- Benefits of a green roof
- Types of roof gardens
- Safety requirements
- Roof garden technology
- DIY roof garden
In this article, we will talk about the advantages of arranging a lawn and a roof garden, the features and varieties of this type of landscaping, the stages of creating a green roof, the possibility of arranging a garden on roofs of different types, requirements for the strength of the base and creating a roof garden with your own hands..
A green roof, on which a lawn or a real lush garden grows instead of the usual slate or soft roof, is now becoming an increasingly popular option for arranging the roof of buildings. Moreover, the garden may appear not only on the roof of an ordinary private house. Such green roofs are no longer a rarity on multi-storey buildings in megacities..
A rooftop garden has many advantages and only one disadvantage – it is not so easy to arrange it without the help of landscape designers and builders. The features, varieties and some technical aspects of creating a roof garden will be discussed in this article..
Benefits of a green roof
If you think that the grass and trees on the roof are a recent, modern trend, you are deeply mistaken. Remember at least the famous Semiramis Gardens in ancient Babylon! In Norway, roofs covered with turf, peat, birch bark and overgrown with grasses and mosses are a national tradition that has existed for several centuries. Today, the authorities of Copenhagen and Oslo are planning to return green roofs to the streets of their cities, considering this arrangement option “relevant, economical and in line with the modern desire to use environmentally friendly materials.” In addition, green roofs can be seen in San Francisco, Toronto, Zurich, Basel, Bordeaux, London, Lyon, Madrid and other cities..
What makes rooftop gardens, including multi-storey ones, so popular? There are several very serious reasons for this:
- Improving the ecological situation. This moment is especially important for large cities, where it is difficult to distinguish a place for a park zone among asphalt and concrete. Greenery on the roof effectively purifies the air by trapping more than 25% of harmful substances and dust contained in the atmosphere. For example, the same authorities in Copenhagen expect to reduce the greenhouse effect in the city to zero by 2015 using green roofs..
- Increased sound and heat insulation. A roof garden will help reduce noise in the interior, which is also important for residents of houses located along busy highways. In addition, the house under the green roof will be warm in winter and cool in summer, which will reduce the cost of air conditioning and heating..
- A roof under a garden or lawn will last several years longer than a regular roof, since the plants and soil layer will reliably protect it from external influences and weather conditions. The service life of such a roof with proper garden maintenance exceeds 20 years..
- Space saving and building compensation. The roof garden, as it were, compensates nature for the area that was occupied during the construction of the house. Thus, the local microclimate is preserved, and the owner of the site again receives his lawn, which was destroyed during the construction of the foundation of the house..
- Retention of rainwater. This advantage is relevant for cities where, during heavy rainfall, the sewage system may not cope with a large amount of water. Rooftop gardens and lawns absorb some of the rainfall, preventing it from entering the streets and mixing with sewage. Quite an effective way to prevent flooding.
- The flat roof garden is an additional resting place for all residents of the house, that is, another useful area.
- A house under a green roof is always beautiful, unusual and immediately attracts attention.
In light of all of the above advantages and benefits, it becomes clear why roof gardens continue to gain popularity in many western metropolitan areas..
Types of roof gardens
Roof landscaping is usually divided into two main types:
- Extensive. Such greening of roofs involves the use of light soil, whose thickness varies from 5 to 15 cm. This is the simplest option to protect the roof from external influences and create an autonomous ecosystem. In the case of extensive landscaping, only unpretentious plants are used that do not need regular watering or careful maintenance. Extensive roof gardening is the creation of a continuous carpet of evergreens; this option does not imply any recreation areas. Most often, this method of landscaping is used on the roofs of gazebos, garages, outbuildings and private houses. It is convenient that the weight of a thin and light layer of soil, together with plants, averages only about 20 kg per square meter of the roof, so additional strengthening of the base will not be required. Another type of extensive landscaping is ordinary tubs with indoor plants, transferred to a flat roof in the spring. In this case, it is possible to equip a recreation area here, but, of course, you cannot call such an option a real garden or lawn..
- Intensive. In this case, a real garden appears on the roof with walking paths, a picnic area, gazebos, pergolas and even ponds. Of course, the planting of shrubs and trees requires a reliable foundation that can withstand a soil layer up to 1.5 m thick. Most often, intensive landscaping is used in multi-storey buildings, hotels, shopping centers and other fairly large objects. If the owners of a private house intend to create such a full-fledged garden on their roof, then they will need the opinion of specialists who will determine whether the load-bearing walls and base will withstand such a solid weight. With intensive landscaping, the total load per square meter of the roof can reach 700 kg.
According to the type of roof on which a garden or lawn will appear, landscaping is usually divided into pitched and flat. On a pitched roof, only extensive landscaping is possible, but on a flat roof, both extensive and intensive landscaping can be applied – it all depends on the strength of the base and the financial capabilities of the owners.
Norwegian green roofs are usually pitched, so there are no seating areas here – just an even layer of green grass
As mentioned in the previous section, extensive landscaping can be used on both pitched and flat roofs. However, the slope of the pitched roof must not exceed 30 ° C. Otherwise, the waterproofing layer, drainage and soil simply will not stay on a too steep surface, and the useful soil layer will be washed off by rains.
The base of a flat roof must withstand a solid load. A layer of ordinary soil with a thickness of only 5 cm and an area of one square meter can weigh up to 100 kg, and the soil is just one of the layers of the foundation of the future garden. The use of special lightweight substrates and lightweight drainage systems will help to reduce the load, but their choice requires a careful approach and consultation with specialists..
It should also be borne in mind that in winter snow will accumulate on a flat roof and the load on the roof can increase up to 400 kg per square meter. And planting trees, even small ones, and shrubs increases the soil layer and, accordingly, increases the weight of the green roof to 700 kg per square meter..
Landscaping experts advise, in order to reduce the load on the roof, plant large trees and place massive objects in those places where the supporting structures are located.
A few more important points when creating a roof garden: you should pay attention to protection from the wind, strengthen vertical structures, create a reliable parapet along the edge of the roof and provide a convenient, safe exit to the garden from the upper floor.
Roof garden technology
If you look at the structure of a roof garden in a section, then most of all it will look like a multi-layered cake, the top layer of which is directly the plants.
The base of the roof garden in section looks like a pie made of several layers, each of which is necessary to create a whole ecosystem with its own microclimate and green inhabitants: 1 – concrete slab; 2 – waterproofing; 3 – thermal insulation; 4 – root protective membrane; 5 – geotextile; 6 – drainage layer; 7 – geotextile; 8 – soil; 9 – plants
Let’s consider each separate layer and technology of roof greening:
- The first layer of a garden or lawn on the roof will be the supporting structures of the roof itself: a concrete floor slab in the case of a flat roof and a continuous sheathing of the pitched roof. Of course, if slate or shingles lie on the pitched roof, they must be removed first. If the foundation of the future garden is a flat concrete slab, you will have to take care of the presence of a slope of 1.5-5 degrees towards the drain. To create such a slight slope on a flat roof, you can use a cement-sand screed.
- The second layer is waterproofing. It should be as reliable as possible, since in the event of a leak, all the top layers will have to be removed for repairs, and this is a very time consuming, costly and lengthy process. As a waterproofing, nowadays, surfacing roll bitumen-polymer materials are usually used. Their bottom layer is mechanically attached to the base, and the top layer is fused, all seams are reliably soldered. The waterproofing layer along the edges of the roof should be bent to a height exceeding the thickness of the insulation.
- The third layer is thermal insulation. This layer is created from cork boards, extruded polystyrene foam or polyurethane foam. Insulation plates are stacked tightly to each other, if the pressure of the upper layers is not enough, you can connect them together with a special glue. There is no need to fix polystyrene or polyurethane boards to the base.
- The fourth layer is protection against root penetration. In some cases, you can refuse to lay this additional layer. For example, if there are no plans to plant trees on the roof and there will be an ordinary lawn here, then waterproofing is quite enough. Otherwise, landscape design experts advise, for reliability, to fix a root protective membrane over the thermal insulation layer, which will prevent the germination of the root system and damage to the base. An elastic polymer pad with special cells that retain moisture, or a film with a metal coating is ideal for these purposes.
- The fifth, intermediate layer is geotextile. It is a roll material, the strips of which overlap each other. Remember that plant roots can easily overcome geotextiles – which is why an additional root protection layer is needed..
- Sixth, drainage layer. The thickness of this layer ranges from 5 to 10 cm. The drainage layer is necessary to drain excess water and also to retain moisture during drought. The drainage layer is connected to the drainage system. Usually, perlite coke, crushed pumice stone, polyamide or expanded clay gravel are used as drainage – fairly light materials. Loose clay and regular gravel can also be used, but this will be heavier. Often perforated tubes are placed in the drainage layer, which improves water flow.
- Seventh layer – another layer of geotextile is laid on the drainage, which will serve as a filter for small particles washed out of the soil.
- The eighth layer is soil. Only now can you start creating the last layer in which the plants will be planted. A special light mixture of soil with the addition of sand, perlite, peat, expanded clay, clay, wood chips, shale and crushed bark is usually used as a substrate for a roof garden. The thickness of the soil usually varies from 5 to 50 cm, the substrate is distributed over the roof depending on the needs of the plants. It is not recommended to use regular ground for a roof garden.
Only after all eight layers of the base have been laid and prepared, you can proceed directly to planting the plants. Remember that rooftop plants will grow in conditions similar to mountainous and desert conditions – in the wind and sun. Therefore, it is worth choosing only the most unpretentious species. Roof trees are usually planted dwarf, decorative, with not too extensive root system.
A roof garden planted with creeping trees, low shrubs, frost-resistant grass and unpretentious flowers looks beneficial. Such a garden will not need daily care and will calmly survive the winter outdoors..
In general, the technology for creating a garden and lawn on a flat and pitched roof is similar. However, the pitched roof already has a slope for water drainage, so a drainage layer can be dispensed with. There is no need for additional insulation – this layer is usually located under the rafters in the attic. Thus, the technology of creating a lawn on a pitched roof usually consists of laying waterproofing, root protection membrane, geotextile and a layer of soil. However, along the edge of the pitched roof, you will have to additionally create a reliable boundary board that will prevent the soil from slipping. It is also advisable to put a special mesh or lattice on top of the root protective layer, which is usually used to strengthen slopes..
DIY roof garden
As you can see, the creation of a roof garden is a rather complicated and lengthy process that requires certain knowledge, experience and special materials. Immediately, without preparation, it is risky to start intensive gardening of the roof with your own hands. However, you can use one of the following, simpler and more affordable options for arranging a garden or lawn on the roof:
- On a flat roof, you can simply beautifully arrange tubs, flowerpots and pots with plants. Surrounded by such a green area, a cozy corner for relaxation with furniture and barbecue may appear.
- Extensive landscaping is less costly and can even be created on a conventional pitched roof of a garage or summer cottage.
- On a flat roof, you can select a separate corner where the green zone will be located. In this area, a flat recess is constructed from a waterproof frost-resistant film that does not contain substances harmful to plants, the edges of which rise by 5 centimeters. The sides can be secured with boards or stones. A layer of gravel is poured inside the excavation for drainage, and on top is the finished substrate. Everything, the flower garden is ready, it remains only to moisten the earth and plant seeds. True, from such a “flower bed” you will have to regularly pour out excess water (for this you need to lower one of the edges of the side of the film). Of course, you can’t plant trees here, but the grass and unpretentious flowers will take root..
- Ready-made landscaping systems from companies specializing in landscape design. Such a system is a ready-made “cake” with all the necessary layers, which will greatly facilitate the process of arranging the garden. Such systems are now offered by the German companies FlorDepot and ZinCo. With these ready-made systems, lightweight and easy to use, you can equip your roof lawn in just one day.
If your dream is a full-fledged roof garden, most likely you will have to turn to specialists. Remember that not only landscape designers, but also builders will take part in the greening of the roof. It is more expedient to contact a landscape design studio that works directly with a construction company. It is the builders who will carry out all the preliminary work on laying the waterproofing and setting up a reliable foundation for the roof garden..
The cost of specialist services depends on many factors and in the overwhelming majority of cases is calculated individually for each customer..
Despite all the difficulties, costs and the need for follow-up maintenance, the idea of a roof garden looks very attractive. And this is not surprising, because even city dwellers for several generations have this desire – to spend as much time in nature as possible and create their own paradise in the city center, even if there is clearly not enough land for this..