Types, benefits, plants, and more

the essentials in brief

• One Green roof has many advantages: Among other things, it keeps heat outside in summer and inside in winter, protects the roof from environmental influences and increases the humidity.
• With extensive green roofs, only a 12 cm thick layer of earth is applied to the roof and planted with succulents and other less undemanding plants.
• With intensive green roofs, a real garden is built on the flat roof, the substrate layer of which is more than 20cm.
• In both cases, a structural engineer must be consulted before the green roof is laid; professional drainage is also extremely important in order to avoid moisture damage to the roof.

What are the advantages of a green roof?

A green roof has a number of tangible advantages for you as well as for nature. The green roof or even a roof garden offers a natural form of insulation that keeps the heat outside in summer and the heat inside and the cold in winter. In this way, both heating and air conditioning costs can be saved, which in turn has a direct impact on the environment due to the raw materials saved. Furthermore, the plants themselves also bind the climate-damaging carbon dioxide (CO2) and thus contribute to an improvement in the climate balance.

A green roof also offers these advantages:

• Increased sound insulation, as the greenery absorbs sound
• Plants as air filters: Removal of fine dust and other air pollutants
• The roof is protected from the weather and temperature fluctuations
• Stored water evaporates and thus ensures cooling and pleasant humidity
• Retention of excess rainwater
• Improvement of the living and working environment
• Green roofs are often supported by subsidies

The best time for a green roof is spring or autumn.

Types of green roofs

In Germany, the undeveloped areas are decreasing more and more, especially in times of acute housing shortage in the big cities. With a green roof you give nature back a piece of growth area and is therefore a kind of compensation. There are basically two types of green roofs.

Extensive greening

So-called extensive green roofs are used for roof areas that are otherwise unusable, such as flat roofs like on carports and garages, but also on pitched roofs, on the roofs of factory halls or other buildings occurrence. Typical of this type of greening is the extremely thin substrate layer, which on average is no more than seven to twelve centimeters. Plants growing here must be adaptable, robust and undemanding as well as regenerative. This means that after a longer period of dryness or frost, the plants will sprout again on their own. The low maintenance requirement is also characteristic: here you basically have nothing more to do after creating the green roof.

Intensive greening

With intensive green roofs, on the other hand, you basically create a garden on your roof. Such a roof garden naturally only works on roofs that can be walked on, after all, such a system requires a lot of maintenance. The substrate layer applied here is more than 20 centimeters, which is why the selection of plants by far is larger and you also rely on plants that are more demanding in terms of nutrient and water requirements can.

The intensive green roof is expensive and complex - but creates a real roof garden

Planning a green roof

Before you are highly motivated to go to work and want to cover your roof with lots of green plants, you should first pause and spend some time planning. In particular, the following points should be considered in advance:

• Statics: Extensive greenery adds an average of 80 to 170 kilograms per square meter to the roof. Not every roof can withstand this, which is why you should consult a structural engineer before starting construction.
• Roof structures: The roof construction itself also has an influence on the type of green roof. While both extensive and intensive greening are basically possible on a warm roof, you can only create extensive forms on a so-called cold roof.
• Roof pitch: Creating a green area on a flat roof is not a problem, slopes of up to about 30 degrees can also be planted. However, fall protection is mandatory from a gradient of 15 degrees.
• Root protection: The roof also needs waterproofing and root protection to prevent damage.
• Irrigation and drainage: A drainage layer makes sense for two reasons. On the one hand, this directs excess rainwater to the drain, on the other hand, it supplies the plants with valuable moisture.

Basically, it makes sense for larger projects - where more is planned than just something Potting soil and to put a few Sedum bars on the garage roof - to hire a specialist company. This is especially true for planning a roof garden.

Greening flat roofs or garages - you have these options

Every green roof is made up of several layers:

• fleece: This bottom layer separates the actual roof from the green roof.
• Protective film: Place a waterproof (root) protective film over it, which has a durability guarantee of at least 20 years.
• Storage mat and drainage layer: Both should both divert and store excess rainwater.
• fleece: Another fleece serves as a filter, otherwise the drainage would be clogged with fine substrate particles over time.

Only now do you apply the layer of soil, which usually consists of a substrate specially mixed for green roofs. This contains a high proportion of light materials such as pumice, lava or brick chippings and only about ten to 15 percent humus. Finally, the planting takes place.

The following article shows how you can easily green a flat roof - for example that of a shed or garage - with potting soil and Sedum sprouts. But be careful: Such a procedure is only recommended for a flat roof on a garage or similar. similar, but not for a residential building!

Possibilities for planting

Once the roof is waterproof and the various layers have been applied, you can now plant the species you want. When making your selection, make sure that certain crops require a minimum substrate thickness. You have various options for bringing the plants onto the roof. Which one you choose depends, among other things, on how quickly the roof should be greened. As a rule, the growth phase is completed after about three to four weeks, during which the plants generally have a higher water requirement. Only after they have taken root can they survive longer periods of drought.

Digression

When is the best time to plant?

plants

It takes some work, but very efficient - after all, this is the fastest way to grow the plants - is the manual planting of them in the substrate. In this way you also have the specific design and distribution of the plants in your hand. Plan about 15 to 20 plants per square meter for extensive greening of sedum species. These should have a bale size of about five to six centimeters (so-called "flat bale shrubs"). The individually set plants grow together after a while and finally form a closed area. If these gaps appear, you can still replant or re-sow.

Usually different types of sedum are used for the roof planting

Sprout planting

It is of course easier and faster with sedum rungs, which you simply sprinkle on and which then grow on by themselves. The disadvantage of the method, however, is that it can take up to a year for the roof to be completely greened. Plan about 80 to 100 grams of sprouts per square meter of planting area. You can purchase these in specialist shops.

Sow

If you're on a budget, special seed mixes might be the solution for you. However, you need patience for this, because it can take one to two years for the seeds to germinate and the plants to grow - even several years for a complete greening. In addition, unwanted grasses can settle on the bare substrate surface due to flight insemination, which you have to remove regularly in the first few months.

Vegetation mat

The green roof works particularly quickly with a vegetation mat, which is basically a type of roll mat that has already been planted. The plants have already grown into a special structure made of fleece and substrate and only need to be applied like with a turf. Vegetation mats for steep or steep slopes are particularly recommended. Pitched roofs. Nevertheless, apply a thin layer of substrate about four to six centimeters thick under the mat so that the plants can grow better.

Suitable plants

Depending on the type of green roof desired and the thickness of the substrate applied, different types of plants can be used. The most important condition for all species, however, is that they are very robust against weather conditions such as wind, cold and rain - and also tolerate drought well.

• Low substrate build-up (up to five centimeters): Mosses, Sedum species
• Low substrate build-up (five to seven centimeters): low herbs such as chives, wild majora, meadowDaisy, Carthusian cloves, dyer's chamomile
• Higher substrate structure (15 centimeters): higher flowering plants as well as grasses

The following table gives an overview of some of the most important plant species for green roofs.

Proper care of the green roof

With extensive green roofs, once the plants have taken root, you don't have much to do. In the first four weeks after planting, however, you should water regularly to promote root growth. Depending on the temperature and the duration of the sunshine, you can reach for the watering can up to four times a week. Then weed about once or twice a year and use this opportunity to remove mainly germinated tree seeds, for example from birch trees, as these should not grow on the roof. The roots grow quickly into the drainage layer and can destroy the roof as they grow.

Funding programs and costs

A green roof is not a cheap affair, although the costs incurred vary greatly depending on the type of greening, the size of the area and other factors. A roof that has been planted with greenery by a specialist company is of course a lot more expensive than one that you planted yourself. For the latter, plan around EUR 20 to 40 per square meter of planting area, provided the green roof is extensively planted. Intensive greening costs around twice as much.

Fortunately, however, you can at least partially recoup the costs, as some municipalities grant for one Such a project grants between ten and 20 EUR per square meter or take over a percentage of your Costs. In turn, funding programs from the Kreditanstalt für Wiederaufbau (KfW) can, for example, be part of a Building renovation can be used, whereby the program "Modernize living space" also includes green roofs financed. Another savings option results from the recognition of green roofs as an unsealing measure - many municipalities reward this with reduced wastewater fees.

frequently asked Questions

Does a green roof prevent the house from heating up in summer?

In fact, a green roof has an insulating effect and keeps the heat out in summer. So it's cooler inside the house.

Does the green roof also have a thermal insulation effect?

While the summer heat stays outside, the green roof keeps the warmth inside during the cold season. The heat-insulating effect of a green roof can even be calculated based on the building materials, the amount of soil and the mass of plants. However, this is a task for experts such as architects or civil engineers.

Can I also plant and harvest herbs on the roof?

Herbs such as oregano, thyme or chives are great for a green roof. They are frost hardy, can cope well with the sun, are easy to care for and do not need a lot of water.

Why are the plants suddenly turning red on the roof?

If the plants on the roof are no longer nice and lush green, but suddenly turn reddish or brownish, there is probably a nutrient deficiency. In general, a nutrient-poor substrate is used for green roofs, so that fertilization is necessary from time to time.

Which plants are particularly good for bees and butterflies?

Many of the plants suitable for a green roof are valuable insect pastures anyway, so that bees, butterflies, Bumblebees and other winged animals can enjoy plenty of food. In this context, it is of course important that the flowering time of the plants does not only last a few weeks, but extends from spring to late autumn if possible.

How many plants do you have to plan per square meter?

If you want to plant out perennials and different types of Sedum, you should plan around 15 to 20 plants per square meter. The exact number, however, depends on the selected species and varieties, as these have quite different requirements in terms of planting spacing. Furthermore, such a roof can also be greened by, for example, planting flower seeds on it. A colorful wildflower meadow on the roof also has something to offer.

How much soil does a green roof need? And which soil should one take?

How much soil you need depends primarily on how thick you want the layer to be. For plants with shallow roots, an approx. six centimeters thick substrate layer. For this you plan around 60 liters of soil per square meter of roof area. A nutrient-poor substrate is usually used for this.

Does such a green roof also have disadvantages?

In principle, such a green roof has no disadvantages, except perhaps the occasional maintenance effort. However, you have to be careful with the building statics, because not every building can withstand the additional load on the roof. Therefore, before starting the construction project, have the statics checked by a specialist and equip you when you have the opportunity Pay a visit to the local building authority right away: Depending on the project, you may need a building permit for your project to need.