This other project was entirely different in terms of climate conditions. The project was executed in the Baltics – in Riga, Latvia – where winter temperatures can easily drop well below -20º C / -5º F.
Like the Dubai case, the Riga green roof was built in a residential area. The roof between the residential buildings was meant to be a recreational space, where families could hang out late in the afternoon and watch the kids playing in the rooftop-playground.
The simplest green roof structure using grass over the entire roof would have been the cheapest alternative; however, this would actually require a lot of maintenance over the years to come, which would be a burden for future residents, so this idea was initially scrapped.
The following requirements were drawn up for us to follow:
- The green roof needs to be fully vegetated on the day the first residents arrive.
- The green roof should remain nice, even in the colder winter months when not covered in snow.
- The green roof should require a minimum of maintenance and mean only low additional costs for the residents.
- The original design should make the roof thicker than the pathways made of concrete paving stones.
- The green roof must act as a storm-water management tool.
The vegetation part was relatively easy for us to comply with. The plants were selected by our global partner Sempergreen, as they are simply the best in the business. The use of all year-round green sedum species – so-called creepers like Album coral carpet, Acre murale, Sexangulare and similar – were musts in order to comply with the year-round appearance requirement. They don’t lose their leaves, but can turn a little reddish in extreme cold.
The difficult part here was to provide sufficient storm-water management with a thin structure that would not exceed the height of the pavers. This can’t be done with regular green roof soil, so we used a structure that employed Urbanscape Growing Media which just 4 cm thick (1.8”), yet could still hold the majority of the annual rainfall (more than 70%) that usually pours down on the roofs of Riga.
Once built and ready the entire place looked fantastic, and complied with all of the initial requirements.