The simplified method versus the detailed method of calculating flanking sound transmission through walls with linings

Transcription

1 PROCEEDINGS of the 22 nd International Congress on Acoustics Challenges and Solutions in Acoustical Measurements and Design: Paper ICA The simplified method versus the detailed method of calculating flanking sound transmission through walls with linings Jeffrey Mahn (a), Christoph Hoeller (b), David Quirt (c) (a) National Research Council Canada, Canada, (b) National Research Council Canada, Canada, (c) JDQ Acoustics, Canada Abstract The simplified and detailed methods of calculating the apparent sound reduction index according to the standard, ISO have often been claimed to result in similar values for the weighted apparent sound reduction index. However, in extended studies on walls with linings at the National Research Council Canada, it has been found that the simplified method to calculate the flanking transmission through building elements with linings sometimes leads to misleading results. An alternative method for calculating the flanking sound transmission through walls with linings was proposed to ensure that the simplified method yields more conservative results than the detailed method. To achieve the best possible estimate of the sound insulation performance of buildings systems with linings, the detailed method should be used. Keywords: sound transmission; flanking; lining; concrete block

2 The simplified method versus the detailed method of calculating flanking sound transmission through walls with linings 1 Introduction The acoustic requirements for dwellings in Canada were recently updated with the publication of the 2105 National Building Code of Canada (NBCC). The new acoustic requirements represent a shift from the STC rating which is a laboratory based requirement to the Apparent Sound Transmission Class (ASTC) which is a field based requirement. The 2015 NBCC allows for three different methods of showing compliance with the acoustic requirements: field testing, the use of the acceptable solutions found in Part 9 of the 2015 NBCC and the calculation of the ASTC rating as detailed in the publication RR-331 Guide to Calculating Airborne Sound Transmission in Buildings: 2nd Edition [1]. The calculation method described in the report, RR- 331 is based on the standards, ISO [2] and ISO [3], but written in terms of ASTM metrics. The NBCC allows for the use of both the simplified and the detailed method for calculating the ASTC rating. The Canadian Concrete Masonry Producers Association (CCMPA) has funded a number of studies for the calculation of the ASTC rating of constructions using concrete masonry walls. The findings of the study are available in the report, RR-334 Apparent Sound Insulation in Concrete Block Buildings [4]. Part 5 of the NBCC states that for a heavyweight wall or floor assembly of concrete or masonry and connected flanking assemblies of concrete or masonry, the ASTC rating shall be determined accordance with the simplified or detailed method presented in ISO This paper details a study to calculate the changes in the STC rating due to the use of linings on one side and on both sides of concrete block wall which are required for the calculations using the simplified method. 2 The application of linings to concrete block walls 2.1 Changes due to the use of linings It is common practice, especially in residential buildings, to add finishing surfaces to the basic concrete masonry wall assemblies (for example, gypsum board wall and ceiling surfaces that conceal both the bare concrete surfaces and building services such as electrical wiring, water pipes and ventilation ducts). The finish commonly comprises gypsum board panels, framing used to support them, and often sound absorptive material filling the inter-stud cavities between the gypsum board and the face of the concrete blocks. These elements are described as linings in this paper. As part of this study, measurements of the sound transmission loss were made in accordance with the ASTM E90 [5] and ASTM E413 [6] standards for bare concrete masonry walls, for concrete masonry walls with linings installed on just one side of the wall and for concrete 2

3 masonry walls with linings installed on both sides of the walls. An example of the measurements using paint as a lining on 140 mm lightweight blocks (134 kg/m 2 ) is shown in Figure 1. Figure 1: The transmission loss of a bare concrete block wall, the concrete block wall with paint on one side and the concrete block wall with paint on both sides. The figure shows that the addition of paint on one side improved the STC rating of the wall from 35 to 39. Painting the second side of the wall further improved the STC rating by an additional two points. Of course, the improvements shown in the figure are not due to the paint itself, but rather due to the paint sealing of sound leaks through the lightweight blocks. That is why sealing the leaks on one side of the wall improved the STC rating by 4 STC points but painting the other achieved a further improvement of only 2 STC points since most of the leaks were sealed by the paint applied to the first side. Another example is shown in Figure 2 for 140 mm lightweight blocks (134 kg/m 2 ) with 16 mm gypsum board on 38 mm wood furring installed on one side and on both sides of the wall. 3

4 Figure 2: The transmission loss of a bare concrete block wall, the concrete block wall with 16 mm gypsum board on 38 mm wood furring on one side and the concrete block wall with 16 mm gypsum board on 38 mm wood furring on both sides. The figure shows again that a large improvement in the STC rating was achieved by applying a lining on one side of the concrete block wall. Adding the same lining on the second side improved the STC further, but the improvement wasn t as great as was achieved by applying the lining to one side since adding the lining to one side also sealed the sound leaks. 2.2 Characterization of the changes due to the addition of linings To characterize the change in the sound transmission loss due to adding a specific lining to a concrete block wall, a single number rating was needed. Any sort of single number metric to describe the changes in the STC rating due to the application of linings to the concrete block walls would need to separate the change in the sound insulation due to sealing the air leaks from the actual change due to the lining since calculations of the flanking transmission would not include improvements due to sealing air leaks. While Annex B of ISO [7] defines the change due to the addition of linings as ΔR w, an equivalent ASTM rating does not exist. A new metric ΔSTC was created to describe the change in the sound transmission loss due to adding a specific lining when using ASTM metrics. A procedure was developed for the calculation of ΔSTC as detailed in Report RR-334. The procedure is based in part on that of ISO with the STC calculation substituted for the ISO single number ratings and using Reference Curve B.1 from ISO which is a smooth sound transmission loss curve typical of a heavy wall of masonry. A schematic showing the procedure for calculating ΔSTC is shown in Figure 3. 4

5 Figure 3: Procedure for calculating STC The figure shows that the data needed for the calculation of the ΔSTC rating includes the STC rating of the wall with the lining applied to one and to both sides. The final value is the lowest value of ΔSTC due the lining applied on one side or the ΔSTC of the lining applied on both sides divided by 1.5. Examples of the calculation of the ΔSTC rating are shown in Table 1 for various linings. The data in the table shows that the method of calculating the ΔSTC rating correctly shows an improvement in the STC rating of 0 when the wall is painted. Not all of the linings improve the STC ratings of the walls. Linings such as 13 mm gypsum board directly fixed to the concrete block wall are shown negatively affect the STC rating of the wall. 5

6 Table 1: STC values for different linings Lining (1-side lined) ΔSTC1-side (2-sides lined) ΔSTC2-sides ΔSTC Paint/sealer covering the surface of the wall mm gypsum board fastened to surface of blocks mm gypsum board fastened to 22 mm metal furring channels ( hat profile) 13 mm gypsum board fastened to 22 mm metal furring channels with 38mm thick glass fiber batts in compressed in cavities mm gypsum board fastened to 38x38 mm wood furring x 13 mm gypsum board fastened to 38x38 mm wood furring mm gypsum board fastened to 38x38 mm wood furring with 38mm 2 x 13 mm gypsum board fastened to 38x38 mm wood furring with 38mm mm gypsum board fastened to 38x38 mm wood furring mm gypsum board fastened to 38x38 mm wood furring with 38mm mm gypsum board fastened to 41 mm steel studs mm gypsum board fastened to 41 mm steel studs with 38mm mm gypsum board fastened to 65 mm steel studs mm gypsum board fastened to 65 mm steel studs with 65 mm 2 x 13 mm gypsum board fastened to 65 mm steel studs with 65 mm 16 mm gypsum board fastened to 65 mm steel studs with 65 mm Calculation of the flanking STC rating An example is given for the calculation of the flanking STC rating through a junction between two concrete block walls as shown in Figure 4. The flanking STC ( STC ij ) is calculated according to: STC ij = STC i + STC j + max(δstc 2 2 i, ΔSTC j ) + min(δstc i,δstc j ) + K 2 ij + 10 log 10 ( S s ) (1) l o l ij 6

7 where STCi is the STC rating of element i, ΔSTC i is the change in the STC rating due to the lining on element i, K ij is the vibration reduction index along path ij and l ij is the length of the junction between the elements. For this example, K ij = 5.7 and 10 log 10 ( S s l o l ij ) = 7. F f Figure 4: Example of a T-junction between two bare concrete block walls. The flanking STC is calculated for paths Ff, Fd and Df in Table 2. For this example, the ΔSTC values are 0 since there are no linings. Table 2: Calculation of the flanking STC for the bare concrete block walls If linings of 13 mm gypsum board supported on 65 mm non-loadbearing steel studs spaced 610 mm on center with no absorptive material filling inter-stud cavities are then added to the concrete block walls as shown in Figure 5, the flanking STC is calculated as shown in Table 3. F f Figure 5: Example of a T-junction between two concrete block walls with linings. 7

8 22 nd International Congress on Acoustics, ICA 2016 Table 3: Calculation of the flanking STC for the bare concrete block walls The STC value used for the linings were taken from Table 1. The addition of the linings is shown to improve the flanking STC of each of the transmission paths from 62 to Simplified versus detailed methods The difference in the flanking transmission loss calculated using the simplified and the detailed method was calculated according to = Simplfied Detailed when different linings were applied to concrete block walls. The value of was calculated using both the STC and the R w metrics when linings were attached to one side and to both sides of the concrete block walls shown in Figure 4 and are compared in Figure sided ISO 2-sided ISO 1-sided NRC 2-sided NRC SS65_GFB65_2G13 SS65_GFB65_G16 SS65_GFB65_G13 SS92_GFB65_G13 SS92_GFB92_G13 WFUR38_GFB38_G13 SS92_GFB92_2G13 BASE PAINT SS41_GFB38_G13 G13 FC25_G13 WFUR38_GFB38_2G13 SS92_GFB38_G13 FC25_GFB38_G13 WFUR38_2G13 WFUR38_G13 WFUR38_GFB38_G16 WFUR38_G16 SS41_G13 SS92_G13 SS65_G13 Figure 6: Difference between simplified and detailed calculation of the flanking STC for linings applied to one and both sides of a concrete block wall. The figure is from Zeitler, et al. [8]. 8

9 The figure shows that in terms of the STC metric when the lining is applied on one side of the wall, the simplified method tends to result in flanking STC values that are the same or up to 4 points lower than the detailed method. When the lining is applied to both sides of the wall, the simplified method can result in values that are up to 6 points lower than the detailed method for some linings, but can also over predict the flanking STC rating for other linings. However, the using the STC metric results in significantly less over predictions using the simplified method than when the R w metric is used since the R w metric does not take into account the sealing of leaks in the walls due to the application of the lining 3 Conclusions A new single number metric, STC has been developed for the calculation of the change in the transmission loss of walls due to the application of linings. The STC metric differentiates between the changes in the transmission loss of walls due to the blockage of leaks and due to the improvements due to the linings. The STC metric has been shown to result in more conservative estimates of the flanking STC ratings than the use of the R w metric as compared to calculations using the detailed method. However, to achieve the best possible estimate of the sound insulation performance of buildings systems with linings, the detailed method should be used. Acknowledgments This work was sponsored by Canadian Concrete Masonry Producers Association (CCMPA) and the National Research Council Canada. References [1] Zeitler B, Quirt D, Hoeller C, Mahn J, Schoenwald S, Sabourin I. Guide to Calculating Airborne Sound Transmission in Buildings: 2nd Edition. Ottawa, Canada: National Research Council Canada; [2] ISO : Building acoustics -- Estimation of acoustic performance of buildings from the performance of elements -- Part 1: Airborne sound insulation between rooms. Geneva, Switzerland: International Standards Organization; [3] ISO : Acoustics -- Laboratory measurement of the flanking transmission of airborne and impact sound between adjoining rooms -- Part 2: Application to light elements when the junction has a small influence. Geneva, Switzerland: International Standards Organization; [4] Zeitler B, Quirt D, Schoenwald S, Mahn J. Apparent Sound Insulation in Concrete Block Buildings. Ottawa, Canada: National Research Council Canada; [5] ASTM E90-09, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements. West Conshohocken, PA: ASTM International; [6] ASTM E413-10, Classification for Rating Sound Insulation. West Conshohocken, PA: ASTM International;

10 [7] ISO : Acoustics -- Measurement of sound insulation in buildings and of building elements -- Part 16: Laboratory measurement of the sound reduction index improvement by additional lining. Geneva, Switzerland: International Standards Organization; [8] Zeitler B, Mahn J, Quirt D. Comparison of the Detailed and Simplified Methods to Calculate the Apparent Sound Transmission Class for the Proposed 2015 National Building Code of Canada. Proceedings of InterNoise 2015, San Francisco, USA: