GREEN ROOFS

The field of green structure incorporates green roofs and facade greening. Their historical predecessors are Scandinavia’s earth and turf lawns, and the green roofs of the Middle East, such as the Hanging Gardens of Ba- bylon. Green roofs have become more widespread with the development of roof seals and root barriers and the emergence of the ecology movement that followed the 1960s. > Fig. 3.14.1

Green roofs compensate for interventions in the land- scape and provide plants and animals with new habi- tats in an urban environment. They are an important aspect of sustainable building planning. Compared with conventional roof constructions, they improve roof pro- tection and building insulation. > Fig. 3.14.2

Developing areas above other structures, such as ter- races, inner courtyards and roofs, creates usable open space. The retentive properties of green roofs also allow water to be better managed. Rainwater runoff is slowed down and reduced, leveling out spikes in precipitation

and taking the pressure off channeling systems. 40–60% annual mean water retention is created by extensive green roofs, 60–90% for intensive green roofs. Conse- quently the microclimate also improves, as the increase in water vapor balances extremes of temperature and the vegetative surface filters fine dust and heavy met- als out of the air.

FORMS OF GREEN ROOF

Technical requirements (roof incline, roof load), climatic conditions in context (amount of precipitation, exposure, wind direction, etc.) as well as intended function and desired appearance determine the type of green roof. A distinction is made between extensive green roofs, sim- ple intensive green roofs, intensive green roofs and hard surfaces. > Figs. 3.14.3–3.14.5

An extensive green roof is indicated when a roof will only tolerate minimal superstructure and loads, and the roof is not intended to be walked on. Creating and

Fig. 3.14.1: Extensive sloping green roof: in the tradition of grass roofs

Fig. 3.14.3: Extensive greening with minimal structure (“light roof”)

Fig. 3.14.2: Construction intervention in a sensitive landscape compensated for by green roofs

Fig. 3.14.4: Small-scale simple intensive greening of a carport with water surfaces

Fig. 3.14.5: Intensive roof greening in an inner courtyard

2 3 4 5 6 1

1 2 3 4 5 6

1 2 3 4 5 6 7

STRUCTURAL ELEMENTS AND BUILDING METHODS

GREEN ROOFS

458

maintaining these is comparatively inexpensive. Except during the growing phase, maintenance is extensive. The superstructure layers are 5 to approximately 15 cm thick. An extensive green roof imposes functional loads

on the roof construction of from 60 kg/m2 _{to approxi-}

mately 240 kg/m2_{. Due to the minimal structure and the}

extensive maintenance, only very robust and drought- resistant plants are used. Shrubs, grasses, lichens and mosses or, more rarely, ground-covering woody plants are used. Many of these plants originate in high alpine locations. > Figs. 3.14.6 and 3.14.7

Simple intensive green roofs are the intermediate form of extensive and intensive green roofs. They can be used where a high roof load is possible (180–300 kg/

m2_{) and a varied range of plants is desired. As well}

as plants used in the extensive green roof, low woody plants and more demanding shrubs can be used. Sim- ple intensive green roofs involve superstructures of about 15–25 cm. When designing a simple intensive green roof, its more labor-intensive care, especially with regard to watering and fertilizing, must be taken into account. > Fig. 3.14.8

With an intensive green roof, there are practically no limits as regards functionality or use of plants. A load- bearing roof is required, with a capacity of over 300 kg/

m2_{. Depending on construction, this can be increased to}

1500 kg/m2_{. As well as the plants already mentioned,}

bushes, small trees and lawn areas can be included. Adequate watering, usually involving water accumu- lation or irrigation systems, is invariably necessary. Height of superstructures varies from about 25 cm to 150 cm in some cases. > Fig. 3.14.9 For lawns “a layer thickness of 15–20 cm is adequate in exceptional cas- es, if one is prepared to put up with a higher degree of maintenance” (Kolb and Schwarz 1999, p. 52).

Hard surfaces and terraces are often created in combi- nation with intensive green roofs. Fig. 3.14.10. Roof load permitting, asphalt, paved or tiled paths, wooden deck- ing or enclosing walls are possible. These surfaces and components usually have the same substructure as the intensive green roof.

Fig. 3.14.6: Standard extensive green roof structure

Fig. 3.14.7: Extensive green roof containing many species in an ecological housing development

Fig. 3.14.8: Standard simple intensive green roof structure

Fig. 3.14.9: Standard intensive green roof structure Fig. 3.14.10: A variety of green roof types on different levels of a building 1 planting 2 approx. 7 cm extensive single-course substrate 3 filter course/mat 4 2.5 cm solid drainage 5 protective course 6 superstructure (warm roof): roof seal (root-proof) thermal insulation vapor seal reinforced concrete 1 planting 2 approx. 20 cm extensive single-course substrate 3 filter course/mat 4 approx. 2.5 cm drainage course 5 protective course 6 superstructure (warm roof):

roof seal (root-proof) thermal insulation vapor seal reinforced concrete 1 planting 2 approx. 25 cm extensive single-course substratet 3 approx. 30 cm mineral subsoil substrate 4 filter course/mat 5 approx. 15 cm drainage course 6 protective course 7 superstructure (warm roof):

roof seal (root-proof) thermal insulation vapor seal reinforced concrete

1 2 3 4 5

1 2 3 4 5

1 2 3 4 5 6 7

1 2 3 4 5 6

1 2 3 4

STRUCTURAL ELEMENTS AND BUILDING METHODS

GREEN ROOFS 459

CONSTRUCTION REQUIREMENTS AND CONSTRUCTIVE ELEMENTS Roof types and loadbearing capacity

When planning a green roof, the first thing to do is to check the construction and loadbearing capacity of the roof. For new structures, the intended form of green roof should be determined at an early stage, so that the roof can be designed accordingly. It should be ensured that the required roof seals are designed to be impenetrable to roots.

For a warm roof, the roof seal is above the thermal insula- tion, which in turn lies atop the loadbearing construction. This form of roof is widespread and is generally suitable for green roofs without special requirements. The ther- mal insulation must be able to tolerate the pressure. A vapor barrier should be installed above the roof skin, cov- ering the above-ground construction, as otherwise con- densation water may get into the building. > Fig. 3.14.11 A single-shell roof with no thermal insulation is different from a warm roof in that insulation and vapor barrier are absent. This roof form is used, for instance, in under- ground garages and unheated outbuildings. Given suffi- cient loadbearing capacity, this creates no problems for a green roof. As the roof may freeze through, cold-sensi- tive plants should not be included. > Fig. 3.14.12 For a cold roof (also known as a multishell roof), con- densation is prevented from forming during roof con- struction by ventilation slits above the insulation. As an additional layer beneath the roof seal, usually a light wood construction, is involved, this often means that only an extensive green roof is possible. > Fig. 3.14.13 The inverted roof is a special case. Here, thermal insula- tion is above the roof seal. This means that the water- carrying layer is beneath the insulation, which in turn means that all materials used for the green roof must allow diffusion. If this is borne in mind, all forms of green roof are possible. > Fig. 3.14.14

With watertight concrete roofs, as with inverted roofs, the insulation is on top of the roof skin, or is absent. Water- tight concrete gives the optimum protection from conden- sation and root damage. This makes whole-surface roof seals, vapor barriers and root barriers unnecessary. The watertight cement roof is generally suitable for all forms of green roof. Any openings and joints in the roof should be protected by a locally applied rootproof seal. > Fig. 3.14.15

1 roof planting structure (extensive): planting vegetation support course filter course/mat drainage course protective course superstructure: 2 roof sealing (root-proof) 3 thermal insulation 4 vapor seal

5 reinforced concrete roof

Fig. 3.14.11: Standard warm roof construction

1 roof planting structure (extensive): planting vegetation support course filter course/mat drainage course protective course superstructure: 2 roof sealing (root-proof) 3 thermal insulation 4 vapor seal

5 trapezoidal sheet metal 6 steel section Fig. 3.14.12: Standard warm roof construction (light shell)

1 roof planting structure (extensive): planting vegetation support

course (e.g. light substrate) filter course/mat drainage course protective course superstructure: 2 roof sealing (root-proof) 3 timber substructure 4 thermal insulation 5 vapor seal 6 beam course 7 reinforced concrete roof

Fig. 3.14.13: Standard cold roof construction

1 roof planting structure (extensive): planting vegetation support course filter course/mat drainage course trickle protection/ separation fleece structure open to diffusion superstructure: 2 thermal insulation 3 protective course 4 roof sealing (root-proof) 5 reinforced concrete roof

Fig. 3.14.14: Standard inverted roof construction

1 roof planting structure (extensive): planting vegetation

support course, filter course/mat drainage course, trickle protec- tion/separation fleece structure open to diffu- sion

superstructure: 2 thermal insulation 3 roof sealing (root- proof—only in areas with penetration) 4 waterproof concrete

(“White Tub”)

2 3 4 5 1

2 3 4 5 6 7 1

STRUCTURAL ELEMENTS AND BUILDING METHODS

GREEN ROOFS

460

Roof incline and pitch

Roof incline is an important technical consideration in choosing a green roof. Roofs with 0–2% roof incline are particularly suited to intensive green roofs with water- accumulation irrigation. Tolerances in building construc- tion do not preclude puddles forming at the drainage layer. For this reason, the roof seal should be laid to measure especially and a drainage level should always be provided (the same applies to extensive green roofs!). Roofs with 2–5% incline are generally optimal for green roofs and are also favorable for water retention. Where water accumulation irrigation is in place, water accu- mulation thresholds may have to be provided. The roof pitch means that excess water quickly flows out of the drainage system. Where construction tolerances permit a siphon effect or insufficient downward water move- ment, these must be eliminated.

Depending on steepness, measures relating to water retention and delivery as well as slippage prevention should be put in place for sloping roofs with a 5–58% incline. These begin with shear barriers at drainage lev- el and extend to the upper vegetation layer, with ero- sion resistant weaves or similar measures. For more demanding vegetation types and intensive utilization, rooftop irrigation should be put in place. In principle, a variety of green roof forms are possible given careful planning. > Figs. 3.14.17–3.14.21

Watering and drainage systems

The number and placement of drainage installations such as roof drains, roof guttering, water spouts, and emergency overflows is a function of the structure’s pitch and the green roof’s construction. Roof drains on the roof skin should be designed to be visible via

a b

Fig. 3.14.16: Flat roof renovation: a) condition before renovation, b) following green roof

implementation

roof planting structure (extensive): 1 vegetation mat 2 approx. 8 cm extensive substrate 3 anti-slippage system 4 drainage mat 5 superstructure (warm roof): roof seal (root-proof) thermal insulation vapor seal reinforced concrete

roof planting structure (intensive): 1 pre-cultivated turf 2 rooting fabric 3 approx. 17 cm lawn substrate 4 anti-slippage system 5 protection for structure

and drainage mat 6 separation and sliding

membrane 7 superstructure (water-

proof concrete roof): bituminous adhesive seal waterproof concrete Fig. 3.14.18: Standard extensive sloping roof construction Fig. 3.14.19: Standard sloping roof lawn construction

Fig. 3.14.20: Intensive sloping green roof with turf and integrated

guttering Fig. 3.14.21: Installing a claw mat to prevent slippage Fig. 3.14.17: Sloping green roof

4 5 1 2 3 6 7 8 4 5 1 2 3 6 7 8 9

STRUCTURAL ELEMENTS AND BUILDING METHODS

GREEN ROOFS 461

Fig. 3.14.22: water draining from a sloping roof into an outer gutter:

a) construction phase with shear barriers,

b) finished green roof

Fig. 3.14.23: Water channel molding Fig. 3.14.24: Drainage and inspection shaft

Fig. 3.14.25: Water accumulation on roof with 0% incline Fig. 3.14.26: Water accumulation with above-ground drip lip 1 slab surface structure:

concrete slab (60 x 30 x 3.5 cm) natural stone chippings solid drainage drainage gutter building protection mat 2 plant bed framed with

steel wall, waterproof screw attachment to mortar strip foundation 3 intensive planting by accumulated water filter mat (plastic fiber) drainage course solid drainage

1 pavement laid in area without water accumulation: approx. 3 cm chippings 2/5 crushed stone 2/32 building protection and drai-

nage mat (car type) 2 superstructure (waterproof

concrete):

roof seal (root-proof), screed (outside water accumulation), reinforced concrete 3 steel band in point foundation

(C12/15)

4 fiber concrete angle (15/15) on mortar bed (C12/15), root protection strip glued to angle 5 intensive planting in water building protection mat

4 inspection shaft (30/30) with accumulated water 5 superstructure (water-

proof concrete): roof seal (root-proof) reinforced concrete 6 area without water accu-

mulation

7 area with water accumu- lation

8 top edge of accumulated water 5 cm under bottom edge of intensive sub- strate

accumulation area: plant bed approx. 37–41 cm,

intensive substrate, filter mat (plastic fiber), approx. 15 cm drainage course, buil- ding protection mat/protec- tion mat

6 superstructure (waterproof concrete):

roof seal (root-proof), rein- forced concrete

7 area without water accumu- lation

8 area with water accumula- tion

9 top edge of accumulated water 5 cm under bottom a b

2 3 4 1 15,0 cm 30,0 cm 2 3 4 1 ≥ 15, 0 cm OKFF +0.00 OKFF -0.03

STRUCTURAL ELEMENTS AND BUILDING METHODS

GREEN ROOFS

462

inspection shafts in the surface. Gravel traps or similar measures should be used to ensure that the roof drains do not become clogged. For sloping roofs, both inner and outer gutters are possibilities. In case of curves in the pitch of the roof, special drainage layers should be provided. > Figs. 3.14.22–3.14.26

Irrigation systems must also be suitable for the type of green roof and for the structure. Accumulation barriers are used, some already integrated into the structure of the roof construction, but installations for automatic water accumulation, recessed sprinklers, or drip ir- rigation can also be added. Ducts should be provided within the roof and inside the building for water de- livery and control leads. For extensive green roofs, at least one water outlet is required for manual watering. > Figs. 3.14.27 and 3.14.28

Edge formation, fire prevention and wind action

In edge formation for green roofs, a distinction must be made between junctions and terminations. Junctions are found around rising components and those that penetrate the roof, e.g. chimneys. Roof seals and root barriers of at least 10 cm—or, for roofs with less of an incline, as much as 15 cm—above the upper edge of the top layer or the green roof should be introduced in these areas. In order to avoid excessive swelling caused by water release, the water-carrying layer can be low- ered by means of gratings. > Fig. 3.14.29

The terminations are at the lateral roof edges (at- tic story). Roof seals and root barriers—5 or 10 cm above the water-carrying layer, depending on the roof’s incline—should be introduced in these areas,

Fig. 3.14.27: Irrigation machine in shaft Fig. 3.14.28: Inspection shaft for a simple water accumulation irrigation device

Fig. 3.14.29: Junction with terrace door with low threshold Fig. 3.14.30: Junction with attic 1 interior with threshold

2 steel gutter with gravel trap and packing: water-bearing course

15 cm lower

3 superstructure (warm roof) roof seal (root-proof) slanting thermal insulation (foam glass sheets) vapor barrier

1 extensive planting in attic area: planting approx. 7 cm extensive single-course substrate filter course/mat 2.5.cm solid drainage protective course 2 edging strip on attic floor: gravel strip (80 x 5) 4 natural stone slab surface

crushed sand 0/5 crushed stone 2/32 drainage mat protective course gravel 8/32 protective layer 3 superstructure (warm roof): roof seal (root-proof) thermal insulation vapor barrier reinforced concrete 4 sheet metal covered

attic storey with seal to a height of 15 cm

2 3 6 1 4 5 7 10 cm 50 cm < 80 cm 15 cm 30 cm 100 cm

STRUCTURAL ELEMENTS AND BUILDING METHODS

GREEN ROOFS 463

and vegetation-free strips—generally 30 cm wide— should be included. > Fig. 3.14.30

Intensive green roofs are considered hard roofing due to their irrigation, and therefore require no special fire precautions. Extensive green roofs have shorter mainte- nance intervals and more minimal construction. They are therefore at greater risk from airborne burning matter. For this reason, the junctions must be provided with veg- etation-free protective strips of gravel or tiles 50–100 cm wide. > Fig. 3.14.31

For loosely laid roof layers, particularly in inverted roofs, precautions should be taken to ensure that the whole roof construction is safe from wind drag. Roofs above 20 m eaves height as well as the corners and edges of the green roof should be protected against wind drift by laying vegetation-free strips (e.g. heavy tiles), or by us- ing filled-in lawn paving or vegetation mats. In exposed areas, the need to increase the weight of superstruc- tures (as protection against wind load) may have to be balanced with the static roof load that can be tolerated. > Figs. 3.14.32–3.14.34

Fig. 3.14.31: Edge strip of gravel and kick plates bordering a rising structural component

Fig. 3.14.33: Attic story edging strip with lawn paving on gravel to resist wind drag

Fig. 3.14.32: Damage caused by wind drag

Fig. 3.14.34: Extensive green roof: fire prevention, wind drag protection, junctions with attics and rising components

1 superstructure: sheet metal covered attic

storey with seal to a height of 30 cm

2 edging strip on attic storey: gravel (8/32)

filter course/mat drainage element (unfilled) protective course 3 edging strip to resist wind

suction

erosion protection fabric lawn grid 40 x 60 x 11 4 extensive roof planting: planting with shallow balls approx. 10 cm extensive

substrate filter course/mat

Fig. 3.14.35: Rope anchor safety system anchored to solid drainage

system Fig. 3.14.36: Personnel protection involving rope anchorage systems drainage element (unfilled) protective course 5 fire protection strip (where

fire cells necessary) 6 edging strip on facade (W = 50 cm) gravel 8/32 gravel strip filter course/mat drainage element (unfilled) protective course 7 facade with seal 15 cm

high and parapet/window ( 80 cm)

STRUCTURAL ELEMENTS AND BUILDING METHODS

GREEN ROOFS

464

Fall protection should be provided for all green roofs. This may comprise either secure rails or special sys- tems of holds for maintenance work, such as rope sock- ets and rope anchors. > Figs. 3.14.35 and 3.14.36

DESIGNS AND LAYERS IN GREEN ROOFS

A fundamental distinction is made between single-lay- er and multilayer designs. One-layer designs consist of a vegetation base layer, which performs both drainage and filtration functions, and sometimes supplementary protective and filtering fleeces.

Depending on the construction chosen, the following ele- ments are found in a multilayered construction method: Protective plies protect the roof seal from mechani- cal damage, especially during the construction phase.

These are usually made of plastic or screed. If the roof seal is not rootproof, root barrier sheets are also in- cluded in the protective plies. > Figs. 3.14.37

The function of the drainage layer is to conduct precip- itation water away evenly so that no waterlogging oc- curs. The aim is controlled storage of water for use while expanding the area for roots. The drainage layer may be formed of natural mineral substances such as sands, gravels or lava, or synthetic mineral substances such as expanded clay, expanded slate, or recycled substances. Drainage layers made from artificial substances, such as hard plastic tiles or foam drainage tiles are also in common use. It is possible to combine these materi- als—for instance, by filling in plastic storage elements with mineral bulk materials. > Figs. 3.14.38 and 3.14.41

Fig. 3.14.37: Protection and storage fleece Fig. 3.14.38: Drainage mats for use on inclined roofs

Fig. 3.14.39: Solid drainage system for extensive green roof, 2.5 cm

thick with protective and filtration fleeces Fig. 3.14.40: Solid drainage system for transport routes (1.2 cm) with mounted filtration fleece

Fig. 3.14.41: Expanded slate 8/16 for drainage layers Fig. 3.14.42: Predominantly mineral substrate for one-layer extensive green roof

4 5 1 2 3 2 3 4 1 15.0 cm OKFF -0.03 OKFF +0.00 4 1 2 3

STRUCTURAL ELEMENTS AND BUILDING METHODS

GREEN ROOFS 465

In multi-layer superstructures, the filtration layer filters out sediments, e.g. humus substances, in order to safe- guard drainage layer function in the long term. Geotex- tiles are commonly used. > Figs. 3.14.41 and 3.14.42 The vegetation base layer is where the plants are actu- ally located. It must be structurally stable—i.e. it must not be allowed to sag. Its plant substrate therefore

In document Landscape Constructing (Page 37-46)