It starts with good design...

Multi-purpose roof use requires risk mitigation

Urban densification and our climate challenge require efficient(er) use of space. Also with regard to our roofs, which places new demands on design, application and finishing. "The flat roof is increasingly regarded as a 'fifth facade' and used multifunctionally," notes Atze Walsweer, Technical Manager at Derbigum. "And that is not surprising, because with more than 400 million square meters of flat roof surface, there is enormous potential here. By implementing the roof as a (combined) sedum roof, solar roof, residential roof, parking roof or water retention roof, sustainability and livability come together and the ground level remains available for other (useful) purposes."

At Derbigum, multifunctional roofs are called "special roofs. This distinguishes between the color groups of green, yellow, red and blue. "Green roofs are roofs with vegetation, which can range from moss, sedum, grass and herbs (extensive) to shrubs and trees (intensive)," says Walsweer. "Sustainable (solar) energy is generated on yellow roofs, while red roofs provide space for recreational purposes. Think terraces, sports fields or swimming pools with high loads. Finally, blue roofs are designed to store and/or buffer as much water as possible, possibly in combination with vegetation (blue-green roof)." Derbigum produces an extensive range of high-quality and KOMO-certified products that enable multifunctional roof use within all color themes. "All our special roofs are insured in the 'titanium insured roof warranty,' in which both product and application are covered."

White roofs

Derbigum supplies high-quality bitumen roofing materials for flat roofs, with high durability and proven longevity of more than 40 years. "In addition to black bitumen, we see a growing demand for white roofing, which we are responding to with Derbigum Aquatop and Derbicolor White," says Walsweer. "The reflective and heat-resistant property of white roof finishes has a positive impact on the efficiency of solar panels. In addition, the reflection and high emission rate (heat emission) of white roofing reduces the heating of the underlying space." 

Green roofs

A second trend that Derbigum is observing is the trend of green roofs where the roof is provided with vegetation. "The reasons for this trend are diverse," Walsweer said. "Consider, for example, aesthetic considerations, CO₂-reduction, enhancing biodiversity, increasing livability, absorbing and delaying stormwater runoff and/or lowering ambient temperatures. In some cases, green roofs are also combined with water collection in crates. In this case, we speak of blue roofs or water retention roofs." To avoid the risk of leaks, green roof structures require a roofing material and execution with a high level of security, he emphasizes. "After all, leaks are not easily detectable through the finish." Derbigum supplies, for example, Derbigum SP WW for this purpose; a root-resistant roofing material with a separated double insert of glass fleece and polyester, high resistance to external forces and excellent walkability. But also Derbigum GC WW; a root-resistant roof covering with heavier inlays that is also suitable as waterproofing for parking roofs or underground seals. In short: for all projects with extreme loads. For smaller roofs, there is the Derbisedum; a sedum finish pre-cultivated in crates that can be applied easily and quickly. For the design of the green roofs, Derbigum works together with specialist in roof vegetation, roof gardens and rainwater management Optigrün.

Leading the way in circularity

Regardless of which roofing material one chooses, Derbigum's products are largely circular. As much as 15 to 30% of our own recycled bitumen (Derbitumen) is used in production, says Walsweer. "This Derbitumen comes from production remnants and cutting pieces/remnants collected from our works in progress. But also from demolition roofs, where the roofing material is collected and recycled in-house and according to a patented system."

Extensive design support

Multipurpose roofs are preferably performed on roofs with a stony substrate where all layers, from vapor retarder to top layer, are fully adhered. For example, to prevent mechanical damage from causing water diffusion in the roofing structure, Walsweer says. "To ensure the waterproofing, quality and durability of special roofs for a long time, risk mitigation is essential. This starts at the design stage, with the selection of the right structural substrate, insulation of sufficient compressive strength and the right underlayment, vapor retarder and top layer. But also with preventing water stagnation, with the exception of blue roofs. It is also important that all roofing materials work well together. Our Derbigum Specification Service helps with this."

This free online tool allows architects, designers and consultants to easily create and download Stabu specifications for their flat roof. The software was developed in cooperation with Bouwconnect and guides users step by step to the desired roof type and the correct roof composition. Unique here is the product selection. For example, if you choose an intensive green roof with a two-layer C-EPS substrate, you can only select the top layer, vapor retarder, carpet pad and insulation that combine with it. The same is true for a substrate with Foamglas, XPS or other insulation materials, eliminating errors in roof construction. "At the end of the selection process, the specification text can easily be downloaded and integrated into the overall specifications of the architect, designer or consultant."

Derbigum has an extensive network of 50-55 experienced Derbigum installers. In combination with extensive roof surveys and inspections of the work in progress - which are also checked by Bureau Dakadvies (BDA) for the insured guarantee - clients are assured of high roof quality and a long life span. A take-back guarantee is offered with each completed Derbigum roof, ensuring that the circular ambition is also secured in the future.