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

Measurements and prediction of sound insulation ofinnovative ventilated façade solutions
Francesca DI NOCCO1; Luca BARBARESI2; Federica MORANDI3 and Massimo GARAI4
University of Bologna, Italy

ABSTRACTThis work is part of Progetto Involucro, a research project funded by the Emilia-Romagna Region in theframe of POR-FESR 2014-2020. It aims at testing innovative ventilated façade solutions for improvingbuildings' energy and acoustic performance. Two identical test buildings (prototypes) are built in real scale on
the same site and different ventilated façade solutions are installed on the South facing walls. In order toevaluate the performance of different alternatives, a benchmark solution is installed on the first prototype,while all the other innovative solutions are installed on the second one and they all are tested under the sameenvironmental conditions. Sound insulation measurements are performed on site with the aim to investigate
the contribution of different rainscreens in relation to their fastening system and individual component
elements such as natural ventilation grills, open joints and potential openings on the external side.
Furthermore, a measurement campaign focused on flanking transmission is conducted to evaluate soundtransmission across the façade junctions for each innovative solution installed. This paper shows thepreliminary results of the measurement campaign. Data obtained from on-site measurements are commented
and discussed in relation to the values calculated using the model proposed in the ISO 12354-3 standard.
Keywords: Innovative Ventilated Façade, ISO 12354-3, Calculation Model

1. INTRODUCTION
This contribution shows the preliminary phases of development of Progetto Involucro, which aims
at testing innovative Opaque Ventilated Façades (OVF) solutions for the improvement of building
energy and acoustic performances. Different OVF solutions are installed on the South facing walls of
two identical building prototypes and are tested under the same environmental conditions.
In parallel with the monitoring of energy performance, a global study was conducted on theacoustic behavior of the ventilated façade. This document illustrates the iterative method and thedifferent types of measurements carried out in situ, in order to refine the forecast calculation model forthe evaluation of façade insulation in the case of ventilated façades. The acoustic measurement
campaign conducted on the test buildings are shown and commented in relation to the modelling
according to the ISO 12354-1,3:2017 standards (1, 2).
Previous literature investigated factors that affect the final sound insulation for ventilated façades
and ventilated double-skin façades. Experimental tests (3) were conducted to evaluate different
insulation layers to be placed in the cavity and the influence of open joints that characterize ventilatedfaçades. The presence of open joints affects the performance determining a decrease in thesingle-number rating of the façade sound insulation up to 3 dB. A detailed measurement campaign ispresented in Ref. (4), where the influence of the opening of the cavity is tested by measuring, step bystep, the sound insulation of the façade as the space of the cavity was varied from hollow to filled, bothwith open and sealed joints. In the open joints condition, the filling ratio of the cavity has stronger
effects on the acoustic behavior of the façade. Other works investigated ventilated double skin façades
(5, 6), proposing simple calculation models based upon the determination of the coincidence frequency,
the structural resonance frequency, cavity resonances and evaluating the presence of openings.
1

francesca.dinocco2@unibo.it
luca.barbaresi@unibo.it
3
federica.morandi6@unibo.it
4
massimo.garai@unibo.it
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2. HIGH-PERFORMANCE ENVELOPE DESIGN
2.1 The test buildings
The twin test buildings are located in San Mauro Pascoli (FC, Italy) and they were completed inFebruary 2019. The building prototypes are tested under the same environmental and weather
conditions in order to allow precise comparison between different alternatives: one of the solutions iskept as a benchmark on the first prototype, while all the other solutions alternate on the secondprototype. A global view of the two buildings is provided in Figure 1.
The test buildings have a rectangular base (external dimensions 3.4 m x 3.2 m) and are two-story
high, for a total external height of about 7 m. The structure of both the prototypes is in Cross
Laminated Timber (CLT), with 3-plies 100 mm panels for the vertical elements and 3-plies 120 mm
panels for the horizontal partition. A 260 mm EPS thermal coat is applied on the North, East and Westwalls. The South facing wall, on which the OVF solutions are mounted, is a masonry wall (250 x 300x 199 mm) with a 100 mm rockwool layer installed on the side of the ventilated façade. The choice ofa mixed structure was deemed of interest for the possibility of investigating sound transmission
through different structures, given the importance that CLT is gathering as a construction material (7,8, 9). A roof with an inclination of approximately 5 degrees, provides shading and protection fromweather exposure.
In order to investigate the thermal and energy behavior of the OVFs, the South facing façade of thetwo buildings is equipped with a resident monitoring system that provide a systematic acquisition of
the hygro-thermal information. For each envelope, the system includes over 80 resistance temperaturedetector, 4 anemometers, a pyranometer and an electric energy meter combined with smart device.

Figure 1 – Global view of the twin test buildings (left) and scheme of the realization of buildings (right).
2.2 Ventilated façade solutions
Figure 2 shows a construction detail of the ventilated façade-floor junction. In particular, thebuildings are built using a balloon frame system, with continuous vertical walls; the floor is only fixed
on two of the four edges and it is not rigidly connected to the brick wall. An aluminum alloy structure(T vertical mullions and L brackets) is directly connected to the brick wall to achieve a 15 cm fixedcavity of ventilated façade.
During the experimentation, the innovative OVF solutions mainly concerned different type s ofrainscreen in relation to their fastening system (dashed box in Figure 2) and the proportion of open
joints. In Table 1 and 2 the different configurations tested are shown with their respective features.
Regarding the selection of the significant solutions, the one made of gres tiles with integrat ed PCM
was not considered, due to two main reasons: first, it would be troublesome to simulate the soundreduction index for direct transmission; second the acoustic performance of the entire system is notaffected by PCM contribution, as also confirmed by recent literature (10). Finally, it should be notedthat the automated shutters (Figure 2) are hermetically closed in all configurations.
2.3 Research method
The two buildings have been object of an extensive measurement campaign: the façade soundinsulation measurements were complemented by evaluating the vibration reduction index for all
junctions that involve the façade, and by measuring the vibration velocity level of all walls when thesound source was active outside. This paves the way to correlating, in a future work, the contribution

3499in terms of radiated sound power provided by each wall to the overall internal sound field. Part of thesemeasurements are described in the paper and have been used for the implementation of the ISO 12354
model.

Figure 2 – Construction details: the ventilated façade-floor (left) and external wall-floor junction (right).
Table 1 – Technical and acoustic features of five configurations testedConf.

LayersAB
C
DE

Total thicknessmˈwallmˈext-tile2(m)(kg/m )

(kg/m2)

Plastered Masonry

0.26

248

-

Plastered masonry + rockwool

0.36255-

0.52255

150.56255

220.57

255

24

Plastered masonry + rockwool + metal structure +Gres tiles 1200x2400 mm
Plastered masonry + rockwool + metal structure +HoneyComb/Gres tiles 1200x2400 mm
Plastered masonry + rockwool + metal structure +Gres standard tiles 600x600 mm

Table 2 – Mechanical characteristics of different rainscreen tested
Fastening

NumberThickness

Dimensions

Sopen-joints/Sfaçadesystem

slabs

(mm)

(mm)

%

Gres tiles

Innovative

46.5

1200 x 2400

1.2

D

HoneyComb/Gres tiles

Traditional

415 + 6.5

1200 x 2400

2.0E

Gres standard tiles

Traditional

3210600 x 600

3.8Conf.

DescriptionC

3. THE ISO 12354 MODEL
According to the standard ISO 12354-3 (2), the sound insulation of a façade can be estimatedthrough the apparent sound reduction index 𝑅 ′ , the influence of the outside shape of the façade ∆𝐿𝑓𝑠
(i.e. presence of balconies and similar) and the room dimensions:
𝐷2𝑚,𝑛𝑇 = 𝑅 ′ + ∆𝐿𝑓𝑠 + 10𝑙𝑜𝑔 (𝑉)
6𝑇0 𝑆𝑡𝑜𝑡(dB)(1)

where 𝑉 is the volume of the receiving room, 𝑆𝑡𝑜𝑡 is the total area of the façade as seen frominside and ∆𝐿𝑓𝑠 is the level difference due to façade shapes, that in our specific case can be assumed
equal to 0 dB.

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The apparent façade sound insulation 𝑅 ′ is given by:
𝑛𝑚′

𝑅 = −10 log (∑ 𝜏𝑒,𝑖 + ∑ 𝜏𝑓 )
𝑖=1

(2)

(dB)

𝑓=1

where 𝜏𝑒,𝑖 is the direct transmission coefficient through all the façade elements, 𝜏𝑓 is thetransmission coefficient relative to flanking transmission paths, n is the number of façade elements for
direct transmission and m is the number of flanking façade elements. Equation 2 can be reformulated
as follows:
𝑛𝑚𝑖=1

𝑓=1

𝑆𝑖
𝑅 = −10 log (∑ 10−𝑅𝑖 /10 + ∑ 10−𝑅𝑖𝑗/10 )𝑆′(dB)(3)

where 𝑅𝑖 is the sound reduction index for element i of the façade and 𝑅𝑖𝑗 is the sound reduction
index for the flanking transmission as explained in the ISO 12354-1 standard (1).

4. MEASUREMENT CAMPAIGN
4.1 Method
The procedure for measuring of the façade sound insulation on site is described in ISO 16823-3 (11).
The standardized level difference is defined as:
𝐷𝑙𝑠,2𝑚,𝑛𝑇 = 𝐷𝑙𝑠,2𝑚 + 10𝑙𝑜𝑔𝑇𝑇0(dB)(5)

where 𝐷𝑙𝑠,2𝑚 is the difference between the sound pressure level 𝐿1,2𝑚 measured at 2 m from thefaçade at a height of 1.5 m and the average of the sound pressure level in the receiving environment
𝐿2 (six random positions for measurement), 𝑇0 is the reference reverberation time (0.5 s fordwellings). The reverberation time has been measured according to ISO 3382-2 (12). Using the global
loudspeaker method, the source is placed in four different positions on the ground outside the building
at a distance 𝐷 > 3.5 m from the façades with a sound incidence angle equal to 45° ± 5° (Figure 3).
The sound pressure level near the façade depends on several factors, investigated by Hopkins (13).
As a rule-of-thumb, for a point source near the ground and façade–receiver distances between 1 and 2m, the diffraction effects are only likely to be significant in the low-frequency range. As in this case, itoccurs for façades with dimensions < 5 m.

Figure 3 – Scheme of the measurement setup used with indication of the position SI, SII, SIII, SIV sources.

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4.2 Results
The source positions analyzed in this paper are S I and S II, both pointing towards the ventilated
façade (Figure 3); the measured façade sound insulation values are shown in Figure 4 in one -thirdoctave bands. Comparing solutions C, D and E with the reference façade A there is general
improvement in the overall acoustic performance. Considering equal material and typology ofconstruction solution (Conf. C and D), a larger area of open joints (Conf. E) affects the results up to 5
dB. Moreover, with the same dimensions and similar surface mass of the slabs (Conf. C and D), thefastening system influences the behavior of the façade at most up to 2 dB.
7060D2m,nT [dB]

50403020100ABCDEf [Hz]Figure 4 – Standardized sound level difference of façade measured on site in one-third octave bands.

5. MODELLING THE ELEMENTS ACCORDING TO ISO 12354
5.1 Input data
The ISO 12354 model is heavily influenced by the input data; therefore, the building acoustic smodelling phase is extremely important for the correct application of the calculation model.
It is recalled that the element i consists of the different configurations of façade shown in Table 1,
while the external wall for flanking transmission paths consist of a wall in CLT 100 mm panels with a260 mm EPS thermal coat. In this case it was not possible to retrieve the input data from laboratory
certificates. Therefore, the input data for the apparent sound reduction index 𝑅𝑖 of the façade underinvestigation and the elements of test building involved in the flanking transmission 𝑅𝑗 werecalculated using a commercial software (14) (Figure 5).
5.2 Flanking transmission
The flanking transmission is generally considered negligible for the façade sound insulation: forthe cases in which rigid elements are connected to rigid elements in the receiving room, a reduction of
2 dB is generally deemed acceptable to account for flanking transmission (2). It can anyway beevaluated according to the ISO 12354-1 standard in frequency, calculating the 𝜏𝐹𝑓 and the 𝜏𝐷𝑓transmission paths. In our specific case, only direct-to-flanking transmission paths Df were present;
moreover, given the peculiar characteristics of the structure under analysis, only the c ontribution of
the vertical elements enclosing the façade were considered.
The Annex of ISO 12354-1 does not provide indications to estimate flanking transmission in thistype of junctions (Figure 2). For this reason, the vibration reduction index 𝐾𝑖𝑗 of the junctions
involving the façade were measured according to the ISO 10848-1 standard (15).
In particular, 𝐾𝑖𝑗 measurements were conducted in façade configurations with and without theexternal rainscreen, namely configurations C and B. In Figure 6, it can be noticed that the flanking
transmission through the façade-CLT wall joint is not influenced by the presence of rainscreens3502

(orange and green lines). Therefore, they were subsequently adapted according to the structural
reverberation time measurements of the involved elements in each configuration. Since the L junction
is a junction composed of different and non-homogeneous elements, there is a noticeable difference
between the transmission path 𝐷𝑣,𝑖𝑗 (continuous line), where the i element (masonry wall) is excited,
and the transmission path 𝐷𝑣,𝑗𝑖 (dashed line), where the j element (CLT wall) is excited. For thesereasons the calculation model was implemented first neglecting the lateral transmission (called “ISO12354”), and then using as input data the measured 𝐾𝑖𝑗 (“ISO 12354_Var. 1”), the measured values of𝐷𝑣,𝑖𝑗 only for the path MASONRY-CLT (“ISO 12354_Var. 2”). Finally, the calculation wasimplemented considering only the 𝑅𝑖 of the masonry wall (“ISO 12354_Var. 3”) for the i element(façade) in the flanking transmission paths 𝑅𝑖𝑗 , given the particularity of the façade connection.
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R [dB]

50
40
30
20
100

A_Ri

B_Ri

C_Ri

D_Ri

E_Ri

Rjf [Hz]

Figure 5 – Input values of the sound reduction index 𝑅𝑖 of the different configurations of façade and thesound reduction index 𝑅𝑗 of the lateral elements.
454035[dB]302520151050-5

B_Dv,ij
C_Dv,ij

B_Dv,ji
C_Dv,ji

B_Kij
C_Kij

f [Hz]

Figure 6 – 𝐷𝑣,𝑖𝑗(𝑗𝑖) and 𝐾𝑖𝑗 for the “L vertical junction” transmission path measured in B and C solutions.

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5.3 Results
Figure 7 shows the results obtained implementing the model considering the different
above-mentioned variables applied to the same solution (Conf. E). There is a progressive improvementin the medium-low frequency range, reducing the calculation error, as illustrated in ISO 12354. The
results can be conveniently discussed in term of comparisons between the standardized level
difference of the different façade configurations measured on site and the calculated values
implemented considering the model “ISO 12354_Var. 3”, see Figure 8. In general, the ISO model isstrongly influenced by the contribution of the direct transmission. For this reason, it can be noticed thathaving no suitable input data can lead to high errors, especially considering masonry with clay blocks
and solution D. The best match between measured and calculated results is observed in Co nf. E, i.e. thesimplest façade assembly.
7060D2m,nT [dB]

50403020100

E_In situ
E_ISO 12354_Var. 1
E_ISO 12354_Var. 3

E_ISO 12354
E_ISO 12354_Var. 2f [Hz]Figure 7 – Difference between measured and calculated values of the standardized sound level difference ofE configuration in relation to different variables.
2520ΔD2m,nT [dB]

151050-5-10-15

A

B

CDEf [Hz]Figure 8 – Difference between measured and calculated values of the standardized sound level difference ofthe façade considering the model “ISO 12354_Var. 3”.

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6. FINAL REMARKSThe paper shows some preliminary results of the study of the acoustic behavior of ventilated
façades done during the experimentation of Progetto Involucro. This work is focused on thecomparison between the measured values of the standardized level difference of façade and the values
obtained from the calculation model in according to ISO 12354 standards. The ISO calculation model
was implemented using simulated values starting with the physical and mechanical properties ofdifferent elements. The flanking transmission was included in the model using the values obtain by themeasurement campaign of vibration transmission through the building elements. From the acoustic
point of view, the ventilated façade system is particularly complex to be modelled, because the ISO
calculation model does not keep into consideration the presence of external layer with open joints. Interms of performance, the ventilated façade has a good performance but is affected by the presence ofopen joints, possibly openings or by the fact that the metal structure of the façade is rigidly connectedto the masonry wall.
In the future work, the analysis will be focused on the lateral elements involved in the flanking
transmission paths. In this respect, the results obtained by measurements of the vibration velocity levelof walls when the sound source was active outside will be correlated to the overall internal sound field.

ACKNOWLEDGEMENTS
The project Progetto Involucro was funded by the Emilia-Romagna Region within the frameworkof the POR-FESR 2014-2020.

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