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Surface temperature of bitumen sheets in the
flat roof structure
Jan Plachý1,*, and Jana Vysoká1
1The Institute of Technology and Business in České Budějovice, Okružní 10, 37001 České
Budějovice
Abstract. This paper deals with the surface temperature problem of flat
roofs, where bitumen sheets are used as the final waterproofing layer.
Currently it is possible to find defects due to the high surface temperature
of the waterproofing layer on flat roofs. The result of such a high surface
temperature is, for example, the release of bitumen sheets and the
sublimation of the thermal insulation from foamed polystyrene. The paper
focuses on the influence of the type, the color of the sprinkling and the
type of background on the surface temperature. The aim of this paper is to
determine the surface temperature of bitumen sheets based on the
experimental measurement depending on the type and the colour of the
surface. Measurements were made during warm summer days. Samples of
bitumen sheets with green, grey, blue-grey, red, white and black-grey
sprinkling were used. Concrete and foamed polystyrene were used as a
background under bitumen sheets.
1 Introduction
This paper focuses on the surface temperature of waterproofing of bitumen sheets in flat
roof compositions with a classical order of layers without the influence of sunlight
reflection. In the composition of the classical order of layers, where the waterproofing is
above the thermal insulation layer, bitumen sheets are directly exposed to sunlight.
High surface temperature is one of the causes of faults on flat roofs with a
waterproofing coating. These failures are manifested, for example, by the release of joints
and the sublimation of the thermal insulation from foamed polystyrene. As a result of the
solar radiation, the temperature of bitumen sheets in the roof structures increases. Due to
high temperatures, the dimensional stability of bitumen sheets is impaired. Bitumen sheets
with polyester support are shrinking. This shrinkage occurred due to the pre-stressing that
was introduced into the liner during the manufacturing process. Previously the topic of the
surface temperature was analysed by authors for example [1], [2] on the European level, for
example [3].
The surface temperature of bitumen sheets is mainly influenced by:
1. properties of bitumen sheets surface (emissivity, reflection),
2. substrate (thermal capacity),
* Corresponding author: plachy@mail.vstecb.cz
© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons
Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).
MATEC Web of Conferences 279, 02017 (2019) https://doi.org/10.1051/matecconf/201927902017
Building Defects 2018
3. ambient (air) temperature,
4. ambient radiation,
5. air flow and humidity.
In terms of surface properties of bitumen sheets, the scatter material, the particle size of
the sprinkle, the sprinkling rate and colour are important for the solar reflectance and the
surface emissivity of bitumen sheets. The most commonly used surface treatment of
bitumen sheets is a coarse-grained or fine-grained mineral dispersion in the form of
siliceous sand or slate. Another option is the ceramic sprinkle.
The aim of this paper is to find out which maximum temperatures are reached on the
surface of bitumen sheets in terms of the type and colour of the sprinkle, whether this
temperature approaches the value of 80 °C. This value is the limit guaranteed by producers
of foamed polystyrene for its stability [4]. The same temperature is then used for bitumen
sheets during the dimensional stability test according to EN 13707 [5], EN 1107-1 [6].
Thus, it is possible to pronounce hypothesis that the surface temperature of bitumen sheets
does not exceed the value of 80 °C. The temperature range between the maximum
temperatures in terms of the colour and type of sprinkling will be more than 10 ° C. The
lowest temperatures will be achieved in bright colours and the highest temperatures in dark
colours.
2 Material and methods of testing
One of possible increasing of the temperature of bitumen sheets can be the upper surface
treatment with the coarse-grained sprinkling. To determine the specific numerical values of
the maximum temperatures on the surface of bitumen sheets for a certain type of the surface
and the colouring of the dispersion, experimental measurements were made. The
measurement has shown how great temperature differences occur on the surface of bitumen
sheets.
2.1 Material
2.1.1 Samples of bitumen sheets
Bitumen sheets produced in TechnoNIKOL were selected for the experimental part. The
top modified sheet was chosen with thickness of 4.2 mm with coarse-grained slate (80 % in
the fraction of 0.5 – 2.0 mm) in the colours red, green, grey, blue-grey, white and red-
yellow, see Figure 1. For the comparison of achieved temperatures, bitumen sheets of black
and grey colour with fine sprinkle (slate) and siliceous sand (80 % in the fraction 0.18 –
0.63 mm) were also measured. These bitumen sheets are used as a base under the coarse-
grained sheet. See Figure 2.
Samples of bitumen sheets of size 200 x 200 mm were loosely laid on a mineral wool
base (λ D = 0.037 W / mK) with thickness of 100 mm. Samples on the substrate were laid
on a flat roof of bitumen sheets and were directly exposed to sunlight without any further
reflection of the sunrays.
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MATEC Web of Conferences 279, 02017 (2019) https://doi.org/10.1051/matecconf/201927902017
Building Defects 2018
Fig. 1. Bitumen sheets with coarse grain. Legend: A – white, B – red, C – red-yellow, D – green, E –
blue-gray, F – gray. Source: author.
Fig. 2. Bitumen sheets with fine grain. Legend: A – micro slate, B – quartz sand. Source: author.
2.1.2 Machines
Two methods were used to measure the temperature: contact and contactless. Non-contact
method using the Voltcraft IR-650-12D IR thermometer with a temperature resolution of
0.1 °C and a basic accuracy of ± 3 °C. The set emissivity of 0.92 corresponds to the
behaviour of the surface of the bitumen strips with IR spectrum scattering.
Contact method was used with universal measuring instrument ALMEMO 2590-4 with
thermocouple TYP K-T190-1 with the temperature resolution of 0.1 °C and the
measurement accuracy of 0.03 %, see Figure 3.
100 mm
100 mm
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MATEC Web of Conferences 279, 02017 (2019) https://doi.org/10.1051/matecconf/201927902017
Building Defects 2018
2.2 Methods of testing
Samples of bitumen sheets were placed on a classic flat lean-to roof with 5 °C inclination
of southeast orientation. From the point of view of air flow, the roof is located in a normal
landscape on a sheltered, stand-alone building at an altitude of about 2.0 m above the
terrain at an altitude of about 425 m above sea level in the village Planá nad Lužnicí (GPS:
49.3630811N, 14.7196306E). Air temperature measurements were made about 15 mm
above the mineral wool base using the thermocouple TyP K, see Figure 4. In order to
partially eliminate the influence of the wind, a low covering was formed around the
samples. See Figure 3.
The measurements were carried out during the summer between August 3 and August 8
in 2018. Due to the availability of individual devices, the measurements were not
performed in parallel. The continuous method was used from August 3 and August 5 in
2018, the contact method from August 6 and August 8 in 2018. In the long-term view,
summer 2018 can be considered the warmest in 244 year history of temperature monitoring
in the Czech Republic [7].
Fig. 3. Contact measurement of surface temperature and solution of the edge of the substrate. Source:
author.
Fig. 4. The air temperature measurement. Source: author.
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MATEC Web of Conferences 279, 02017 (2019) https://doi.org/10.1051/matecconf/201927902017
Building Defects 2018
3 Results
The results of both methods are shown in Table 1. Maximum surface temperatures were
recorded at an air temperature on August 8, 2018 at 43.8 °C. The maximum temperature at
the measuring station of the Czech Hydrometeorological Institute (CHMU) in this day in
the Czech Republic was measured in Dobřichovice in the value of 36.4 °C [8].
Table 1. A survey of measured maximum temperature values for bitumen sheets during a warm
summer day depending on the surface colour. Legend: HMP – coarse-grained mineral spread, JMP –
fine-grained mineral spraying. Source: author.
Colour
Type of
spreading
Non-contact method
(3-5.8.2018)
Contact method
(6-8.8.2018)
[°C]
[°C]
green HMP 73.8 71.1
grey HMP 73.3 75.3
red HMP 76.8 72.3
blue-grey HMP 74.2 70.9
white HMP 69.4 70.0
yellow-red HMP 70.5 67.6
slate JMP 74.4 71.8
sand JMP 74.7 73.1
4 Discussion
The maximum temperature of 80 °C was not achieved on any surface using any one of the
measurement methods. Therefore hypothesis has been confirmed.
In the case of the non-contact method, temperatures ranged from 69.4 °C to 76.8 °C.
The temperature range is therefore 7.4 °C. In the case of the contact method, temperatures
ranged from 67.6 °C to 75.3 °C, the temperature range is 7.7 °C. Therefore the hypothesis
of a maximum temperature range of more than 10 °C was not confirmed.
The results of both methods differ in the order of maximum temperatures depending on
the colour of the sprinkle. Maximum temperatures can be divided into three intervals for
both measurement methods. Three intervals were selected for the accuracy of a non-contact
method. One interval was approximately 2.5 °C. See Table 2.
Table 2. A survey of measured maximum temperature values for bitumen sheets during a warm
summer day depending on the surface colour. Source: author.
Surface temperature
measurement method
Interval A [°C] Interval B [°C] Interval C [°C]
Non contact method 76.80 – 74.33 74.32 – 71.87 71.86 – 69.40
red, slate, sand green, grey, blue-
grey,
white, yellow-red
Contact method 75.30 – 72.73 72.72 – 70.17 70.16 – 67.60
grey, sand green, red, blue- grey,
slate
white, yellow-red,
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MATEC Web of Conferences 279, 02017 (2019) https://doi.org/10.1051/matecconf/201927902017
Building Defects 2018
For both methods, it was confirmed that the highest temperatures were achieved on
bitumen sheets with treatment in the form of sand, although no maximum temperature was
measured on the sheet. The highest temperatures were in dark colours: red, grey, lower
temperatures on green and blue-grey and the lowest on white and yellow-red. The low
temperature in the yellow-red colour is especially surprising. The hypothesis was therefore
confirmed.
5 Conclusion
The results show that the colour of the sprinkle has, in practical terms, a considerable
influence on the surface temperature of bitumen sheets and thus their aging rate. From the
selection of the colour range of the sprinkle, the light colours should be preferred to dark
colours such as red. Above all, combined with the reflection of the sunlight, the temperature
can be exceeded in the long run by about 80 °C.
The next phase of the research will be focused on the influence of the substrate
comparison of the temperature on the waterproofing layer from one and more bitumen
sheets.
References
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composition of single-membrane roof,. (Brno University of Technology, Faculty of
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prosklených ploch v polystyrenu na střeše s povlakovou hydroizolací. (DEKTRADE,
Praha, 2017). Available on https://www.dekpartner.cz/aktuality/detail/224
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(2017)
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(2018a)
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MATEC Web of Conferences 279, 02017 (2019) https://doi.org/10.1051/matecconf/201927902017
Building Defects 2018
