Can you install a green roof in winter?

Posted on Thursday 18 February, 2021

Frost on SedumThe answer is yes. A lot of people are not aware of the possibility to install a green roof in winter. In fact, installing green roofs can be done year-round in most regions. In this article we explain what you need to be aware of when installing a green roof in winter.

The power and flexibility of Sedum

Our green roofs consist of vegetation blankets or trays which are pregrown with Sedum plants. Sedum - also often known as stonecrop - is a genus of the Crassulaceae family of succulent plants. This family consists of four to five hundred species and thousands of different varieties. Succulents are plants that store water in a part of the plant. Sedum stores water in the leaves, and this is why Sedum is often referred to as a leaf succulent.

Sedum is a strong plant that can withstand extreme weather conditions. This plant genus is therefore extremely suitable as a planting for green roofs. Sempergreen's Sedum-mix blankets consist of a balanced mix of coarse-leaved deciduous Sedum species, such as Sedum Reflexum, and evergreen creepers, such as Sedum Album and Sedum Sexangulare. The mix is tailored to give the green roof an evergreen appearance, even in the colder months.

Text continues below imageSempergreen Sedum-mix blanket in bloomA Sempergreen Sedum-mix blanket in bloom

What to bear in mind when installing a green roof in winter

Suppose you have a project that needs a green roof, but it is the middle of winter. Can you still finish your project and install a green roof? Yes, you can, there are just a few things you have to take into account. We explain these below, based on frequently asked questions.

Can all types of green roofs be installed in winter?

Winter installation is only possible with pre-cultivated vegetation blankets and trays. If you want to use cuttings or plugs, you’ll have to wait until the end of spring. These plants are not yet properly rooted and therefore very weak. The plants are dormant during the winter, so the roots will only start growing in the spring. In addition, cuttings can be blown off the roof by strong winds in winter or washed away by heavy rainfall.

Vegetation blankets do not suffer from this, because on delivery the blankets always boast at least 95% coverage with fully-grown Sedum plants that can easily survive in winter.

Text continues below imageA green roof with plugs (l.) and a green roof with vegetation blankets (r.) after installation
A green roof with plugs (l.) and a green roof with vegetation blankets (r.) after installation

What do you need to be aware of when installing a green roof in winter?

The roots of plants are inactive in winter and only become active again in spring. It’s therefore important that vegetation blankets are rolled out carefully in winter to prevent damage to the plants. After all, the roots can only recover in the spring.

Is it freezing on the day of installation? Then make sure that the vegetation blankets are installed as soon as possible, or placed in a frost-free location so that they do not freeze when rolled up. If it is slippery on the roof, please ensure that the safety of those walking on the roof is guaranteed.

Read here which green roof system suits your project best

When can a green roof not be installed?

During a prolonged period of frost, the nursery can’t deliver any Sedum blankets. This is because the ground frost prevents us to roll up, or walk on the vegetation blankets. Otherwise there will be leaf damage.

What are the consequences of frost after the installation of a green roof?

The Sedum plants are able to withstand frost well. However, it’s important that they receive the necessary nourishment and water in spring. If the green roof does not receive enough water during a dry spring, the plants can become stressed and turn red. This is a normal and reversible process. As soon as the plants receive water, they will turn green again.

Text continues below imageA 'stressed' green roof
A 'stressed' green roof

How does snow affect a green roof?

Snow has a positive influence on a green roof: it insulates and provides additional protection against frost. In addition, snow is a useful source of water when it starts to thaw.

Text continues below imageA green roof installation in winter and the beautiful result in spring
A green roof installation in winter and the beautiful result in spring

What are the possible risks?

A long, hard winter without rainfall can cause the plants to dry out. When they 'wake up' again in spring, the first thing they need is moisture. A moisture-absorbent substrate in combination with a drainage layer is therefore extremely important for a green roof.

Can you install green roofs all year round?

In regions where long periods of severe frost are rare, it is possible to install green roofs virtually all year round.

Are you interested in installing a green roof? Then request a quote or contact us. We’re always happy to help!

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