Preparing Green Roofs for Winter: Essential Maintenance Tips

Just few weeks ago, we published a blog about unbearable heat wave and its consequences - which can be mitigated with the vegetated rooftops and other types of green urban infrastructure. And now, holding cup of tea in hand and looking through the window at morning freeze, we shall think about winter ahead of us. Seasons change quickly and so does the nature, including precious habitats in urban areas - the green roofs.

Winter with lowered energy bills for heating

https://www.creditoninandaround.co.uk/posts/how-to-reduce-your-energy-bills-and-stay-warm

Vegetated roofs are helping us to get through the winter season with lower energy bills for heating. Green roofs with their insulation effect provide better living conditions in summer while decreasing the ambient temperature and in winter, preventing the heat losses and lowering the energy loss.

Green roofs offer many benefits that conventional roofs do not: increase of buinding value, longevity of roofing membranes due to UV radiation protection. Noise reduction,  stormwater management, water runoff reduction, urban heat islad effect reduction, improved air quality, LEED or other incentives credit points. If we want to keep these benefits of our green roofs for decades to come, we must not forget to maintain the green roof.

How much maintenance work does a green roof need?

What is the most common mistake of green roof maintenance? That the owners:

• do not take any roof inspections at all, or
• over - maintain it. If the owner for example uses inappropriate type or too much fertiliser on a green roof, the runoff water will be polluted with fertiliser elements as initial consequence, while on the long run the vegetation will not develop as it normally should.

Either way, green roof will likely lose its performance and the owner will not profit from its wide benefits. How much is enough maintenance? It depends on several factors, with outmost important one – whether it is intensive or extensive green roof. If you have a lightweight extensive green roof, the maintenance is less demanding and time consuming compared to intensive green roof system. For sedum based extensive green roofs, two maintenance sessions will do in average, whilst for intensive green roofs, depending on the plant selection, it will take lot more effort to take proper care of the vegetation on regular basis - soil testing for nutrients composition, planting, re-planting, pruning, cutting, trimming… (Mihalchick, 2023).

With extensive green roofs, sedums are popular choices for green roofs due to their low maintenance requirements and ability to withstand harsh conditions. Few (likely two) maintenance sessions a year, mostly in spring and early autumn, will enable you to undergo all necessary activities for long-term thriving green roof. During this process, you will notice the colour changes of sedum roofs which occur throughout the year. This is a natural seasonal and eye-pleasing cycle of plants’ life, as seen in case of Urbanscape green roof seasonal looks:

• winter time on left, late spring/early summer on right side:
  

• end summer on the left and in autumn on the right side:
  
  

  White winter on a green roof

  During the winter, the plants go to dormancy phase – means they are resting. With regular service on a green roof, they will thrive every spring and bring all expected long-term benefits.

  https://queensbotanical.org/sustainability/green-roof/
  

  Remember what is on to-do list for health and longevity of the green roof and read ten practical tips for regular maintenance checks:

  1. 1. Regular maintenance checks are generally done in spring and autumn.
     2. Safety comes first! Correct safety solutions must be implemented during all stages (design, planning, installation, maintenance).
     3. Ensure easy access to the roof. The roof access must be accessible and without obstacles, remove potential rubbish and debris.
     4. Remove weeds and unwanted vegetation. In case of near-by trees, remove fallen leaves from gutters and drains.
     5. For healthy and strong plants, nutrients’ application (once or twice a year) is recommended. Use special slow-release fertiliser for Sedum green roofs.
     6. Empty, vegetation-free patches can be filled with sedum cuttings. These are pressed gently into the topsoil and in mild weather, they will root soon.
     7. Prepare for possible wind or water erosion. Check all caulking and ensure that all access areas are easily accessible, sealed properly and free of debris.
     8. Clean drains and gutters. Large quantities of moisture, snow, ice and melt in winter time must drain of quickly, not to pose the additional stress on waterproofing.
     9. Avoid extensive walking on Sedum plants during frosty weather. You risk damaging the succulent plant cells and it could take time for the plants to recover.
     10. Prepare for possible wind or water erosion. Check all caulking and ensure that all access areas are easily accessible, sealed properly and free of debris.
         
         
         
         https://mikesbackyardnursery.com/2014/12/propagate-succulents-2/
     11. Clean drains and gutters. Large quantities of moisture, snow, ice and melt in winter time must drain of quickly, not to pose the additional stress on waterproofing.
     12. Avoid extensive walking on Sedum plants during frosty weather. You risk damaging the succulent plant cells and it could take time for the plants to recover.
         
         
         https://essentialhouseplants.com/cold-hardy-succulents/?utm_content=cmp-true
         
     13. Snow removal: in case you live in area with possible large accumulation of snow, this represents a load hazard on all, not just vegetated roofs. Make sure the snow is evenly spread out on the roof with no snow drifts, to avoid exceeded load limits. When load capacity of a roof is endangered, and snow removal is needed, leave cca 20 cm buffer layer of snow above the green roof. If you remove more snow, you might disturb the plants or dig into the system layers.

     Literature:

     Michalcik, 2023. The Importance of Proactive Green Roof Maintenance. Living Architecture Monitor, 2023.