Blue Roofing

A blue roof system is a type of flat or low‑slope roofing design that temporarily stores rainwater on the roof and releases it slowly to help manage stormwater runoff. Unlike traditional roofs that drain water immediately, blue roofs use controlled drainage — such as flow restrictors, trays, modified drains, or passive ponding — to attenuate (slow down) water flow and help manage the rate at which rainfall from the roof enters the site drainage system, subject to the project-specific design. 
 

Sika® RetentionRoof Blue Roof Systems can be integrated within a Sika® NatureRoof Green Roof, a Sika® NatureRoof PV BioSolar system or beneath a variety of permeable hard landscaping pedestrian surfaces.

A project-specific Sika® RetentionRoof Blue Roof design can contribute to the surface water attenuation requirements identified within a site's wider SuDS strategy. Whether it meets all relevant requirements will depend on the approved drainage design and site-specific calculations. 

Each roof is designed individually to help meet planning restrictions placed on the development, such as a limited discharge consent through the attenuation of rainfall as it falls on the roof. 

When designed, installed and maintained in accordance with the project-specific specification, the Sika® RetentionRoof Blue Roof is designed to temporarily store rainfall within the roof build-up and discharge it through a specified flow-control device. This will limit discharge from the roof whilst other hard landscaped surrounding areas are drained. 

The Sika® RetentionRoof Blue Roof will gradually discharge water from the roof after a storm event at the controlled rate over a set period. The calculated discharge period is project-specific and may be designed for a period of up to 48 hours, subject to the agreed discharge rate, rainfall assumptions and available attenuation capacity. 

Rainwater outlets not fitted with restricted flow-control will be utilised as overflow devices, enabling the roof to drain faster at the point of maximum capacity (known as ‘H Max’). 

The London Plan 2021 promotes sustainable drainage and requires development proposals to manage surface-water runoff in line with its drainage hierarchy. Blue roofs may form part of the site-specific drainage solution where appropriate. Some local planning authorities may require or encourage blue roof solutions as part of site-specific sustainable drainage requirements. Requirements should be confirmed with the relevant planning authority. 

When specifying a Blue Roof it is critical to ensure the waterproofing system used in either a Warm Roof or an Inverted Warm Roof installation has the appropriate BBA Certification.  Your local Sika® Area Technical Manager can advise on the correct SikaShield® 2 Layer Reinforced Bitumen Membrane or SikaShield® Hot Melt specification.