You can find a video at the end of this article that follows the entire installation and explains the benefits and technical parameters of green roofs.
Green roofs are no longer just an architectural trend. They make sense in terms of functionality, sustainability and the everyday operation of buildings. A good example is the green roof on the timber childcare centre in Kamenný Újezd, built by Vesper Homes, with the vegetation roof installed by Hradecká zahrady under the direction of its owner, Aneta Hradecká. How is a green roof built, what requirements must it meet, and why do investors choose one? Read the full story of the installation.
Why choose a green roof?
A green roof brings benefits that are appreciated not only by investors but also by the people who use the building, in this case children. “A green roof brings greenery to a building, so we get vegetation in a place where there would otherwise be none, where there might be some other roofing material,” explains Aneta Hradecká. This is one of the main reasons green roofs are appearing more and more often, not only on family homes but also in the public sector.
Besides the aesthetic function, a green roof has major practical advantages. “There are studies showing that a green roof lowers the temperature inside a building by one to two degrees on summer days,” adds Hradecká.
Water management is just as important. “Another benefit is that it retains rainwater, so we are managing stormwater.” Thanks to these properties, green roofs are becoming an important element of modern sustainable architecture, and their use is growing in both the private and public sectors.
Extensive green roof: an ideal solution for a timber building
For the childcare centre, an extensive green roof was chosen. It is one of the least demanding types and, at the same time, the one most commonly used on timber buildings. “The least demanding green roofs are extensive ones. They use succulent plants that don’t require any special growing conditions,” Aneta Hradecká describes. Specifically, sedum mats were used here. They tolerate drought and harsh climatic conditions well, and they form a continuous green cover across the roof. An extensive green roof also suits both flat and pitched roofs, which makes it a versatile solution for a wide range of building types.
How a green roof build-up is made, layer by layer
Every green roof rests on a precisely designed build-up of layers. In this case, the starting point was the prepared waterproofing, which first passed a flood test carried out by the construction company Vesper Homes. “The designed layer build-up that was here goes from the waterproofing upwards,” explains Hradecká.
The whole green roof build-up is a carefully considered system in which every layer has an irreplaceable role. Directly above the prepared waterproofing comes a protective geotextile, whose job is to shield the waterproofing membrane from mechanical damage from the layers above. It is followed by a dimpled drainage membrane, whose profiled shape creates small pockets that catch and hold rainwater. To stop the substrate from the upper layers gradually sinking into these pockets, a separation fabric covers the dimpled membrane. The next layer consists of Izover Flora water-retention boards, which act like a sponge. They absorb an additional reserve of water and gradually release it back to the plants. On these boards lies the extensive substrate, a special lightweight material that forms the nutrient base for the vegetation. At the very top, the build-up is completed by sedum mats: pre-grown strips of succulent plants that are laid onto the substrate and, within a short time, form a continuous living green surface. The whole build-up is only 12 cm thick, yet it contains a complete system that retains water, protects the structure and turns the roof into a living green space.
How much does a green roof weigh? Don’t forget the structural design!
A green roof is not just about plants and aesthetics. It is also about the laws of physics. The weight of a vegetation roof is a parameter that must be taken into account at the design stage of the entire building. “An extensive green roof is 12 cm thick and the load is roughly 150 kg per square metre. Given the area of this green roof, that comes to 21 tonnes,” states Aneta Hradecká.
This is a figure that should not be underestimated. “Before starting any green roof installation, it is always necessary to verify the structural design and have a structural assessment, so that the building can carry the green roof.” For the timber childcare centre in Kamenný Újezd, the structural design was verified and the structure was dimensioned so that the green roof can safely fulfil its purpose throughout the building’s service life.
Green roof maintenance: what to expect through the year
One of the most common myths about green roofs is that they look after themselves. The opposite is true, and Aneta Hradecká says so plainly: “A green roof is definitely not maintenance-free either, so it requires at least spring and autumn maintenance, and then during the year certainly some watering and weeding.”
In practice, though, this is nothing that would place an excessive burden on the owner. In spring, the key task is a thorough inspection of the whole roof after winter: checking its overall condition, removing fallen leaves and debris, and paying attention to the drain outlets. “During spring maintenance, you need to go through all the drain chambers, open them and check whether they are clogged with leaves or other material after the winter, because that is where water drains from the roof down into the wastewater system,” Hradecká specifies.
Spring care also includes fertilising, which kick-starts the vegetation for the new season. During summer, watering is needed on dry, hot days, along with ongoing weeding so that unwanted plants don’t take over the space that belongs to the sedums. In autumn, the cycle closes with a final inspection and preparing the roof for the winter months. Caring for a green roof is therefore a matter of regularity rather than effort, and a properly maintained roof rewards you with a long service life and an attractive appearance all year round.
A green roof as part of a modern timber building
Combining a timber building with a green roof makes exceptional sense from a sustainability perspective. Timber, a natural and renewable building material, complemented by a living vegetation layer creates a functional whole that responds naturally to today’s climate challenges: urban overheating, lack of greenery and stormwater management. A green roof also adds value not only from an ecological perspective but also in terms of comfort for the building’s users. In this case, the children benefit from a more pleasant indoor environment, lower noise levels and natural contact with living nature right above their heads.
For more inspiration from family homes built by Vesper Homes, see the References section. As a general contractor, we also deliver public buildings for municipalities and other investors. If this topic interests you, you will find more information on our website in the Public Buildings section.
The green roof in Kamenný Újezd was installed in full by Hradecká zahrady. If you are interested in their work, take a look at their website.
You can also watch the entire green roof installation in Kamenný Újezd in this video.
