- Email: [email protected]
Acoustic failure analysis of windows in buildings
Engineering Failure Analysis 18 (2011) 1761–1774
Contents lists available at ScienceDirect
Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal
Acoustic failure analysis of windows in buildings M. Blasco a,b,⇑, J. Belis b, H. De Bleecker c a b c
Blasco Ltd., Sint-Bartholomeusstraat 91, B-2170 Merksem, Belgium Laboratory for Research on Structural Models, Ghent University, Technologiepark-Zwijnaarde 904, B-9052 Ghent, Belgium Scheldebouw B.V., Herculesweg 17, 4330 EA Middelburg, The Netherlands
a r t i c l e
i n f o
Article history: Available online 2 April 2011 Keywords: Acoustic emission Defects Design Joint failures Non-destructive testing
a b s t r a c t Poor acoustic insulation of building façades is largely influenced by the component assembly of the window and by the installation of the window in the wall. For the first, a poor gasket design and poor gasket installation during the window assembly will usually lead to whistle noises inside the rooms, especially next to busy roads. For the latter, the choice and installation of obturating materials in the cavity between the window and the wall may lead to a decrease in acoustic insulation in a wider range of frequencies. Consequently, the objectives of this investigation are to evaluate different methods to detect acoustical failures in openable windows in walls, and to present an efficient approach to optimise the sound insulation of a façade. By means of experimental measurements on a standard openable window, two different and complimentary approaches are compared to evaluate the acoustical quality and failures of the gaskets and the final setup of the window. More specifically, the first type of measurement is based on a standard sound insulation measurement of the façade according to ISO 140-5, and the second consists of ultrasonic measurements. The acoustic impact of the cavity between the window and the wall is evaluated in the laboratory according to ISO 140-3. For this research two different and most common materials are used to obturate the gap: polyurethane foam and mineral wool. The impact of these different types of materials is evaluated against different types of glazing. On the one hand side, standard sound insulation measurements enable to evaluate the quantitative impact of different parameters governing acoustical failures, such as discontinuity, incorrect placement and wrong selection of both gaskets and obturating material. On the other hand, ultrasonic measurements enable a quick qualitative assessment that is very efficient to determine the exact position of the acoustic leaks in the façade. Finally, a combined use of standard and ultrasonic measurements is proposed to deliver an efficient approach to detect acoustical failures of windows. The ultrasonic approach is a quick and cost-effective way to instantly track workmanship deficiencies of a window on site, whereas the standard measurements are more time consuming but needed to guarantee the performance of a building element. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction It is well known that acoustic failures of windows in buildings are highly dependent on the component assembly of the window and on the quality of workmanship during its installation in the wall [5]. Consequently, the main objective of this ⇑ Corresponding author at: Laboratory for Research on Structural Models, Ghent University, Technologiepark-Zwijnaarde 904, B-9052 Ghent, Belgium. Tel.: +32 486 181544; fax: +32 9 264 5838. E-mail address: [email protected] (M. Blasco). 1350-6307/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2011.03.027
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research is to have a quantitative and qualitative idea of the acoustic impact of different parameters of windows with aluminium frames, such as the continuity of the gaskets, the pressure on the gasket, and the type of material used to fill the cavity between the window and the wall. To investigate this impact, experimental measurements have been conducted both in laboratory and on site. The measurement results are obtained using different measuring methods: a standard acoustic insulation measurement procedure using wide range sound frequencies and a more qualitative method using ultrasounds. For the laboratory measurements standard dimensions for the windows were used. The impact of the surface of the window is not considered in this research. The impact of the perimeter is more important as the surface of the window diminishes: for supercritical frequencies, the impact of the surface of the sample is theoretically negligible, although experiments show that a bigger sample surface is leading to a better sound reduction index (SRI) in this frequency area for windows [1]. 2. Materials and methods 2.1. Laboratory measurements according to ISO 140-3 Initially, different window configurations have been investigated experimentally at LARGE (Laboratory for Acoustic Research on Glass and large Envelopes), located at Ghent University, Belgium. The SRI is measured on a standard small sample (1.23 m 1.48 m) according to ISO 140-3. The sample consists of a window, i.e. aluminium frame combined with different types of glazing. The cavity between the window frame and the wall, depicted in Fig. 1, is approximately 7 cm in width and is completely obturated with self-expanding polyurethane foam (PU – TYPE ‘‘Rubson – All seasons’’) or mineral wool respectively (MW – TYPE ‘‘Rockwool’’). On site the cavity between the window and the construction is usually not obturated completely. The cavity between window and wall is closed off using two gypsum boards (12.5 mm thickness each) on both sides, to simulate on site conditions, as illustrated in Fig. 2a and b. The glazing used in the setup is 6-12-8 and 10-18-66.2A, being a low and high acoustic performing glazing respectively. An overview of materials used in the different test samples is listed in Table 1. As a reference test to determine the impact of the cavity between the frame and the wall the best acoustic performing glazing and frame were screened with four layers of gypsum board, illustrated in Fig. 2c. Screening was realised by mounting two gypsum boards (each 12.5 mm thick) on both sides of the glass and aluminium frame. 2.2. On site sound insulation measurements according to ISO 140-5 To enable a simulation of different component assemblies during the on site measurements, an openable window has been chosen which enables different setups, such as a modification of the continuity of the gasket and the pressure level on the gasket. The window is depicted in Fig. 3.
Fig. 1. Mounting of 1.23 m 1.48 m standard window in laboratory with a construction cavity at the perimeter of the window: (a) overview; (b) detail of the construction cavity (the perimeter is protected by orange tape). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Fig. 2. Standard window in laboratory setup: (a) finished mounting; (b) detail of screening of the construction cavity; (c) screening of the complete window; (d) construction cavity obturated with PU-foam.
Table 1 Overview of 1.23 m 1.48 m standard aluminium window frame test samples according to ISO 140-3, indicating glazing type and obturating material in the cavity between the window and the wall for different window configurations. MW = mineral wool; PU = polyurethane foam. Test name
Obturating material in cavity between window and wall
Glazing type
Screening of glazing
Testlab Testlab Testlab Testlab Testlab Testlab
MW MW MW PU PU PU
6-12-8 10-18-66.2A 10-18-66.2A 6-12-8 10-18-66.2A 10-18-66.2A
No No Yes No No Yes
1 2 3 4 5 6
The acoustic insulation of the window has been measured for the different setups according to ISO 140-5, as illustrated in Fig. 4. In addition, the acoustic leakages have been checked using an ultrasonic measurement device, which enables to give an indication of the acoustic air leakages at the perimeter of the window.
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Fig. 3. (a) Interior view of the window; (b) detail of the gasket on the fixed part; (c) fixed and openable parts of the window; (d) detail of the gasket on the openable part of the window.
Fig. 4. Different positioning of the gasket. The gasket is represented by the bold line at the perimeter: (a) continuous gasket; (b) discontinuous gasket (open corners); (c) no gasket.
2.3. On site ultrasonic measurements Ultrasonic measurements can be used to detect acoustic leakages in a construction. As the wave length is small (9 mm or 38.4 kHz), small acoustic failures can be detected with ultrasonic waves.
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(a)
(b)
Fig. 5. Ultrasonic measurements: (a) detector and emittor; (b) the 16 measuring points at the perimeter of the window.
Table 2 Results of sound reduction index Rw (C; Ctr) measurements of different window configurations according to ISO 140-3. Configuration
Rw (C; Ctr) without cavity (dB)
Rw (C; Ctr) with cavity and polyurethane (dB)
Rw (C; Ctr) with cavity and mineral wool (dB)
6-12-8 6-12-8 in ALU 10-18-66.2A 10-18-66.2A in ALU 10-18-66.2A in ALU screened
35 35 45 40 –
– 35 ( 1; – 39 ( 1; 44 ( 2;
– 36 ( 2; – 40 ( 1; 45 ( 2;
( ( ( (
1; 1; 1; 1;
4) 3) 4) 4)
dB dB dB dB
4) 5) 6)
4) 5) 6)
During the measurements an ultrasonic sound wave is emitted from outside by an ultrasonic emitter. Simultaneously, the acoustic leakages are quantified by scanning the perimeter of the same window, as in Fig. 3, from the inside with a handheld ultrasonic detector, able to measure the amount of ultrasonic waves. Fig. 5a illustrates the measuring equipment, of which the measurement precision was 0.1 dBlV. The window was scanned at the perimeter in 16 points, which are indicated in Fig. 5b. 3. Results 3.1. Laboratory measurement results An overview of the acoustic single value results is presented in Table 2. 3.2. On site sound insulation measurement results As expected, the creation of a discontinuity in the gasket resulted in a lowering of the acoustic insulation in the mid and higher frequencies , see Fig. 7, starting at a frequency of 172 divided by the biggest dimensions of the window, in this case 0.7 m. The usage of no gasket at all clearly impacts the sound insulation also in the lower frequencies. In Table 3 one can find the single value results of the window insulation on site. 3.3. On site ultrasonic measurement results The strength of ultrasonic waves detected is a continuous value (mean value) and is expressed in dBlV. The reference value measured at the center of the glass was 7 dBlV. Different configurations of the window were analysed as before, namely continuity and discontinuity of the gasket and the pressure on the gasket. In Fig. 8 the impact of the different configurations can clearly be seen. To quantify the acoustic leakages using the ultrasonic measurements, a single value can be used, being the mean value of the acoustic transmission of ultrasonic waves at the 16 measuring points. Table 4 gives an overview for the different configurations using a mean value for the ultrasonic transmission and the acoustic insulation of the window. 4. Discussion 4.1. Laboratory measurements Earlier research [2–4] demonstrated that the use of an aluminium frame does diminish the acoustic performance of the glazing when the glazing has a high acoustic performance. This is confirmed here: for lower performing glazings (e.g. 6-12-8)
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(a)
(b)
Fig. 6. Resulting laboratory sound reduction index measurements on a 1.23 m 1.48 m standard window indicating the effect of different glazing and different obturating material in the cavity between the window and the wall: (a) with glazing 6-12-8 and PU or MW in the cavity; (b) with glazing 10-1866.2A and PU or MW in the cavity; (c) with glazing 10-18-66.2A and PU or MW in the cavity, compared to the glazing alone and the window without cavity; (d) with glazing 6-12-8 and PU or MW in the cavity, compared to the glazing alone and the window without cavity; (e) with a completely screened off window surface and PU or MW in the cavity.
M. Blasco et al. / Engineering Failure Analysis 18 (2011) 1761–1774
(c)
(d)
Fig. 6 (continued)
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(e)
Fig. 6 (continued)
the frame does not have a significant influence on the overall performance, where for higher performing glazings (e.g. 10-1866.2A) the influence can amount to 5 dB. Similarly, the influence of the type of material in the cavity between the window and the wall is more visible for higher performing glazings (Fig. 6). Here, using PU in the cavity instead of MW lowers the SRI by almost 2 dB in the whole frequency range, although the impact on the single value is limited to 1 dB. When using polyurethane in the cavity, in the low frequencies the impact compared to a window without construction cavity is 1 dB (in single value) for lower performing glazings, whereas it is 2 dB (in single value) when using higher performing glazings. In the mid and high frequencies the impact of using polyurethane compared to a window without construction cavity is only 1 dB (in single value) when using higher performing glazings. However, for low performing glazings no impact is visible in this frequency range. When using MW in the cavity and comparing that configuration to a window without construction cavity, in the low frequencies the impact is 0 dB (in single value) for lower performing glazings, whereas it is 1 dB (in single value) when using higher performing glazings. In the mid and high frequencies the impact of using MW is not visible in this frequency range. In Fig. 6c and d, all comparisons are visualised. In Fig. 9a one can see the expected positive and negative influence of using PU or MW in the cavity between the window and the wall in relation to different acoustic insulation values of a window without construction cavity. The 45° inclined line represents the condition where no influence of the cavity is to be expected. If the results are below this line, then the cavity has a negative impact on the expected SRI of the window alone. If the results are higher than the 45° inclined line, then the cavity has a positive acoustic impact. The value of 35–40 dB seems to be a transition point for respectively the materials PU and MW (Fig. 9a). Up to a SRI of 40 dB of the window alone, the cavity of the window does not have a negative impact on the overall performance of the window when the cavity is filled with MW. Up to 35 dB for the window alone, the cavity of the window does not have a negative impact on the overall performance of the window when the cavity is filled with PU. Interesting to know for a window is how and to which extent a specific choice of material to fill up the construction cavity will on its turn influence the choice of a specific glazing. After all, in practice the frame of a window for dwellings is relatively standard, whereas for the glazing there are many options. To be able to answer this question, the acoustic impact of an aluminium frame on a window is depicted in Fig. 9b. Combining Fig. 9a and b results in Fig. 9c, in which the relationship is visualised between a glazing and a window built in a wall using PU or MW in the cavity. From Fig. 9c can be concluded that the use of MW in the construction cavity of a window allows for more margin in the acoustic performance of the system, i.e. the maximum acoustic performance of the glazing is approximately 38 dB, before the
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(a)
(b)
Fig. 7. Effect of different gasket configurations on sound insulation measurements: (a) effect of lowering the pressure on the gasket; (b) effect of eliminating the gaskets in either the fixed or rotating profile or both; (c) effect of gasket discontinuity.
cavity has a negative impact on the performance of the window. When using PU in the construction cavity the maximum performance of the glazing is limited to 36 dB approximately, before the negative impact of the cavity takes place.
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(c)
Fig. 7 (continued)
Table 3 Single value measurement results of the acoustic insulation of the window for different gasket configurations. Gasket in openable part
Gasket in fixed part
Pressure
D2m,ls,nT,w (C; Ctr) (dB)
Continuous Continuous Not continuous Continuous Not continuous Not continuous Continuous None None
Continuous Continuous Continuous Not continuous Not continuous Not continuous None Continuous None
Low High High High Low High High High –
47 50 49 50 45 48 45 47 28
( ( ( ( ( ( ( ( (
1; 1; 1; 2; 1; 1; 1; 2; 1;
3) 4) 4) 4) 3) 4) 3) 3) 2)
4.2. On site measurements according to ISO 140-5 In Fig. 7c the impact of the pressure (100% and 50%) on the gasket is shown. Two cases were looked at, namely 1) full continuous gaskets and 2) discontinuous gaskets, meaning that the gasket was removed at the corners. The results reveal that in both cases the impact is very similar. From 250 Hz onwards, the negative impact of lowering the gasket pressure is approximately 2–5 dB in the rest of the frequency bands. This emphasises the importance of increasing the pressure on the gaskets as much as possible. Fig. 7b demonstrates that the gasket positioned at the fixed part of the window is the most important gasket. This can be understood when looking at the section of the window: the gasket on the fixed part seals off a cavity between the profile of the rotating part and the fixed part. When eliminating the gasket of the fixed part, the cavity is in contact with the receiving room, forcing more sound to enter the room. Finally, the discontinuity of a gasket has been analysed. Often the gaskets are discontinuous at the corners of rotating constructions, such as windows and doors, which again reduces the sound insulation of the window, as can be seen in Fig. 7c. However, this discontinuity is not crucial when dealing with two gaskets (one in the fixed profile and one in the rotating profile) as is the case here. Although when the discontinuity is present in both gaskets, the results are very similar to continuous gaskets where the gasket pressure is reduced to 50%. From the measurement results has been seen that lowering the pressure on the gasket to 50% of the normal (airtight) pressure lowered the sound insulation value with 3 dB expressed in single value. Not using a gasket on the fixed part of
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(a)
(b)
(c)
(d)
(e)
Fig. 8. Ultrasonic leakage through the window perimeter, measured in 16 points, for different gasket configurations [dBlV]: (a) effect of different pressure on continuous gasket; (b) effect of different pressure on discontinuous gasket (open corners); (c) effect of gasket presence in fixed part of window (i.e. inside); (d) effect of gasket presence in openable part of window (i.e. outside) (e) comparison of different gasket configurations.
Table 4 Overview mean value ultrasonic transmission normalised to the reference value of
7 dBlV and façade insulation values.
Configuration
Mean ultrasonic transmission (MUT) (dBlV)
Façade insulation Dls,2m,nT (C; Ctr) (dB)
Gasket continuous Gasket cont 1/2 pressure Corners no gasket Corners no gasket 1/2 pressure No gasket No gasket inside No gasket inside 1/2 pressure No gasket outside No gasket outside 1/2 pressure
17.5 28 17.7 29.3 50.4 32.3 37.1 18.2 31.0
50 47 48 45 28 45 43 47 45
( ( ( ( ( ( ( ( (
1; 1; 1; 1; 1; 1; 1; 2; 2;
4) 3) 4) 3) 2) 3) 3) (estimated) 3) 3) (estimated)
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Fig. 9. Sound reduction index (Rw) of a 1.23 m 1.48 m standard window: (a) comparison of using either PU or MW as fill in material in the cavity between window and wall; (b) influence of the frame on the performance of a glazing. The continuous line represents no acoustic influence of the frame on the window. The dashed line is an interpolation of different tests and represents the acoustic influence of a thermally decoupled aluminium frame when combined with a glazing (Ref.: Saint-Gobain Glass); (c) expected relationship of the sound reduction index (Rw) between a glazing and that same glazing used in combination with a thermally decoupled aluminium frame mounted in a wall, where the construction cavity is filled up with PU or MW.
the window lowered the sound insulation with 5 dB in single value. Not using a gasket on the rotating part of the window lowered the sound insulation with 3 dB in single value. Not using a gasket on both parts of the window lowered the sound insulation with 22 dB in single value. A discontinuity of the gasket at the corners of the rotating part reduces its sound insulation with only 1 dB in single value. No gasket at the corners of the fixed part had no significant acoustic impact. 4.3. On site ultrasonic measurements As stated in section 2.3, ultrasonic analysis can be used to instantly trace the acoustic leakages. Fig. 8a illustrates how the gasket in a window limits the acoustic ultrasonic transmission. However, when the pressure on that gasket is limited, then the positive effect of the gasket is reduced extremely. Furthermore, it can also be noticed that a continuous gasket with normal pressure does not act equally efficiently along the whole perimeter of the window. Typically at the side of the hinges of the window the performance of the gasket is less efficient due to tolerances of the profiles. In Fig. 8b the effect of deleting part of the gasket at the corners of the window can be observed, both for gaskets situated on the outside, i.e. in the rotating profile, and inside, i.e. in the fixed profile. In case of normal pressure on the gaskets and in comparison to the continuous gasket, the acoustic impact is most noticeable at the sides of the hinges, as already explained.
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(c)
Fig. 9 (continued)
Obviously, the impact is also noticeable at the corners. When releasing the pressure on the gasket the acoustic leakage becomes evident. It should be noticed that the acoustic impact is less important at the hinged side of the window when the pressure on the gasket is released, as could be expected due to the geometry of the window i.e. hinges are the rotating point of the frame. Subsequently, Fig. 8c illustrates the effect of eliminating the gasket from the fixed profile (inside gasket). Eliminating the inner gasket has an immediate impact on the acoustic leakage, while further reducing the pressure on the remaining gasket has less impact. Subsequently, the effect of eliminating the gasket from the rotating profile (outer gasket) is visualised in Fig. 8d. Eliminating the outer gasket has only a marginal impact on the acoustic leakage of the window, although a further reduction of the pressure on the inside gasket has a more important impact. The hinged part of the window is acoustically more transparent than the other parts when using maximal pressure on the gasket, due to fabrication tolerances on the hinges and the profiles. It is most likely that this is depending on the type of window, or at least on the materials used. In this case the window was made out of aluminium profiles. In normal serviceability conditions it was also concluded that the outer gasket, i.e. on the openable part, is acoustically the least important of the two gaskets. This is also confirmed by the sound pressure measurements.
Fig. 10. Relationship (quadratic interpolation) between mean ultrasonic transmission (MUT) and façade insulation for one type of window.
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Subsequently, Fig. 8e displays different configurations compared on a single graph. Finally, a relationship could be established between the ultrasonic leakage (Mean Ultrasonic Transmission: MUT) and the single value façade insulation for this type of window, as depicted in Fig. 10. It can be observed that the maximum façade sound insulation is obtained when the MUT is lower than 17.5 dBlV. More specifically, the ultrasonic transmission is not determining the sound insulation of the window anymore at these low values of the MUT; this MUT value is an initial requirement for this window to perform well. 5. Conclusions 5.1. Laboratory measurements The acoustic impact of an aluminium frame on the sound reduction index (SRI) of a glazing depends on the acoustic quality of the glazing itself: the lower the SRI of the glazing the lower the impact of the frame. A value of 37 dB for the SRI of the glazing is the transition point: for higher values than 37 dB the frame will have a negative acoustic impact on the SRI of the window. The same can be concluded for the impact of the cavity between the frame and the wall: the lower the SRI of the window the lower the impact of the cavity. Here the SRI transition points are 35 dB and 40 dB when filling the cavity with PU and MW respectively. In general, it can be concluded that when PU is used to fill up the cavity, the transition point is a sound insulation value of 36 dB for the glazing. However, when a window is used with a MW filling of the cavity then the transition point is a sound insulation value of 38 dB (not 40 dB) for the glazing alone. For values higher than the transition point, the acoustic impact of the filled cavity is always negative. This leaves the use of MW in the cavity to have more margin on the choice of glazing. In addition, the experimental results revealed that the use of either MW or PU-foam in the perimeter of the window does not influence the acoustic insulation values of the window without cavity when using lower sound insulating windows in the mid and high frequencies, i.e. single values lower than 35 dB. In all other cases the improvement of using MW versus PU in the cavity is just 1 dB, which is not a very significant improvement. It is important to mention that the cavity was completely filled with PU-foam or MW. Taking into account the use of PU-foam for stability reasons of the window and easiness of interior finishing, i.e. finished with plaster, the use of PU-foam is appropriate. On the other hand the use of PU-foam is more time consuming due to drying periods of the foam. 5.2. In situ measurements An important conclusion is that the usage of continuous gaskets at the perimeter of the window is not so crucial for windows with an inner and outer gasket. Comparing different measurement setups, a lowering of the single value window insulation of 1 dB was found when a discontinuity of the gasket was introduced at the window corners. In addition, a maximum pressure on the gaskets must be guaranteed at all times. A reduction to 50% of the maximum - air tight - pressure on the gasket revealed a lowering of 3 dB on the single value sound insulation of the window. Consequently, when using a gasket in a window the pressure on the gasket is the most crucial factor. Also the inner gasket is more crucial than the outer gasket. Finally, ultrasonic measurements revealed to be a quick and good indicator of the acoustic performances of the window. A further study might be to indicate the relationship between the MUT and the sound insulation of the window for different types of windows. References [1] Michelsen N. Effect of size on measurements of the sound reduction index of a window or pane. Appl Acoust 1983;16(3):215–22. [2] Vermeir G, Roelens A, Van Dommelen H. Geluidisolatie van vensterramen en de invloed van raamkaders. Leuven: KULeuven; 2005. [3] Blasco M. Double ventilated glass façades acoustical performances. In: Proceedings Actieve en Interactieve Dubbelschalige Glasgevels – Dubbele Gevels, 7–16, Delft; 2004. [4] Marsh JA. The airborne sound insulation of glass: part 1. Appl Acoust 1971;4(1):55–70. [5] Quirt JD. Sound transmission through windows I. Single and double glazings. J Acoust Soc Am 1982;72(3):834–44.
Contents lists available at ScienceDirect
Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal
Acoustic failure analysis of windows in buildings M. Blasco a,b,⇑, J. Belis b, H. De Bleecker c a b c
Blasco Ltd., Sint-Bartholomeusstraat 91, B-2170 Merksem, Belgium Laboratory for Research on Structural Models, Ghent University, Technologiepark-Zwijnaarde 904, B-9052 Ghent, Belgium Scheldebouw B.V., Herculesweg 17, 4330 EA Middelburg, The Netherlands
a r t i c l e
i n f o
Article history: Available online 2 April 2011 Keywords: Acoustic emission Defects Design Joint failures Non-destructive testing
a b s t r a c t Poor acoustic insulation of building façades is largely influenced by the component assembly of the window and by the installation of the window in the wall. For the first, a poor gasket design and poor gasket installation during the window assembly will usually lead to whistle noises inside the rooms, especially next to busy roads. For the latter, the choice and installation of obturating materials in the cavity between the window and the wall may lead to a decrease in acoustic insulation in a wider range of frequencies. Consequently, the objectives of this investigation are to evaluate different methods to detect acoustical failures in openable windows in walls, and to present an efficient approach to optimise the sound insulation of a façade. By means of experimental measurements on a standard openable window, two different and complimentary approaches are compared to evaluate the acoustical quality and failures of the gaskets and the final setup of the window. More specifically, the first type of measurement is based on a standard sound insulation measurement of the façade according to ISO 140-5, and the second consists of ultrasonic measurements. The acoustic impact of the cavity between the window and the wall is evaluated in the laboratory according to ISO 140-3. For this research two different and most common materials are used to obturate the gap: polyurethane foam and mineral wool. The impact of these different types of materials is evaluated against different types of glazing. On the one hand side, standard sound insulation measurements enable to evaluate the quantitative impact of different parameters governing acoustical failures, such as discontinuity, incorrect placement and wrong selection of both gaskets and obturating material. On the other hand, ultrasonic measurements enable a quick qualitative assessment that is very efficient to determine the exact position of the acoustic leaks in the façade. Finally, a combined use of standard and ultrasonic measurements is proposed to deliver an efficient approach to detect acoustical failures of windows. The ultrasonic approach is a quick and cost-effective way to instantly track workmanship deficiencies of a window on site, whereas the standard measurements are more time consuming but needed to guarantee the performance of a building element. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction It is well known that acoustic failures of windows in buildings are highly dependent on the component assembly of the window and on the quality of workmanship during its installation in the wall [5]. Consequently, the main objective of this ⇑ Corresponding author at: Laboratory for Research on Structural Models, Ghent University, Technologiepark-Zwijnaarde 904, B-9052 Ghent, Belgium. Tel.: +32 486 181544; fax: +32 9 264 5838. E-mail address: [email protected] (M. Blasco). 1350-6307/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2011.03.027
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research is to have a quantitative and qualitative idea of the acoustic impact of different parameters of windows with aluminium frames, such as the continuity of the gaskets, the pressure on the gasket, and the type of material used to fill the cavity between the window and the wall. To investigate this impact, experimental measurements have been conducted both in laboratory and on site. The measurement results are obtained using different measuring methods: a standard acoustic insulation measurement procedure using wide range sound frequencies and a more qualitative method using ultrasounds. For the laboratory measurements standard dimensions for the windows were used. The impact of the surface of the window is not considered in this research. The impact of the perimeter is more important as the surface of the window diminishes: for supercritical frequencies, the impact of the surface of the sample is theoretically negligible, although experiments show that a bigger sample surface is leading to a better sound reduction index (SRI) in this frequency area for windows [1]. 2. Materials and methods 2.1. Laboratory measurements according to ISO 140-3 Initially, different window configurations have been investigated experimentally at LARGE (Laboratory for Acoustic Research on Glass and large Envelopes), located at Ghent University, Belgium. The SRI is measured on a standard small sample (1.23 m 1.48 m) according to ISO 140-3. The sample consists of a window, i.e. aluminium frame combined with different types of glazing. The cavity between the window frame and the wall, depicted in Fig. 1, is approximately 7 cm in width and is completely obturated with self-expanding polyurethane foam (PU – TYPE ‘‘Rubson – All seasons’’) or mineral wool respectively (MW – TYPE ‘‘Rockwool’’). On site the cavity between the window and the construction is usually not obturated completely. The cavity between window and wall is closed off using two gypsum boards (12.5 mm thickness each) on both sides, to simulate on site conditions, as illustrated in Fig. 2a and b. The glazing used in the setup is 6-12-8 and 10-18-66.2A, being a low and high acoustic performing glazing respectively. An overview of materials used in the different test samples is listed in Table 1. As a reference test to determine the impact of the cavity between the frame and the wall the best acoustic performing glazing and frame were screened with four layers of gypsum board, illustrated in Fig. 2c. Screening was realised by mounting two gypsum boards (each 12.5 mm thick) on both sides of the glass and aluminium frame. 2.2. On site sound insulation measurements according to ISO 140-5 To enable a simulation of different component assemblies during the on site measurements, an openable window has been chosen which enables different setups, such as a modification of the continuity of the gasket and the pressure level on the gasket. The window is depicted in Fig. 3.
Fig. 1. Mounting of 1.23 m 1.48 m standard window in laboratory with a construction cavity at the perimeter of the window: (a) overview; (b) detail of the construction cavity (the perimeter is protected by orange tape). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Fig. 2. Standard window in laboratory setup: (a) finished mounting; (b) detail of screening of the construction cavity; (c) screening of the complete window; (d) construction cavity obturated with PU-foam.
Table 1 Overview of 1.23 m 1.48 m standard aluminium window frame test samples according to ISO 140-3, indicating glazing type and obturating material in the cavity between the window and the wall for different window configurations. MW = mineral wool; PU = polyurethane foam. Test name
Obturating material in cavity between window and wall
Glazing type
Screening of glazing
Testlab Testlab Testlab Testlab Testlab Testlab
MW MW MW PU PU PU
6-12-8 10-18-66.2A 10-18-66.2A 6-12-8 10-18-66.2A 10-18-66.2A
No No Yes No No Yes
1 2 3 4 5 6
The acoustic insulation of the window has been measured for the different setups according to ISO 140-5, as illustrated in Fig. 4. In addition, the acoustic leakages have been checked using an ultrasonic measurement device, which enables to give an indication of the acoustic air leakages at the perimeter of the window.
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Fig. 3. (a) Interior view of the window; (b) detail of the gasket on the fixed part; (c) fixed and openable parts of the window; (d) detail of the gasket on the openable part of the window.
Fig. 4. Different positioning of the gasket. The gasket is represented by the bold line at the perimeter: (a) continuous gasket; (b) discontinuous gasket (open corners); (c) no gasket.
2.3. On site ultrasonic measurements Ultrasonic measurements can be used to detect acoustic leakages in a construction. As the wave length is small (9 mm or 38.4 kHz), small acoustic failures can be detected with ultrasonic waves.
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(a)
(b)
Fig. 5. Ultrasonic measurements: (a) detector and emittor; (b) the 16 measuring points at the perimeter of the window.
Table 2 Results of sound reduction index Rw (C; Ctr) measurements of different window configurations according to ISO 140-3. Configuration
Rw (C; Ctr) without cavity (dB)
Rw (C; Ctr) with cavity and polyurethane (dB)
Rw (C; Ctr) with cavity and mineral wool (dB)
6-12-8 6-12-8 in ALU 10-18-66.2A 10-18-66.2A in ALU 10-18-66.2A in ALU screened
35 35 45 40 –
– 35 ( 1; – 39 ( 1; 44 ( 2;
– 36 ( 2; – 40 ( 1; 45 ( 2;
( ( ( (
1; 1; 1; 1;
4) 3) 4) 4)
dB dB dB dB
4) 5) 6)
4) 5) 6)
During the measurements an ultrasonic sound wave is emitted from outside by an ultrasonic emitter. Simultaneously, the acoustic leakages are quantified by scanning the perimeter of the same window, as in Fig. 3, from the inside with a handheld ultrasonic detector, able to measure the amount of ultrasonic waves. Fig. 5a illustrates the measuring equipment, of which the measurement precision was 0.1 dBlV. The window was scanned at the perimeter in 16 points, which are indicated in Fig. 5b. 3. Results 3.1. Laboratory measurement results An overview of the acoustic single value results is presented in Table 2. 3.2. On site sound insulation measurement results As expected, the creation of a discontinuity in the gasket resulted in a lowering of the acoustic insulation in the mid and higher frequencies , see Fig. 7, starting at a frequency of 172 divided by the biggest dimensions of the window, in this case 0.7 m. The usage of no gasket at all clearly impacts the sound insulation also in the lower frequencies. In Table 3 one can find the single value results of the window insulation on site. 3.3. On site ultrasonic measurement results The strength of ultrasonic waves detected is a continuous value (mean value) and is expressed in dBlV. The reference value measured at the center of the glass was 7 dBlV. Different configurations of the window were analysed as before, namely continuity and discontinuity of the gasket and the pressure on the gasket. In Fig. 8 the impact of the different configurations can clearly be seen. To quantify the acoustic leakages using the ultrasonic measurements, a single value can be used, being the mean value of the acoustic transmission of ultrasonic waves at the 16 measuring points. Table 4 gives an overview for the different configurations using a mean value for the ultrasonic transmission and the acoustic insulation of the window. 4. Discussion 4.1. Laboratory measurements Earlier research [2–4] demonstrated that the use of an aluminium frame does diminish the acoustic performance of the glazing when the glazing has a high acoustic performance. This is confirmed here: for lower performing glazings (e.g. 6-12-8)
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(a)
(b)
Fig. 6. Resulting laboratory sound reduction index measurements on a 1.23 m 1.48 m standard window indicating the effect of different glazing and different obturating material in the cavity between the window and the wall: (a) with glazing 6-12-8 and PU or MW in the cavity; (b) with glazing 10-1866.2A and PU or MW in the cavity; (c) with glazing 10-18-66.2A and PU or MW in the cavity, compared to the glazing alone and the window without cavity; (d) with glazing 6-12-8 and PU or MW in the cavity, compared to the glazing alone and the window without cavity; (e) with a completely screened off window surface and PU or MW in the cavity.
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(c)
(d)
Fig. 6 (continued)
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(e)
Fig. 6 (continued)
the frame does not have a significant influence on the overall performance, where for higher performing glazings (e.g. 10-1866.2A) the influence can amount to 5 dB. Similarly, the influence of the type of material in the cavity between the window and the wall is more visible for higher performing glazings (Fig. 6). Here, using PU in the cavity instead of MW lowers the SRI by almost 2 dB in the whole frequency range, although the impact on the single value is limited to 1 dB. When using polyurethane in the cavity, in the low frequencies the impact compared to a window without construction cavity is 1 dB (in single value) for lower performing glazings, whereas it is 2 dB (in single value) when using higher performing glazings. In the mid and high frequencies the impact of using polyurethane compared to a window without construction cavity is only 1 dB (in single value) when using higher performing glazings. However, for low performing glazings no impact is visible in this frequency range. When using MW in the cavity and comparing that configuration to a window without construction cavity, in the low frequencies the impact is 0 dB (in single value) for lower performing glazings, whereas it is 1 dB (in single value) when using higher performing glazings. In the mid and high frequencies the impact of using MW is not visible in this frequency range. In Fig. 6c and d, all comparisons are visualised. In Fig. 9a one can see the expected positive and negative influence of using PU or MW in the cavity between the window and the wall in relation to different acoustic insulation values of a window without construction cavity. The 45° inclined line represents the condition where no influence of the cavity is to be expected. If the results are below this line, then the cavity has a negative impact on the expected SRI of the window alone. If the results are higher than the 45° inclined line, then the cavity has a positive acoustic impact. The value of 35–40 dB seems to be a transition point for respectively the materials PU and MW (Fig. 9a). Up to a SRI of 40 dB of the window alone, the cavity of the window does not have a negative impact on the overall performance of the window when the cavity is filled with MW. Up to 35 dB for the window alone, the cavity of the window does not have a negative impact on the overall performance of the window when the cavity is filled with PU. Interesting to know for a window is how and to which extent a specific choice of material to fill up the construction cavity will on its turn influence the choice of a specific glazing. After all, in practice the frame of a window for dwellings is relatively standard, whereas for the glazing there are many options. To be able to answer this question, the acoustic impact of an aluminium frame on a window is depicted in Fig. 9b. Combining Fig. 9a and b results in Fig. 9c, in which the relationship is visualised between a glazing and a window built in a wall using PU or MW in the cavity. From Fig. 9c can be concluded that the use of MW in the construction cavity of a window allows for more margin in the acoustic performance of the system, i.e. the maximum acoustic performance of the glazing is approximately 38 dB, before the
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(a)
(b)
Fig. 7. Effect of different gasket configurations on sound insulation measurements: (a) effect of lowering the pressure on the gasket; (b) effect of eliminating the gaskets in either the fixed or rotating profile or both; (c) effect of gasket discontinuity.
cavity has a negative impact on the performance of the window. When using PU in the construction cavity the maximum performance of the glazing is limited to 36 dB approximately, before the negative impact of the cavity takes place.
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(c)
Fig. 7 (continued)
Table 3 Single value measurement results of the acoustic insulation of the window for different gasket configurations. Gasket in openable part
Gasket in fixed part
Pressure
D2m,ls,nT,w (C; Ctr) (dB)
Continuous Continuous Not continuous Continuous Not continuous Not continuous Continuous None None
Continuous Continuous Continuous Not continuous Not continuous Not continuous None Continuous None
Low High High High Low High High High –
47 50 49 50 45 48 45 47 28
( ( ( ( ( ( ( ( (
1; 1; 1; 2; 1; 1; 1; 2; 1;
3) 4) 4) 4) 3) 4) 3) 3) 2)
4.2. On site measurements according to ISO 140-5 In Fig. 7c the impact of the pressure (100% and 50%) on the gasket is shown. Two cases were looked at, namely 1) full continuous gaskets and 2) discontinuous gaskets, meaning that the gasket was removed at the corners. The results reveal that in both cases the impact is very similar. From 250 Hz onwards, the negative impact of lowering the gasket pressure is approximately 2–5 dB in the rest of the frequency bands. This emphasises the importance of increasing the pressure on the gaskets as much as possible. Fig. 7b demonstrates that the gasket positioned at the fixed part of the window is the most important gasket. This can be understood when looking at the section of the window: the gasket on the fixed part seals off a cavity between the profile of the rotating part and the fixed part. When eliminating the gasket of the fixed part, the cavity is in contact with the receiving room, forcing more sound to enter the room. Finally, the discontinuity of a gasket has been analysed. Often the gaskets are discontinuous at the corners of rotating constructions, such as windows and doors, which again reduces the sound insulation of the window, as can be seen in Fig. 7c. However, this discontinuity is not crucial when dealing with two gaskets (one in the fixed profile and one in the rotating profile) as is the case here. Although when the discontinuity is present in both gaskets, the results are very similar to continuous gaskets where the gasket pressure is reduced to 50%. From the measurement results has been seen that lowering the pressure on the gasket to 50% of the normal (airtight) pressure lowered the sound insulation value with 3 dB expressed in single value. Not using a gasket on the fixed part of
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(a)
(b)
(c)
(d)
(e)
Fig. 8. Ultrasonic leakage through the window perimeter, measured in 16 points, for different gasket configurations [dBlV]: (a) effect of different pressure on continuous gasket; (b) effect of different pressure on discontinuous gasket (open corners); (c) effect of gasket presence in fixed part of window (i.e. inside); (d) effect of gasket presence in openable part of window (i.e. outside) (e) comparison of different gasket configurations.
Table 4 Overview mean value ultrasonic transmission normalised to the reference value of
7 dBlV and façade insulation values.
Configuration
Mean ultrasonic transmission (MUT) (dBlV)
Façade insulation Dls,2m,nT (C; Ctr) (dB)
Gasket continuous Gasket cont 1/2 pressure Corners no gasket Corners no gasket 1/2 pressure No gasket No gasket inside No gasket inside 1/2 pressure No gasket outside No gasket outside 1/2 pressure
17.5 28 17.7 29.3 50.4 32.3 37.1 18.2 31.0
50 47 48 45 28 45 43 47 45
( ( ( ( ( ( ( ( (
1; 1; 1; 1; 1; 1; 1; 2; 2;
4) 3) 4) 3) 2) 3) 3) (estimated) 3) 3) (estimated)
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Fig. 9. Sound reduction index (Rw) of a 1.23 m 1.48 m standard window: (a) comparison of using either PU or MW as fill in material in the cavity between window and wall; (b) influence of the frame on the performance of a glazing. The continuous line represents no acoustic influence of the frame on the window. The dashed line is an interpolation of different tests and represents the acoustic influence of a thermally decoupled aluminium frame when combined with a glazing (Ref.: Saint-Gobain Glass); (c) expected relationship of the sound reduction index (Rw) between a glazing and that same glazing used in combination with a thermally decoupled aluminium frame mounted in a wall, where the construction cavity is filled up with PU or MW.
the window lowered the sound insulation with 5 dB in single value. Not using a gasket on the rotating part of the window lowered the sound insulation with 3 dB in single value. Not using a gasket on both parts of the window lowered the sound insulation with 22 dB in single value. A discontinuity of the gasket at the corners of the rotating part reduces its sound insulation with only 1 dB in single value. No gasket at the corners of the fixed part had no significant acoustic impact. 4.3. On site ultrasonic measurements As stated in section 2.3, ultrasonic analysis can be used to instantly trace the acoustic leakages. Fig. 8a illustrates how the gasket in a window limits the acoustic ultrasonic transmission. However, when the pressure on that gasket is limited, then the positive effect of the gasket is reduced extremely. Furthermore, it can also be noticed that a continuous gasket with normal pressure does not act equally efficiently along the whole perimeter of the window. Typically at the side of the hinges of the window the performance of the gasket is less efficient due to tolerances of the profiles. In Fig. 8b the effect of deleting part of the gasket at the corners of the window can be observed, both for gaskets situated on the outside, i.e. in the rotating profile, and inside, i.e. in the fixed profile. In case of normal pressure on the gaskets and in comparison to the continuous gasket, the acoustic impact is most noticeable at the sides of the hinges, as already explained.
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(c)
Fig. 9 (continued)
Obviously, the impact is also noticeable at the corners. When releasing the pressure on the gasket the acoustic leakage becomes evident. It should be noticed that the acoustic impact is less important at the hinged side of the window when the pressure on the gasket is released, as could be expected due to the geometry of the window i.e. hinges are the rotating point of the frame. Subsequently, Fig. 8c illustrates the effect of eliminating the gasket from the fixed profile (inside gasket). Eliminating the inner gasket has an immediate impact on the acoustic leakage, while further reducing the pressure on the remaining gasket has less impact. Subsequently, the effect of eliminating the gasket from the rotating profile (outer gasket) is visualised in Fig. 8d. Eliminating the outer gasket has only a marginal impact on the acoustic leakage of the window, although a further reduction of the pressure on the inside gasket has a more important impact. The hinged part of the window is acoustically more transparent than the other parts when using maximal pressure on the gasket, due to fabrication tolerances on the hinges and the profiles. It is most likely that this is depending on the type of window, or at least on the materials used. In this case the window was made out of aluminium profiles. In normal serviceability conditions it was also concluded that the outer gasket, i.e. on the openable part, is acoustically the least important of the two gaskets. This is also confirmed by the sound pressure measurements.
Fig. 10. Relationship (quadratic interpolation) between mean ultrasonic transmission (MUT) and façade insulation for one type of window.
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Subsequently, Fig. 8e displays different configurations compared on a single graph. Finally, a relationship could be established between the ultrasonic leakage (Mean Ultrasonic Transmission: MUT) and the single value façade insulation for this type of window, as depicted in Fig. 10. It can be observed that the maximum façade sound insulation is obtained when the MUT is lower than 17.5 dBlV. More specifically, the ultrasonic transmission is not determining the sound insulation of the window anymore at these low values of the MUT; this MUT value is an initial requirement for this window to perform well. 5. Conclusions 5.1. Laboratory measurements The acoustic impact of an aluminium frame on the sound reduction index (SRI) of a glazing depends on the acoustic quality of the glazing itself: the lower the SRI of the glazing the lower the impact of the frame. A value of 37 dB for the SRI of the glazing is the transition point: for higher values than 37 dB the frame will have a negative acoustic impact on the SRI of the window. The same can be concluded for the impact of the cavity between the frame and the wall: the lower the SRI of the window the lower the impact of the cavity. Here the SRI transition points are 35 dB and 40 dB when filling the cavity with PU and MW respectively. In general, it can be concluded that when PU is used to fill up the cavity, the transition point is a sound insulation value of 36 dB for the glazing. However, when a window is used with a MW filling of the cavity then the transition point is a sound insulation value of 38 dB (not 40 dB) for the glazing alone. For values higher than the transition point, the acoustic impact of the filled cavity is always negative. This leaves the use of MW in the cavity to have more margin on the choice of glazing. In addition, the experimental results revealed that the use of either MW or PU-foam in the perimeter of the window does not influence the acoustic insulation values of the window without cavity when using lower sound insulating windows in the mid and high frequencies, i.e. single values lower than 35 dB. In all other cases the improvement of using MW versus PU in the cavity is just 1 dB, which is not a very significant improvement. It is important to mention that the cavity was completely filled with PU-foam or MW. Taking into account the use of PU-foam for stability reasons of the window and easiness of interior finishing, i.e. finished with plaster, the use of PU-foam is appropriate. On the other hand the use of PU-foam is more time consuming due to drying periods of the foam. 5.2. In situ measurements An important conclusion is that the usage of continuous gaskets at the perimeter of the window is not so crucial for windows with an inner and outer gasket. Comparing different measurement setups, a lowering of the single value window insulation of 1 dB was found when a discontinuity of the gasket was introduced at the window corners. In addition, a maximum pressure on the gaskets must be guaranteed at all times. A reduction to 50% of the maximum - air tight - pressure on the gasket revealed a lowering of 3 dB on the single value sound insulation of the window. Consequently, when using a gasket in a window the pressure on the gasket is the most crucial factor. Also the inner gasket is more crucial than the outer gasket. Finally, ultrasonic measurements revealed to be a quick and good indicator of the acoustic performances of the window. A further study might be to indicate the relationship between the MUT and the sound insulation of the window for different types of windows. References [1] Michelsen N. Effect of size on measurements of the sound reduction index of a window or pane. Appl Acoust 1983;16(3):215–22. [2] Vermeir G, Roelens A, Van Dommelen H. Geluidisolatie van vensterramen en de invloed van raamkaders. Leuven: KULeuven; 2005. [3] Blasco M. Double ventilated glass façades acoustical performances. In: Proceedings Actieve en Interactieve Dubbelschalige Glasgevels – Dubbele Gevels, 7–16, Delft; 2004. [4] Marsh JA. The airborne sound insulation of glass: part 1. Appl Acoust 1971;4(1):55–70. [5] Quirt JD. Sound transmission through windows I. Single and double glazings. J Acoust Soc Am 1982;72(3):834–44.