One of the more significant developments in low slope commercial roofing in the New Zealand market in recent years has been the rise of ‘cool roofs’. Relatively new in our country, the choice to adopt lighter coloured roofing membranes is becoming more popular.
Common in Europe and America, Thermoplastic roofing membranes have been specified on countless roofs during the 50 plus years they have been around. The majority of TPOs being light coloured and highly reflective single ply. Manufacturer GAF supplies over 1 billion sq. feet every year.
The increase in light coloured single ply roofs can be attributed to a number of factors, namely energy savings, environmental benefits and added durability of the product. The realisation that ‘cool roofs’ can be retrofitted on remedial projects and new builds opens the opportunity for considerable cost savings long term as well.
Cool roofs are designed to reflect sunlight from the roof surface and help prevent heat being absorbed into the building structure. With a reflectance value (LRV) of around 90%, light coloured membranes can 'bounce' back a lot of the sun’s effects. As heat isn’t absorbed in the roof cavity, considerable energy savings can be made with less of a need for air conditioning, cheaper energy bills and consistent living temperatures for owners.
In terms of environmental benefits, cool roofs can help reduce the urban heat island effect and decrease energy consumption thanks to their reflective surfaces. A lighter coloured membrane has these qualities and provides a simple, yet effective method to achieve energy efficiency.
The durability of a cool roof is another reason specifiers and building owners are drawn to it. The solar reflectivity of the roofing product extends the service life, as the surface is cooler in hotter temperatures in comparison to darker alternatives.
The use of darker coloured thermoplastic membranes is not recommended in New Zealand as our UV exposure levels are considerably higher than in Europe and America which can add to higher surface temperatures. Although large manufacturers such as GAF have a diverse range of colours available, for New Zealand conditions they strictly recommended to only supply light colours such as white and light grey.
Nuralite has taken note of New Zealand’s unique and specific environmental factors and sourced an appropriate single ply thermoplastic membrane for our climate. Nuraply Everguard TPO is a reinforced thermoplastic polymer sheet which has been proven competent in extreme heat. The SRI independent TPO study that proved the GAF TPO membrane is the most durable amongst the four manufacturers tested.
In our opinion, there are considerations to cool roofs that need to be taken into account during design stage.
1) There have been some reports that cool roofs are more prone to internal condensation due to the lack of heat gain within the structure and not creating the thermal drive necessary to remove moisture. The specification and installation of a Nuratherm Warm roof, where the insulation is installed outside the structure, is one way to eliminate this issue.
2) Highly reflective roof surfaces could have the potential to become a nuisance to neighbouring buildings, particularly when installed adjacent to taller, overlooking buildings. To mitigate this effect, consideration for light grey colours will provide the opportunity to reach a compromise.
3) Similarly to the reason I no longer wear a white shirt anymore, is that white, or very light coloured membranes have a tendency to show dirt and grime quite quickly. There are effective methods for cleaning these areas but do add an ongoing cost element to maintaining the asset. This is exacerbated by having adjacent building elements running off onto the roof.
As each project is unique, it is recommended to consult with your flat roof expert to understand the best option for you to specify. To ensure that the appropriate system is applied on the roof Nuralite take it upon ourselves to advise and educate on best practice.