Designing of a Self-sustained Roof-Top Eco-System

Roof garden not only has a good effect of cooling and heat insulation, but also can beautify the environment, purify the air, improve the local microclimate, but also can enrich the urban pitching landscape, can compensate the buildings occupied the green ground, greatly improve the city’s green coverage rate, is a kind of roof is worth promoting.

The existence of roof garden helps to open up green space for human beings, build garden city, improve people’s living conditions, improve the quality of life, and beautify the urban environment, improve the ecological effect is of great significance.

I. basic types of roof greening:

(1) garden-style roof greening

(2) combined roof greening

(3) lawn roof greening

Different types of roof greening should have different design contents. Roof greening should give play to the ecological benefits of greening and should be guaranteed by appropriate area index.

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Two, roof garden should pay attention to the problem

1. Load reduction:

The roof that USES garden to make a scene should use integral pouring or the reinforced concrete roofing board of precast assemble to make structural layer, have a condition, usable and adiabatic impermeable impermeable material is made “zoologic housetop piece”. In general, 350 kg/m or above is required.

In the specific design, in order to reduce the load, pavilion, gallery, flower bed, pool, rockery and other heavy attractions should be designed in the load-bearing structure or the location of the smaller span, while trying to choose artificial soil, peat soil, humus and other light materials.

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2. Waterproof facilities and drainage system:

After meeting the load bearing requirements, the whole roof should be treated for leakage prevention, and its waterproof layer should be treated with composite waterproof facilities, that is, set up two lines of defense: coated waterproof layer and reinforced fine stone concrete rigid waterproof layer. The waterproof layer of coating film shall be made of non-woven cloth for one cloth, two coats or two coats and six coats. On this basis, the rigid waterproof layer shall be made. The rigid waterproof layer and roof flooding shall be made at one time to ensure its waterproof quality. After the construction of the coating waterproof layer, a waterproof test shall be carried out. The details are explained in detail in the next chapter.

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At the same time, in the implementation of roof garden construction, no matter what kind of facilities must not open or damage the roof waterproof layer or protective layer. It is to install perfect drainage system next, besides excessive water hole, gutter outside, still should install outlet, drainage conduit to wait, do regular cleanness, scanty Amoy job well.

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3. Path construction:

General path is wide 50 to 70 centimeters, the roadbed of the path can be built by laying bricks or stones of 6 centimeters wide, every 1.5 meters or so by laying bricks or stones leaves stick stick ground dark hole channel drainage, dark hole is wide about 7 to 8 centimeters. Use cement mortar to serve as roadbed, on roadbed shop sticks cobble, make the path shows primitive simplicity flavour.

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In addition, downspout of face of some housetop, drainpipe and garden atmosphere are extremely inharmonious, can use rockery stone to wrap its to hide, also can use sculpture gimmick to wrap it concealed model trunk to wait.

4. Management of roof garden greening

Roof garden greening blocks the connection between plants and the earth, and the roof climate environment is much worse than the ground, which is not conducive to plant growth. Poor management will result in poor plant growth, which will seriously affect the effect of roof greening, and even cause the failure of roof garden greening. Must do a good job regularly clean, dredge the job, assure moisture supply is the need of plant survival and growth.

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Should set conduit on afforest housetop, should set inside 100m2 commonly one, had better use sprinkler irrigation or drip irrigation form to complement soil moisture, grow for the plant and evaporate, set all sorts of sprinkler head to undertake adjusting, make sure moisture is sprayed the area that has plant to grow. Proper fertilization to supplement soil nutrients, loose soil, density regulation, support, pruning, shade, pest control, traction, insulation and other daily management measures are still indispensable.

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Iii. Requirements for roof greening buildings:

(1) roof load:

The roof greening design must take the load of greening into full consideration. 4.50kn /m2 of roof load for garden and combined roof greening roof design (service roof garden 6.0kn /m2); The roof load of the lawn roof greening roof design should be 2.5KN/m2. The roof greening design shall be reinspected by the relevant units with the qualification of roof load checking, and the certification shall be issued.

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(2) roof slope:

Flat roof and roof slope less than 15 degrees of slope roof, appropriate to do roof greening. Flat roof is suitable for garden type, combination type or lawn type roof greening, slope roof is suitable for lawn type roof greening.

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(3) building height:

The roof of a building below 6 floors and 18m in height.

(4) waterproof:

Roof greening roof must meet the “roof engineering technical specifications” gb50345-2004 building level 2 waterproof standards, important buildings must meet the level 1 waterproof standards.

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(5) drainage:

Roof greening roof should be designed reasonable drainage system, ensure the drainage within 1 hour after the storm, there should be filter structure in the drainage outlet.

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4. Roof greening design

China’s climate is very different, the roof garden structure is also different, so there are three special cases, the roof structure is different.

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1) in areas with little rainfall, the planting soil should be 30cm thick, which can be regarded as an insulation layer, so the roof structure does not need to add an additional insulation layer, nor does it need to add a drainage layer.

2) in warm and rainy areas, drainage layer should be set under the planting soil, and insulation layer should be set under the waterproof layer. In cold and rainy areas, a drainage layer is set under the planting soil, and an insulation layer should be set under the waterproof layer. The slope roof with a slope of more than 20% can be made into terrace type, and the slope can be found by using drainage layer and overburden soil layer.

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3) planting structure on the roof of the basement: this kind of planting roof is different from that of the building roof. The covering soil is generally thicker, usually more than 50cm. If trees are planted, cover at least 1m. Because the covering soil is very thick, regardless of the size of water content in the soil has the function of heat preservation, so there is no need to set up another insulation layer. The planting soil is connected with the earth soil. The rainwater infiltrates into the soil and can be dispersed evenly. Therefore, no drainage layer is needed.

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Structure of roof garden

In order to ensure that the plants on the planting roof can be cultivated and grown, it needs to be waterproof and eliminate water, so as not to leak or leak, so as to meet the use function of the building. If once occurrence leakage phenomenon, whole roofing must turn over work to do afresh, accordingly, waterproof problem is the most important problem after solving good load problem. Deng tianning, director of the waterproof professional committee of the national building association, believes that the waterproof of the roof garden should be one level higher than that of the general residence, that is, at least two levels of waterproof, two layers of flexible waterproof layer. Ye linbiao of Beijing institute of architectural engineering divided the structure layers of planting roof into seven layers: planting medium, isolation filter layer, drainage layer, puncture-resistant root waterproof layer, rolled material or coated waterproof layer, leveling layer and slope finding layer. The planting medium is the soil layer on which the roof plants grow. It is required that the selected planting medium should have the properties of light weight, no hardening, water and fertilizer retention, suitable for plant cultivation and growth, simple construction and economic and environmental protection.

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1) planting soil layer: generally, the soil that can be cultivated in the field is used as the base soil, and then mixed with loose materials to form the planting soil.

2) filter layer: the isolation layer can be made of non-woven cloth, glass cloth, or plastic cloth, in order to avoid adhesion of permeable lap joint.

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3) discharge (storage) layer:

The drainage (storage) layer should be designed according to the situation of roof drainage ditch and the requirements of plants on the soil. The water loss rate of the planting soil layer is too fast, and plants are prone to dry up, and the excessive water content of the planting soil layer will cause the root rot and affect the growth.

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Therefore, in the past, the drainage layer was set as 125px thick river pebbles, and a filter layer was laid on the pebbles, followed by 3-125px thick bentonite, so as to achieve the purpose of storage and drainage.

Also can use special, stay the plastic catchment board that has enough space and certain bearing capacity, rubber catchment board or grain diameter is 20 millimeter ~ 40 millimeter, ply the cobblestone composition of 80 millimeter above. The waterproof layer of resistant root piercing is used to partition the root system so as not to destroy the waterproof layer. Aluminum alloy roll, high-density polyethylene (hdpe), low-density polyethylene (ldpe) geo film and polyvinyl chloride (PVC) are usually used as the waterproof layer of resistant root piercing.

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The material also available in hot summer and cold winter areas is ecological bag: a kind of non-woven geotextile, which is a high-strength, flat and stable material made of polypropylene man-made fiber material needled into a web. The specially prepared polypropylene is resistant to ultraviolet light and is not affected by chemicals in the soil.

4) moisturizing layer: provides water needed during drought.

5) isolation filter layer:

The isolation filter layer is between the planting medium and the drainage layer, using non-woven cloth or glass fiber felt, which can permeate water and prevent soil loss. The lower part of the isolation filter layer is the drainage layer.

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The isolation filter layer is generally made of polyester fiber non-woven cloth and other materials that can be both permeable and filtered. Above the discharge (storage) water layer under the substrate layer, the effective width of the joints should reach 10-20cm and extend to the side wall of the building to 5cm below the surface layer of the substrate.

6) waterproof layer:

Waterproof layer to two fortification. If use synthetic high polymer roll material and coating, can choose to go up for 1. 5mm thick p-type wide-width polyvinyl chloride rolling material or 1mm thick high-density polyethylene, 2mm thick polyurethane or silicone rubber coating film; High density polyethylene (hdpe) film and silicone rubber or polyurethane film are also available. If asphalt base rolling material is used, it can be laminated with SBS and APP modified asphalt rolling material with polyester tire. The thickness is more than 5mm. It can be bonded with full adhesion method, and the covering material is metal foil.

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7) vegetation layer:

The green roof is suitable for flat roof with slope less than 3%, and the waterproof grade is 1-2, and the durability is more than 25 years.

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Tree planting should be in the bearing beam and column top position. The planting position of trees should be more than 2.5m away from parapet.

Section diagram of the structure layer in the roof greening planting area

Schematic diagram of microtopography treatment method for roof greening plant planting

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Schematic diagram of roof greening plant planting pond treatment method

8) original construction item:

Mortar screed: cement mortar screed is directly applied on the roof board without slope finding.

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Structure layer: the roof board of planting roof is preferably cast-in-place reinforced concrete board, and the roof covering soil, plants and rain, snow and water load should be fully considered.

Six, our country roof greening present situation

It is understood that in Beijing, Shanghai, guangzhou, shenzhen, hangzhou, ningbo, wenzhou and other cities, have put the roof greening on the city construction schedule, and put into action.

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However, it is undeniable that roof greening in hot summer and cold winter areas in China is not satisfactory and has not fully played its beneficial role in living space.

Due to the rapid development of the real estate industry, China’s buildings are getting higher and higher, building spacing is getting more and more intensive, resulting in more and more limited green back. Building garden city, forest city, ecological city, roof greening is a new space and a new direction. Roof greening is an important measure to improve urban livable, beautify the environment, cope with urban climate change, promote urban energy saving and emission reduction and ecological protection. Therefore, it should be vigorously promoted and implemented.

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