Building acoustic performance prediction – Feedback from Adivbois CLT building mockup Catherine Guigou-Carter 1 Health and Comfort Department, CSTB 24 Rue Joseph Fourier, 38400 Saint Martin d’Hères, France Nicolas Balanant 2 CERQUAL Qualitel Certification 28 Rue du Rocher, 75008 Paris, France Jean-Luc Kouyoumji 3 FCBA Allée de Boutaut, 33000 Bordeaux, France

ABSTRACT The acoustic performance of a CLT based building mockup was investigated within the scope of AdivBois acoustic technical commission with the objective of defining wood building constructions fulfilling requirements. The CLT based building is a three floor construction, with four rooms on each level. Measurements from junction characterization to air-borne and impact sound insulations have been performed. Furthermore, acoustic measurements have been performed before and after linings and floor coverings were implemented. Moreover, several acoustic teams have carried out measurements in the building. This paper concentrates on the comparison between measured acoustic performance and the predicted one. Predictions are based on the EN ISO 12354-1 and -2 standards, using floor and wall acoustic performances measured in laboratory conditions. The effect of junction characteristics, floor covering and receiving room size is discussed.

1. INTRODUCTION

Wood fixes CO2 during its growth. The new French environmental regulation RE2020, for new buildings applicable from January 1, 2022, promotes the use of renewable materials to store carbon. Used as structural element in construction, where its lifespan is around 100 years, wood is an interesting source of carbon capture. The development of wood in the construction and renovation of buildings is also recognized by the French public authorities as an effective means of contributing to the objectives of the National Low Carbon Strategy.

In addition, to achieve the carbon objectives of the Paris 2024 Olympic and Paralympic Games aligned with the Paris Agreement, many projects are developed in wood.

1 catherine.guigou@cstb.fr 2 n.balanant@cerqual.fr 3 jean-luc.kouyoumji@fcba.fr

If the lightweight aspect of wood is appreciated for elevations and extensions, in multi-storey buildings, the predictability of the acoustic and vibration performance of lightweight structures requires special know-how. Behavior at low frequencies and flanking transmissions must be monitored with care. Fortunately, research has made much progress in recent years, particularly in France due to the momentum generated within the framework of the ADIVBois project. The aim of the ADIVBois association is to help removing technical and regulatory obstacles and to share the expertise acquired in the field of high-rise wooden constructions, with project owners, project managers and companies. The technical working groups of ADIVBois have carried out work in recent years on the aspects of structure, envelope, fire safety and acoustics.

Regarding the acoustic investigation, a laboratory test campaign on the CLT floor was carried out by CSTB in 2018. Then, the project for a life-size mockup of a multi-storey wooden construction was launched at the FCBA in 2019. This new project managed by FCBA was baptized “ADIVBois Acoustic Mockup”; it brings together CSTB, CERQUAL and FCBA.

This three-level wooden mockup with four rooms per level was built on the FCBA site in Bordeaux. The mockup is intended to study the floors, the flanking transmissions, and the transmissions via the wooden supporting elements such as posts and beams.

Preliminary results were presented in 2021 [1] ; a companion paper [2] concentrates more specifically on the effect of apparent wood elements on the acoustic performance.

This paper presents measurement results performed by different teams, using either the survey or the engineering method, and compared them to predicted results. The effect of junction characteristics, floor covering and receiving room size is discussed.

2. BUILDING DESCRIPTION

The prototype, or “ADIVBois Acoustic Mockup” is a three storey wooden structure building comprising 4 rooms on each floor, including 2 rooms with an overall surface area of approximately 14 m² each, and 2 rooms with an overall surface area of approximately 19.8 m² each. The construction is based on CLT panels for walls and floors, laminated wood posts and beams, and lightweight wood frame façade. Some double frame plasterboard based separating walls are also included. Some junctions incorporate resilient elements in order to evaluate their effect and advantages in the acoustic performance. A general view of the “ADIVBois Acoustic Mockup” is depicted in Figure 1; temporary stairs on each of the four façades allow to access the different room.

2.1. Walls and Floors Two different floor types have been implemented : Floor 1 with apparent underside and Floor 2 with rigidly suspended ceiling.

Two types of vertical wall were mounted: the first is based on a 140 mm thick CLT panel and the second corresponds to a 180 mm thick double frame plasterboard based separating wall (denoted SAD180 in the rest of the paper).

The façades are standard lightweight wood frame wall with an independent interior lining (composed of 2 BA13 plasterboards on an independent metal frame with 45 mm mineral wool).

The different treatments on the CLT floor have been tested at CSTB acoustic laboratory so their acoustic performance is available (see [2] for the different tested floors). Due to lack of data, the transmission loss for the CLT wall was taken identical to the CLT floor. The performance  R of the lining on the CLT wall was deduced from previous measurements performed on a CLT wall with a thickness of 94 mm (see Acoubois project [3]).

Figure 2 illustrates the structure and localizes the different walls and floors implemented.

Figure 1: View of the “ADIVBois Acoustic Mockup”.

Lightweight separating wall

Floor 2 Rooms S13, S14, S23, S24 50 mm screed on thin resilient

SAD180

layer CLT 140 mm Suspended ceiling : air 20 mm,

glass wool 80 mm, 2 BA13

Floor 1 Rooms S11, S12, S21, S22 60 mm screed on 15 mm mineral

wool resilient layer

80 mm Gravel

CLT 140 mm

Separating wall

Separating wall

2 BA13 45 mm mineral wool and 35 mm air gap

2 BA13 45 mm mineral wool and 35 mm air gap

CLT 140 mm 45 mm mineral wool and 35 mm air gap

CLT 140 mm 45 mm mineral wool and 35 mm air gap

2 BA13

2 BA13

Figure 2: Construction principle of the “ADIVBois Acoustic Mockup”.

2.2. Junctions Figure 3 presents the different junctions implemented between the different components. The junction denoted with “b” do not include resilient layer; those with “a” do. In cross-junction LN°04, the CLT floors are connected to the vertical CLT walls using L-shaped metallic brackets spaced every 50 cm. The junctions LN°01 implement a secondary supporting beam (section of size 80 mm x 200 mm) on top of which the floor is attached. Junctions LN°02 are similar to LN°01 but without the secondary supporting beam; these junctions are not structural junctions since they are parallel to the floor span. Junction LN°05 is not symmetric; the floor is supported on a supporting beam (section of size 80 mm x 200 mm) on one side of the CLT wall and on an angle iron on the other side; furthermore, the junction LN°05b is rather a T-junction due to the presence a lightweight separating floor in the top floor. The resilient is a 12.5 mm thick Sylodyn NB by Getzner; it is

compressed to 10 mm. Some compressed mineral wool is also incorporated for fire hazard.

Junction vibration reduction indices measured on the “ADIVBois Acoustic Mockup” were presented in [1] and compared to the empirical ones given in ISO 12354 [4]; These results are not reproduced here. In general, it was observed that the empirical data for the junction vibration reduction indices did deviate from the measured ones. Furthermore, it was rather difficult to conclude about the benefit of including a resilient layer in the junctions.

Middle floor

Top floor

C d i l l

Figure 3: Different junctions in the “ADIVBois Acoustic Mockup”.

2.3. Acoustic performance evaluation The following building performance corresponding to a dwelling configuration with the entry level of the NF Habitat certification was selected as the target performance :

• D nT,w +C  53 dB for airborne sound insulation • L’ nT,w ≤ 55 dB et L’ nT,w + C I50-2500 ≤ 55 dB for impact sound insulation Regarding the acoustic measurements, different teams participated; the FCBA team used the in- situ engineering measurement method (EN ISO 16283 standards [5]) and the other teams the survey method (EN ISO 10052 standard [6] and the French Acoustic Measurement Guide [7]). In the following tables presenting the measured performance, the result in brackets denotes the one obtained with the survey measurement method.

Laison N®03 - Liaison File B entre 2 et 3 BD komm, set se

All measurements were performed in one-third octave bands from 50 to 5000 Hz for airborne and impact sound insulation. It should be mentioned that no room in the “ADIVBois Acoustic Mockup” was below 25 m 3 and corner measurements as required by ISO 16283 for small rooms were not necessary.

The acoustic performance predictions are performed according to the EN ISO 12354-1 and -2

Liaison N° - Liason File B entre 2 et 3(R+2) eotrn ce / Semen ne is

aison N°05, « Liaison Fle B entre 1 et 2 iar xo rah Sesset aa

standards [4]. These predictions are based on the performance of the components measured in the laboratory (or the AcouBat software database for the lightweight SAD 180 wall) and on both the vibration reduction values at the junctions measured on the “ADIVBois Acoustic Mockup” and the empirical ones from ISO 12354 [4].

It should also be mentioned that measurements with the rubber ball as excitation were also performed; however, these results are not presented in this paper.

Finally, measurements and predictions were performed for different situations of the “ADIVBois Acoustic Mockup”:

• Phase 1: bare CLT structure, with only the façade linings in place • Phase 2: structure with added linings on CLT walls and added treatments on CLT floors, but beams and posts remaining apparent • Phase 3: structure with added linings on CLT walls and added treatments on CLT floors, and beams and posts encased (enclosure made of 45 mm mineral wool with 2 layers of BA13 plaster boards on an independent metallic frame) for rooms with large volumes (SX3 and SX4) The present paper concentrates on the results of Phase 3; for the effect of apparent wood and more specifically beams and post, see companion paper [2]. One of the large rooms on the ground floor (Room S03) was divided in two by a lightweight plasterboard-based partition wall; the corresponding room with a volume just above 25 m 3 will be denoted S03r and could be considered as a good representation of a small bedroom.

Different floor coverings were tested. First, a simple plastic floor covering (denoted “RdS” in the following) with a performance of ∆L w = 18 dB on a 140 mm thick concrete floor (with in particular ∆L  7 dB at 50 Hz) was used and then ceramic tiles were mounted using mortar. It should be noted that for simplicity the complete floor was not covered by the floor finishing as shown in Figure 4. These two floor coverings have also been tested in the laboratory on the same CLT-based floor systems.

Plastic floor covering (RdS)

Tiles

Figure 4: Floor coverings in the “ADIVBois Acoustic Mockup”. 3. ACOUSTIC PERFORMANCE RESULTS

The obtained results from measurement and prediction are compared to the selected target acoustic performance objectives: D nT,w +C ≥ 53 dB, L’ nT,w ≤ 55 dB and L’ nT,w + C I50-2500 ≤ 55 dB; results not meeting the target performance are shown with pink background color in the tables below.

It should be noted that in the following sections, in order to simplify the notation, D nT,A corresponds to D nT,w +C and D nT,A50 to D nT,w + C 50-3150 for airborne sound insulation, and C I50 to the adaptation term C I50-2500 for impact sound insulation.

In the following tables giving the predicted acoustic performance, the levels in brackets correspond to the performance evaluated using the empirical vibration reductions for CLT junctions from ISO 12354 [4]. In the following figures, only the predicted acoustic performance using the vibration reduction measured indices on the “ADIVBois Acoustic Mockup” s shown.

3.1. Airborne sound insulation

Table 1 presents the results obtained for the airborne sound insulation in terms of single-number values from measurements and the prediction. Figure 7 shows some of the airborne sound insulation results as a function of frequency.

The results obtained from the different measurement methods are rather consistent with the predicted ones in terms of D nT,A except for the horizontal transmission between rooms S13 and S14 (separating wall being a lightweight double frame plasterboard-based wall). On average, the predicted results are more in line with the measured ones following the engineering measurement method. Integrating the low frequency adaptation terms also leads also to comparable results but the different on average is larger. The predicted performance overestimates in general the measured one. The difference between the predicted performance using the measured vibration reduction indices or those empirical one is rather limited (up to 2 dB difference).

In general, the airborne sound insulation results for the “ADIVBois Acoustic Mockup” fulfil the objective of 53 dB in terms of D nT,A based on the prediction or the measurements as long as no apparent wood is involved (see companion paper [2] for apparent wood effect on the acoustic performance).

Table 1: Airborne sound insulation performance.

Rooms Prediction D nT,A | D nT,A50 (dB)

Measurement Survey

Measurement Engineering

D nT,A | D nT,A50 (dB)

D nT,A | D nT,A50 (dB)

S03/S04 65 (65) 57 (57) 65 49 – – S03/S13 60 (60) 57 (57) 58 56 60 58 S04/S14 60 (60) 57 (57) 58 57 60 58 S13/S12 65 (66) 58 (58) – – 66 53 S13/S14 59 (60) 53 (54) 54 50 54 51 S13/S23 66 (67) 63 (63) 62 57 65 63 S13/S24 66 (64) 62 (64) 61 60 63 62 S23/S24 57 (55) 52 (51) – – 55 52 S23/S22 65 (65) 57 (58) – – 67 58

3.2. Impact sound insulation

Table 4 presents the results obtained for the impact sound insulation in terms of single-number values from measurements and the prediction. Figure 8 shows some of the impact sound insulation results as a function of frequency.

The results obtained from the different measurement methods are again rather consistent with the predicted ones. On average, the predicted results are more in line with the measured ones following the engineering measurement method. Some measurements using the survey methods yields results that do not fulfil the target performance when the low frequency adaptation term is taken into account. The predicted performance underestimates in general the measured one. The difference between the predicted performance using the measured vibration reduction indices or those empirical one is rather limited except for the horizontal transmission between rooms S13 and S14 (separating wall being a lightweight double frame plasterboard-based wall). In this case, the prediction using the empirical vibration index underestimate the floor-to-floor transmission path in the mid frequency range (empirical vibration index higher than those measured in the mid frequency range).

S03-S13 or S04-S14

S13-S12

“soeaguanaeaeaeneaaseg

S23-S24

S13-S14

S13-S24

S13-S23

SoeSRSR RES SEES REREEES|

Figure 5: Airborne sound insulation.

Table 2: Impact sound insulation performance.

Rooms Prediction L’ nT,w | L’ nT,w +C I50 (dB)

Measurement Survey L’ nT,w | L’ nT,w +C I50 (dB)

Measurement Engineering

L’ nT,w | L’ nT,w +C I50 (dB)

S14/S04 53 (53) 54 (54) 54 56 52 55 S14/S04 (RdS) 50 (50) 51 (54) 51 54 50 54 S13/S03 53 (53) 54 (54) 54 55 – – S13/S03 (RdS) 50 (50) 51 (52) – – 49 54 S23/S13 47 (50) 51 (51) – – 50 52 S24/S13 50 (50) 51 (51) 53 57 52 54 S24/S13 (RdS) 47 (47) 48 (48) 51 55 47 52 S13/S14 52 (44) 51 (44) 51 48 48 46 S13/S14 (Tiles) 50 (44) 50 (44) – – 50 47

SoeSHSR RES SEES RER EEE S|

Figure 6: Impact sound insulation – S14/S04 or S13/S03.

S24-S13

S13-S14

Figure 7: Impact sound insulation – S24/S13 and S13/S14.

3.3. Effect of the room volume reduction The effect of room size is investigated in this section. Figure 8 shows the rooms configuration before and after dividing the room S03 on the ground floor using a plasterboard based partition wall. The volume of the reduced size room S03r is just above 25 m 3 .

Figure 8: Configuration for the effect of room size.

Table 3 presents the effect of the room size reduction on the airborne sound insulation. Dividing the room volume by a factor of 2 on the emission side, is associated to an improvement of the airborne sound insulation; in terms of D nT,A the increase is of 6 dB for the prediction method and 5 dB for the measurement (survey method). Figure 9 shows the associated spectra, the improvement of the airborne sound insulation due to the change from S03 to S03r is clear visible for the prediction and the measurements.

Table 3: Airborne sound insulation performance – Effect of room volume reduction.

Rooms Prediction D nT,A | D nT,A50 (dB)

Measurement Survey

Measurement Engineering

tesa Lelitt ltt

D nT,A | D nT,A50 (dB)

D nT,A | D nT,A50 (dB)

S03/S13 60 57 58 56 60 58 S03r/S13 66 63 63 60 – – S13/S03r 61 58 59 53 – –

Figure 9: Airborne sound insulation – Effect of room volume reduction.

813

Table 4 presents the effect of the room size reduction on the impact sound insulation. For the impact sound insulation without floor covering, the prediction method yields no effect due to the room size reduction on both the L' nT,w and L' nT,w +C I50 . On the other hand, measurements following the survey method leads no effect on L' nT,w and an increase of 4 dB of L' nT,w +C I50 .

A similar behavior is obtained for the prediction method when floor covering is involved. On the other hand, measurements following the engineering method leads an increase of both L' nT,w and L' nT,w +C I50 for the plastic floor covering (3 dB increase) and for the tiles (2 and 1 dB increase respectively).

Measurements demonstrate that the target performance in terms of sound insulation is therefore not reached due to the low frequencies behavior for the reduced size room configuration.

Figure 10 presents the corresponding impact sound spectra ; it is clearly shown the prediction model is unable reproduce the behavior observed in the measurements around the one-third octave bands of 160 and 200 Hz when the room size is reduced. Indeed, all measurements performed in he reduced room show an important increase of the impact sound level around the one-third octave bands of 160 and 200 Hz. This behavior can be explained in particular by room mode effects in the reduced size room; the acoustic field is then not diffuse, and the assumptions of the prediction method therefore do not longer apply.

For safety, it is therefore recommended to consider a certain margin on the prediction results for rooms with small volume. Predictions using a suspended ceiling integrating 2 BA18 plasterboards (instead of 2 BA13 plasterboards) or a suspended ceiling integrating 2 BA13 plasterboards mounted on resilient hangers could meet the target when a plastic floor covering is considered.

Table 4: Impact sound insulation performance.

Rooms Prediction L’ nT,w | L’ nT,w +C I50 (dB)

Measurement Survey L’ nT,w | L’ nT,w +C I50 (dB)

Measurement Engineering

L’ nT,w | L’ nT,w +C I50 (dB)

S13/S03 53 54 54 55 – – S13/S03 (RdS) 50 51 – – 49 54 S13/S03 (Tiles) 54 57 – – 52 58 S13/S03r 53 54 54 59 55 58 S13/S03r (R d S) 50 51 51 56 52 57 S13/S03r (Tiles) 54 57 54 59 54 59 4. CONCLUSIONS

The construction and acoustic investigation of the “ADIVBois Acoustic Mockup” have enabled a significant advance in the understanding of the acoustics of wooden constructions, in particular that of high-rise buildings made of cross laminated wooden panels (CLT). All the data collected made it possible to verify and determine constructive solutions, integrating floors with and without a suspended ceiling.

In this paper, prediction results ware compared to measured ones in terms of airborne sound and impact sound insulation. The results obtained from the different measurement methods were found rather consistent with the predicted ones and on average, the predicted results were more in line with the measured ones following the engineering measurement method. For the impact sound insulation, the predicted performance underestimates in general the measured one. Some impact sound insulation measurements using the survey methods yielded results that do not fulfil the target performance when integrating the low frequency adaptation term. The difference between the predicted performance using the measured vibration reduction indices or those empirical one was found limited except in a specific case.

The effect of room size reduction was also investigated, in order to reach the size of a bedroom. For airborne sound insulation, the predicted and measured results yield similar effect with an increase of 5 to 6 dB in D nT,A . However, for the impact sound insulation without floor covering, the prediction method yields no effect due to the room size reduction on both the L' nT,w and L' nT,w +C I50 ,

while the measurement survey method leads no effect on L' nT,w and an increase of 4 dB of L' nT,w +C I50 .

In general, the airborne sound insulation results for the “ADIVBois Acoustic Mockup” fulfil the objective of 53 dB in terms of D nT,w + C based on the prediction or the measurements as long as no apparent wood is involved (see companion paper [2] for apparent wood effect on the acoustic performance). Care should be taken regarding impact sound insulation and the effect of floor covering, especially in small rooms.

The full reports of this study are undergoing final review and should be available soon. It is expected that the “ADIVBois Acoustic Mockup” will remain for testing other constructive solutions.

Figure 10: Impact sound insulation performance – Effect of room volume reduction.

5. ACKNOWLEDGEMENTS

The authors would like to thank ADIVBois, CODIFAB and the French Nouvelle-Aquitaine region for the financial support provided to this project. In addition, the authors would particularly like to thank the various contributors who participated free of charge in this study, in particular the companies that provided materials, the acoustic design offices and industrial acousticians who carried out additional acoustic measurements and finally the members of the ADIVBois acoustic working group for their contributions and constructive exchanges. 6. REFERENCES

1. C. Guigou Carter, C., Kouyoumji, J.-L., Balanant, N., De Bastiani, B., Acoustic performance of

a CLT-based 3 floor building mockup, Proceedings of Euronoise 2021 , October 2021. 2. C. Guigou Carter, C., Balanant, N., Kouyoumji, J.-L., Building acoustic performance prediction

– Feedback from Adivbois CLT building mockup, Proceedings of Internoise 2022 , August 2022 3. Acoubois project, https://www.codifab.fr/actions-collectives/bois/acoub ois- pe rf ormance- acoustique-des-constructions-ossature-bois-1310 , « Mesure acoustique en laboratoire » report. 4. EN ISO 12354 Building acoustics - Estimation of acoustic performance of buildings from the

performance of elements - Part 1: Airborne sound insulation between rooms and Part 2 : impact sound insulation between rooms (2017) 5. EN ISO 16283 Acoustics - Field measurement of sound insulation in buildings and of building

elements – Part 1 : airborne sound insulation (2014) and Part 2 : impact sound insulation (2020) 6. EN ISO 10052 Acoustics - Field measurements of airborne and impact sound insulation and of

service equipment sound - Survey method (2021) 7. Guide de mesures acoustiques, Version août 2014 (in French), https://www.ecologie.gouv.fr/sites/default/files/dgaln_guide_mesures_acoustiques_aout_2014.pdf