AIA-DAGA 2013 Merano
Comparison between Sound Reduction Index of single and double massive walls realised in Italy and Great Britain Renzo Cremonini1, Patrizio Fausti1, Elisa Nannipieri2, Simone Secchi2, Sean Smith3 1
Department of Engineering, University of Ferrara, Italy,
[email protected] Department of Industrial Engineering, University of Florence, Italy,
[email protected] 3 Institute for Sustainable Construction, Edinburgh Napier University, Great Britain,
[email protected] 2
Introduction In European countries, the acoustic performance of internal partitions between apartments are subject to very different limit values. This is a result of different habits and cultures in the various countries, as well as often different construction technologies. In this paper the results of a comparison of some of the common partition walls, used both in Italy and Great Britain, are reported. On the basis of a statistical survey conducted on partitions measured in situ on finished buildings, the average values of the apparent sound reduction index of these different construction systems were compared. All measurements were performed according to ISO 140-4 by the Universities of Ferrara and Florence for Italian buildings and by Robust Detail Ltd for British buildings. The types of walls analysed in this study were double-leaf cavity walls and single-layer concrete walls. The comparison was made on the frequencies performance in order to better understand the reasons for the different performances that can be observed at mid and high frequencies for some of these technological solutions.
It consists of a layer of hollow bricks 80 mm thick (with an apparent density between 700 and 800 kg/m3) and a layer of half full bricks 120 mm thick (with an apparent density between 800 and 1000 kg/m3), plastered with 10-15 mm of mortar on both sides and on one side of the cavity.
Description of the partitions tested
In the cavity there are 40 mm of mineral wood and 30 mm of air.
Cavity masonry walls with insulating material
The total number of walls tested in different buildings for this typology is 33.
Figure 1 – Italian double wall type 1 (ITA-WM-1)
The second kind of Italian partition analyzed (figure 2) is more diffused in recent years because of its better performance in comparison with the previous solution.
The first kind of Italian partition analyzed (figure 1) was quite largely used in buildings realized in Italy after 2000 and is still used in many cases [1]. It consists of two layers of hollow bricks, each 80 mm thick, with an apparent density between 700 and 800 kg/m3, plastered with 10-15 mm of mortar on both sides and on one side of the cavity. In the cavity there are two layers of mineral wood, each 40 mm thick. The total number of walls tested in different buildings for this typology is 7.
Figure 2 – Italian Double wall type 2 (ITA-WM-2)
The first kind of British partition analyzed (figure 3) is lightweight aggregate blockwork masonry encoded E-WM-8 in the Robust Detail Limited (RDL) handbook [2].
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AIA-DAGA 2013 Merano It consists of two layers of blocks, each 100 mm (min) thick, with an apparent density between 1350 and 1600 kg/m3, with a cavity 75 mm (min) thick partly filled with 35 mm (min) of mineral wool (Saint-Gobain Isover RD35). Both sides of the double wall are lined with gypsum based board (surface mass of 9,8 kg/m2) mounted on dabs.
expanded clay aggregate and concrete, characterized by an apparent density between 1200 and 1400 kg/m3, plastered with 10-15 mm of mortar on both sides. The first one (ITAWM 3 – 250 mm) is realized with blocks 250 mm thick, while the second (ITA-WM3 – 300 mm) with 300 mm thick blocks [3].
The total number of walls tested in different buildings for this typology is 409.
The total number of walls tested in different buildings for this typology is 69 for 250 mm blocks and 18 for 300 mm blocks.
Figure 3 – Britain double wall type 1 (E-WM-8)
Figure 5 – Italian single wall (ITA-WM-3)
The second kind of British partition analyzed (figure 4) is the Robust Detail Limited solution described in RDL handbook with the code E-WM-15 [2].
The single layer British partition analyzed (figure 6) is a solid dense aggregate blockwork masonry encoded E-WM-9 in the Robust Detail Limited (RDL) handbook [2].
It is an aircrete blockwork masonry; each layer of blocks is 100 mm (min) thick, with an apparent density between 700 and 800 kg/m3, the cavity is 75 mm (min) thick partly filled with 35 mm of mineral wool (Saint-Gobain Isover RD35). Both sides of the double wall are lined with gypsum based board (surface mass of 9,8 kg/m2) mounted on dabs.
It consists of a layer of clay blocks 215 mm thick, with an apparent density between 1850 and 2300 kg/m3. Both sides of the wall are lined with gypsum based board (surface mass of 12,5 kg/m2) mounted on dabs, on cement. The total number of walls tested in different buildings for this typology is 6.
The total number of walls tested in different buildings for this typology is 10.
Figure 6 – Britain single wall (E-WM-9)
Results of the measurements Figures 7 and 8 show the comparison between averaged values of SRI of Italian and British double and single partitions tested in different real buildings.
Figure 4 – Britain double wall type 2 (E-WM-15)
Block masonry walls There are two kinds of single wall Italian partition analyzed (figure 5), both realized with blocks made with light
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AIA-DAGA 2013 Merano The Italian walls show a worse behavior at medium frequencies, probably because the presence of a rigid junction with the floor increases the structural flanking transmission which constitutes the dominant transmission path for this type of walls. In fact, the realization of rigid joints at the base of the wall is due to the need to allow the passage of the pipes of the plants from the floor to the wall. The rigid junctions impose a behavior close to a monolithic wall of equal mass. Moreover, Italian partitions have rigid junctions also with flanking walls in order to avoid seismic collapse. Robust Details Ltd give recommendations (notes and diagram) for the construction of the elements where it is necessary to control flanking transmission. For example, the connection between the two leaves of the wall is realized with elastic ties, while the connection between the wall and other building elements is made with resilient layers. In a junction with another cavity wall, the cavity is filled with an absorbent layer. The standard deviation data show similar results for the same type of walls. The Italian and the British block walls show quite a different behavior when analyzed in frequency. In particular British walls show a reduction of performance at higher frequencies that are likely due to critical frequency of the gypsum board linings.
Figure 7 – Comparison between average values of SRI for different Italian and British cavity wall partitions. Vertical lines indicate the standard deviation at single frequencies.
It is important to note that the number of British walls (RD) analyzed was low. The method of construction of singlelayer walls has few variables, hence the possibility of workmanship errors is lower than for cavity walls.
Conclusions The results of measurements carried out in recent years point out the necessity of improving the acoustic performance of Italian double layer masonry walls. To investigate the influence of resilient layers the Italian data have been compared with RDL data. The results show differences especially at the medium frequencies, where there could be an increase in structural flanking transmission between the two layers of the wall. In the continuation of this work, more data of in situ measurements will be compared. Moreover, the analysis of the laboratory data referred to the same kind of partitions could be useful to better understand these results.
References [1] Nannipieri, E., Secchi, S., The Evolution of Acoustic Comfort in Italian Houses. In Building Acoustics, Vol. 19, n. 2, 2012.
Figure 8 – Comparison between average values of SRI for different Italian and British single wall partitions. Vertical lines indicate the standard deviation at single frequencies.
[2] RDL, The Robust Details Handbook - Part E: Resistance to the Passage of Sound. Robust Details Ltd, Milton Keynes, UK, RD, 2011.
Consideration on results
[3] Fausti, P., Secchi, S., Statistical analysis of Sound Reduction Index measurements on typical Italian lightweight concrete block walls. In proceedings of Euronoise 2012, Prague, 10 – 13 June 2012.
The acoustic performance of cavity walls is strongly influenced by the method used to connect the wall with its flanking structures.
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