Flat roof design in the net zero future

[edit] How the design of flat roofs will change to meet the net zero future ?

The built environment is estimated to contribute approximately 40% of the UK’s carbon emissions as such early consideration for design, construction, refurbishment, building management and maintenance will be essential as the industry works to achieve the ambitious targets that have been set.

In 2019 the UK became the first major economy to pass a net zero emissions law, with a target of net zero by 2050 and interim emissions reduction targets of 68% by 2030 and 78% by 2035.

There is now a plethora of strategies, guides, policies, and initiatives that designers and builders can utilise to ensure the buildings they construct and manage are either net zero, or at least net zero ready. Whether new build or retrofit, the importance of placing net zero at the heart of all our decision-making processes is critical if we are to help achieve the UK’s ambitious targets.

Equally, when considering what products and systems are best suited to deliver net zero, we need to understand not just how they help the built environment to decarbonise, but also how they can mitigate against the worst effects of climate change as we experience ever more extreme weather conditions.

[edit] What does all this mean for the design and functionality of flat roofs?

According to the Energy Savings Trust, the average home in the UK loses 25% of its heat through the roof. Taking a fabric first approach to reduce this heat loss is one of the key pillars of any decarbonisation strategy.

Insulating well, with robust detailing to eliminate cold bridging, is fundamental to the design of any project. This will lead to thicker insulation depths to achieve the increased U-values which could also have an impact on other elements of the buildings design such as upstands and thresholds.

Using materials and systems that are circular in design, with as low embodied carbon as possible will help to decarbonise the built environment. However, it is important to understand what impact this may have on durability and other elements of the building. For example, using a lower embodied carbon insulant in a flat roof scenario may on the face of it be the obvious choice, however if this product is significantly heavier or thicker what impact will that have on the buildings structure? Does the additional material required negate the initial benefit of the lower embodied carbon solution? Will the roof system meet fire regulations and withstand imposed loads?

Equally, a standalone product may be ‘circular’ in that it can be fully recycled in its initial state, but once it has been embedded as part of a system, it may not be possible to practically recycle or repurpose at the end of its usable life.

In a flat roof scenario, the primary function should always be to keep the building watertight and secure. It is therefore vital to ensure that any materials and systems chosen for their circular or net zero properties do not detract from this and that any systems will meet the required standards.

A flat roof is also a useful platform for other technologies such as green and blue roofs, and solar technologies that can provide a wide range of benefits to our built environment. A flat roof can provide carbon sequestration, biodiversity enhancement, storm-water attenuation and renewable energy generation. This makes flat roofs unique as it is possible to combine all of these environmental solutions from a single, often underutilised building element.

Green roofs also help to keep urban areas cooler, limiting the urban heat island effect and reducing the use of energy intensive technologies such as air conditioning. When combined, green roofs and photovoltaic arrays (bio-solar roofs) work together to provide increased energy generation from the solar (circa 6% compared
to a standard flat roof system) and a more varied habitat across the green roof, magnifying the benefits of each technology.

A well designed and installed flat roof can not only help to decarbonise our building stock, but also provide numerous climate mitigation solutions. As the recent document from the NFRC ‘Building resilience of roofing technologies in a changing climate’ report points out, ‘almost every roof has the opportunity to tackle the climate emergency—whether that be through electricity generation through built-in solar PV, water harvesting through a blue roof, or reducing overheating through a cool roof, our industry has a solution.’

To understand further how your flat roof can be designed to meet net zero initiatives, book CPD with your local Bauder Technical Manager.

This article originally appeared as: ‘How the design of flat roofs will change to meet the net zero future" published in the summer 2022 issue of AT Journal. Incorrectly listed as being authored by Alok Sharma, it is likely to have been authored by the Bauder representative picture above.

--CIAT

[edit] Related articles on Designing Buildings.

• Bio-solar roofs.
• Carbon footprint.
• Climate change act.
• Climate change science.
• Climate Emergency Design Guide.
• Embodied carbon.
• Extensive green roof.
• Intensive green roof.
• Green roofs.