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World Green Roof Congress, 15-16 September 2010, London
Page 1
Construction of a retrofit green roof
system: a case study in Istanbul, Turkey
M. Cem Altun, Istanbul Technical University, Architecture Faculty, Istanbul, Turkey, (mcemaltun@gmail.com)
Caner Gocer, Istanbul Technical University, Architecture Faculty, Istanbul, Turkey, (gocercan@itu.edu.tr)
Nil Turkeri, Istanbul Technical University, Architecture Faculty, Istanbul, Turkey, (sahal@itu.edu.tr)
Abstract
Benefits of green roofs are known by designers and the construction industry in
Turkey, but their application is limited to a few examples. Consequently
experienced labour force, locally manufactured materials, relevant tools and
cost data in public sector price guides are not available, which can also be
highlighted as reasons for the limited application. A research project is set at
Istanbul Technical University, which aims to develop hygrothermal-effective,
structural-effective, hydrological-effective, construction-effective extensive type
green roof systems for Istanbul, considering local conditions. A sub module of
the project is to retrofit a portion of a low-slope existing roof system as an
extensive green roof system and to monitor the thermal performance. The
construction process of the retrofit green roof system is analysed. For the
analysis, each construction phase is observed in the context of the construction
inputs, namely; materials, tools, labour force and construction time. As results,
availability of materials, type of tools used, skill and education level of labour
force is discussed in the context of construction quality of the retrofit green roof
system.
Keywords: retrofit, green roof, construction phases, construction analysis
Construction of Green Roofs in Turkey
A green roof is a synthesis of a “natural” part with an artificial “man-made” part in generating a
building element. Those two different “parts” have not only to fulfill a large number of
requirements by their own but they have also to be harmonized so that they can work together
as a whole. Consequently, both the design and the construction phases are of high complexity
in achieving a certain level of “quality” avoiding failures of the roof systems or the whole
building. Quality in construction can be described as the totality of a building’s attributes that
enable it to perform a stated task or to fulfill a given need satisfactorily for an acceptable period
of time (Atkinson, 1995). Quality of a building system or a building subsystem is mainly
dependant on the characteristics of the design process, the construction process, the “in use”
phase and the properties of products used in construction. When focused on the construction
process, quality derives from; ı. reliability of organization, skills of builder to interpret the
design, organizing required resources and provide the end product in accordance with design
and at contracted price, ıı. skilled labour force and ııı. products of specified quality (Atkinson,
1995).
World Green Roof Congress, 17-18 September,
London Page 2
Environmental, economical, social advantages of green roof systems are given in detail in
relevant literature (Weiler&Scholz-Barth, 2009; Dunnett&Kingsbury, 2008; Earth Pledge, 2005;
Osmundson, 1999). Although those benefits of green roofs are known by designers and the
construction industry in Turkey, their application is limited to a few examples. Nearly 100
million m2 of roof coverings are applied in Turkey every year and mostly clay tile is preferred
followed by shingle and bituminous waterproofing membranes (Ozturk, 2008). There is also a
large building stock which needs to be retrofitted energy efficiently. As green roof systems have
limited application in Turkey, experienced labour force, locally manufactured materials and
relevant tools, for some components specific to green roofs, are missing. Drainage boards, filter
sheets and moisture retention mats can be cited as examples of green roof specific
components. Consequently also cost data in public sector price guides like the construction
cost analysis and unit cost list of the Ministry of Public Works for cost estimating related to the
given green roof specific components is not available. Conversely those aspects can also be
highlighted as reasons for the limited application.
A research project is set at Istanbul Technical University, which aims to develop hygrothermal-
effective, structural-effective, hydrological-effective, construction-effective extensive type green
roof systems for Istanbul, considering local conditions. One of the sub modules of the project
is to retrofit a portion of a low-slope existing roof system as an extensive green roof system
and to monitor the thermal performance of both the existing and retrofit green roof systems
for a comparative assessment (Türkeri, et al., 2010). The aim of this paper is to analysis the
construction process of the retrofit green roof system in terms of labour, materials and tools
and to evaluate its effectiveness.
Approach for Analysis of the Retrofit Green Roof System
Construction Phases
The construction process of the retrofit green roof system to be used for monitoring is
analysed. This is also a “pilot study” for the research project’s sub module “development of
construction-effective systems”. Photographs are taken in certain intervals of each distinctive
construction phase to determine the construction sequence. For the analysis, each construction
phase is observed in the context of the construction inputs, namely; materials, tools and labour
force. Materials are analysed with the criteria of local availability and their application technique
proposed for best practice by relevant literature, guidelines and manufacturer’s instructions
(FLL, 2008; Simmons, 2001). Tools are analysed with the criteria of power source, easiness in
use and availability. Labour force is analysed with criteria of experience and education level. The
duration of each construction phase is measured in determining the total construction time and
to calculate the construction time per unit (Ashworth, 2004).
Analysis of the Retrofit Green Roof System Construction Phases
A low-slope roof of a low-rise office building located in the Maslak Campus of the Istanbul
Technical University in Istanbul was retrofitted as an extensive green roof system. The
retrofitted part comprises 55m2 of the existing roof system, which has a total area of 740m2
and is located 7.68m above ground level (Figure 1). Components of the retrofit green roof
system and existing roof system are provided in Figure 2.
World Green Roof Congress, 15-16 September 2010, London
Page 3
Figure 1. Plan of the existing roof with the retrofitted green roof portion (hatched area).
Figure 2. Components of the green roof system (left hand side of the parapet wall) and the
existing roof (right hand side of the parapet wall)
World Green Roof Congress, 17-18 September,
London Page 4
Below, construction phases of the retrofitting - starting with the demolition of existing layers
and ending with planting - are described briefly together with techniques used for application.
Information on materials, tools, labour force, construction time, for each construction phase
are given in Table 1.
Demolition of existing layers (Figure 3a):
The existing layers of waterproofing, thermal insulation and sloped screed were demolished. All
rubble was packed into rubble sacks and removed from the roof.
Application of sloped screed (Figure 3b):
The mortar for the screed was prepared and pumped up to the roof with a mixer and
pneumatic conveyor machine located in front of the building. The mortar for the screed was
evenly laid onto the existing r.c. slab. The screed was approximately sloped 1.5 % to the drain.
At the edges, the screed was applied to the parapet wall with an angle of 45˚.
Application of primer (Figure 3c):
A bitumen based primer coating was applied with a brush on the sloped screed surface and the
inner surface of the parapet walls.
Application of vapour barrier (Figure 3d):
As a vapour barrier polymer modified bitumen sheets reinforced with polyester fabric were laid
on the primer coated screed and applied onto the inner surface of the parapet walls. The
bitumen sheets were cut to size where necessary and fit around the roof penetrating steel pipe,
which is bearing the test instruments. The bitumen sheets were 10 cm overlapped and sealed at
joints and fully adhered to the screed.
Application of thermal insulation (Figure 3e):
Three layers of 3 cm thick extruded polystyrene rigid foam boards were installed creating a
thermal insulation layer of 9 cm thickness. The insulation boards were laid with edges tightly
butted and layers were staggered to each other.
Application of waterproofing and rootproofing (Figure 3f, g):
As waterproofing, polymer modified bitumen sheets reinforced with polyester fabric were
installed on the thermal insulation and inner surface and the horizontal surface of the parapet
walls. The bitumen sheets were 10 cm overlapped at joints and sealed with torch-welding. As
rootproofing and the second waterproofing layer a special type of polymer modified bitumen
sheets reinforced with polyester fabric were installed on the waterproofing layer and inner
surface of the parapet walls. The bitumen sheets were 10 cm overlapped and sealed at joints
and and fully adhered to the underlying waterproofing layer with torch-welding. Side and end
laps were staggered. Both the waterproofing and rootproofing sheets were cut to size where
necessary and fit around the roof penetrating steel pipe. Polymer modified bitumen sheets
reinforced with polyester fabric and top face covered with mineral granules were applied on
the horizontal, inner and outer vertical surfaces of the parapet wall. Sheets were 10 cm
overlapped and sealed at joints and fully adhered to the underlying rootproofing layer or
parapet. During the waterproofing works the terpolymer parapet type drain element with
horizontal outlet was installed. Waterproofing sheets were fully adhered to the drain element.
Application of moisture retention and protection layer (Figure 3h):
For moisture retention and protection a polypropylene geotextile fleece backed mat was
installed by loose laying directly onto the waterproofing layer, with 150mm overlaps. At the
World Green Roof Congress, 15-16 September 2010, London
Page 5
edges the moisture retention and protection mats were turned up to the parapet wall by 10cm.
The fabric was cut to size and fit around the roof penetrating steel pipe.
Application of drainage layer (Figure 3i):
For drainage and water storage, a lightweight board manufactured from thermoformed recycled
polyethylene was installed by loose laying directly onto the moisture retention and protection
layer. The boards were butt jointed. The boards were cut to size and fit around the roof
penetrating steel pipe.
Application of filter sheet (Figure 3j):
The polypropylene geotextile filter sheets were installed by loose laying directly onto the
drainage layer, with 150mm overlaps. At the edges filter sheets were turned up to the parapet
wall by 30cm. The fabric was cut to size and fit around the roof penetrating steel pipe.
Application of vegetation layer (Figure 3k):
The 15 cm deep vegetation layer consisting of 1/3 mineral soil, 1/3 peat and 1/3 organic
fertilizers was laid onto the filter sheets and was levelled.
Planting of plants (Figure 3l):
The test roof area is divided into three planting zones. The first zone was planted with
Cerastium Tomentosum, the second zone was planted with Mesembrianthemum Roseum and
Cerastium Tomentosum mixed together and the third zone was planted with
Mesembrianthemum Roseum. Plants were planted in 25cm distance from each other in both
directions. After planting the soil was levelled.
Vertical transportation:
Rubble sacks were pulled downwards from the roof to the ground level with the help of a rope.
The mortar for the screed was pumped up onto the roof with a mixer and pneumatic conveyor
machine located in front of the building. The soil sacks and plant containers were pulled
upwards from the ground level to the roof again with the help of a rope. All other materials
and tools were carried to the roof by construction workers using the stairs and ladder onto
the roof.
The construction was carried out by two small scaled construction firms, between November
and December of the year 2009. The first firm realized the phases starting with the demolition
and ending with the application of the filter sheets. The second firm applied the vegetation layer
and planted the plants. Both construction firms have done “green roof” related work for the
first time.
All construction work was supervised carefully by the construction firms’ representatives and
by the researchers.
World Green Roof Congress, 17-18 September,
London Page 6
Figure 3. Construction phases of the retrofit green roof system. Starting with the demolition of
existing layers (a) and ending with planting (l).
World Green Roof Congress, 15-16 September 2010, London
Page 7
Table 1. Construction phases analysis of the retrofitted green roof system.
Work phase
Materials
Tools
Labour force
Quantity of
work
Construction
time
Time per unit
Demolition
-
1 hammer
drill,
2 pickaxes,
2 shovels,
rubble sacks
1 skilled
construction
worker,
2 unskilled
workers
~55m2
~480min.
8.7min./m2
Application of
sloped screed
Mixture of
180ltr. sand,
50kg cement
and 40ltr.
water
1 mixer and
pneumatic
conveyor
machine,
1 leveling
rod,
1 leveling,
1 rake,
1 trowel,
1 leveling
plank
1 skilled
concrete
finisher (25
years
experience),
2 unskilled
workers,
1 technician
~55m2
~45min.
0.8min./m2
Application of
primer
coating
Bituminous
emulsion
1 brush,
1 bucket
1 unskilled
worker
~70m2
(55m2
horizontal
surface +
15m2
vertical
surface)
~17min.
0.24min./m2
Application of
vapour
barrier
Polymer
modified
bitumen sheets
reinforced
with polyester
fabric
2 fuel tanks
+ torches,
2 gauging
trowels,
1 craft knife
2 skilled
waterproofing
workers
(experience 12-
6 years),
2 unskilled
workers
~70m2
(55m2
horizontal
surface +
15m2
vertical
surface)
~76min.
~1.08min./m2
Application of
thermal
insulation
Extruded
polystyrene
rigid foam
boards
1 craft knife
3 skilled
waterproofing
workers
(experience 12-
6 years)
~55m2
~50min.
~0.91min./m2
Application of
waterproofing
and
rootproofing
Polymer
modified
bitumen sheets
reinforced
with polyester
fabric and
(normal type,
special type,
top face
covered with
mineral
granules type)
2 fuel tanks
+ torches,
2 gauging
trowels,
1 craft knife
3 skilled
waterproofing
workers
(experience 12-
6 years)
~85m2
(55m2
horizontal
surface +
30m2
vertical
surface)
~210min.
~2.47min./m2
World Green Roof Congress, 17-18 September,
London Page 8
Table 1. (continued) Construction phases analysis of the retrofitted green roof system.
Work phase
Materials
Tools
Labour force
Quantity
of work
Construction
time
Time per unit
Application of
moisture
retention and
protection
mat
Polypropylene
geotextile fleece
backed mat
1craft knife,
1 scissor
1 skilled
construction
worker,
2 unskilled
workers
~55m2
~23min.
~0.42min./m2
Application of
drainage
board
Thermoformed
recycled
polyethylene
lightweight board
1 craft knife
1 skilled
construction
worker,
2 unskilled
workers
~55m2
~34min.
~0.62min./m2
Application of
filter sheet
Polypropylene
geotextile
1 craft knife,
1 scissor
1 skilled
construction
worker,
2 unskilled
workers
~55m2
~25min.
~0.45min./m2
Application of
vegetation
layer
Mixture of 1/3
mineral soil, 1/3
peat and 1/3 organic
fertilizers
1
wheelbarrow
3 shovels
1 rake
3 skilled
workers
(experienced
5-15 years)
~55m2 (of
~15cm
thickness)
~360min.
~6.55min./m2
Planting of
plants
Mesembrianthemum
Roseum and
Cerastium
Tomentosum
3 hoes
1 retractable
tape,
1 rake
4 skilled
workers
(experienced
5-15 years)
~880
pieces (on
55m2)
~140min.
~2.55min./m2
Results
Results based on observations and analysis of the construction process of the retrofit green
roof system are listed below:
Analysis of the materials needed for construction revealed that, most of them are locally
manufactured and available. Only drainage boards, filter sheets and moisture retention
mats used in the construction are imported materials. Though geotextiles are locally
manufactured, materials with required properties couldn’t be found easily.
Analysis of the tools used in the construction process revealed that, most of them were
simple hand tools, available in the Turkish construction sector and using man power.
Only the electric driven hammer drill used for demolition and the fuel engine driven
mortar mixer and pneumatic conveyor machine used for the screed are not man
powered. All tools were used easily by the skilled labour force.
Analysis of the labour force in the construction process revealed that, skilled and
experienced construction workers of different trades are available even in small scaled
construction firms. Only one waterproofing worker was certificated through a training
course. All other workers were trained on-the-job. All green roof specific applications,
namely installation of moisture retention mats, drainage boards and filter sheets were
done for the first time by the construction workers. Also vegetation layer application
World Green Roof Congress, 15-16 September 2010, London
Page 9
and planting was done by the workers “on a roof” for the first time. Nevertheless
required quality in terms of workmanship was achieved through proper supervision.
The most time consuming construction phase was the demolition of existing layers,
resulting from the difficult process of packing of rubble into sacks. Application of the
vegetation layer and installation of waterproofing and rootproofing layers were the
other time consuming activities. The green roof specific applications, namely installation
of moisture retention mats, drainage boards and filter sheets were least time consuming
phases. In most of the phases, applications in areas including geometrical anomalies, such
as parapet edges or roof penetrating pipes, was more time consuming than in areas
without anomalies.
Vertical transportation of materials and tools was done by man power without using any
construction machines and turned out to be time consuming. An exception was the
pumping of mortar onto the roof.
The “quality” of the construction in terms of waterproofing performance and thermal
performance was observed and/or monitored. No water leakage of the retrofitted
system is detected or reported for six months since the completion of the construction.
It was also monitored that the retrofitted green roof systems performed thermally
better than the existing roof system. In June 2010, five months after the completion of
the construction the vegetation layer has been removed for replanting. During this
process, layers of moisture retention, drainage and filter were inspected and no
anomalies have been detected.
Conclusions
The construction process of a retrofit green roof system, build in the context of a research
project aiming to develop hygrothermal-effective, structural-effective, hydrological-effective,
construction-effective extensive type green roof systems for Istanbul is observed and analysed.
As green roof systems have limited application in Turkey the analysis focused on construction
inputs, namely; materials, tools, labour force and construction time.
Conclusions obtained from the results of the case study can be listed as the following:
“Green roof” specific materials are available on the local market, though some of them
are imported.
For “green roof” application; only locally available, easy to use and mostly man powered
tools are needed.
With proper supervision the required construction quality is achieved, even with
inexperienced labour force, in “green roof” related applications.
The green roof specific applications, namely installation of moisture retention mats,
drainage boards and filter sheets are least time consuming phases. Application of the
vegetation layer and installation of waterproofing and rootproofing layers are the most
time consuming activities, which should be considered in time scheduling.
The above listed findings should not be generalised, as they are related to a specific case study.
Further research work is ongoing to obtain data which will lead to generalised conclusions.
World Green Roof Congress, 17-18 September,
London Page 10
Acknowledgement
Authors gratefully acknowledge to the Scientific and Technological Research Council of Turkey,
as well as the Istanbul Technical University for funding the research project.
References
Ashworth, A. (2004) Cost Studies of Buildings, Pearson Education Limited, ISBN: 0-13-145322.
Atkinson, G. (1995) Construction Quality and Quality Standards, E&FN Spon, ISBN: 0-419-
18490-2.
Dunnett, N., Kingsbury, N. (2008) Planting Green Roofs and Living Walls, Timber Press Inc.,
ISBN: 9780881929119.
FLL (2008) Richtlinie für die Planung, Ausführung und Pflege von Dachbegrünungen, Bonn: FLL
Forschungsgesellschaft - Landschaftsentwicklung - Landschaftsbau e.V., ISBN: 978-3-
940122-08-7.
Osmundson, T. (1999) Roof Gardens – History, Design and Construction, W.W. Norton &
Company Inc., ISBN:0-393-73012-3.
Oztürk, M. (2008) “Roofing Materials for Sloped Roofs: 2007 Sector’s Quantitative Research”,
Proceedings of the 4th National Symposium on Roof & Facade Finishing Materials and
Technologies, October 2008, Istanbul. (in Turkish)
Simmons, H.L. (2001) Construction - Principles, Materials and Methods, John Wiley & Sons,
ISBN:0-471-35640-9.
Türkeri, N., Altun, M.C. and Göçer, C. (2010) Field monitoring of thermal performance of a
retrofit green roof in Istanbul, Turkey, World Green Roof Conference 2010, London,
UK.
Weiler, S., Scholz-Barth, K. (2009) Green Roof Systems – A Guide to the Planning, Design and
Construction of Landscapes over Structure, John Wiley & Sons., ISBN: 9780471674955.
World Green Roof Congress, 15-16 September 2010, London
Page 11
Authors’ Biographies
M. Cem Altun is Assistant Professor at ITU Faculty of Architecture, where he
received his B.Sc. (1986), M.Sc. (1988) and PhD (1997) degrees. His research
areas are; “detail design”, “building construction techniques” and “building
physics”. He has contributed to a number of research projects and has taken
part in various design team work.
Caner Göçer graduated from ITU Faculty of Architecture in 1993. He received
his M.Sc. in 1997 at ITU Department of Construction and his PhD degree in
2006 in the same department. His research areas are external wall systems,
roof systems and prefabrication systems. Presently, he is working as research
assistant at ITU Faculty of Architecture.
Nil Turkeri is Associate Professor at ITU Faculty of Architecture, where she
received her B.Sc. (1987), M.Sc. (1992) and PhD (2001) degrees. Her research
areas are; “sustainable building element design”, “building construction
techniques” and “building physics”. She has contributed and conducted a
number of research projects.