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Sound insulation of domestic roofing systems—Part 3
AppliedAcoustics13(1980)313-329
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART 3*
KENNETH R. Coo~
Applied Physics Department, Royal Melbourne Institute of Technology, Melbourne (Australia) (Received: 14 May, 1979)
SUMMARY
In the two previous parts of this group of papers, l"2 the results of measurements of the sound transmission properties of each of the two components of a domestic roofing system were presented and discussed. In this third and final part, the effect on the transmission properties of combining the roof and ceiling components will be investigated and discussed. Comments will also be made on the contribution by the roofing system to the sound insulation provided by the whole building external envelope against the principal types of external noise.
INTRODUCTION
It is useful for an architect or builder to have information at his disposal concerning the transmission loss values of a roofing system. It is convenient, however, if separate information is at hand regarding the separate performances of the ceiling and roof components. An even more important consideration, in the application of the above data to real dwellings, is an awareness of the nature of the noise incident on the roofing system from outside, since it has a bearing on the effective noise insulation. The transmission properties of various roofing systems were measured and are discussed. Choosing relevant test data from other sources of components on the dwelling external envelope, an estimate is made of the fraction of the sound energy admitted by the roofing system. * Part 1 of this paper appeared in Applied Acoustics, Vol. ! 3, No. 2, ! 980, pp. 109-20 and Part 2 in Vol. 13, No. 3, 1980, pp. 203-10.
313 Applied Acoustics 0003-682X/80/0013-0313/$02.25 © Applied Science Publishers Ltd, England, 1980 Printed in Great Britain
314
KENNETH
FLANKING
R. COOK
TRANSMISSION
Clause 3.1 of the Fourth Proposal for Revision of ISO/R 1403 requires a negligible contribution to the sound transmitted to the adjoining room via any indirect path. Accordingly, flanking transmission tests were carried out by measuring the apparent transmission loss, R'. To provide a high-isolating construction, a 150 mm reinforced concrete slab was placed in the aperture, with sealing effected at the boundaries with dry sand. An additional 125 mm slab of lightweight aggregate concrete was then positioned above this slab, with an air gap of 100 mm between, into which was laid a 50 mm blanket of glass fibre. The measured transmission loss values are shown in Fig. I. Although it was not possible to conclude that the R~a ~ values had been attained, it was decided that any measured transmission loss values for a sample would be valid, on the condition that they were at least 5 dB below R'.
70
60
50
40 v 30
20
10
I 125
~ 250
I 500
I 1000
FREQUENCY F i g . 1.
Flanking
I 2000
I 4000
(HZ)
transmission
loss.
I 8000
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PITCHED-ROOF ROOFING SYSTEMS
Preparation for measurements The ceiling section was placed in the aperture, with the same sealing provisions as previously described in Part 1 of this paper. The roof section, contained by its steel perimeter frame, was placed over the aperture, with joint-sealing compound applied between the steel frame and the steel aperture boundary. Figure 2 of Part 1 showed two hangers for the ceiling, whilst Fig. 1 of Part 2 showed additional ties for the roof. For roofing-system samples, the roof and ceiling components were interconnected by using nuts and bolts to link the ties and hangers.
Samples for testing The most common and basic type of pitched-roof roofing system in Australian dwellings comprises the concrete-tiled roof, R/A, and the 9 mm plasterboard ceiling with no infill, C/A. Such a sample is CR/A--see Appendix for codes assigned to roofing system samples. The results for this sample are shown graphically in Fig. 2. Up to 630 Hz the slope of transmission loss (TL) versus frequency was fairly uniform
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FREQUENCY
Fig. 2.
20~0
I
4000
(Hz)
Roofing system TL value.
sdot
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KENNETHR. COOK
at about 6 dB per octave, so resembling a mass law behaviour. Some flattening was evident between 630 and 3150 Hz, but above 4kHz the slope increased to about 10 dB per octave. If any resonance is presumed to be below 100 Hz, this variation with frequency resembles that proposed by Beranek 4 (after Watters) as a practical design chart for single panels. However, Rettinger 5 suggests that, for double partitions (which, admittedly, the sample was not) the average slope expected will exceed that of a single panel. Even though not large in magnitude, a coincidence dip was evident at 4 kHz, so the presence of the roof component had not been able to remove the coincidence effect due to the plasterboard ceiling. At all frequencies, the TL values for this sample greatly exceeded the combined values of ceiling, C/A, and roof, R/A. As a subsidiary study, transmission loss measurements were made when the ceiling and roof components were not inter-connected. Comparisons with values when the ceiling and roof were connected showed that, between 630 Hz and 5 kHz, the provision of structure-borne sound energy paths between roof and ceiling had significantly lowered the TL values. This means that difficulties will be encountered if an attempt is made to estimate the roofing-system TL values from a knowledge of the transmission performances of the component ceiling and roof. The next sample tested, CR/B,was constructed by combining the basic ceiling without infill, C/A, with the concrete-tiled roof to which sarking had been added between the tiles and rafters, R/B. The results of measurements have been included in Fig. 2. Comparing these two samples, CR/A and CR/B, the pairs of TL values were significantly the same below 630 Hz whilst, at higher frequencies, the CR/B values were progressively higher with increasing frequency than the CR/A values. For roof sample R/B (from Part 2 of this paper), the addition of sarking had decreased the TL values below 800 Hz. Thus, the combination of this roof with the ceiling has over-ridden the effect of the sarking addition at low frequencies. In addition to the roof sarking, 50 mm glass-fibre blanket was then laid between the ceiling joists, forming roofing-system sample CR/C. The results of measurements are shown in Fig. 3. The TL enhancement, as compared with the basic sample, CR/A, was between 2 dB at 160 Hz and 10 dB at 10 kHz. Up to 1250 Hz the slope of the curve was 7 dB per octave, followed by one of 2½dB per octave to 4 kHz, then by one of 10 dB per octave. The smaller slope between 1250 Hz and 4 kHz had been brought about by the 4kHz coincidence dip of the ceiling component. Considering the effect of the sarking to the roof, the improvement in TL values of the roofing system caused by it was, on the average, at least 2 dB below 800 Hz and about 1 dB at higher frequencies. Sample CR/D was brought about by removing the sarking in the roof component from the previous sample, CR/C, and the results are included in Fig. 3. At frequencies up to 630 Hz, this change had no significant effect, but above 630 Hz the effect was quite substantial. The decreases in TL values ranged from 2 dB at mid-
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART
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70
0
c~Vc 50
30
20
10
I
I
I
125
250
500
I
i000
FREQUENCY
Fig. 3.
I
2000
I
4000
I
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(Hz)
Influence of roof sarking on TL values of systems containing absorbent ceiling infill.
frequencies to about 9dB at high frequencies. Hence the roof sarking exerted approximately the same influence on the roofing system TL values whether the ceiling component was with or without infill. Because an absorbent ceiling infill had enhanced the mid- and high-frequency TL values, it was decided to augment the infill by adding a second 50 mm layer of glassfibre to the ceiling component, but without any sarking to the roof. The results for this sample, CR/E, are shown in Fig. 4. As expected, the low-frequency TL enhancement was small, but increased to between 4 and 6dB at mid- and highfrequencies. The effect of the original ceiling coincidence dip was to restrain the TL enhancements up to 4 kHz. Such changes in TL values support the findings of Utley e t al. 6
The effect of using a ceiling infill of considerably higher surface density was studied. For sample CR/F, a 122 mm thickness of cellulose fibre fluff was blown in between the ceiling joists. This layer had a surface density of 5.6 kg/m 2, although 122 mm was a thickness slightly in excess of that employed in actual dwelling applications. The results for this sample have been included in Fig. 4. Compared
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KENNETH R. COOK
with values of the previous sample, CR/E, there was some enhancement in TL values, even at low frequencies, giving a slope of 10 dB per octave up to 800 Hz. This enhancement was between 7 and 10 dB between 800 and 3150 Hz, although the curve slope was only 5 dB per octave. The use of this high density ceiling infill yielded overall the highest values of transmission loss. It yet remains, however, to investigate its sound insulation performance from a practical point of view, when the nature of the intruding noise is considered.
70
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CR/F
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CR/E
v 30
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1215
I 350
I 500
I I000
FREQUENCY
I 2000
I 4000
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(Hz)
Fig. 4. Effect of variation in sur~ce density of ceiling infill: concrete-tiled roof component. Referring back to the flanking transmission tests discussed above, the measured T L values for this sample, CR/F, above 4 k H z , were less than 5 dB below the measured R' values. Consequently, such measured values for C R / F in this frequency region cannot be adopted as having been true values of sample transmission loss.
Change in roof cladding The concrete tiles were now removed from the roof and replaced by 6 m m corrugated asbestos-cement sheeting, previously discussed in Part 2 of this paper under roof sample R/C. When connected to the 9 mm plasterboard ceiling with no
SOUND
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infill, this combination became sample CR/G and the results are shown in Fig. 5, along with the corresponding values for sample CR/A (when the roof cladding had been concrete tiles). Up to 800 Hz, the TL values for this sample were slightly lower (with exceptions) and significantly higher above 800 Hz than for CR/A. The Part 2 results had shown the asbestos-cement roof to be a slightly inferior insulator to the concrete-tiled roof, especially in the mid-frequency region. Hence, such deficiencies had been significantly reduced by the coupling with a basic ceiling and, in fact, above 800 Hz had been increased.
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I 2000
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(Hz)
cladding on system TL values.
To the above sample, 50 mm glass-fibre blanket was laid between the ceiling joists and the results for this sample, CR/H, are shown in Fig. 6. Except at low frequencies, the TL enhancements ranged between 4 and 10dB, whilst the curve slope was increased from 4½ to 6 dB per octave. Comparing these results with those with the concrete-tiled roof component, CR/D, the differences in TL values were minimal, except towards the high-frequency region. The same figure shows the results for sample CR/I, when the ceiling component had an infiil of 74 mm mineral wool batts between the joists. The increases in TL values due to this infill, except at low frequencies, were quite significant, being as high as 15 dB at high frequencies. Any ceiling coincidence dip at 4 kHz was reflected in the roofing system as a slight flattening of the curve in that frequency region.
320
KENNETH R. COOK
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FREQUENCY
Fig. 6.
(Hz)
Enhancement of TL values by increa~ in surface density of ceiling infilh corrugated asbestos-cement roof cladding.
Second change in roof cladding The roof cladding now used was 0.5 mm corrugated galvanised steel sheeting, earlier discussed in Part 2 of this paper under roof sample R/D. This roof was combined with the basic ceiling, C/A, forming sample CR/J, the results obtained being shown in Fig. 7. If now the results are compared for the three samples CR/A, CR/G and CR/J, when the basic ceiling was the component common to each, any significant differences in TL values are seen to be only local, frequency-wise. The arithmetic average TL values, both in the frequency ranges 100-3150 Hz and 100 Hz-10 kHz, are approximately the same. Sample CR/K was constructed by adding to the above CR/J the 74 mm mineral wool batts between the ceiling joists, and the results are also seen in Fig. 7. Comparison with the corresponding results when the asbestos-cement formed the roof cladding showed similar performances, an expected result when the two roof components are compared.
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS---PART
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321
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FREQUENCY (Hz)
Fig. 7.
Comparison ofbasicroofingsystcm with differentroof~omponentcladdings,and changesin TL (one sample)dueto ceilinginfill.
ALMOST FLAT ROOF SYSTEMS
General As previously discussed in Part 2 of this paper, the wooden frame for the low-pitch roof had been constructed as part of the wooden ceiling frame. The single roof cladding used for this series of tests was 0.56 mm galvanised steel decking, previously sample R/E of Part 2.
Samples tested The first sample tested, CR/L, was that of this flat roof connected to the basic 9 mm plasterboard ceiling. The TL values measured are shown in Fig. 8, together with those of sample CR/J, when the similar roof cladding lay on a pitched roof. Averaged over the whole frequency range, the CR/L value was 6 dB lower, although this was brought about mainly by the lower TL values in the low-frequency region.
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(Hz)
Pitched- and fiat-roof component: effect on T L values of roofing systems.
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Influence o n T L values o f l o c a t i o n o f a b s o r b e n t infill.
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART
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The next two samples tested involved the inclusion of a 50 mm glass-fibre infill. For sample CR/M this infill was laid between the ceiling joists, whilst, for sample CR/N, the infill blanket was held in contactwith the roof by placing double-sided aluminium foil over the purlins. Such a placement for this latter sample is in accord with the roof manufacturer's recommendations for use of an absorbent material with a low-pitch galvanised steel roof. The measurements conducted on these two samples are shown in Fig. 9. The addition of the infill caused substantial increases in TL values at mid- and high frequencies. The differences in TL between these two samples were minimal at low frequencies, with CR/N values slightly higher at midfrequencies and significantly lower at high frequencies. The effect of increased mass was investigated by nailing a second 9 mm layer of plasterboard to the ceiling component. (The effect on ceiling-alone properties was discussed under sample C/AA in Part 1.) Figure 10 shows the results of this sample, CR/LL, along with corresponding values for sample CR/L, when using a single plasterboard layer. The expected mass controlled low frequency enhancements were evident, but mid-frequency improvements were slight. Such enhancements were
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Fig. 10.
TL enhancement due to doubling the thickness of ceiling cladding.
324
KENNETHR. COOK
significantly lower than those found when the two ceiling components were compared. The final two samples tested in this section involved the inclusion of ceiling infills of higher surface density--of 74 mm mineral wool batts for sample CR/O and of 122 mm cellulose fibre fluff for sample CR/P. Both samples showed, as can be seen from Fig. 11, TL increases at low frequencies with respect to the previous samples, an expected result, although mid-frequency increases were slight. The increases in TL values at high frequencies were substantial.
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FREQUENCY
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Fig. 11. Effectof increasingthe surfacedensityof ceilinginfilhalmost-flatroofcomponentwith galvanised-steeldecking.
SINGLE-VALUERATINGS General
The transmission properties of various roofing systems have been expressed by means of the TL value in each third-octave frequency band. Such information is a requirement for the proper design for acoustic insulation. However, many
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART
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architects, builders and governmental authorities feel it more convenient to represent the properties of a building element by a single value. Such, in their opinion, permits a simple comparison of building elements and a means of specifying minimum acceptable acoustic performances of elements. Many possible single-value ratings exist, for instance: (a) (b) (c) (d)
Arithmetic average dB of TL values in a chosen frequency range. Airborne Sound Insulation Index, I a, as specified by ISO/R 717, 7 by use of a standard reference curve. Sound Transmission Class STC, specified by ASTM E4138 (or Draft Australian Standard DR 741639), a rating similar to I a. dB(A) level reduction, the difference in dB(A) between the outside and inside sound levels.
As pointed out by Northwood and Clark, 1° the factors governing building element sound insulation are the character of the intruding noise and of ambient noise in the room and the occupant's assessment of intruding noise. They concluded that the inverse of the STC contour gave good agreement with judgements of annoyance, although this had been based on noise due to male speech.
dB(A) Reduction It is the opinion of the author that, in relation to the intrusion of noise in a room from the outside, the most appropriate single-value rating of an external envelope building component is that of the dB(A) reduction, so long as special provisions are attached thereto. The dB(A) reduction, LRA, for an element may be found from the outside noise level, Ls dB at frequencyf Hz, the A-weighting network and the thirdoctave band TL values. It must be realised that, because of the contribution by the room equivalent absorption area, A 2, the actual level in the room will require some modification. Because the LRA value will depend on the frequency spectrum of the outside noise, it will be necessary in this paper to select three principal types of noise spectra. This will, in turn, lead to specific LRA values, namely: (a) (b) (c)
LRaeforthe reduction of'pink' noise, i.e. where outside levels are equal at all frequencies. LR,~Rfor the reduction of road traific noise, with the outside levels being taken from the work by Oosting.11 LRaAfor reduction of composite aircraft movement noise, with outside levels being taken from the NEF contour 33 for Sydney (Australia) domestic/international airport, tabulated in Draft Australian Standard DR 74163. 9
The values, L~ of outside noise at frequencyf Hz for LRARand LRAAare tabulated in Appendix 2.
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KENNETH R. COOK
Single-value ratings: Roofing systems For the samples discussed in this paper, some single-value ratings are shown in Table 1. TABLEI ROOFING SYSTEMS: SINGLE-VALUE RATINGS
Sample
CR/A CR/B CR/C CR/D CR/E CR/F CR/G CR/H CR/I CR/J CR/K
CR/L CR/LL CR/M CR/N CR/O CR/P
Arith. Av. dB
1~
A
B
30 33 38 36 39 45 31 36 41 30 42 30 34 36 36 39 38
33 36 43 40 43 50 34 40 47 33 48 33 38 41 40 44 44
33 36 42 40 43 46 34 39 42 34 43 34 37 39 40 41 41
STC
33 36 42 40 43 47 34 39 43 34 43 34 37 39 40 42 41
LRAp
LRA¢
LRAA
(dB)
(dB(A))
(dB(A))
A
B
A
B
A
B
33 35 40 39 41 44 33 37 40 33 40 32 35 37 37 39 39
34 37 41 40 43 46 34 39 42 34 42 33 37 39 38 41 41
28 30 33 32 34 35 27 30 31 26 31 25 31 29 28 33 30
28 30 33 32 34 35 27 30 31 26 31 25 31 29 28 33 33
32 35 39 38 41 43 33 37 39 32 39 31 35 36 35 38 38
33 36 39 39 41 43 34 38 40 33 39 32 36 37 36 39 39
A = Frequency range 100 Hz-3150 Hz. B = Frequency range 100 Hz-10 kHz.
Some general observations from Table 1 are that: (a) (b) (c) (d)
(e)
The extension of the frequency range to 10 k Hz from 3150 Hz increases the arithmetic average by an average of 4dB. The I, and STC ratings are generally equal, any higher value STC having been due to the 100Hz band TL. For the LR A values, no important information is lost by restricting the frequency range for determination to between 100 and 3150 Hz. The differences (I a - LRAp) and (I, - LRAA) are generally of 2 points, but the difference (I, - LRAR ) varies between 5 and 16 points. Thus, since the practical goal of sound insulation is to create a satisfactorily low noise level within a room, on the subjective scale, the single-value rating, I, (or STC) is not a suitable means of assessing the insulating properties of a sample. Where the low frequency TL values for samples are similar, such as for samples CR/C and CR/D, the effective insulation from the most-common road traffic noise is similar, even though the I, (and STC) values differ and the mid- and high frequency TL values differ widely.
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART 3
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For the usual home-dweller the most common type of external noise is that due to road traffic. Accordingly, it is considered that the most relevant single-value rating is that of the dB(A) level reduction, LRAR. Perusal of Table 1 shows that the best insulation response, for all single-value ratings listed, was due to the sample having as a ceiling infill that material with the highest surface density--sample CR/F. From the point of view of the LRARrating only, the rating value was significantly lower when the sample included no ceiling infill. Also, when the ceiling infill was of material of low surface density compared with the fibre fluff, the LRAR values were still low. Considering the last two samples, CR/O and CR/P, there is no difference, LRARwise, with regard to the location of the glass-fibre infill. However, it is probable that locating the infill in contact with the roof component would bring about a superior insulation against impulsive noise sources, such as that of falling rain. No study was made in this project of the effects of impulsive noise.
Roofing system contribution to dwelling insulation By selecting TL values for various components of the external building envelope, such as from the EBS Technical Study 48,12 it is possible to estimate the relative effects on envelope insulation of various component contributions. In this regard it was necessary to assume that no significant sound path is provided by the envelope floor, that the (external) sound energy incident on the envelope is uniform in magnitude and that there is no interchange of sound energy between rooms. In such a subsidiary study, the external wall is taken to be either brick veneer or stud-framed weatherboard (the most commonly used in Australian dwellings), whilst the module for the window is 6 mm glass, 1210 by 1220 mm aluminium framed with a horizontally sliding sash. The effect of using more than one window was studied as was that of having the window(s) partly opened. In the southern Australian state of Victoria, Uniform Building Regulations 13 require that the window area of a room be at least one-eighth of the room floor area and that at least half of the window area to be openable. This study showed that: (a)
(b)
(c)
A simple openable window has an over-riding influence on the dwelling envelope sound insulation, even when of minimum regulatory area and kept closed. Variations in the type of roofing system show a significant effect only at high frequencies, but have little influence on the three dB(A) level reduction values. When even the minimum size window is open just one-eighth, the noise level in the dwelling interior due to road traffic becomes unacceptably high. DISCUSSION
This paper has given an indication of the changes in transmission loss and sound
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KENNETH R. COOK
insulation brought about by the addition of commercially available infills. Such changes in the low-frequency region were found to be small, with varying effects in the mid-frequency region, whilst some infills had the ability to cause substantial increases at high frequencies. The influence o f the r o o f c o m p o n e n t , whose T L values were generally low t h r o u g h o u t the frequency range regardless o f the r o o f cladding, was to prevent the roofing system samples from having high T L values. The measurements in this project had been extended beyond the usual frequency range of interest. However, when the transmission loss values are utilised to provide data on the sound insulating capabilities, no additional useful information is forthcoming. This is due to the over-riding influence of the low-frequency T L values in determining the dB(A) level reduction of road traffic noise. A comparison of samples with respect to various single-value ratings was made, with special attention being paid to the dB(A) level reduction o f road traffic noise, LRAR. N o convenient inter-relationship was found to exist between the LRAR value and the c o m m o n l y used mean sound insulation index, I a. If relatively high T L values for a roofing system are sought, it is essential that close detail be paid to the effective sealing of the r o o f c o m p o n e n t from sound leaks, more especially at the r o o f perimeter. This is a suggestion for further study. However, when the contributions by all c o m p o n e n t s of the external building envelope were considered, it was found that the weakest link in the system was by far due to the window(s). This effect is so p r o n o u n c e d that attempts to achieve a roofing system o f high insulation properties is largely negated by the window c o m p o n e n t . REFERENCES 1. K.R. COOK,Sound insulation of domestic roofing systems--Part 1, Applied Acoustics, 13(2)(1980), pp. 109-20. 2. K.R. COOK,Sound insulation of domestic roofing systems--Part 2, Applied Acoustics, 13(3)(1980), pp. 203-10~ 3. ANON.Field and Laboratory Measurements of Airborne and Impact Sound Transmission. ISO/R 140-1960(E), International Organisation for Standardisation, 1st edn, 1960. 4. L. L. BERANEK,Noise reduction, McGraw-Hill, New York, 1960. Chapter 13, Fig, 13.9. 5. M. R~T'nNGER,Acoustics room design andnoise control, Chem. Pub. Co., New York, 1969. Section 11, Chapter 3, p. 117. 6. W.A. UTLEY,A. CUMMINGSand H. D. PARBROOK,The use of absorbent material in double-leaf wall constructions, J. Sound and Vibration, 9(1) (1969), pp. 91Y6. 7. ANON.Rating of Sound Insulation in Buildings. ISO/R 717 (E), International Organisation for Standardisation, 1968. 8. ANON.Tentative Classification for Determination of Sound Transmission Class, American Society for Testing and Materials, E413-70T, 1970. 9. ANON.Building Siting and Construction Against Traffic Noise Intrusion, DR 74163. Australian Standards Association, Appendix B, 1974. 10. T. D. NORTHWOODand D. M. CLARK,Frequency considerations in the subjective assessment of sound insulation, Paper E3-8 presented to 6th International Congress in Acoustics, Japan, 1968. 11. W. A. OOSTING,Method for Calculating Road Traffic Noise for Zoning Purposes, TPD-TNO-TH Report VL-HR-22-01, 1975. 12. ANON.Airborne Sound Transmission Through Elements of Buildings. Department of Housing and Construction, Experimental Building Station, Technical Study 48, Appendix B, 1973. 13. ANON.Victoria: Uniform Building Regulations. Regulations ll01, 1975.
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART
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APPENDIX 1 ; CODES FOR ROOFING SYSTEMS
Code
Description
CR/A CR/B
Concrete-tiled pitched roof, plus 9 mm plasterboard ceiling. As above, but with 0.23 mm double-sided aluminium foil sarking between roof tiles and rafters. CR/C As above, but with 50 mm glass-fibre blanket laid between ceiling joists. CR/D As above, but with foil sarking removed. CR/E As above, but with second layer of 50 mm glass-fibre blanket laid between ceiling joists. CR/F Concrete-tiled pitched roof, plus 9 mm plasterboard ceiling with 122 mm cellulose fibre fluff blown between ceiling joists. CR/G Pitched-roof frame with corrugated asbestos-cement cladding, plus 9 mm plasterboard ceiling. CR/H As above, but with 50 mm glass-fibre blanket laid between ceiling joists. CR/I As CR/G, but with 74 mm mineral wool batts laid between ceiling joists. Pitched-roof frame with 0.5 mm corrugated galvanised steel cladding, plus cg/J 9 mm plasterboard ceiling. CR/K As above, but with 74 mm mineral wool batts laid between ceiling joists. Almost flat wooden roof frame with 0.56 mm galvanised steel decking, plus CR/L 9 mm plasterboard ceiling. CR/LL As above, but with a second 9 mm layer of plasterboard nailed to original ceiling cladding. CR/M As above, but with 50 mm glass-fibre blanket laid between ceiling joists. CR/N As CR/L, but with 50 mm glass-fibre blanket placed in contact with roof decking and held in position with 0.23 mm double-sided aluminium foil. CR/O As CR/L, but with 74 mm mineral wool batts laid between ceiling joists. CR/P As CR/L, but with 122 mm cellulose fibre fluffblown between ceiling joists.
APPENDIX
2:
SPECTRA: OUTSIDE SOUND LEVELS, L f
(dB)
LIR: Road traffic noise at frequency f Hz (dB) LIA: Composite aircraft-movement noise at frequencyf Hz (dB) fHz LIR
LfA f Hz LyR
ZfA
100 125 160 200 250 315 400 500 630 74-3 73"5 71 "5 68"5 69-0 68"8 67-7 67"0 67.2 49-0 50"6 50-2 46-6 46"2 46.0 45.6 45.2 45"0 800 1000 1250 1600 2000 2500 3150 4000 66.3 66.0 65.2 63"8 62.5 60.2 58.3 55.0 44.6 44.0 44"0 43.8 47.0 50.8 49.8 46.4
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART 3*
KENNETH R. Coo~
Applied Physics Department, Royal Melbourne Institute of Technology, Melbourne (Australia) (Received: 14 May, 1979)
SUMMARY
In the two previous parts of this group of papers, l"2 the results of measurements of the sound transmission properties of each of the two components of a domestic roofing system were presented and discussed. In this third and final part, the effect on the transmission properties of combining the roof and ceiling components will be investigated and discussed. Comments will also be made on the contribution by the roofing system to the sound insulation provided by the whole building external envelope against the principal types of external noise.
INTRODUCTION
It is useful for an architect or builder to have information at his disposal concerning the transmission loss values of a roofing system. It is convenient, however, if separate information is at hand regarding the separate performances of the ceiling and roof components. An even more important consideration, in the application of the above data to real dwellings, is an awareness of the nature of the noise incident on the roofing system from outside, since it has a bearing on the effective noise insulation. The transmission properties of various roofing systems were measured and are discussed. Choosing relevant test data from other sources of components on the dwelling external envelope, an estimate is made of the fraction of the sound energy admitted by the roofing system. * Part 1 of this paper appeared in Applied Acoustics, Vol. ! 3, No. 2, ! 980, pp. 109-20 and Part 2 in Vol. 13, No. 3, 1980, pp. 203-10.
313 Applied Acoustics 0003-682X/80/0013-0313/$02.25 © Applied Science Publishers Ltd, England, 1980 Printed in Great Britain
314
KENNETH
FLANKING
R. COOK
TRANSMISSION
Clause 3.1 of the Fourth Proposal for Revision of ISO/R 1403 requires a negligible contribution to the sound transmitted to the adjoining room via any indirect path. Accordingly, flanking transmission tests were carried out by measuring the apparent transmission loss, R'. To provide a high-isolating construction, a 150 mm reinforced concrete slab was placed in the aperture, with sealing effected at the boundaries with dry sand. An additional 125 mm slab of lightweight aggregate concrete was then positioned above this slab, with an air gap of 100 mm between, into which was laid a 50 mm blanket of glass fibre. The measured transmission loss values are shown in Fig. I. Although it was not possible to conclude that the R~a ~ values had been attained, it was decided that any measured transmission loss values for a sample would be valid, on the condition that they were at least 5 dB below R'.
70
60
50
40 v 30
20
10
I 125
~ 250
I 500
I 1000
FREQUENCY F i g . 1.
Flanking
I 2000
I 4000
(HZ)
transmission
loss.
I 8000
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PITCHED-ROOF ROOFING SYSTEMS
Preparation for measurements The ceiling section was placed in the aperture, with the same sealing provisions as previously described in Part 1 of this paper. The roof section, contained by its steel perimeter frame, was placed over the aperture, with joint-sealing compound applied between the steel frame and the steel aperture boundary. Figure 2 of Part 1 showed two hangers for the ceiling, whilst Fig. 1 of Part 2 showed additional ties for the roof. For roofing-system samples, the roof and ceiling components were interconnected by using nuts and bolts to link the ties and hangers.
Samples for testing The most common and basic type of pitched-roof roofing system in Australian dwellings comprises the concrete-tiled roof, R/A, and the 9 mm plasterboard ceiling with no infill, C/A. Such a sample is CR/A--see Appendix for codes assigned to roofing system samples. The results for this sample are shown graphically in Fig. 2. Up to 630 Hz the slope of transmission loss (TL) versus frequency was fairly uniform
60
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20
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I
12s
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I
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1000
FREQUENCY
Fig. 2.
20~0
I
4000
(Hz)
Roofing system TL value.
sdot
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KENNETHR. COOK
at about 6 dB per octave, so resembling a mass law behaviour. Some flattening was evident between 630 and 3150 Hz, but above 4kHz the slope increased to about 10 dB per octave. If any resonance is presumed to be below 100 Hz, this variation with frequency resembles that proposed by Beranek 4 (after Watters) as a practical design chart for single panels. However, Rettinger 5 suggests that, for double partitions (which, admittedly, the sample was not) the average slope expected will exceed that of a single panel. Even though not large in magnitude, a coincidence dip was evident at 4 kHz, so the presence of the roof component had not been able to remove the coincidence effect due to the plasterboard ceiling. At all frequencies, the TL values for this sample greatly exceeded the combined values of ceiling, C/A, and roof, R/A. As a subsidiary study, transmission loss measurements were made when the ceiling and roof components were not inter-connected. Comparisons with values when the ceiling and roof were connected showed that, between 630 Hz and 5 kHz, the provision of structure-borne sound energy paths between roof and ceiling had significantly lowered the TL values. This means that difficulties will be encountered if an attempt is made to estimate the roofing-system TL values from a knowledge of the transmission performances of the component ceiling and roof. The next sample tested, CR/B,was constructed by combining the basic ceiling without infill, C/A, with the concrete-tiled roof to which sarking had been added between the tiles and rafters, R/B. The results of measurements have been included in Fig. 2. Comparing these two samples, CR/A and CR/B, the pairs of TL values were significantly the same below 630 Hz whilst, at higher frequencies, the CR/B values were progressively higher with increasing frequency than the CR/A values. For roof sample R/B (from Part 2 of this paper), the addition of sarking had decreased the TL values below 800 Hz. Thus, the combination of this roof with the ceiling has over-ridden the effect of the sarking addition at low frequencies. In addition to the roof sarking, 50 mm glass-fibre blanket was then laid between the ceiling joists, forming roofing-system sample CR/C. The results of measurements are shown in Fig. 3. The TL enhancement, as compared with the basic sample, CR/A, was between 2 dB at 160 Hz and 10 dB at 10 kHz. Up to 1250 Hz the slope of the curve was 7 dB per octave, followed by one of 2½dB per octave to 4 kHz, then by one of 10 dB per octave. The smaller slope between 1250 Hz and 4 kHz had been brought about by the 4kHz coincidence dip of the ceiling component. Considering the effect of the sarking to the roof, the improvement in TL values of the roofing system caused by it was, on the average, at least 2 dB below 800 Hz and about 1 dB at higher frequencies. Sample CR/D was brought about by removing the sarking in the roof component from the previous sample, CR/C, and the results are included in Fig. 3. At frequencies up to 630 Hz, this change had no significant effect, but above 630 Hz the effect was quite substantial. The decreases in TL values ranged from 2 dB at mid-
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART
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0
c~Vc 50
30
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I
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I
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FREQUENCY
Fig. 3.
I
2000
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Influence of roof sarking on TL values of systems containing absorbent ceiling infill.
frequencies to about 9dB at high frequencies. Hence the roof sarking exerted approximately the same influence on the roofing system TL values whether the ceiling component was with or without infill. Because an absorbent ceiling infill had enhanced the mid- and high-frequency TL values, it was decided to augment the infill by adding a second 50 mm layer of glassfibre to the ceiling component, but without any sarking to the roof. The results for this sample, CR/E, are shown in Fig. 4. As expected, the low-frequency TL enhancement was small, but increased to between 4 and 6dB at mid- and highfrequencies. The effect of the original ceiling coincidence dip was to restrain the TL enhancements up to 4 kHz. Such changes in TL values support the findings of Utley e t al. 6
The effect of using a ceiling infill of considerably higher surface density was studied. For sample CR/F, a 122 mm thickness of cellulose fibre fluff was blown in between the ceiling joists. This layer had a surface density of 5.6 kg/m 2, although 122 mm was a thickness slightly in excess of that employed in actual dwelling applications. The results for this sample have been included in Fig. 4. Compared
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KENNETH R. COOK
with values of the previous sample, CR/E, there was some enhancement in TL values, even at low frequencies, giving a slope of 10 dB per octave up to 800 Hz. This enhancement was between 7 and 10 dB between 800 and 3150 Hz, although the curve slope was only 5 dB per octave. The use of this high density ceiling infill yielded overall the highest values of transmission loss. It yet remains, however, to investigate its sound insulation performance from a practical point of view, when the nature of the intruding noise is considered.
70
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CR/F
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CR/E
v 30
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1215
I 350
I 500
I I000
FREQUENCY
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Fig. 4. Effect of variation in sur~ce density of ceiling infill: concrete-tiled roof component. Referring back to the flanking transmission tests discussed above, the measured T L values for this sample, CR/F, above 4 k H z , were less than 5 dB below the measured R' values. Consequently, such measured values for C R / F in this frequency region cannot be adopted as having been true values of sample transmission loss.
Change in roof cladding The concrete tiles were now removed from the roof and replaced by 6 m m corrugated asbestos-cement sheeting, previously discussed in Part 2 of this paper under roof sample R/C. When connected to the 9 mm plasterboard ceiling with no
SOUND
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infill, this combination became sample CR/G and the results are shown in Fig. 5, along with the corresponding values for sample CR/A (when the roof cladding had been concrete tiles). Up to 800 Hz, the TL values for this sample were slightly lower (with exceptions) and significantly higher above 800 Hz than for CR/A. The Part 2 results had shown the asbestos-cement roof to be a slightly inferior insulator to the concrete-tiled roof, especially in the mid-frequency region. Hence, such deficiencies had been significantly reduced by the coupling with a basic ceiling and, in fact, above 800 Hz had been increased.
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I 2000
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cladding on system TL values.
To the above sample, 50 mm glass-fibre blanket was laid between the ceiling joists and the results for this sample, CR/H, are shown in Fig. 6. Except at low frequencies, the TL enhancements ranged between 4 and 10dB, whilst the curve slope was increased from 4½ to 6 dB per octave. Comparing these results with those with the concrete-tiled roof component, CR/D, the differences in TL values were minimal, except towards the high-frequency region. The same figure shows the results for sample CR/I, when the ceiling component had an infiil of 74 mm mineral wool batts between the joists. The increases in TL values due to this infill, except at low frequencies, were quite significant, being as high as 15 dB at high frequencies. Any ceiling coincidence dip at 4 kHz was reflected in the roofing system as a slight flattening of the curve in that frequency region.
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KENNETH R. COOK
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(Hz)
Enhancement of TL values by increa~ in surface density of ceiling infilh corrugated asbestos-cement roof cladding.
Second change in roof cladding The roof cladding now used was 0.5 mm corrugated galvanised steel sheeting, earlier discussed in Part 2 of this paper under roof sample R/D. This roof was combined with the basic ceiling, C/A, forming sample CR/J, the results obtained being shown in Fig. 7. If now the results are compared for the three samples CR/A, CR/G and CR/J, when the basic ceiling was the component common to each, any significant differences in TL values are seen to be only local, frequency-wise. The arithmetic average TL values, both in the frequency ranges 100-3150 Hz and 100 Hz-10 kHz, are approximately the same. Sample CR/K was constructed by adding to the above CR/J the 74 mm mineral wool batts between the ceiling joists, and the results are also seen in Fig. 7. Comparison with the corresponding results when the asbestos-cement formed the roof cladding showed similar performances, an expected result when the two roof components are compared.
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS---PART
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321
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Fig. 7.
Comparison ofbasicroofingsystcm with differentroof~omponentcladdings,and changesin TL (one sample)dueto ceilinginfill.
ALMOST FLAT ROOF SYSTEMS
General As previously discussed in Part 2 of this paper, the wooden frame for the low-pitch roof had been constructed as part of the wooden ceiling frame. The single roof cladding used for this series of tests was 0.56 mm galvanised steel decking, previously sample R/E of Part 2.
Samples tested The first sample tested, CR/L, was that of this flat roof connected to the basic 9 mm plasterboard ceiling. The TL values measured are shown in Fig. 8, together with those of sample CR/J, when the similar roof cladding lay on a pitched roof. Averaged over the whole frequency range, the CR/L value was 6 dB lower, although this was brought about mainly by the lower TL values in the low-frequency region.
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Pitched- and fiat-roof component: effect on T L values of roofing systems.
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SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART
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The next two samples tested involved the inclusion of a 50 mm glass-fibre infill. For sample CR/M this infill was laid between the ceiling joists, whilst, for sample CR/N, the infill blanket was held in contactwith the roof by placing double-sided aluminium foil over the purlins. Such a placement for this latter sample is in accord with the roof manufacturer's recommendations for use of an absorbent material with a low-pitch galvanised steel roof. The measurements conducted on these two samples are shown in Fig. 9. The addition of the infill caused substantial increases in TL values at mid- and high frequencies. The differences in TL between these two samples were minimal at low frequencies, with CR/N values slightly higher at midfrequencies and significantly lower at high frequencies. The effect of increased mass was investigated by nailing a second 9 mm layer of plasterboard to the ceiling component. (The effect on ceiling-alone properties was discussed under sample C/AA in Part 1.) Figure 10 shows the results of this sample, CR/LL, along with corresponding values for sample CR/L, when using a single plasterboard layer. The expected mass controlled low frequency enhancements were evident, but mid-frequency improvements were slight. Such enhancements were
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Fig. 10.
TL enhancement due to doubling the thickness of ceiling cladding.
324
KENNETHR. COOK
significantly lower than those found when the two ceiling components were compared. The final two samples tested in this section involved the inclusion of ceiling infills of higher surface density--of 74 mm mineral wool batts for sample CR/O and of 122 mm cellulose fibre fluff for sample CR/P. Both samples showed, as can be seen from Fig. 11, TL increases at low frequencies with respect to the previous samples, an expected result, although mid-frequency increases were slight. The increases in TL values at high frequencies were substantial.
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Fig. 11. Effectof increasingthe surfacedensityof ceilinginfilhalmost-flatroofcomponentwith galvanised-steeldecking.
SINGLE-VALUERATINGS General
The transmission properties of various roofing systems have been expressed by means of the TL value in each third-octave frequency band. Such information is a requirement for the proper design for acoustic insulation. However, many
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART
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architects, builders and governmental authorities feel it more convenient to represent the properties of a building element by a single value. Such, in their opinion, permits a simple comparison of building elements and a means of specifying minimum acceptable acoustic performances of elements. Many possible single-value ratings exist, for instance: (a) (b) (c) (d)
Arithmetic average dB of TL values in a chosen frequency range. Airborne Sound Insulation Index, I a, as specified by ISO/R 717, 7 by use of a standard reference curve. Sound Transmission Class STC, specified by ASTM E4138 (or Draft Australian Standard DR 741639), a rating similar to I a. dB(A) level reduction, the difference in dB(A) between the outside and inside sound levels.
As pointed out by Northwood and Clark, 1° the factors governing building element sound insulation are the character of the intruding noise and of ambient noise in the room and the occupant's assessment of intruding noise. They concluded that the inverse of the STC contour gave good agreement with judgements of annoyance, although this had been based on noise due to male speech.
dB(A) Reduction It is the opinion of the author that, in relation to the intrusion of noise in a room from the outside, the most appropriate single-value rating of an external envelope building component is that of the dB(A) reduction, so long as special provisions are attached thereto. The dB(A) reduction, LRA, for an element may be found from the outside noise level, Ls dB at frequencyf Hz, the A-weighting network and the thirdoctave band TL values. It must be realised that, because of the contribution by the room equivalent absorption area, A 2, the actual level in the room will require some modification. Because the LRA value will depend on the frequency spectrum of the outside noise, it will be necessary in this paper to select three principal types of noise spectra. This will, in turn, lead to specific LRA values, namely: (a) (b) (c)
LRaeforthe reduction of'pink' noise, i.e. where outside levels are equal at all frequencies. LR,~Rfor the reduction of road traific noise, with the outside levels being taken from the work by Oosting.11 LRaAfor reduction of composite aircraft movement noise, with outside levels being taken from the NEF contour 33 for Sydney (Australia) domestic/international airport, tabulated in Draft Australian Standard DR 74163. 9
The values, L~ of outside noise at frequencyf Hz for LRARand LRAAare tabulated in Appendix 2.
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KENNETH R. COOK
Single-value ratings: Roofing systems For the samples discussed in this paper, some single-value ratings are shown in Table 1. TABLEI ROOFING SYSTEMS: SINGLE-VALUE RATINGS
Sample
CR/A CR/B CR/C CR/D CR/E CR/F CR/G CR/H CR/I CR/J CR/K
CR/L CR/LL CR/M CR/N CR/O CR/P
Arith. Av. dB
1~
A
B
30 33 38 36 39 45 31 36 41 30 42 30 34 36 36 39 38
33 36 43 40 43 50 34 40 47 33 48 33 38 41 40 44 44
33 36 42 40 43 46 34 39 42 34 43 34 37 39 40 41 41
STC
33 36 42 40 43 47 34 39 43 34 43 34 37 39 40 42 41
LRAp
LRA¢
LRAA
(dB)
(dB(A))
(dB(A))
A
B
A
B
A
B
33 35 40 39 41 44 33 37 40 33 40 32 35 37 37 39 39
34 37 41 40 43 46 34 39 42 34 42 33 37 39 38 41 41
28 30 33 32 34 35 27 30 31 26 31 25 31 29 28 33 30
28 30 33 32 34 35 27 30 31 26 31 25 31 29 28 33 33
32 35 39 38 41 43 33 37 39 32 39 31 35 36 35 38 38
33 36 39 39 41 43 34 38 40 33 39 32 36 37 36 39 39
A = Frequency range 100 Hz-3150 Hz. B = Frequency range 100 Hz-10 kHz.
Some general observations from Table 1 are that: (a) (b) (c) (d)
(e)
The extension of the frequency range to 10 k Hz from 3150 Hz increases the arithmetic average by an average of 4dB. The I, and STC ratings are generally equal, any higher value STC having been due to the 100Hz band TL. For the LR A values, no important information is lost by restricting the frequency range for determination to between 100 and 3150 Hz. The differences (I a - LRAp) and (I, - LRAA) are generally of 2 points, but the difference (I, - LRAR ) varies between 5 and 16 points. Thus, since the practical goal of sound insulation is to create a satisfactorily low noise level within a room, on the subjective scale, the single-value rating, I, (or STC) is not a suitable means of assessing the insulating properties of a sample. Where the low frequency TL values for samples are similar, such as for samples CR/C and CR/D, the effective insulation from the most-common road traffic noise is similar, even though the I, (and STC) values differ and the mid- and high frequency TL values differ widely.
SOUND INSULATION OF DOMESTIC ROOFING SYSTEMS--PART 3
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For the usual home-dweller the most common type of external noise is that due to road traffic. Accordingly, it is considered that the most relevant single-value rating is that of the dB(A) level reduction, LRAR. Perusal of Table 1 shows that the best insulation response, for all single-value ratings listed, was due to the sample having as a ceiling infill that material with the highest surface density--sample CR/F. From the point of view of the LRARrating only, the rating value was significantly lower when the sample included no ceiling infill. Also, when the ceiling infill was of material of low surface density compared with the fibre fluff, the LRAR values were still low. Considering the last two samples, CR/O and CR/P, there is no difference, LRARwise, with regard to the location of the glass-fibre infill. However, it is probable that locating the infill in contact with the roof component would bring about a superior insulation against impulsive noise sources, such as that of falling rain. No study was made in this project of the effects of impulsive noise.
Roofing system contribution to dwelling insulation By selecting TL values for various components of the external building envelope, such as from the EBS Technical Study 48,12 it is possible to estimate the relative effects on envelope insulation of various component contributions. In this regard it was necessary to assume that no significant sound path is provided by the envelope floor, that the (external) sound energy incident on the envelope is uniform in magnitude and that there is no interchange of sound energy between rooms. In such a subsidiary study, the external wall is taken to be either brick veneer or stud-framed weatherboard (the most commonly used in Australian dwellings), whilst the module for the window is 6 mm glass, 1210 by 1220 mm aluminium framed with a horizontally sliding sash. The effect of using more than one window was studied as was that of having the window(s) partly opened. In the southern Australian state of Victoria, Uniform Building Regulations 13 require that the window area of a room be at least one-eighth of the room floor area and that at least half of the window area to be openable. This study showed that: (a)
(b)
(c)
A simple openable window has an over-riding influence on the dwelling envelope sound insulation, even when of minimum regulatory area and kept closed. Variations in the type of roofing system show a significant effect only at high frequencies, but have little influence on the three dB(A) level reduction values. When even the minimum size window is open just one-eighth, the noise level in the dwelling interior due to road traffic becomes unacceptably high. DISCUSSION
This paper has given an indication of the changes in transmission loss and sound
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KENNETH R. COOK
insulation brought about by the addition of commercially available infills. Such changes in the low-frequency region were found to be small, with varying effects in the mid-frequency region, whilst some infills had the ability to cause substantial increases at high frequencies. The influence o f the r o o f c o m p o n e n t , whose T L values were generally low t h r o u g h o u t the frequency range regardless o f the r o o f cladding, was to prevent the roofing system samples from having high T L values. The measurements in this project had been extended beyond the usual frequency range of interest. However, when the transmission loss values are utilised to provide data on the sound insulating capabilities, no additional useful information is forthcoming. This is due to the over-riding influence of the low-frequency T L values in determining the dB(A) level reduction of road traffic noise. A comparison of samples with respect to various single-value ratings was made, with special attention being paid to the dB(A) level reduction o f road traffic noise, LRAR. N o convenient inter-relationship was found to exist between the LRAR value and the c o m m o n l y used mean sound insulation index, I a. If relatively high T L values for a roofing system are sought, it is essential that close detail be paid to the effective sealing of the r o o f c o m p o n e n t from sound leaks, more especially at the r o o f perimeter. This is a suggestion for further study. However, when the contributions by all c o m p o n e n t s of the external building envelope were considered, it was found that the weakest link in the system was by far due to the window(s). This effect is so p r o n o u n c e d that attempts to achieve a roofing system o f high insulation properties is largely negated by the window c o m p o n e n t . REFERENCES 1. K.R. COOK,Sound insulation of domestic roofing systems--Part 1, Applied Acoustics, 13(2)(1980), pp. 109-20. 2. K.R. COOK,Sound insulation of domestic roofing systems--Part 2, Applied Acoustics, 13(3)(1980), pp. 203-10~ 3. ANON.Field and Laboratory Measurements of Airborne and Impact Sound Transmission. ISO/R 140-1960(E), International Organisation for Standardisation, 1st edn, 1960. 4. L. L. BERANEK,Noise reduction, McGraw-Hill, New York, 1960. Chapter 13, Fig, 13.9. 5. M. R~T'nNGER,Acoustics room design andnoise control, Chem. Pub. Co., New York, 1969. Section 11, Chapter 3, p. 117. 6. W.A. UTLEY,A. CUMMINGSand H. D. PARBROOK,The use of absorbent material in double-leaf wall constructions, J. Sound and Vibration, 9(1) (1969), pp. 91Y6. 7. ANON.Rating of Sound Insulation in Buildings. ISO/R 717 (E), International Organisation for Standardisation, 1968. 8. ANON.Tentative Classification for Determination of Sound Transmission Class, American Society for Testing and Materials, E413-70T, 1970. 9. ANON.Building Siting and Construction Against Traffic Noise Intrusion, DR 74163. Australian Standards Association, Appendix B, 1974. 10. T. D. NORTHWOODand D. M. CLARK,Frequency considerations in the subjective assessment of sound insulation, Paper E3-8 presented to 6th International Congress in Acoustics, Japan, 1968. 11. W. A. OOSTING,Method for Calculating Road Traffic Noise for Zoning Purposes, TPD-TNO-TH Report VL-HR-22-01, 1975. 12. ANON.Airborne Sound Transmission Through Elements of Buildings. Department of Housing and Construction, Experimental Building Station, Technical Study 48, Appendix B, 1973. 13. ANON.Victoria: Uniform Building Regulations. Regulations ll01, 1975.
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APPENDIX 1 ; CODES FOR ROOFING SYSTEMS
Code
Description
CR/A CR/B
Concrete-tiled pitched roof, plus 9 mm plasterboard ceiling. As above, but with 0.23 mm double-sided aluminium foil sarking between roof tiles and rafters. CR/C As above, but with 50 mm glass-fibre blanket laid between ceiling joists. CR/D As above, but with foil sarking removed. CR/E As above, but with second layer of 50 mm glass-fibre blanket laid between ceiling joists. CR/F Concrete-tiled pitched roof, plus 9 mm plasterboard ceiling with 122 mm cellulose fibre fluff blown between ceiling joists. CR/G Pitched-roof frame with corrugated asbestos-cement cladding, plus 9 mm plasterboard ceiling. CR/H As above, but with 50 mm glass-fibre blanket laid between ceiling joists. CR/I As CR/G, but with 74 mm mineral wool batts laid between ceiling joists. Pitched-roof frame with 0.5 mm corrugated galvanised steel cladding, plus cg/J 9 mm plasterboard ceiling. CR/K As above, but with 74 mm mineral wool batts laid between ceiling joists. Almost flat wooden roof frame with 0.56 mm galvanised steel decking, plus CR/L 9 mm plasterboard ceiling. CR/LL As above, but with a second 9 mm layer of plasterboard nailed to original ceiling cladding. CR/M As above, but with 50 mm glass-fibre blanket laid between ceiling joists. CR/N As CR/L, but with 50 mm glass-fibre blanket placed in contact with roof decking and held in position with 0.23 mm double-sided aluminium foil. CR/O As CR/L, but with 74 mm mineral wool batts laid between ceiling joists. CR/P As CR/L, but with 122 mm cellulose fibre fluffblown between ceiling joists.
APPENDIX
2:
SPECTRA: OUTSIDE SOUND LEVELS, L f
(dB)
LIR: Road traffic noise at frequency f Hz (dB) LIA: Composite aircraft-movement noise at frequencyf Hz (dB) fHz LIR
LfA f Hz LyR
ZfA
100 125 160 200 250 315 400 500 630 74-3 73"5 71 "5 68"5 69-0 68"8 67-7 67"0 67.2 49-0 50"6 50-2 46-6 46"2 46.0 45.6 45.2 45"0 800 1000 1250 1600 2000 2500 3150 4000 66.3 66.0 65.2 63"8 62.5 60.2 58.3 55.0 44.6 44.0 44"0 43.8 47.0 50.8 49.8 46.4