What are some of the main differences between blue roof and green roofs?

What are the differences between blue roofs and green roofs?

When specifying a new roof for a commercial or multi-residential building, there are doubtless multiple considerations to take into account.

As a minimum the roofing system will achieve the required structural integrity and thermal efficiency, but there is also the potential impact on the broader environment to account for.

To this end architects increasingly need to compare the benefits and BREEAM credentials of specifying a blue roof, green roof or combined systems for a given site, and consider the applicability – or otherwise – of these products to the specific building location.

It is therefore useful to give an overview of some of the main differences.

Blue roofs vs green roofs – and why the distinction matters

Both blue roofs and green roofs are designed to make better use of the valuable and useable space that the roof level represents.

In short, a blue roof is a type of roof that is designed to collect falling rainwater, before gradually and steadily releasing this rainwater over a 24-hour period following a storm event. This helps to guard against excess water and flooding and meet the local SuDS planning discharge consent, particularly in city centre locations.


Specifying a green roof, meanwhile, means investing in a roof that typically comprises a shallow layer of growing media and vegetation on top of the building. An obvious attraction of a green roofing system is its aesthetic appeal, although green roofs can also enhance the given building’s acoustic and thermal properties, and play a part in minimising surface water runoff.

One of the most important things to know about the distinction between green roofs and blue roofs, is that there are elements of overlap in the benefits they can bring. Indeed, there are many buildings for which both a blue-roof, green-roof or combined solution might be suitable.

Both types of roofing system play an important role in slowing down the release of water that falls and is collected on the roof. A blue roof is designed to discharge rainwater over an extended period of time to control flow rates according to local rainfall data for 1-in-100 year storm events, plus an allowance for climatic change. This is as opposed to draining rainfall from the roof as quickly as possible, as is the aim of more traditional roof drainage design.

A green roof, meanwhile will collect some of the rainwater in the Roofdrain geocomposite drainage reservoir layer, which also serves as an additional source of irrigation for sedum or wildflower planting in dry weather. Some rainwater is also retained in the growing media layer.

Blue roofs and green roofs also both offer all-round positive benefits to the environment and the BREEAM rating of the building – the former by helping to minimise the risk of flooding and the filtration of pollutants at source, and the latter by helping to provide a habitat for birds and insects that would otherwise not be present on a new building development.

Contact ABG to find out more about our blue roof and green roof expertise.

Whatever SuDS roofing solution you might be considering for your next development, with our in-depth knowhow of high-performance geosynthetic systems and many years’ design experience, ABG are the sustainable drainage experts that can help deliver your project.