Some cities and towns mandate the installation of extensive green roofs on new flat roofs. Their goal is to provide a temporary water buffer on rooftops that helps prevent sewer overflows during heavy rainfall. While the other benefits of an extensive green roof, such as improved thermal and acoustic insulation, increased biodiversity, and better protection of the roof's waterproofing, are also noteworthy, these advantages are not always directly perceived by the client or user. With an intensive green roof, the benefits of the roof garden are extended to active uses, such as a roof terrace, a lawn, a petanque court, ... or a wider choice of plants including planters, shrubs or even trees.
"It is not always easy for everyone to understand or remember the difference between an extensive and an intensive green roof. One trick is to associate it with the required maintenance. An intensive green roof needs intensive maintenance, while an extensive roof does not. However, that doesn't mean it doesn't need maintenance at all. No green roof is maintenance-free," explains Philip Bruon, product manager at Tectum Group.
It is not only on the maintenance front where knowledge of green roofs is still limited. In the daily practice at Tectum Group, Project Manager Sven Devlieghere observes that green roofs and roof construction are still often considered separately in the design.
"However, the two are inextricably linked. After all, the type of green roof has an impact on the overall load and this inevitably affects the stability and structure of the roof package. The BUtgb has different requirements for an extensive green roof than for an intensive green roof. For an extensive green roof, insulation materials with a compressibility class of P3 or P4 can be used. For intensive vegetation, it is recommended to use only P4 compressibility insulation. This is not illogical, as the load of an intensive roof garden can reach 600 à 700 kg/m². Especially when larger plants are included in the design, you get locally high loads. PIR insulation with its compressibility class P3 cannot withstand such loads.
Prescribers are not yet sufficiently versed with the issues.
Not only PIR, but other common roof insulation materials, such as mineral wool, cannot handle the heavy load of an intensive green roof. "In fact, only cellular glass, XPS and certain types of EPS are suitable for this application. Regarding XPS, I would like to emphasize that it can only be used for an inverted roof (cold roof)," says Sven Devlieghere.
Cellular glass and EPS are, from a technical point of view, the only recommended insulation solutions in a warm roof. However, we still often see PIR and the aluminum-coated PIR variant prescribed in specifications.
"So it sometimes happens that we have a roof structure with PIR insulation on which an intensive roof garden is planned. In this case, the landscaper is forced to adjust the roof garden design to stay within the allowed load. Consequently, an intensive green roof may transform into an extensive one, and little remains of the original design's good intentions. At Tectum Group, we like to brainstorm to achieve a technically correct and performant description in the specifications. This is very important, as the architect is responsible for the final result for 10 years".
The roofing specialist is also pleased to act as a reliable partner in the execution phase. Tectum Group possesses expertise in the various components of extensive green roofs, ranging from waterproofing to planting. "This is a reassuring factor for the client. We have noticed that in the event of damage, discussions often arise between the roofer and the green roof installer. With the total package we offer, we eliminate such discussions, offering the client a single point of contact for both the waterproofing and the finishing of the roof."
Some cities and towns mandate the installation of extensive green roofs on new flat roofs. Their goal is to provide a temporary water buffer on rooftops that helps prevent sewer overflows during heavy rainfall. While the other benefits of an extensive green roof, such as improved thermal and acoustic insulation, increased biodiversity, and better protection of the roof's waterproofing, are also noteworthy, these advantages are not always directly perceived by the client or user. With an intensive green roof, the benefits of the roof garden are extended to active uses, such as a roof terrace, a lawn, a petanque court, ... or a wider choice of plants including planters, shrubs or even trees.
"It is not always easy for everyone to understand or remember the difference between an extensive and an intensive green roof. One trick is to associate it with the required maintenance. An intensive green roof needs intensive maintenance, while an extensive roof does not. However, that doesn't mean it doesn't need maintenance at all. No green roof is maintenance-free," explains Philip Bruon, product manager at Tectum Group.
It is not only on the maintenance front where knowledge of green roofs is still limited. In the daily practice at Tectum Group, Project Manager Sven Devlieghere observes that green roofs and roof construction are still often considered separately in the design.
"However, the two are inextricably linked. After all, the type of green roof has an impact on the overall load and this inevitably affects the stability and structure of the roof package. The BUtgb has different requirements for an extensive green roof than for an intensive green roof. For an extensive green roof, insulation materials with a compressibility class of P3 or P4 can be used. For intensive vegetation, it is recommended to use only P4 compressibility insulation. This is not illogical, as the load of an intensive roof garden can reach 600 à 700 kg/m². Especially when larger plants are included in the design, you get locally high loads. PIR insulation with its compressibility class P3 cannot withstand such loads.
Not only PIR, but other common roof insulation materials, such as mineral wool, cannot handle the heavy load of an intensive green roof. "In fact, only cellular glass, XPS and certain types of EPS are suitable for this application. Regarding XPS, I would like to emphasize that it can only be used for an inverted roof (cold roof)," says Sven Devlieghere.
Cellular glass and EPS are, from a technical point of view, the only recommended insulation solutions in a warm roof. However, we still often see PIR and the aluminum-coated PIR variant prescribed in specifications.
"So it sometimes happens that we have a roof structure with PIR insulation on which an intensive roof garden is planned. In this case, the landscaper is forced to adjust the roof garden design to stay within the allowed load. Consequently, an intensive green roof may transform into an extensive one, and little remains of the original design's good intentions. At Tectum Group, we like to brainstorm to achieve a technically correct and performant description in the specifications. This is very important, as the architect is responsible for the final result for 10 years".
The roofing specialist is also pleased to act as a reliable partner in the execution phase. Tectum Group possesses expertise in the various components of extensive green roofs, ranging from waterproofing to planting. "This is a reassuring factor for the client. We have noticed that in the event of damage, discussions often arise between the roofer and the green roof installer. With the total package we offer, we eliminate such discussions, offering the client a single point of contact for both the waterproofing and the finishing of the roof."
Some cities and towns mandate the installation of extensive green roofs on new flat roofs. Their goal is to provide a temporary water buffer on rooftops that helps prevent sewer overflows during heavy rainfall. While the other benefits of an extensive green roof, such as improved thermal and acoustic insulation, increased biodiversity, and better protection of the roof's waterproofing, are also noteworthy, these advantages are not always directly perceived by the client or user. With an intensive green roof, the benefits of the roof garden are extended to active uses, such as a roof terrace, a lawn, a petanque court, ... or a wider choice of plants including planters, shrubs or even trees.
"It is not always easy for everyone to understand or remember the difference between an extensive and an intensive green roof. One trick is to associate it with the required maintenance. An intensive green roof needs intensive maintenance, while an extensive roof does not. However, that doesn't mean it doesn't need maintenance at all. No green roof is maintenance-free," explains Philip Bruon, product manager at Tectum Group.
Prescribers are not yet sufficiently versed with the issues.
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