainage provisions but is not a complete siphonic design standard. The National standards for sustainable drainage systems provide context for downstream SuDS. Relevant rainfall criteria may draw on flood risk climate change allowances for the project.
Siphonic Roof Drainage Design FAQs
Is siphonic roof drainage suitable for my roof?
Suitability is assessed from roof geometry, rainfall criteria, available head, outlet positions, routing constraints, discharge arrangements and maintenance needs. RIDA will review these factors before confirming scope.
What information do you need to review or quote for a siphonic system?
Send roof plans, sections, levels, catchment information, proposed outlets, structural and MEP drawings, discharge details and your programme. These define the technical scope and coordination needs.
What drawings and calculations will I receive?
The quotation will list the agreed outputs. These may include design assumptions, hydraulic calculations, an outlet schedule, coordinated layouts and interface or design-risk notes.
Can RIDA work from existing architectural, structural and MEP drawings?
Yes. Current coordinated drawings provide the basis for reviewing outlets, available head, pipe routes, supports and service clashes. Missing or provisional information will be identified during scope review.
Discuss Your Siphonic Roof Drainage Requirement
Send your available drawings and project requirements for capability review, scope confirmation and quotation. RIDA will confirm whether it can undertake the proposed specialist scope before appointment.