PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Acoustic properties of façade fragments of historical monuments
Lukáš VARGIC1; Jana GREGOROVÁ1; Monika RYCHTÁRIKOVÁ1,21

Slovak University of Technology in Bratislava, Faculty of Civil Engineering, Department of Architecture,
Radlinského 11, 81005, Bratislava, Slovakia

2KU Leuven, Faculty of Architecture, Hoogstraat 51, 9000 Gent/ Paleizenstraat 65, 1030 Brussel, Belgium

ABSTRACT
Retrofitting of historical monuments in terms of their improvement in energy performance and overallsustainability is one of the frequently discussed questions in building sector and architecture. However, therenovation of monuments is highly interdisciplinary task and therefore, the global assessment of proposedsolutions is needed.
In this article we discuss the impact of additional thermal insulation in historical buildings while keeping thereversibility of the action, on its sound insulation performance. Typical cases of energetic retrofit in Slovakia
are shown and sound transmission index R (dB) is predicted in Norflag software 4.0 that uses transfer matrix
method as calculation algorithm. The solutions are discussed in term of its thermo – acoustic performance.
Keywords: Architectural heritage, Thermal and Sound Insulation, Building acoustics

1. INTRODUCTION
During the last decades many research projects and initiatives have been undertaken, that deal withthe energy efficiency and various comfort issues in historic buildings (1). Most of the previously
performed research has been focused on moisture and humidity transfer in constructions of buildings,
insulated from inside, typical in cases where the insulation from exterior side is not acceptable becauseof art-historical decoration or authenticity of the façade. Preservation of architectural heritage alsodoesn’t always allow for invasive ways of building envelope restoration. The methodology forimprovement of energy efficiency and sustainability of historic buildings is therefore mostly based on
solutions with reversible technologies (4).
The impact of different proposed renovation solutions has been already sufficiently investigated interms of thermal comfort, however only little attention has been given to their consequences on otheraspects, such as sound insulation. This paper is a part of systematic investigation of thermal andacoustic insulation in historic buildings where energy efficiency and thermos-acoustic comfort (5)should be put in balance, while preserving their architectural authenticity.
The presented study is based on a simple experiment in which 3 types of historical walls (stone
masonry of 600 mm, brick masonry of 450 and 300 mm thick) are thermally insulated. For each typeof wall, 3 solutions of thermal retrofit are considered in a way to have the same U-value of ca 0.21
W/(m2 .K). The differences in acoustic performance as calculated in Norflag software are shown anddiscussed.

2. DESCRIPTION OF THE CASE STUDY
The study is structured in the following parts: (i) choice of historic masonry constructions, (ii)selection of the thermal insulation variants, (iii) assessment of the acoustic benefits related to theinsulation variants.
1
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lukas.vargic@stuba.sk ; jana.gregorova@stuba.sk
monika.rychatrikova@kuleuven.be2.1 Definition of types of historic masonry walls
Study has been applied on selected representatives of masonries of traditional historic buildings
from Central Europe area. Based on the literature review and other available materials, two basic
groups of envelope structures were defined, presenting the basic principles of architectural culture of
the past centuries and forming the structures of dominant group of preserved architectural heritage:
masonries based on stone and brick elements.
The difficulty of the process to select suitable representatives was to define appropriate dimensions,especially of stone masonry type, as unification was not used in historical construction and manydifferent factors influenced the design of this structures. 600 mm thick sandstone wall was chosen torepresent the stone masonries of historic buildings, the most common variant in terms of materialityof investigated territory. Although the chosen thickness does not represent an average value, it is themost appropriate representative for stone masonry in terms of application the thermal insulation. Brickfragment is made up of solid silicate bricks at a total thickness of 450 mm, which can be said to be
the most common brick wall variant in Central Europe. The last group can be considered as an
academic example of brick masonry with 300 mm thickness and was chosen for sake of comparison
with cases where the initial sound reduction index is initially low.

Figure 1 – Typical Slovakian gothic burgher house with 600 mm thick stone (sandstone) wall (left picture)and typical town house from turn of the 19th and 20th century with 450 mm thick brick wall (right picture)
2.2 Selection of Thermal Insulation Variants
The external envelope is the most exposed part of building and therefore must fulfill certain
acoustic and thermal requirements. In case of historical heritage, monuments or in cases in whichbuildings have a cultural value, façade is sensitively perceived and thoroughly protected. These facts
often result in discussions in terms of building renewal. The presented results aim at the impact of theadditional thermal insulation of the building façade, which can be applied in three different ways,exterior insulation and two types of thermal insulation placed from building interior.
Most effective strategy in renovation of existing buildings related to the energy consumption andthe improvement of indoor environment is the use of exterior thermal insulation of the façades.
However, this solution is not always applicable to objects with historical and architectural value, aswell as objects protected by monument rule, as they meet the requirements for preserving the originalappearance of the façade. An alternative and nowadays very popular way of increasing the thermalprotection of buildings envelope is the interior application method of thermal insulation, which isoften the only possible solution.
For the study, the following cases were chosen (Figure 2): Three types of of the abovementioned
masonry types 600 mm stone, 450 mm brick and 300 mm brick) were chosen and for each, 3 different
systems of facade insulation were applied. The thermal protection aspects are in all cases set to meetthe current requirements of energy performance of renovated buildings. From the material point ofview, it is the use of mineral wool in different thickness depending on (i) material base of masonry,(ii) position and (iii) technology of application of insulation material. In the example of the external
thermal insulation the extruded polystyrene (EPS) with very thin layer of plaster was used.
The selection of the insulation variants aims at comparing the acoustic benefits of different systems.

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Original stone wall
~ 600 mmETICS (140 mm EPS +3mm plaster)Int. insulation #1/ties
120 mm mineral wool +1 gypsum board

Int. insulation #1/studs
120 mm mineral wool +1 gypsum board

Figure 2 – Simulated stone wall fragments – thermal insulation variants

Original brick wall
450mm
(resp.
300mm)ETICS (140 mm EPS +3mm plaster)Int. insulation #1/ties
120 mm mineral wool +1 gypsum board

Int. insulation #1/studs
120 mm mineral wool +1 gypsum board

Figure 3 – Simulated brick wall fragments – thermal insulation variants CALCULATIONS

2.3 Description of the calculation algorithm
Simulations were performed in the acoustic software Norflag 4.0. Norflag, known also as WinFlagsoftware) is made to calculate the theoretical sound reduction index R (dB) for constructions that canbe combined by different types of layers of different materials (11). Simulation algorithm allows forcalculation of mean values in one-third-octave bands using the transfer matrix method. Calculations
can be performed for chosen angle of incidence or for diffuse sound field.
In the calculation, each layer is assumed to be an infinite plate and is presented by a matrix whichis combined with other matrix layers. The two types of plates can be chosen for the prediction ofsound insulation of wall: thin plates and thick plates. Thin plates are chosen in cases in which thewavelength of a bending wave is large than 6x thickness of the given plate. In this case 2x2 matrix isused since there is no question about the wave motion inside the plate. Porous layers are simulated inthe same way, by 2x2 matrixes. In cases, where the two layers are glued together, thick platedescription comes into consideration as one layer should be then describing both of the layers as thickplates. Calculations using the thick plate method are applicable for wall constructions of sandwich
elements which are glued together and are then described by a 4x4 matrix.
For sake of comparisons in the article, the sound reduction index R (dB) and the weighted soundreduction index Rw (C, Ctr) in dB was calculated. Sound transmission simulations were performed inthird octave bands in diffuse field (i.e. with integration angles from 0 to 90 degree), and transmission
window of 10 m2 .

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3. RESULTS AND ANALYSIS
Results of simulated sound transmission are summarized in graphical way, by means of thefollowing figure (Fig.4) and Table 1. The results show the sound reduction index for all cases, groupedin three graphs. In all cases a significant improvement can be seen when insulation is applied frominside. When only little contact is used to connect the plaster board, the Rw increases with 10-11 dB,in cases with studs are used sound insulation increases with around 8 dB. In both cases of mass spring
mass systems we can see the coincidence dip of the masonry wall at low frequencies (and a dip ataround 2500 Hz, cased by gypsum board of 12 mm. 100 Hz for brick wall of 450 mm and similar tostone wall, since these has less density and lower Young modulus (brick wall 600 mm thick would
have coincidence frequency around 75 Hz). The brick wall of 300 mm has coincidence at 150 Hz.
Sound reduction index

Sound reduction index

Sound reduction index

90909080808070

707060R (dB)100

R (dB)100

R (dB)

100

60

50

50

40

30

wall
int.studs

40

int.ties
ext

30

50

wallint.studs
int.ties
ext

20

20
63

125

250

500

1000 2000 4000

60

wall

40

int.studs
int.ties

30

ext

20
63

125

250

500

1000 2000 4000

63

125

250

f (Hz)f (Hz)

500

1000 2000 4000f (Hz)

Figure 4 – Simulated variants. Left – variants for brick wall 300 mm, Middle figure – variants for brickwall 450 mm, Right picture – variants of 600 mm stone masonry wall. (black thick line shows the Sound
transmission index R (dB) of the original wall without thermal insulation (TI). The green dashed line
expresses the internal TI fixed by ties, red dashed line when fixed by studs. Blue line is the situation withlayer of EPS applied on the facades from outside.
The three cases with polystyrene (EPS) applied on a façade from the building exterior show similar
behaviour. The EPS was simulated as connected with ties to the masonry wall, presuming a gap of
0.5-1mm between the wall and EPS boards caused by irregularities of the historical wall. The visible
dip around 2000 Hz can be seen in simulations of all wall thicknesses.
Table 1– Results of weighed sound reduction index Rw (C, Ctr)
Weighed sound reduction
index Rw (C, Ctr) in dB

No insulation

EPS

Int. Insul. #1

Int. Insul. #2

ties

studs

Stone masonry (600 mm)

63 (-2,-8)

62 (-2;-8)

74 (-3;-9)70 (-2;-9)

Brick masonry (450 mm)

61 (-2,-8)

61 (-2,-8)

72 (-2;-9)69 (-3;-9)

Brick masonry (300 mm)

56 (-2,-6)

56 (-2,-6)

68 (-3;-7)

64 (-2;-7)0,210,22

Heat transfer coefficient
U [W/(m2.K)]

1,200,222977

4. CONCLUSIONS
When restoring the architecturally valuable façade, increased attention should be paid to the degreeof intervention to the origin and the resulting impact on the authenticity of the object, whether interms of material authenticity (physical matter of object) or the authenticity of the whole work
(cultural-historical essence of the monument). Here, the placement of thermal insulation from insidehas in the winter period many disadvantages when looking purely to humidity and moisture transfer.
This is however true only in winter time and renovation of historical monument must be always
considered in given climate.
From the point of view of acoustics, the simulations have yield the acoustic benefits of the thermal
insulation variants in which the insulation was placed from inside the building. This paper have shown
only simulations of typical wall fragments. In reality, the sound insulation of building façade is much
more complicated issue and must be therefore considered as a whole, including windows and doors.

ACKNOWLEDGEMENTS
This work was supported by the European Commission, H2020-MSCA-RISE-2015 project 690970,“PAPABUILD” and Erasmus+ for students exchange.

REFERENCES
1. Häkkinen T, Ruuska A, Vares S, Pulakka S, Kouhia I, Holopainen R. Methods and concepts for sustainable
renovation of buildings, VTT Technical Research Centre of Finland, Espoo, Finland 2012.
2. UNEP 2007. Buildings and Climate Change - Status, Challenges and Opportunities. United Nations
Environment Programme, Paris, France March 2007.
3. EN 16883:2017. Conservation of cultural heritage. Guidelines for improving the energy performance ofhistoric building.
4. Gregorová J, Pagáčová P. Ecological aaspects of monument preservation - potential and limits? TERRASPECTRA STU. Planning Studies: Central European Journal of Spatial and Landscape Planning STU,
Vol. 5, No. 2, p. 17-25, STU Bratislava, SPECTRA Centre of Excellence EU, Bratislava, Slovakia 2013.
5. Šujanová P, Rychtáriková M, Sotto Mayor T, Hyder A. A healthy, energy-efficient and comfortable indoorenvironment, a review. Energies. 2019, 12, 1414.
6. Foret R, Guigou-Carter C, Villot M. Effect of thermal insulation systems on acoustic performances ofancient building construction elements. Proc Internoise and Noise-on Institute of Noise Control
Engineering, Portugal, 13-16 June 2010.
7. Urbán D, Roozen NB, Muellner H, Zaťko P, Niemczanowski A, Rychtáriková M, Glorieux C. Vibrometry
assessment of the external thermal composite insulation systems influence on the façade airborne soundinsulation. Applied Sciences. 2018.
8. Zaťko P, Urbán D, Tomašovič P, Rychtáriková M. Acoustic performance of the External Thermal
Composite Insulation Systems Influence in Slovakia. Proc Fortschritte der Akustik-DAGA; 14-17March 2016; Aachen, Germany 2016.
9. Guigou-Carter C, Foret R, Villot M, Chéné JB. Effect of thermal renovation on acoustic performance ofbuilding. Proc Euronoise 2009; Edinburgh, United Kingdom 2009.
10. Guigou-Carter C, Foret R, Wetta R, Ducruet P, Villot M. Comparison of measured and predicted soundinsulation for a thermal retrofitted building. Noise Control Eng. J.; Edinburgh, United Kingdom 2009.
11. Vigran E. Manual for Norflag, version 4.0. Trondheim, Norway. 20182978